# Posts Tagged gamma ray

## Recent Postings from gamma ray

### Identifying the nature of high energy Astroparticles [Cross-Listing]

High energy Astroparticles include Cosmic Ray, gamma ray and neutrinos, all of them coming from the universe. The origin and production, acceleration and propagation mechanisms of ultrahigh-energy CR (up to $10^{20}$ eV) are still unknown. Knowledge on particle interactions taking place at those energies, useful for studying current theories on particle physics, can be obtained only from measurements of high energy astroparticles. In the present document some techniques on data analysis of mass composition of UHECR with the Pierre Auger Observatory are described. The relevance of the muon component of air showers produced by the primary CR, as well as some low energy simulations of that component, are explained.

### Identifying the nature of high energy Astroparticles

High energy Astroparticles include Cosmic Ray, gamma ray and neutrinos, all of them coming from the universe. The origin and production, acceleration and propagation mechanisms of ultrahigh-energy CR (up to $10^{20}$ eV) are still unknown. Knowledge on particle interactions taking place at those energies, useful for studying current theories on particle physics, can be obtained only from measurements of high energy astroparticles. In the present document some techniques on data analysis of mass composition of UHECR with the Pierre Auger Observatory are described. The relevance of the muon component of air showers produced by the primary CR, as well as some low energy simulations of that component, are explained.

### Short GRBs at the dawn of the gravitational wave era [Cross-Listing]

We derive the luminosity function and redshift distribution of short Gamma Ray Bursts (SGRBs) using (i) all the available observer-frame constraints (i.e. peak flux, fluence, peak energy and duration distributions) of the large population of Fermi SGRBs and (ii) the rest-frame properties of a complete sample of Swift SGRBs. We show that a steep $\phi(L)\propto L^{-a}$ with a>2.0 is excluded if the full set of constraints is considered. We implement a Monte Carlo Markov Chain method to derive the $\phi(L)$ and $\psi(z)$ functions assuming intrinsic Ep-Liso and Ep-Eiso correlations or independent distributions of intrinsic peak energy, luminosity and duration. To make our results independent from assumptions on the progenitor (NS-NS binary mergers or other channels) and from uncertainties on the star formation history, we assume a parametric form for the redshift distribution of SGRBs. We find that a relatively flat luminosity function with slope ~0.5 below a characteristic break luminosity ~3$\times10^{52}$ erg/s and a redshift distribution of SGRBs peaking at z~1.5-2 satisfy all our constraints. These results hold also if no Ep-Liso and Ep-Eiso correlations are assumed. We estimate that, within ~200 Mpc (i.e. the design aLIGO range for the detection of GW produced by NS-NS merger events), 0.007-0.03 SGRBs yr$^{-1}$ should be detectable as gamma-ray events. Assuming current estimates of NS-NS merger rates and that all NS-NS mergers lead to a SGRB event, we derive a conservative estimate of the average opening angle of SGRBs: $\theta_{jet}$~9-17 deg. Our luminosity function implies an average luminosity L~1.5$\times 10^{52}$ erg/s, nearly two orders of magnitude higher than previous findings, which greatly enhances the chance of observing SGRB "orphan" afterglows. Efforts should go in the direction of finding and identifying such orphan afterglows as counterparts of GW events.

### Short GRBs at the dawn of the gravitational wave era

We derive the luminosity function and redshift distribution of short Gamma Ray Bursts (SGRBs) using (i) all the available observer-frame constraints (i.e. peak flux, fluence, peak energy and duration distributions) of the large population of Fermi SGRBs and (ii) the rest-frame properties of a complete sample of Swift SGRBs. We show that a steep $\phi(L)\propto L^{-a}$ with a>2.0 is excluded if the full set of constraints is considered. We implement a Monte Carlo Markov Chain method to derive the $\phi(L)$ and $\psi(z)$ functions assuming intrinsic Ep-Liso and Ep-Eiso correlations or independent distributions of intrinsic peak energy, luminosity and duration. To make our results independent from assumptions on the progenitor (NS-NS binary mergers or other channels) and from uncertainties on the star formation history, we assume a parametric form for the redshift distribution of SGRBs. We find that a relatively flat luminosity function with slope ~0.5 below a characteristic break luminosity ~3$\times10^{52}$ erg/s and a redshift distribution of SGRBs peaking at z~1.5-2 satisfy all our constraints. These results hold also if no Ep-Liso and Ep-Eiso correlations are assumed. We estimate that, within ~200 Mpc (i.e. the design aLIGO range for the detection of GW produced by NS-NS merger events), 0.007-0.03 SGRBs yr$^{-1}$ should be detectable as gamma-ray events. Assuming current estimates of NS-NS merger rates and that all NS-NS mergers lead to a SGRB event, we derive a conservative estimate of the average opening angle of SGRBs: $\theta_{jet}$~9-17 deg. Our luminosity function implies an average luminosity L~1.5$\times 10^{52}$ erg/s, nearly two orders of magnitude higher than previous findings, which greatly enhances the chance of observing SGRB "orphan" afterglows. Efforts should go in the direction of finding and identifying such orphan afterglows as counterparts of GW events.

### Possible Gamma-Ray Burst radio detections by the Square Kilometre Array. New perspectives

The next generation interferometric radio telescope, the Square Kilometre Array (SKA), which will be the most sensitive and largest radio telescope ever constructed, could greatly contribute to the detection, survey and characterization of Gamma Ray Bursts (GRBs). By the SKA, it will be possible to perform the follow up of GRBs even for several months. This approach would be extremely useful to extend the Spectrum Energetic Distribution (SED) from the gamma to the to radio band and would increase the number of radio detectable GRBs. In principle, the SKA could help to understand the physics of GRBs by setting constraints on theoretical models. This goal could be achieved by taking into account multiple observations at different wavelengths in order to obtain a deeper insight of the sources. Here, we present an estimation of GRB radio detections, showing that the GRBs can really be observed by the SKA. The approach that we present consists in determining blind detection rates derived by a very large sample consisting of merging several GRB catalogues observed by current missions as Swift, Fermi, Agile and INTEGRAL and by previous missions as BeppoSAX, CGRO, GRANAT, HETE-2, Ulysses and Wind. The final catalogue counts 7516 distinct sources. We compute the fraction of GRBs that could be observed by the SKA at high and low frequencies, above its observable sky. Considering the planned SKA sensitivity and through an extrapolation based on previous works and observations, we deduce the minimum fluence in the range 15-150 keV. This is the energy interval where a GRB should emit to be detectable in the radio band by the SKA. Results seem consistent with observational capabilities.

