Posts Tagged high energy

Recent Postings from high energy

Searching for Traces of Planck-Scale Physics with High Energy Neutrinos

High energy cosmic neutrino observations provide a sensitive test of Lorentz invariance violation, which may be a consequence of quantum gravity theories. We consider a class of non-renormalizable, Lorentz invariance violating operators that arise in an effective field theory description of Lorentz invariance violation in the neutrino sector inspired by Planck-scale physics and quantum gravity models. We assume a conservative generic scenario for the redshift distribution of extragalactic neutrino sources and employ Monte Carlo techniques to describe superluminal neutrino propagation, treating kinematically allowed energy losses of superluminal neutrinos caused by both vacuum pair emission and neutrino splitting. We consider EFTs with both non-renormalizable CPT-odd and non-renormalizable CPT-even operator dominance. We then compare the spectra derived using our Monte Carlo calculations in both cases with the spectrum observed by IceCube in order to determine the implications of our results regarding Planck-scale physics. We find that if the drop off in the neutrino flux above ~2 PeV is caused by Planck scale physics, rather than by a limiting energy in the source emission, a potentially significant pileup effect would be produced just below the drop off energy in the case of CPT-even operator dominance. However, such a clear drop off effect would not be observed if the CPT-odd, CPT-violating term dominates.

High Energy Elastic pp Scattering in Additive Quark Model

High energy $pp$ elastic scattering is treated in the framework of Additive Quark Model. The reasonable agreement with experimental data is achieved with natural parameters for the strong matter distribution inside proton.

High Energy Elastic pp Scattering in Additive Quark Model [Replacement]

High energy $pp$ and $p\bar p$ elastic scattering is treated in the framework of Additive Quark Model. The reasonable agreement with experimental data is achieved with the natural parameters for the strong matter distribution inside proton.

Cross Section to Multiplicity Ratios at Very High Energy [Replacement]

Recent data from the LHC makes it possible to examine an old speculation that at very high energy the total multiplicity and the cross section in elementary particle interactions vary in parallel with energy. Using fits incorporating the new data, it appears that the ratios of the total, elastic, and inelastic cross sections to the average multiplicity N can in fact approach constants at very high energy. The approach to the limit is however quite slow for the total and inelastic cross sections and is not yet reached at LHC energies. The elastic ratio sigma^{el}/N at 7 TeV, however, is not far from its asymptotic value.

Cross Section to Multiplicity Ratios at Very High Energy [Replacement]

Recent data from the LHC makes it possible to examine an old speculation that at very high energy the total multiplicity and the cross section in elementary particle interactions vary in parallel with energy. Using fits incorporating the new data, it appears that the ratios of the total, elastic, and inelastic cross sections to the average multiplicity N can in fact approach constants at very high energy. The approach to the limit is however quite slow for the total and inelastic cross sections and is not yet reached at LHC energies. The elastic ratio sigma^{el}/N at 7 TeV, however, is not far from its asymptotic value.

Astrophysical constraints on Planck scale dissipative phenomena

The emergence of a classical spacetime from any quantum gravity model is still a subtle and only partially understood issue. If indeed space-time is arising as some sort of large scale condensate of more fundamental objects then it is natural to expect that matter, being a collective excitations of the spacetime constituents, will present modified kinematics at sufficiently high energies. We consider here the phenomenology of the dissipative effects necessarily arising in such a picture. Adopting dissipative hydrodynamics as a general framework for the description of the energy exchange between collective excitations and the spacetime fundamental degrees of freedom, we discuss how rates of decays for elementary particles can be derived from dispersion relations and used to provide strong constraints on the base of current astrophysical observations of high energy particles.

Time-dependent Modeling of Pulsar Wind Nebulae

A spatially independent model that calculates the time evolution of the electron spectrum in a spherically expanding pulsar wind nebula (PWN) is presented, allowing one to make broadband predictions for the PWN’s non-thermal radiation. The source spectrum of electrons injected at the termination shock of the PWN is chosen to be a broken power law. In contrast to previous PWN models of a similar nature, the source spectrum has a discontinuity in intensity at the transition between the low and high-energy components. To test the model, it is applied to the young PWN G21.5–0.9, where it is found that a discontinuous source spectrum can model the emission at all wavelengths better than a continuous one. The model is also applied to the unidentified sources HESS J1427–608 and HESS J1507–622. Parameters are derived for these two candidate nebulae that are consistent with the values predicted for other PWNe. For HESS J1427–608 a present-day magnetic field of $B\s{age}=0.4\,\mu\text{G}$ is derived. As a result of the small present-day magnetic field, this source has a low synchrotron luminosity, while remaining bright at GeV/TeV energies. It is therefore possible to interpret HESS J1427–608 within the ancient PWN scenario. For the second candidate PWN HESS J1507–622, a present-day magnetic field of $B\s{age}=1.7\,\mu\text{G}$ is derived. Furthermore, for this candidate PWN a scenario is favoured in the present paper in which HESS J1507–622 has been compressed by the reverse shock of the supernova remnant.

The Crab pulsar wind nebula: our laboratory of the non-thermal Universe

The Crab nebula and its pulsar (referred to together as "Crab") have historically played a central role in astrophysics. True to this legacy, several unique discoveries have been made recently. The Crab was found to emit gamma-ray pulsations up to energies of 400 GeV, beyond what was previously expected from pulsars. Strong gamma-ray flares, of durations of a few days were discovered from within the nebula, while the source was previously expected to be stable in flux on these time scales. In this article, we review our current understanding of pulsar wind nebulae and discuss the importance of the Crab to our general understanding of high-energy phenomena, in the context of these exciting developments.

Yakutsk array radio emission registration results in the energy range of 3*10^16-5*10^18 eV

This paper presents the set of measurements of ultra-high energy air shower radio emission at frequency 32 MHz in period of 2008-2012. The showers are selected by geomagnetic and azimuth angles and then by the energy in three intervals: 3*10^16 3*10^17 eV, 3*10^17 6*10^17 eV and 6*10^17 5*10^18 eV. In each energy interval average lateral distribution function using mathematically averaged data from antennas with di?fferent directions are plotted. In the paper, using experimental data the dependence of radio signal averaged amplitude from geomagnetic angle, the shower axis distance and the energy are determined. Depth of maximum of cosmic ray showers Xmax for the given energy range is evaluated. The evaluation is made according QGSJET model calculations and average lateral distribution function shape.

Anisotropy test of the axion-like particle Universe opacity effect: a case for the Cherenkov Telescope Array

The Universe opacity to gamma rays is still an open question, in particular anomalies may have been observed. Assuming that such anomalies find their origin in conventional physics like intrinsic source spectra or the density of the extragalactic background light, they would be evenly distributed over the sky. If they exist, axion-like particles (ALPs) would have a potential effect on the opacity of the Universe to gamma rays, possibly related to the anomalies in the spectral indices of distant gamma-ray sources. In the scenario where ALPs from distant sources convert back to photons in the Galactic magnetic field, their effect on the opacity is expected to depend on the position of the sources. In that case the anomaly is expected to exhibit peculiar correlations on the sky. We propose a method to test the origin of the opacity anomaly, based on angular correlations of spectral softening anomalies. Such a diagnosis requires a wide-field survey of high-energy gamma-ray sources over a broad range of energy. The future Cherenkov Telescope Array (CTA) is perfectly suited to perform such a study. It is shown that while the current sample of sources is not large enough to base conclusions on, with this method CTA will be sensitive to ALP couplings to gamma rays of the order of 3e-11 GeV^-1 for ALP masses below 1e-8 eV.

Remote control and telescope auto-alignment system for multiangle LIDAR under development at CEILAP, Argentina [Cross-Listing]

At CEILAP (CITEDEF-CONICET), a multiangle LIDAR is under development to monitor aerosol extinction coefficients in the frame of the CTA (Cherenkov Telescope Array) Project. This is an initiative to build the next generation of ground-based instruments to collect very high energy gamma-ray radiation (>10 GeV). The atmospheric conditions are very important for CTA observations, and LIDARs play an important role in the measurement of the aerosol optical depth at any direction. The LIDAR being developed at CEILAP was conceived to operate in harsh environmental conditions during the shifts, and these working conditions may produce misalignments. To minimize these effects, the telescopes comprising the reception unit are controlled by a self-alignment system. This paper describes the self-alignment method and hardware automation.