### The habitability of the Universe through 13 billion years of cosmic time

The field of astrobiology has made tremendous progress in modelling galactic-scale habitable zones which offer a stable environment for life to form and evolve in complexity. Recently, this idea has been extended to cosmological scales by studies modelling the habitability of the local Universe in its entirety (e.g. Dayal et al. 2015; Li & Zhang 2015). However, all of these studies have solely focused on estimating the potentially detrimental effects of either Type II supernovae (SNII) or Gamma Ray Bursts (GRBs), ignoring the contributions from Type Ia supernovae (SNIa) and active galactic nuclei (AGN). In this study we follow two different approaches, based on (i) the amplitude of deleterious radiation and (ii) the total planet-hosting volume irradiated by deleterious radiation. We simultaneously track the contributions from the key astrophysical sources (SNII, SNIa, AGN and GRBs) for the entire Universe, for both scenarios, to determine its habitability through 13.8 billion years of cosmic time. We find that SNII dominate the total radiation budget and the volume irradiated by deleterious radiation at any cosmic epoch closely followed by SNIa (that contribute half as much as SNII), with GRBs and AGN making up a negligible portion (<1%). Secondly, as a result of the total mass in stars (or the total number of planets) slowly building-up with time and the total deleterious radiation density, and volume affected, falling-off after the first 3 billion years, we find that the Universe has steadily increased in habitability through cosmic time. We find that, depending on the exact model assumptions, the Universe is 2.5 to 20 times more habitable today compared to when life first appeared on the Earth 4 billion years ago. We find that this increase in habitability will persist until the final stars die out over the next hundreds of billions of years.

### Exceptional outburst of the blazar CTA 102 in 2012: The GASP-WEBT campaign and its extension

After several years of quiescence, the blazar CTA 102 underwent an exceptional outburst in 2012 September-October. The flare was tracked from gamma-ray to near-infrared frequencies, including Fermi and Swift data as well as photometric and polarimetric data from several observatories. An intensive GASP-WEBT collaboration campaign in optical and NIR bands, with an addition of previously unpublished archival data and extension through fall 2015, allows comparison of this outburst with the previous activity period of this blazar in 2004-2005. We find remarkable similarity between the optical and gamma-ray behaviour of CTA 102 during the outburst, with a time lag between the two light curves of ~1 hour, indicative of co-spatiality of the optical and gamma-ray emission regions. The relation between the gamma-ray and optical fluxes is consistent with the SSC mechanism, with a quadratic dependence of the SSC gamma-ray flux on the synchrotron optical flux evident in the post-outburst stage. However, the gamma-ray/optical relationship is linear during the outburst; we attribute this to changes in the Doppler factor. A strong harder-when-brighter spectral dependence is seen both the in gamma-ray and optical non-thermal emission. This hardening can be explained by convexity of the UV-NIR spectrum that moves to higher frequencies owing to an increased Doppler shift as the viewing angle decreases during the outburst stage. The overall pattern of Stokes parameter variations agrees with a model of a radiating blob or shock wave that moves along a helical path down the jet.

### A model for gamma-ray binaries, based on the effect of pair production feedback in shocked pulsar winds

We analyze the model of gamma-ray binaries, consisting of a massive star and a pulsar with ultrarelativistic wind. We consider radiation from energetic particles, accelerated at the pulsar wind termination shock, and feedback of this radiation on the wind through production of secondary electron-positron pairs. We show that the pair feedback limits the Lorentz factor of the pulsar wind and creates a population of very energetic pairs, whose radiation may be responsible for the observed gamma-ray signal.

### A Revised Analysis of Gamma Ray Bursts' prompt efficiencies

The prompt Gamma-Ray Bursts' (GRBs) efficiency is an important clue on the emission mechanism producing the $\gamma$-rays. Previous estimates of the kinetic energy of the blast waves, based on the X-ray afterglow luminosity $L_X$, suggested that this efficiency is large, with values above 90\% in some cases. This poses a problem to emission mechanisms and in particular to the internal shocks model. These estimates are based, however, on the assumption that the X-ray emitting electrons are fast cooling and that their Inverse Compton (IC) losses are negligible. The observed correlations between $L_X$ (and hence the blast wave energy) and $E_{\gamma\rm ,iso}$, the isotropic equivalent energy in the prompt emission, has been considered as observational evidence supporting this analysis. It is reasonable that the prompt gamma-ray energy and the blast wave kinetic energy are correlated and the observed correlation corroborates, therefore, the notion $L_X$ is indeed a valid proxy for the latter. Recent findings suggest that the magnetic field in the afterglow shocks is significantly weaker than was earlier thought and its equipartition fraction, $\epsilon_B$, could be as low as $10^{-4}$ or even lower. Motivated by these findings we reconsider the problem, taking now IC cooling into account. We find that the observed $L_X-E_{\gamma\rm ,iso}$ correlation is recovered also when IC losses are significant. For small $\epsilon_B$ values the blast wave must be more energetic and we find that the corresponding prompt efficiency is significantly smaller than previously thought. For example, for $\epsilon_B\sim10^{-4}$ we infer a typical prompt efficiency of $\sim15\%$.

### Investigation of cosmic ray penetration with wavelet cross-correlation analysis

Aims. We use Fermi and Planck data to calculate the cross correlation between gamma ray signal and gas distribution in different scales in giant molecular clouds (GMC). Then we investigate the cosmic rays (CRs) penetration in GMCs with these informations. Methods.We use the wavelet technique to decompose both the gamma ray and dust opacity maps in different scales, then we calculate the wavelet cross correlation functions in these scales. We also define wavelet response as an analog to the impulsive response in Fourier transform and calculate that in different scales down to Fermi angular resolution. Results. The gamma ray maps above 2 GeV show strong correlation with the dust opacity maps, the correlation coefficient is larger than 0.9 above a scale of 0.4 degree.The derived wavelet response is uniform in different scales. Conclusions. We argue that the CR above 10 GeV can penetrate the giant molecular cloud freely and the CRs distributions in the same energy range are uniform down to parsec scale.