The role of fast magnetic reconnection in acceleration zones of microquasars and AGNs

Fast magnetic reconnection events can be a very powerful mechanism operating at the jet launching region of microquasars and AGNs. We have recently found that the power released by reconnection between the magnetic field lines of the coronal inner disk region and the lines anchored into the black hole is able to accelerate relativistic particles through a first-order Fermi process and produce the observed radio luminosity from both microquasars and low luminous AGNs (LLAGNs). We also found that the observed correlation between the radio luminosity and the mass of these sources, spanning 10^9 orders of magnitude in mass, is naturally explained by this process. In this work, assuming that the gamma-ray emission is probably originated in the same acceleration zones that produce the radio emission, we have applied the scenario above to investigate the origin of the high energy outcomes from an extensive number of sources including high (HLAGNs) and LLAGNs, microquasars and GRBs. We find correlation of our model with the gamma emission only for microquasars and a few LLAGNs, while none of the HLAGNs or GRBs are fitted, neither in radio nor in gamma. We attribute the lack of correlation of the gamma emission for most of the LLAGNs to the fact that this processed emission doesn’t depend only on the local magnetic field activity around the source/accretion disk, but also on other environmental factors like the photon and density fields. We conclude that the emission from the LLAGNs and microquasars comes from the nuclear region of their sources and therefore, can be driven by nuclear magnetic activity. However, in the case of the HLAGNs and GRBs, the nuclear emission is blocked by the surrounding density and photon fields and therefore, we can only see the jet emission further out.

A search for enhanced very-high-energy gamma-ray emission from the March 2013 Crab Nebula flare

In March 2013, a flaring episode from the Crab Nebula lasting ~2 weeks was detected by the Fermi-LAT (Large Area Telescope on board the Fermi Gamma-ray Space Telescope). VERITAS provides simultaneous observations throughout this period. During the flare, the Fermi-LAT detected a 20-fold increase in flux above the average synchrotron flux >100 MeV seen from the Crab Nebula. Simultaneous measurements with VERITAS are consistent with the non-variable long-term average Crab Nebula flux at TeV energies. Assuming a linear correlation between the very-high-energy flux change >1 TeV and the flux change seen in the Fermi-LAT band >100 MeV during the period of simultaneous observations, the linear correlation factor can be constrained to be at most 8.6 * 10^-3 with 95% confidence.

Testing chemical composition of highest energy comic rays

We study basic characteristics of distributions of the depths of shower maximum in air showers caused by cosmic rays with the highest energies. The consistency between their average values and widths, and their energy dependences are discussed within a simple phenomenological model of shower development independently of assumptions about detailed features of high–energy interactions. It is shown that reliable information on primary species can be derived within a partition method. We present examples demonstrating implications for the changes in mass composition of primary cosmic rays.

Hadronic interaction models and the angular distribution of cosmic ray muons

Muons serve as the best probes of the physics of hadronic interactions in the upper atmosphere because of their simple physics. All the properties of detected muons, such as their energy and angle of incidence, are governed by the properties of their parent hadrons. The angular distribution of the detected muons is a result of a superposition of multiple effects, and is governed by a number of parameters, such as the cutoff rigidity (magnetic field), atmospheric attenuation, interaction cross sections, production height, multiplicity and pseudorapidity. Since particle interactions are handled by the low and high-energy hadronic interaction models in air shower simulations, subtle differences in their physics should manifest in the differences in the angular distribution. Here, we compare air shower simulations with experimental data and investigate how the choice of hadronic interaction models in air shower simulations affects the angular distribution of cosmic ray muons.

Perturbations to aquatic photosynthesis due to high-energy cosmic ray induced muon flux in the extragalactic shock model

We modify a mathematical model of photosynthesis to quantify the perturbations that high energy muons could make on aquatic primary productivity. Then we apply this in the context of the extragalactic shock model, according to which Earth receives an enhanced dose of high-energy cosmic rays when it is at the galactic north. We obtain considerable reduction in the photosynthesis rates, consistent with potential drops in biodiversity.

Numerical study of broadband spectra caused by internal shocks in magnetized relativistic jets of blazars

The internal-shocks scenario in relativistic jets has been used to explain the variability of blazars’ outflow emission. Recent simulations have shown that the magnetic field alters the dynamics of these shocks producing a whole zoo of spectral energy density patterns. However, the role played by magnetization in such high-energy emission is still not entirely understood. With the aid of \emph{Fermi}’s second LAT AGN catalog, a comparison with observations in the $\gamma$-ray band was performed, in order to identify the effects of the magnetic field.

Average spectral properties of galactic X-ray binaries with 3 years of MAXI data

The energy spectra of X-ray binaries (XRBs) have been investigated during the last few decades with many observatories in different energy bands and with different energy resolutions. However, these studies are carried out in selected states of XRBs like during outbursts, transitions, quiescent states, and are always done in limited time windows of pointed observations. It is now possible to investigate the long term averaged spectra of a large number of X-ray binaries with the all sky monitor MAXI, which also has a broad energy band. Here we present the average spectral behaviour of a few representative XRBs. The long term averaged spectrum of Cyg X-1 is described by a sum of two power-laws having $\Gamma_{1}$ ~ 2.8 and $\Gamma_{2}$ ~ 1.2, along with a multi color disk blackbody having an inner disk temperature of 0.5 keV, GX 301-2 is described by a power-law with a high energy cut-off at $E_{c}$ ~ 15 keV and a blackbody component at 0.2 keV and that of Aql X-1 is described by a multi color disk blackbody at 2 keV and a power-law of $\Gamma$ ~ 2.2. We have also constructed the combined X-ray spectrum of the X-ray binaries in the Milky Way, which can be compared to the XRBs spectra of other galaxies observed with Chandra and XMM-Newton. These measurements are also relevant to investigate the X-ray interaction with the ISM and its contribution to the ionising X-ray background in the early universe.

First Results from NuSTAR Observations of Mkn 421

Mkn 421 is a nearby active galactic nucleus dominated at all wavelengths by a very broad non-thermal continuum thought to arise from a relativistic jet seen at a small angle to the line of sight. Its spectral energy distribution peaks in the X-ray and TeV gamma-ray bands, where the energy output is dominated by cooling of high-energy electrons in the jet. In order to study the electron distribution and its evolution, we carried out a dedicated multi-wavelength campaign, including extensive observations by the recently launched highly sensitive hard X-ray telescope NuSTAR, between December 2012 and May 2013. Here we present some initial results based on NuSTAR data from January through March 2013, as well as calibration observations conducted in 2012. Although the observations cover some of the faintest hard X-ray flux states ever observed for Mkn 421, the sensitivity is high enough to resolve intra-day spectral variability. We find that in this low state the dominant flux variations are smooth on timescales of hours, with typical intra-hour variations of less than 5%. We do not find evidence for either a cutoff in the hard X-ray spectrum, or a rise towards a high-energy component, but rather that at low flux the spectrum assumes a power law shape with a photon index of approximately 3. The spectrum is found to harden with increasing brightness.

Probing the Galactic Origin of the IceCube Excess with Gamma-Rays

The IceCube Collaboration has recently reported evidence for a high-energy extraterrestrial neutrino flux. During two years of operation 28 events with energies between 30 TeV and 1.2 PeV were observed while only 10.6 events were expected from conventional atmospheric backgrounds. The hadronic interactions responsible for this IceCube excess will also produce a flux of high-energy gamma-rays that can serve as a probe of source direction and distance. We show that existing TeV to PeV diffuse gamma-ray limits support the interpretation that the IceCube excess is mostly of extragalactic origin and disfavor possible sub-dominant contributions from Galactic neutrino sources like remnants of supernovae and hypernovae. However, we point out that gamma-ray surveys are biased in the Northern Hemisphere whereas the IceCube data shows a weak preference for the Southern Sky. This emphasizes the importance of future diffuse TeV to PeV gamma-ray surveys in the Southern Hemisphere, particularly in the extended region around the Galactic Center including the Fermi Bubbles.