### Hard X-ray Emission from Sh2-104: A NuSTAR search for Gamma-ray Counterparts [Replacement]

We present NuSTAR hard X-ray observations of Sh 2-104, a compact HII region containing several young massive stellar clusters (YMSCs). We have detected distinct hard X-ray sources coincident with localized VERITAS TeV emission recently resolved from the giant gamma-ray complex MGRO J2019+37 in the Cygnus region. Faint, diffuse X-ray emission coincident with the eastern YMSC in Sh2-104 is likely the result of colliding winds of component stars. Just outside the radio shell of Sh 2-104 lies 3XMM J201744.7+365045 and a nearby nebula NuSTAR J201744.3+364812, whose properties are most consistent with extragalactic objects. The combined XMM-Newton and NuSTAR spectrum of 3XMM J201744.7+365045 is well-fit to an absorbed power-law model with NH = (3.1 +/- 1.0)E22 cm^-2 and photon index Gamma = 2.1 +/- 0.1. Based on possible long-term flux variation and the lack of detected pulsations (< 43% modulation), this object is likely a background AGN rather than a Galactic pulsar. The spectrum of the NuSTAR nebula shows evidence of an emission line at E = 5.6 keV suggesting an optically obscured galaxy cluster at z = 0.19 +/- 0.02 (d = 800 Mpc) and Lx = 1.2E44 erg/s. Follow-up Chandra observations of Sh 2-104 will help identify the nature of the X-ray sources and their relation to MGRO J2019+37. We also show that the putative VERITAS gamma-ray excess south of Sh 2-104 is most likely associated with the newly discovered Fermi pulsar PSR J2017+3625 and not the HII region.

### Gamma Ray Burst reverse shock emission in early radio afterglows

Reverse shock (RS) emission from Gamma Ray Bursts is an important tool in investigating the nature of the ejecta from the central engine. If the ejecta magnetization is not high enough to suppress the RS, a strong RS emission component, usually peaking in the optical/IR band early on, would give important contribution to early afterglow light curves. In the radio band, synchrotron self-absorption may suppress early RS emission, and also delay the RS peak time. In this paper, we calculate the self-absorbed RS emission in the radio band for different dynamical conditions. In particular, we stress that the RS radio emission is subject to self-absorption in both reverse and forward shocks. We calculate the ratio between the reverse to forward shock flux at the RS peak time for different frequencies, which is a measure of the detectability of the RS emission component. We then constrain the range of physical parameters for a detectable RS, in particular the role of magnetization. We notice that unlike optical RS emission which is enhanced by moderate magnetization, a moderately magnetized ejecta does not necessarily produce a brighter radio RS due to the self-absorption effect. For typical parameters, the RS emission component would not be detectable below 1 GHz unless the medium density is very low (e.g. $n < 10^{-3} ~{\rm cm^{-3}}$ for ISM and $A_* < 5\times 10^{-4}$ for wind). These predictions can be tested with the afterglow observations with current and upcoming radio facilities such as JVLA, LOFAR, FAST, and SKA.

### Gamma ray signals of the annihilation of Higgs-portal singlet dark matter

This article is an exploration of gamma ray signals of annihilating Higgs-portal singlet scalar and vector dark matter. Gamma ray signals are considered in the context of contributions from annihilations of singlets in the galactic halo to the Isotropic Gamma Ray Background (IGRB), in the context of the Galactic center excess, and in the context of observations of dwarf spheroidal galaxies. We find that Higgs-portal singlets of both species with a mass of $~$65 GeV can explain the Galactic center excess with reasonable accuracy, but that this mass range is in tension with current direct detection bounds. We also find that singlets in the mass range of 250-1000 GeV are consistent with both the Fermi-LAT IGRB observations and direct detection bounds. Additionally, bounds from gamma ray observations of the dwarf spheroidal galaxy Segue I are translated into bounds on the Higgs-portal couplings.

### Gamma ray signals of the annihilation of Higgs-portal singlet dark matter [Replacement]

This article is an exploration of gamma ray signals of annihilating Higgs-portal singlet scalar and vector dark matter. Gamma ray signals are considered in the context of contributions from annihilations of singlets in the galactic halo to the Isotropic Gamma Ray Background (IGRB), in the context of the Galactic center excess, and in the context of observations of dwarf spheroidal galaxies. We find that Higgs-portal singlets of both species with a mass of $~$65 GeV can explain the Galactic center excess with reasonable accuracy, but that this mass range is in tension with current direct detection bounds. We also find that singlets in the mass range of 250-1000 GeV are consistent with both the Fermi-LAT IGRB observations and direct detection bounds. Additionally, bounds from gamma ray observations of the dwarf spheroidal galaxy Segue I are translated into bounds on the Higgs-portal couplings.

### Gamma ray signals of the annihilation of Higgs-portal singlet dark matter [Cross-Listing]

This article is an exploration of gamma ray signals of annihilating Higgs-portal singlet scalar and vector dark matter. Gamma ray signals are considered in the context of contributions from annihilations of singlets in the galactic halo to the Isotropic Gamma Ray Background (IGRB), in the context of the Galactic center excess, and in the context of observations of dwarf spheroidal galaxies. We find that Higgs-portal singlets of both species with a mass of $~$65 GeV can explain the Galactic center excess with reasonable accuracy, but that this mass range is in tension with current direct detection bounds. We also find that singlets in the mass range of 250-1000 GeV are consistent with both the Fermi-LAT IGRB observations and direct detection bounds. Additionally, bounds from gamma ray observations of the dwarf spheroidal galaxy Segue I are translated into bounds on the Higgs-portal couplings.

### Gamma ray signals of the annihilation of Higgs-portal singlet dark matter [Replacement]

This article is an exploration of gamma ray signals of annihilating Higgs-portal singlet scalar and vector dark matter. Gamma ray signals are considered in the context of contributions from annihilations of singlets in the galactic halo to the Isotropic Gamma Ray Background (IGRB), in the context of the Galactic center excess, and in the context of observations of dwarf spheroidal galaxies. We find that Higgs-portal singlets of both species with a mass of $~$65 GeV can explain the Galactic center excess with reasonable accuracy, but that this mass range is in tension with current direct detection bounds. We also find that singlets in the mass range of 250-1000 GeV are consistent with both the Fermi-LAT IGRB observations and direct detection bounds. Additionally, bounds from gamma ray observations of the dwarf spheroidal galaxy Segue I are translated into bounds on the Higgs-portal couplings.