Pair-production opacity at high and very-high gamma-ray energies

The propagation of high energy (HE, $E_\gamma>100$ MeV) and very high-energy gamma-rays (VHE, $E_\gamma>100$ GeV) in the extra-galactic photon field leads to pair-production and consequently energy- and distance-dependent attenuation of the primary intensity. The spectroscopy of an increasing number of extra-galactic objects at HE and VHE energies has demonstrated indeed the presence of such an attenuation which in turn has been used to constrain the photon density in the medium. At large optical depth ($\tau\gtrsim 2$) potential modifications of pair-production due to competing but rare processes (as, e.g., the presence of sub-neV axion-like particle) may be found. Indications for a pair-production anomaly have previously been found with VHE-spectra. Here, we present further indications (at the level of $3.68 \sigma$) for a reduced optical depth at high energies from an analysis of Fermi-\textit{LAT} data.

NuSTAR detection of the blazar B2 1023+25 at redshift 5.3

B2 1023+25 is an extremely radio-loud quasar at z=5.3 which was first identified as a likely high-redshift blazar candidate in the SDSS+FIRST quasar catalog. Here we use the Nuclear Spectroscopic Telescope Array (NuSTAR) to investigate its non-thermal jet emission, whose high-energy component we detected in the hard X-ray energy band. The X-ray flux is ~5.5×10^(-14) erg cm^(-2)s^(-1) (5-10keV) and the photon spectral index is Gamma_X=1.3-1.6. Modeling the full spectral energy distribution, we find that the jet is oriented close to the line of sight, with a viewing angle of ~3deg, and has significant Doppler boosting, with a large bulk Lorentz factor ~13, which confirms the identification of B2 1023+25 as a blazar. B2 1023+25 is the first object at redshift larger than 5 detected by NuSTAR, demonstrating the ability of NuSTAR to investigate the early X-ray Universe and to study extremely active supermassive black holes located at very high redshift.

The Galactic Center Origin of a Subset of IceCube Neutrino Events [Replacement]

The center of the Milkyway is a host to energetic phenomena across many electromagnetic wave-bands and now possibly of high-energy neutrinos. We show that 5 out of 21 IceCube shower-like events, including a PeV event, likely originated from the Galactic Center region. Hard spectrum and flux inferred from these events are inconsistent with atmospheric neutrinos. The flux of these neutrinos is consistent with an extrapolation of the gamma-ray flux measured by Fermi-LAT from the inner Galactic region. This indicates a common hadronic origin of both, powered by supernovae. Three other shower-like events are spatially correlated with the Fermi bubbles, originating from the Galactic Center activity, within the uncertainty of reconstructing their arrival directions. Origin of the other neutrino events, including 7 track-like events, is still elusive.

The Galactic Center Origin of a Subset of IceCube Neutrino Events

The center of the Milkyway is a host to energetic phenomena across many electromagnetic wave-bands and now possibly of high-energy neutrinos. We show that 5 out of 21 IceCube shower-like events, including a PeV event, likely originated from the Galactic Center region. Hard spectrum and flux inferred from these events are inconsistent with atmospheric neutrinos. The flux of these neutrinos is consistent with an extrapolation of the gamma-ray flux measured by Fermi-LAT from the inner Galactic region. This indicates a common hadronic origin of both, powered by supernovae. Three other shower-like events are spatially correlated with the Fermi bubbles, originating from the Galactic Center activity, within the uncertainty of reconstructing their arrival directions. Origin of the other neutrino events, including 7 track-like events, is still elusive.

Search for TeV $\gamma$-ray emission from AE Aqr coincident with high optical and X-ray states with the MAGIC telescopes

We report on observations of the nova-like cataclysmic variable AE Aqr performed by MAGIC. The observations were part of a quasi-simultaneous multi-wavelength campaign carried out between 2012 May and June covering the optical, UV, X-ray and gamma-ray ranges. MAGIC conducted the campaign and observed the source during 12 hours. The other instruments involved were KVA, Skinakas, and Vidojevica in the optic and Swift in the X-ray. We also used optical data from the AAVSO. The goals were to: monitor the variability of the source at different wavelengths, perform gamma-ray studies coincident with the highest states of the source at the other wavelengths, and confirm or rule out previous claims of detection of very-high-energy emission from this object. We report on a search for steady TeV emission during the whole observation, for variable TeV emission coincident with the highest optical and X-ray states and periodic TeV emission at the 33.08 s rotation period (30.23 mHz rotation frequency) of the white dwarf and its first harmonic (60.46 mHz rotation frequency). These are the first observations under good weather conditions performed by the present generation of IACTs for this object.

Modeling gamma ray production from proton-proton interactions in high-energy astrophysical environments

Gamma rays are the best probes to study high-energy particle interactions occurring in astrophysical environments. Space based instruments such as Fermi Large Area Telescope (Fermi LAT) and ground based experiments such as VERITAS, H.E.S.S. and MAGIC have provided us with valuable data on various production mechanisms of gamma rays within our Galaxy and beyond. Depending on astronomical conditions, gamma rays can be produced either by hadronic or leptonic interactions. In this paper, we probe the production of gamma rays by the hadronic channel where gamma rays are primarily produced by the decay of secondary neutral pions and $\eta$ mesons from proton-proton interactions in a wide energy range. We use state of the art high-energy hadronic interaction models, calibrated with the new LHC results and widely used in ground based ultra-high energy air shower experiments. We also compare SIBYLL 2.1, QGSJET-II-04 and EPOS LHC models and provide lookup tables which can be used by researchers to model gamma ray production from the hadronic channel and ultimately extract the underlying proton spectrum from gamma ray observations.

A Simple Explanation of the Ultra-high Energy Neutrino Events at IceCube [Cross-Listing]

The recent observation of two PeV events at IceCube, followed by an additional 26 events between 20 – 300 TeV, has generated considerable speculations on its origin, and many exotic New Physics explanations have been invoked. For a reliable interpretation, it is however important to first scrutinize the Standard Model (SM) expectations carefully, including the theoretical uncertainties, mainly due to the parton distribution functions. Assuming an isotropic cosmic neutrino flux with a simple unbroken power-law spectrum, we find that the SM neutrino-nucleon interactions are sufficient to explain all the observed events so far, without the need for any exotic phenomena. With more statistics, this powerful detector could provide a unique test of the SM up to the PeV scale, and lead to important clues to New Physics.

The loss-limited electron energy in SN 1006: effects of the shock velocity and of the diffusion process

The spectral shape of the synchrotron X-ray emission from SN 1006 reveals the fundamental role played by radiative losses in shaping the high-energy tail of the electron spectrum. We analyze data from the XMM-Newton SN 1006 Large Program and confirm that in both nonthermal limbs the loss-limited model correctly describes the observed spectra. We study the physical origin of the observed variations of the synchrotron cutoff energy across the shell. We investigate the role played by the shock velocity and by the electron gyrofactor. We found that the cutoff energy of the syncrotron X-ray emission reaches its maximum value in regions where the shock has experienced its highest average speed. This result is consistent with the loss-limited framework. We also find that the electron acceleration in both nonthermal limbs of SN 1006 proceeds close to the Bohm diffusion limit, the gyrofactor being in the range 1.5-4. We finally investigate possible explanations for the low values of cutoff energy measured in thermal limbs.

Gamma-rays from Blazars and the Extragalactic Background Light

Recent observations of blazars at high energy (HE, 0.1-100 GeV) and very high energy (VHE, >0.1 TeV) have provided important constraints on the intensity and spectrum of the diffuse Extragalactic Background Light (EBL), shedding light on its main origin. Several issues remain open, however, in particular in the mid- and far-infrared bands and in the blazar emission at multi-TeV energies. This review summarizes the observational and theoretical progress in the study of the EBL with gamma-rays and the most promising future improvements, which are mainly expected from spectra in the multi-TeV range.

On the prospects of ultra-high energy cosmic rays detection by high altitude antennas

Radio emission from Ultra-High Energy Cosmic Rays (UHECR) showers detected after specular reflection off the Antarctic ice surface has been recently demonstrated by the ANITA balloon-borne experiment. An antenna observing a large area of ice or water from a mountaintop, a balloon or a satellite may be competitive with more conventional techniques. We present an estimate of the exposure of a high altitude antenna, which provides insight on the prospects of this technique for UHECR detection.