### Spectral lags of flaring events in $LSI +61^{o}$ 303 from RXTE Observations

This work reports the first discovery of (negative) spectral lags in the X-ray emission below 10 keV from the gamma ray binary $LSI +61^{o}$ 303 during large flaring episodes using the Rossi X-ray Timing Explorer (RXTE) observations. It is found from the RXTE data that during the flares, low energy (3-5 KeV) variations lead the higher energy (8-10 keV) variations by few tens of seconds whereas no significant time lag is observed during the non-flaring states. The observed spectral lag features for flaring events suggest that inverse Compton scattering may be operative, at least in some part of the system. Another possibility is that the sites of particle acceleration may be different for flaring and non-flaring events such as in the microquasar model the flaring radiation may come from hot spots sitting above the black hole while steady state emissions are due to the jets.

### The High-Energy Tail of the Galactic Center Gamma-Ray Excess

Observations by the Fermi-LAT have uncovered a bright, spherically symmetric excess surrounding the center of the Milky Way galaxy. The spectrum of the gamma-ray excess peaks sharply at an energy ~2 GeV, exhibiting a hard spectrum at lower energies, and falls off quickly above an energy ~5 GeV. The spectrum of the excess above ~10 GeV is potentially an important discriminator between different physical models for its origin. We focus our study on observations of the gamma-ray excess at energies exceeding 10 GeV, finding: (1) a statistically significant excess remains in the energy range 9.5-47.5 GeV, which is not degenerate with known diffuse emission templates such as the Fermi Bubbles, (2) the radial profile of the excess at high energies remains relatively consistent with data near the spectral peak (3) the data above ~5 GeV prefer a slightly greater ellipticity with a major axis oriented perpendicular to the Galactic plane. Using the recently developed non-Poissonian template fit, we find mild evidence for a point-source origin for the high-energy excess, although given the statistical and systematic uncertainties we show that a smooth origin of the high-energy emission cannot be ruled out. We discuss the implication of these findings for pulsar and dark matter models of the gamma-ray excess. Finally we provide a number of updated measurements of the gamma-ray excess, utilizing novel diffuse templates and the Pass 8 dataset.

### The High-Energy Tail of the Galactic Center Gamma-Ray Excess [Cross-Listing]

Observations by the Fermi-LAT have uncovered a bright, spherically symmetric excess surrounding the center of the Milky Way galaxy. The spectrum of the gamma-ray excess peaks sharply at an energy ~2 GeV, exhibiting a hard spectrum at lower energies, and falls off quickly above an energy ~5 GeV. The spectrum of the excess above ~10 GeV is potentially an important discriminator between different physical models for its origin. We focus our study on observations of the gamma-ray excess at energies exceeding 10 GeV, finding: (1) a statistically significant excess remains in the energy range 9.5-47.5 GeV, which is not degenerate with known diffuse emission templates such as the Fermi Bubbles, (2) the radial profile of the excess at high energies remains relatively consistent with data near the spectral peak (3) the data above ~5 GeV prefer a slightly greater ellipticity with a major axis oriented perpendicular to the Galactic plane. Using the recently developed non-Poissonian template fit, we find mild evidence for a point-source origin for the high-energy excess, although given the statistical and systematic uncertainties we show that a smooth origin of the high-energy emission cannot be ruled out. We discuss the implication of these findings for pulsar and dark matter models of the gamma-ray excess. Finally we provide a number of updated measurements of the gamma-ray excess, utilizing novel diffuse templates and the Pass 8 dataset.

### Gamma rays from muons from WIMPs: Implementation of radiative muon decays for dark matter analyses [Cross-Listing]

Dark matter searches in gamma ray final states often make use of the fact that photons can be produced from final state muons. Modern Monte Carlo generators and DM codes include the effects of final state radiation from muons produced in the dark matter annihilation process itself, but neglect the O(1%) radiative correction that arises from the subsequent muon decay. After implementing this correction we demonstrate the effect that it can have on dark matter phenomenology by considering the case of dark matter annihilation to four muons via scalar mediator production. We first show that the AMS-02 positron excess can no longer easily be made consistent with this final state once the Fermi-LAT dwarf limits are calculated with the inclusion of radiative muon decays, and we next show that the Fermi-LAT galactic centre gamma excess can be improved with this final state after inclusion of the same effect. We provide code and tables for the implementation of this effect in the popular dark matter code micrOMEGAs, providing a solution for any model producing final state muons.

### Gamma rays from muons from WIMPs: Implementation of radiative muon decays for dark matter analyses

Dark matter searches in gamma ray final states often make use of the fact that photons can be produced from final state muons. Modern Monte Carlo generators and DM codes include the effects of final state radiation from muons produced in the dark matter annihilation process itself, but neglect the O(1%) radiative correction that arises from the subsequent muon decay. After implementing this correction we demonstrate the effect that it can have on dark matter phenomenology by considering the case of dark matter annihilation to four muons via scalar mediator production. We first show that the AMS-02 positron excess can no longer easily be made consistent with this final state once the Fermi-LAT dwarf limits are calculated with the inclusion of radiative muon decays, and we next show that the Fermi-LAT galactic centre gamma excess can be improved with this final state after inclusion of the same effect. We provide code and tables for the implementation of this effect in the popular dark matter code micrOMEGAs, providing a solution for any model producing final state muons.

### A Latitude-Dependent Analysis of the Leptonic Hypothesis for the Fermi Bubbles

The Fermi Bubbles are giant Galactic structures observed in both gamma-rays and microwaves. Recent studies have found support for the hypothesis that the gamma-ray and microwave emission can both be understood as arising from a hard cosmic-ray electron population within the volume of the Bubbles, via inverse Compton scattering and synchrotron radiation respectively. The relative rates of these processes are set by the relative energy density of the interstellar radiation field and the magnetic field within the Bubbles; consequently, under the hypothesis of a common origin, the combination of the gamma-ray and microwave measurements can be used to estimate the magnetic field within the Bubbles. We revisit the consistency of this hypothesis on a latitude-by-latitude basis, using data from Fermi, WMAP and Planck; estimate the variation of the electron spectrum within the Bubbles; and infer bounds on the magnetic field within the Bubbles as a function of distance from the Galactic plane. We find that while the microwave and gamma-ray spectra are generally consistent with the leptonic hypothesis for few-microGauss magnetic fields, there appears to be a preference for spectral hardening in the microwaves at mid-latitudes (especially in the |b|~ 25-35 degree range) that is not mirrored in the gamma rays. This result may hint at a non-leptonic contribution to the gamma-ray spectra; however, the discrepancy can be reconciled in purely leptonic models if the cutoff energy for the electrons is lower in this latitude range, while at the same time the spectrum below the cutoff is harder.

### A Latitude-Dependent Analysis of the Leptonic Hypothesis for the Fermi Bubbles [Replacement]

The Fermi Bubbles are giant Galactic structures observed in both gamma-rays and microwaves. Recent studies have found support for the hypothesis that the gamma-ray and microwave emission can both be understood as arising from a hard cosmic-ray electron population within the volume of the Bubbles, via inverse Compton scattering and synchrotron radiation respectively. The relative rates of these processes are set by the relative energy density of the interstellar radiation field and the magnetic field within the Bubbles; consequently, under the hypothesis of a common origin, the combination of the gamma-ray and microwave measurements can be used to estimate the magnetic field within the Bubbles. We revisit the consistency of this hypothesis on a latitude-by-latitude basis, using data from Fermi, WMAP and Planck; estimate the variation of the electron spectrum within the Bubbles; and infer bounds on the magnetic field within the Bubbles as a function of distance from the Galactic plane. We find that while the microwave and gamma-ray spectra are generally consistent with the leptonic hypothesis for few-microGauss magnetic fields, there appears to be a preference for spectral hardening in the microwaves at mid-latitudes (especially in the |b|~ 25-35 degree range) that is not mirrored in the gamma rays. This result may hint at a non-leptonic contribution to the gamma-ray spectra; however, the discrepancy can be reconciled in purely leptonic models if the cutoff energy for the electrons is lower in this latitude range and the spectrum below the cutoff is harder.

### Critical Test Of Gamma Ray Burst Theories [Replacement]

Very long and precise follow-up measurements of the X-ray afterglow of very intense gamma ray bursts (GRBs) allow a critical test of GRB theories. Here we show that the single power-law decay with time of the X-ray afterglow of GRB 130427A, the record long and most accurately measured X-ray afterglow of an intense GRB by the Swift, Chandra and XMM Newton space observatories, and of all other known intense GRBs, is that predicted by the cannonball (CB) model of GRBs from their measured spectral index, while it disagrees with that predicted by the widely accepted fireball (FB) models of GRBs.

### Critical Test Of Gamma Ray Burst Theories [Replacement]

Very long and precise follow-up measurements of the X-ray afterglow of very intense gamma ray bursts (GRBs) allow a critical test of GRB theories. Here we show that the single power-law decay with time of the X-ray afterglow of GRB 130427A, the record long and most accurately measured X-ray afterglow of an intense GRB by the Swift, Chandra and XMM Newton space observatories, and of all other known intense GRBs, is that predicted by the cannonball (CB) model of GRBs from their measured spectral index, while it disagrees with that predicted by the widely accepted fireball (FB) models of GRBs.

### Critical Test Of Gamma Ray Burst Theories

Long and precise follow-up measurements of the X-ray afterglow (AG) of very intense gamma ray bursts (GRBs) provide a critical test of GRB afterglow theories. Here we show that the power-law decline with time of X-ray AG of GRB 130427A, the longest measured X-ray AG of an intense GRB with the Swift, Chandra and XMM Newton satellites, and of all other well measured late-time X-ray afterglow of intense GRBs, is that predicted by the cannonball (CB) model of GRBs from their measured spectral index, while it disagrees with that predicted by the widely accepted fireball (FB) models of GRBs.

### Inner Engine Shutdown from Transitions in the Angular Momentum Distribution in Collapsars

For the collapsar scenario to be effective in the production of Gamma Ray Bursts, the infalling star's angular momentum $J(r)$ must be larger than the critical angular momentum needed to form an accretion disk around a blackhole (BH), namely $J_{\rm crit} = 2r_{g}c$ for a Schwarzschild BH. By means of 3D SPH simulations, here we study the collapse and accretion onto black holes of spherical rotating envelopes, whose angular momentum distribution has transitions between supercritical ($J>J_{\rm crit}$) and subcritical ($J<J_{\rm crit}$) values. Contrary to results obtained in previous 2D hydrodynamical simulations, we find that a substantial amount of subcritical material fed to the accretion disk, lingers around long enough to contribute significantly to the energy loss rate. Increasing the amount of angular momentum in the subcritical material increases the time spent at the accretion disk, and only when the bulk of this subcritical material is accreted before it is replenished by a massive outermost supercritical shell, the inner engine experiences a shutdown. Once the muffled accretion disk is provided again with enough supercritical material, the shutdown will be over and a quiescent time in the long GRB produced afterwards could be observed.

### Study of GRB light curve decay indices in the afterglow phase

In this work we study the distribution of temporal power-law decay indices, $\alpha$, in the Gamma Ray Burst (GRB) afterglow phase, fitted for $176$ GRBs (139 long GRBs, 12 short GRBs {\it with extended emission} and 25 X-Ray Flashes (XRFs)) with known redshifts. These indices are compared to the values of characteristic afterglow luminosity, $L_a$, the time, $T_a^*$, and the decay index, $\alpha_W$, derived with global light curve fitting using the \cite{willingale07} model. This model fitting yields similar distributions of $\alpha_W$ to the fitted $\alpha$, but for individual bursts a difference can be significant. Analysis of the ($\alpha$, $L_a$) distribution reveals only a weak correlation of these quantities. However, we discovered a significant regular trend when studying GRB $\alpha$ values along the $L_a$ versus $T_a^*$ (LT) distribution, with systematic variation of $\alpha$ parameter distribution with luminosity for any selected $T_a^*$. We analyze this systematics with respect to the fitted LT correlation line \citep{dainotti2008}. Study of the presented trend may allow one for constraining the physical models for GRBs. We also attempted to use the derived correlation of $\alpha(T_a^*)$ versus $L_a(T_a^*)$ to diminish the luminosity scatter related to the variations of $\alpha$ along the LT distribution, a step in searching a standardizing procedure for GRBs. A proposed toy model accounting for this systematics applied to the analyzed GRB distribution results in a slight increase of the LT correlation coefficient.