Long GRBs and massive stellar explosions from frame dragging around rotating black holes

The most energetic GRB-supernovae probably derive from rotating stellar mass black holes. Based on BeppoSax data, we identify a mechanism for exploding a remnant stellar envelope by disk winds. A specific signature is high frequency modulations in the accompanying prompt GRB emission from dissipation in high energy emissions along the black hole spin axis due, in part, to forced turbulence in the inner disk or torus mediated by frame dragging. A majority of long GRBs are found to have significant autocorrelation below 10 Hz with chirps extending up to 1000 Hz. Their comoving Fourier spectra satisfy a power law with index $\alpha\simeq-0.82$ up to about one hundred Hz and comoving chirp spectra show broken power laws with $\alpha\simeq-0.65$ up to 10 Hz, $\alpha\simeq-0.25$ up to a few hundred Hz and $\alpha\simeq0$ beyond. These high frequency signatures are the most direct signature of long-lived turbulence down to the ISCO of rotating black holes, pointing directly accompanying long duration bursts in gravitational wave emission.

The multi-frequency multi-temporal sky

Contemporary astronomy benefits of very large and rapidly growing amounts of data in all bands of the electromagnetic spectrum, from long-wavelength radio waves to high energy gamma-rays. Astronomers normally specialize in data taken in one particular energy window, however the advent of data centers world-wide and of the Virtual Observatory, which provide simple and open access to quality data in all energy bands taken at different epochs, is making multi-frequency and multi-epoch astronomy much more affordable than in the past. New tools designed to combine and analyze these data sets are being developed with the aim of visualizing observational results and extracting information about the physical processes powering cosmic sources in ways that were not possible before. In this contribution blazars, a type of cosmic sources that emit highly variable radiation at all frequencies, are used as an example to describe the possibilities of this type of astronomy today, and the discovery potential for the near future.

Constraints on Lorentz Invariance Violation with Fermi-LAT Observations of Gamma-Ray Bursts

Some Quantum Gravity (QG) theories allow for a violation of Lorentz invariance (LIV), manifesting as a dependence of the velocity of light in vacuum on its energy. If such a dependence exists, then photons of different energies emitted together by a distant source will arrive at the Earth at different times. High-energy (GeV) transient emissions from distant astrophysical sources such as Gamma-ray Bursts (GRBs) and Active Galaxy Nuclei can be used to search for and constrain LIV. The Fermi collaboration has previously analyzed two GRBs in order to put constraints on the dispersion parameter in vacuum, and on the energy scale at which QG effects causing LIV may arise. We used three different methods on four bright GRBs observed by the Fermi-LAT to get more stringent and robust constraints. No delays have been detected and strong limits on the QG energy scale are derived: for linear dispersion we set tight constraints placing the QG energy scale above the Planck mass; a quadratic leading LIV effect is also constrained.

Microwave Signature of Relativistic Positrons in Solar Flares

Relativistic antiparticles can be created in high-energy nuclear interactions; thus, detection of antiparticles in an astrophysical source can tell us something remarkable about the underlying high-energy processes and nuclear interactions. However, once created, the antiparticles remain a minor fraction of their conjugant normal particles, so the detection of the antiparticles represents a big science challenge. To address this challenge we employ imaging and polarimetry of microwave radiation produced as the positrons gyrate in the ambient magnetic field. The key property of the radiation used in this method is that the oppositely charged particles, electrons and positrons, produce radiation with opposite helicity, easily distinguishable by currently operating radio facilities. Analysis of available spatially resolved microwave data augmented by independent magnetic field measurements allows us to remotely detect the relativistic positron component in several solar flares.

Testing Relativity with High-Energy Astrophysical Neutrinos

The recent observation of high-energy astrophysical neutrinos can be used to constrain violations of Lorentz invariance emerging from a quantum theory of gravity. We perform threshold and Cherenkov analyses that improve existing bounds by factors ranging from about a million to 10^{20}.

Prospects for future very high-energy gamma-ray sky survey: impact of secondary gamma rays

Very high-energy gamma-ray measurements of distant blazars do not clearly show the signature of the attenuation due to the pair production with the extragalactic background light. Recent studies showed that these objects can be well explained by secondary gamma rays emitted by cascades induced by ultra-high-energy cosmic rays. The secondary gamma rays will enable one to detect a large number of blazars with future ground based gamma- ray telescopes such as Cherenkov Telescope Array (CTA). We show that the secondary emission process will allow CTA to detect 100, 130, 150, 87, and 8 blazars above 30 GeV, 100 GeV, 300 GeV, 1 TeV, and 10 TeV, respectively, up to z~8 assuming the intergalactic magnetic field (IGMF) strength B = 10^-17 G and an unbiased all sky survey with 0.5 hr exposure at each Field of View, where total observing time is ~540 hr. These numbers will be 79, 96, 110, 63, and 6 up to z~5 in the case of B = 10^-15 G. This large statistics of sources will be a clear evidence of the secondary gamma-ray scenarios and a new key to studying the IGMF statistically. We also find that a wider and shallower survey is favored to detect more and higher redshift sources even if we take into account secondary gamma rays.