### Study of GRB light curve decay indices in the afterglow phase [Replacement]

In this work we study the distribution of temporal power-law decay indices, $\alpha$, in the Gamma Ray Burst (GRB) afterglow phase, fitted for $176$ GRBs (139 long GRBs, 12 short GRBs {\it with extended emission} and 25 X-Ray Flashes (XRFs)) with known redshifts. These indices are compared with the temporal decay index, $\alpha_W$, derived with the light curve fitting using the \cite{willingale07} model. This model fitting yields similar distributions of $\alpha_W$ to the fitted $\alpha$, but for individual bursts a difference can be significant. Analysis of ($\alpha$, $L_a$) distribution, where $L_a$ is the characteristic luminosity at the end of the plateau, reveals only a weak correlation of these quantities. However, we discovered a significant regular trend when studying GRB $\alpha$ values along the \cite{dainotti2008} correlation between $L_a$ and the end time of the plateau emission in the rest frame, $T_a^*$, hereafter LT correlation. We note a systematic variation of the $\alpha$ parameter distribution with luminosity for any selected $T_a^*$. We analyze this systematics with respect to the fitted LT correlation line, expecting that the presented trend may allow to constrain the GRB physical models. We also attempted to use the derived correlation of $\alpha(T_a)$ versus $L_a(T_a)$ to diminish the luminosity scatter related to the variations of $\alpha$ along the LT distribution, a step forward in the effort of standardizing GRBs. A proposed toy model accounting for this systematics applied to the analyzed GRB distribution results in a slight increase of the LT correlation coefficient.

### Evidence for a Local "Fog" of Sub-Ankle UHECR

During their propagation through intergalactic space, ultrahigh energy cosmic rays (UHECRs) interact with the background radiation fields. These interactions give rise to energetic electron/positron pairs and photons which in turn feed electromagnetic cascades, resulting in a diffuse gamma-ray background radiation. The gamma-ray flux level generated in this way highly depends upon the UHECR propagation distance, as well as the evolution of their sources with redshift. Recently, the \fermi collaboration has reported that the majority of the total extragalactic gamma-ray flux originates from extragalactic point sources. This posits a stringent upper limit on the diffuse gamma-ray flux generated via UHECR propagation, and subsequently constrains their abundance in the distant Universe. Focusing on the contribution of UHECR at energies below the ankle within a narrow energy band ($(1-4)\times 10^{18}$eV), we calculate the diffuse gamma-ray flux generated through UHECR propagation, normalizing the total cosmic ray energy budget in this band to the measured flux. We find that in order to not overproduce the cascade gamma-ray flux, a local "fog" of UHECR produced by nearby sources must exist, with a possible non-negligible contribution from our Galaxy. Following the assumption that a given fraction of the observed IGRB at 820GeV originates from UHECR, we obtain a constraint on the maximum distance for the majority of their sources. With UHECR above the ankle invariably also contributing to the diffuse gamma-ray backgound, the results presented here are conservative.

### General relativistic massive vector field effects in Gamma Ray Burst production [Cross-Listing]

To explain the extremely high energy release, $>10^{53}$~erg, suggested by the observations of some Gamma Ray Bursts (GRBs) we propose a new energy extraction mechanism from the rotation energy of a Kerr-Newman black hole (BH) by a massive photon field. Numerical results show that this mechanism is stable with respect to the black hole rotation parameter, $a$, with a clear dependence on the BH mass, $M$, and charge, $Q$, and can extract energies up to $10^{54}$ erg. The controversial "energy crisis" problem of GRBs that does not show evidence for collimated emission may benefit of this energy extraction mechanism. With these results we set a lower bound on the coupling between electromagnetic and gravitational fields.

### General relativistic massive vector field effects in Gamma Ray Burst production

To explain the extremely high energy release, $>10^{53}$~erg, suggested by the observations of some Gamma Ray Bursts (GRBs) we propose a new energy extraction mechanism from the rotation energy of a Kerr-Newman black hole (BH) by a massive photon field. Numerical results show that this mechanism is stable with respect to the black hole rotation parameter, $a$, with a clear dependence on the BH mass, $M$, and charge, $Q$, and can extract energies up to $10^{54}$ erg. The controversial "energy crisis" problem of GRBs that does not show evidence for collimated emission may benefit of this energy extraction mechanism. With these results we set a lower bound on the coupling between electromagnetic and gravitational fields.

### General relativistic massive vector field effects in Gamma Ray Burst production [Replacement]

To explain the extremely high energy release, $>10^{53}$~erg, suggested by the observations of some Gamma Ray Bursts (GRBs) we propose a new energy extraction mechanism from the rotation energy of a Kerr-Newman black hole (BH) by a massive photon field. Numerical results show that this mechanism is stable with respect to the black hole rotation parameter, $a$, with a clear dependence on the BH mass, $M$, and charge, $Q$, and can extract energies up to $10^{54}$ erg. The controversial "energy crisis" problem of GRBs that does not show evidence for collimated emission may benefit of this energy extraction mechanism. With these results we set a lower bound on the coupling between electromagnetic and gravitational fields.

### General relativistic massive vector field effects in Gamma Ray Burst production [Replacement]

To explain the extremely high energy release, $>10^{53}$~erg, suggested by the observations of some Gamma Ray Bursts (GRBs) we propose a new energy extraction mechanism from the rotation energy of a Kerr-Newman black hole (BH) by a massive photon field. Numerical results show that this mechanism is stable with respect to the black hole rotation parameter, $a$, with a clear dependence on the BH mass, $M$, and charge, $Q$, and can extract energies up to $10^{54}$ erg. The controversial "energy crisis" problem of GRBs that does not show evidence for collimated emission may benefit of this energy extraction mechanism. With these results we set a lower bound on the coupling between electromagnetic and gravitational fields.

### Multi-band Variability Analysis of Mrk 421

We have assembled the historical variability data of Mrk 421 at radio 15 GHz, X-ray and gamma-ray bands, spanning about 6.3, 10.3 and 7.5 yr, respective- ly. We analyzed the variability by using three methods. The results indicated that there is a period of 287.6 +- 4.4 days for 15 GHz, 309.5 +- 5.8 days for X- ray and 283.4+- 4.7 days for gamma-ray, respectively. This period can be reasonably explained by the nonballistic helical motion of the emitting material. The cor- relation analysis suggested that the variabilities of radio 15 GHz, X-ray and 0-ray are remarkable correlated, and the emission of radio 15 GHz lags behind that of X-ray, and the X-ray flux lags behind the gamma-ray. This suggests that the gamma-ray derives from inverse Compton (IC) scattering of the synchrotron photons, supporting the synchrotron self-Compton (SSC) model. Moreover, the time delay between different wavebands could be explained by the shock-in-jet models, in which a moving emission region produces the radio to gamma-ray activity, implying that the emission region of gamma-ray is closer to the center than ones of X-ray and radio emission.

### The transparency of the universe for very high energy gamma-rays

The propagation of very high energy gamma-rays ($E>100$~GeV) over cosmological distances is suppressed by pair-production processes with the ubiquitous extra-galactic soft photon background, mainly in the optical to near infra-red. The detailed spectroscopy of gamma-ray emitting blazars has revealed the signature of this absorption process leading to a meaningful measurement of the background photon field which is linked to the star-forming history of the universe. Deviations from the expected absorption have been claimed in the past. Here the status of the observations is summarized, an update on the search for the persisting anomalous transparency is given and discussed.

### Di-photon excess at LHC and the gamma ray excess at the Galactic Centre

Motivated by the recent indications for a 750 GeV resonance in the di-photon final state at the LHC, in this work we analyse the compatibility of the excess with the broad photon excess detected at the Galactic Centre. Intriguingly, by analysing the parameter space of an effective models where a 750 GeV pseudoscalar particles mediates the interaction between the Standard Model and a scalar dark sector, we prove the compatibility of the two signals. We show, however, that the LHC mono-jet searches and the Fermi LAT measurements strongly limit the viable parameter space. We comment on the possible impact of cosmic antiproton flux measurement by the AMS-02 experiment.

### Di-photon excess at LHC and the gamma ray excess at the Galactic Centre [Cross-Listing]

Motivated by the recent indications for a 750 GeV resonance in the di-photon final state at the LHC, in this work we analyse the compatibility of the excess with the broad photon excess detected at the Galactic Centre. Intriguingly, by analysing the parameter space of an effective models where a 750 GeV pseudoscalar particles mediates the interaction between the Standard Model and a scalar dark sector, we prove the compatibility of the two signals. We show, however, that the LHC mono-jet searches and the Fermi LAT measurements strongly limit the viable parameter space. We comment on the possible impact of cosmic antiproton flux measurement by the AMS-02 experiment.

### $Fermi$ GBM Observations of V404 Cyg During its 2015 Outburst [Replacement]

V404 Cygni was discovered in 1989 by the $Ginga$ X-ray satellite during its only previously observed X-ray outburst and soon after confirmed as a black hole binary. On June 15, 2015, the Gamma Ray Burst Monitor (GBM) triggered on a new outburst of V404 Cygni. We present 13 days of GBM observations of this outburst including Earth occultation flux measurements, spectral and temporal analysis. The Earth occultation fluxes reached 30 Crab with detected emission to 100 keV and determined, via hardness ratios, that the source was in a hard state. At high luminosity, spectral analysis between 8 and 300 keV showed that the electron temperature decreased with increasing luminosity. This is expected if the protons and electrons are in thermal equilibrium during an outburst with the electrons cooled by the Compton scattering of softer seed photons from the disk. However, the implied seed photon temperatures are unusually high, suggesting a contribution from another source, such as the jet. No evidence of state transitions is seen during this time period. The temporal analysis reveals power spectra that can be modeled with two or three strong, broad Lorentzians, similar to the power spectra of black hole binaries in their hard state.

### $Fermi$ GBM Observations of V404 Cyg During its 2015 Outburst

V404 Cygni was discovered in 1989 by the $Ginga$ X-ray satellite during its only previously observed X-ray outburst and soon after confirmed as a black hole binary. On June 15, 2015, the Gamma Ray Burst Monitor (GBM) triggered on a new outburst of V404 Cygni. We present 13 days of GBM observations of this latest outburst including Earth occultation flux measurements, spectral and temporal analysis. The Earth occultation fluxes reached 30 Crab with detected emission to 100 keV and determined, via hardness ratios, that the source was in a hard state. At high luminosity, spectral analysis between 8 and 300 keV showed that the electron temperature decreased with increasing luminosity. This is expected if the protons and electrons are in thermal equilibrium during an outburst with the electrons cooled by the Compton scattering of softer seed photons from the disk. However, the implied seed photon temperatures are unusually high, suggesting a contribution from another source, such as the jet. No evidence of state transitions is seen during this time period. Temporal analysis reveals the rich harmonic content of the outburst and confirmed that the source was in a hard state.

### $Fermi$ GBM Observations of V404 Cyg During its 2015 Outburst [Replacement]

V404 Cygni was discovered in 1989 by the $Ginga$ X-ray satellite during its only previously observed X-ray outburst and soon after confirmed as a black hole binary. On June 15, 2015, the Gamma Ray Burst Monitor (GBM) triggered on a new outburst of V404 Cygni. We present 13 days of GBM observations of this outburst including Earth occultation flux measurements, spectral and temporal analysis. The Earth occultation fluxes reached 30 Crab with detected emission to 100 keV and determined, via hardness ratios, that the source was in a hard state. At high luminosity, spectral analysis between 8 and 300 keV showed that the electron temperature decreased with increasing luminosity. This is expected if the protons and electrons are in thermal equilibrium during an outburst with the electrons cooled by the Compton scattering of softer seed photons from the disk. However, the implied seed photon temperatures are unusually high, suggesting a contribution from another source, such as the jet. No evidence of state transitions is seen during this time period. The temporal analysis reveals power spectra that can be modeled with two or three strong, broad Lorentzians, similar to the power spectra of black hole binaries in their hard state.

### Constraints On Holographic Cosmological Models From Gamma Ray Bursts

We use Gamma Ray Bursts (GRBs) data to put additional constraints on a set of holographic dark energy models. GRBs are the most energetic events in the Universe and provide a complementary probe of dark energy by allowing the measurement of cosmic expansion history that extends to redshifts greater than 6 and they are complementary to SNIa test. We found that the LCDM model is the best fit to the data, although a preliminary statistical analysis seems to indicate that the holographic models studied show interesting agreement with observations, except Ricci Scale CPL model. These results show the importance of GRBs measurements to provide additional observational constraints to alternative cosmological models, which are necessary to clarify the way in the paradigm of dark energy or potential alternatives.

### Constraints On Holographic Cosmological Models From Gamma Ray Bursts [Replacement]

We use Gamma Ray Bursts (GRBs) data to put additional constraints on a set of holographic dark energy models. GRBs are among the most complex, energetic and regular astrophysical events known universe providing us the opportunity to obtain information from the history of cosmic expansion up to about redshift of $z\sim 6$ offering us a complementary observational test to determine the nature of dark energy and they are also complementary to SNIa test. We found that the $\Lambda CDM$ model is the best fit to the data, although a preliminary statistical analysis seems to indicate that the holographic models studied show interesting agreement with observations, except \textit{Ricci Scale CPL} model. These results show the importance of GRBs measurements to provide additional observational constraints to alternative cosmological models, which are necessary to clarify the way in the paradigm of dark energy or potential alternatives.

### Constraints On Holographic Cosmological Models From Gamma Ray Bursts [Replacement]

We use Gamma Ray Bursts (GRBs) data from Y. Wang (2008) to put additional constraints on a set of cosmological dark energy models based on the holographic principle. GRBs are among the most complex and energetic astrophysical events known in the universe offering us the opportunity to obtain information from the history of cosmic expansion up to about redshift of $z\sim 6$. These astrophysical objects provide us a complementary observational test to determine the nature of dark energy by complementing the information of data from Supernovas (e.g. Union 2.1 compilation). We found that the $\Lambda CDM$ model gives the best fit to the observational data, although our statistical analysis ($\Delta AIC$ and $\Delta BIC$) shows that the models studied in this work ("Hubble Radius Scale" and "Ricci Scale Q") have a reasonable agreement with respect to the most successful, except for the "Ricci Scale CPL" and "Future Event Horizon" models, which can be ruled out by the present study. However, these results reflect the importance of GRBs measurements to provide additional observational constraints to alternative cosmological models, which are mandatory to clarify the way in which the paradigm of dark energy or any alternative model is correct.

### Novel Features of Gamma Ray from Dark Matter [Cross-Listing]

In this study, we present some general and novel features of gamma ray from dark matter. We find that gamma-ray spectra with sharp features exist in a wide class of dark matter models and mimic the gamma line signals. The generated gamma rays would generally have polynomial-type spectra or power-law with positive index. We illustrate our results in a model-independent framework with generic kinematic analysis. Similar results can also apply for cosmic rays or neutrino cases.

### Novel Features of Gamma Ray from Dark Matter

In this study, we present some general and novel features of gamma ray from dark matter. We find that gamma-ray spectra with sharp features exist in a wide class of dark matter models and mimic the gamma line signals. The generated gamma rays would generally have polynomial-type spectra or power-law with positive index. We illustrate our results in a model-independent framework with generic kinematic analysis. Similar results can also apply for cosmic rays or neutrino cases.

### Calibration of Gamma-ray Burst Polarimeter POLAR

Gamma Ray Bursts (GRBs) are the strongest explosions in the universe which might be associated with creation of black holes. Magnetic field structure and burst dynamics may influence polarization of the emitted gamma-rays. Precise polarization detection can be an ultimate tool to unveil the true GRB mechanism. POLAR is a space-borne Compton scattering detector for precise measurements of the GRB polarization. It consists of a 40$\times$40 array of plastic scintillator bars read out by 25 multi-anode PMTs (MaPMTs). It is scheduled to be launched into space in 2016 onboard of the Chinese space laboratory TG2. We present a dedicated methodology for POLAR calibration and some calibration results based on the combined use of the laboratory radioactive sources and polarized X-ray beams from the European Synchrotron Radiation Facility. They include calibration of the energy response, computation of the energy conversion factor vs. high voltage as well as determination of the threshold values, crosstalk contributions and polarization modulation factors.

### Probing vacuum birefringence under a high-intensity laser field with gamma-ray polarimetry at the GeV scale [Cross-Listing]

Probing vacuum structures deformed by high intense fields is of great interest in general. In the context of quantum electrodynamics (QED), the vacuum exposed by a linearly polarized high-intensity laser field is expected to show birefringence. We consider the combination of a 10 PW laser system to pump the vacuum and 1 GeV gamma-rays to probe the birefringent effect. The vacuum birefringence can be measured via the polarization flip of the probe gamma-rays. We discuss the design of the gamma-ray polarimeter and then evaluate the measurability of the reduction of the degree of linear polarization due to the appearance of birefringence. We found that the measurement is indeed feasible given a realistic set of laser parameters and achievable pulse statistics.

### Search of MeV-GeV counterparts of TeV sources with AGILE in pointing mode

Context. Known TeV sources detected by major Cerenkov telescopes are investigated to identify possible MeV-GeV gamma-ray counterparts. Aims. A systematic study of the known sources in the web-based TeVCat Catalog has been performed to search for possible gamma-ray counterpart on the AGILE data collected during the first period of operations in observing pointing mode. Methods. For each TeV source, a search for a possible gamma-ray counterpart based on a multi-source Maximum Likelihood algorithm is performed on the AGILE data taken with the GRID instrument from July 2007 to October 2009. Results. In case of high-significance detection, the average gamma-ray flux is estimated. For the cases of low-significance detection the 95 % Confidence Level (C.L.) flux upper limit is given. 52 TeV sources out of 152 (corresponding to ~34 % of the analysed sample) show a significant excess in the AGILE data covering the pointing observation period. Conclusions. This analysis found 26 new AGILE sources with respect to the AGILE reference catalogs, 15 of which are Galactic, 7 are extragalactic and 4 are unidentified. Detailed tables with all available information on the analysed sources are presented.

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