Constraints on the source of ultra-high energy cosmic rays using anisotropy vs chemical composition

The joint analysis of anisotropy signals and chemical composition of ultra-high energy cosmic rays offers strong potential for shedding light on the sources of these particles. Following up on an earlier idea, this paper studies the anisotropies produced by protons of energy >E/Z, assuming that anisotropies at energy >E have been produced by nuclei of charge Z, which share the same magnetic rigidity. We calculate the number of secondary protons produced through photodisintegration of the primary heavy nuclei. Making the extreme assumption that the source does not inject any proton, we find that the source(s) responsible for anisotropies such as reported by the Pierre Auger Observatory should lie closer than ~20-30, 80-100 and 180-200 Mpc if the anisotropy signal is mainly composed of oxygen, silicon and iron nuclei respectively. A violation of this constraint would otherwise result in the secondary protons forming a more significant anisotropy signal at lower energies. Even if the source were located closer than this distance, it would require an extraordinary metallicity >120, 1600, 1100 times solar metallicity in the acceleration zone of the source, for oxygen, silicon and iron respectively, to ensure that the concomitantly injected protons not to produce a more significant low energy anisotropy. This offers interesting prospects for constraining the nature and the source of ultra-high energy cosmic rays with the increase in statistics expected from next generation detectors.

Registration of the signal of a star and PCR sources optical radiation by means of the installation, aimed at the investigation of EAS of high energy cosmic rays

With the help of the experimental installation aimed at the investigation of high energy cosmic rays (Tien-Shan high mountain laboratory) the signal of Solar and star optical radiation is registered. The signal is well provided statistically and possesses the strictly expressed maximum in the region of EAS sizes Ne 1.19 106 particles (primary energy Eo 1.33 1015 eV). This signal is the peak from gamma EAS, generated by gamma quanta from decay of pi zero mesons, photo produced by the Primary Cosmic Radiation (PCR) nuclei on the photons of stars and of PCR sources. The assumption is made, that exactly this process provides the main contribution in the formation of so called knee on the primary spectrum. Due to the universality and distinct maximum of this signal, its usage for independent and reliable calibration of the EAS installations, for the mutual calibration of these installations and, possibly, for the merger of experimental data obtained by means of these installations to increase the statistics, is proposed. It is especially vital to day, when the further essential increase of the energy range under investigation is necessary.

A Search for Neutrino Emission from the Fermi Bubbles with the ANTARES Telescope

Analysis of the Fermi-LAT data has revealed two extended structures above and below the Galactic Centre emitting gamma rays with a hard spectrum, the so-called Fermi bubbles. Hadronic models attempting to explain the origin of the Fermi bubbles predict the emission of high-energy neutrinos and gamma rays with similar fluxes. The ANTARES detector, a neutrino telescope located in the Mediterranean Sea, has a good visibility to the Fermi bubble regions. Using data collected from 2008 to 2011 no statistically significant excess of events is observed and therefore upper limits on the neutrino flux in TeV range from the Fermi bubbles are derived for various assumed energy cutoffs of the source.

Emission Height and Temperature Distribution of White-Light Emission Observed by Hinode/SOT from the 2012 January 27 X-class Solar Flare

White-light emissions were observed from an X1.7 class solar flare on 27 January 2012, using three continuum bands (red, green, and blue) of the Solar Optical Telescope (SOT) onboard the Hinode satellite. This event occurred near the solar limb, and so differences in locations of the various emissions are consistent with differences in heights above the photosphere of the various emission sources. Under this interpretation, our observations are consistent with the white-light emissions occurring at the lowest levels of where the Ca II H emission occurs. Moreover, the centers of the source regions of the red, green, and blue wavelengths of the white-light emissions are significantly displaced from each other, suggesting that those respective emissions are emanating from progressively lower heights in the solar atmosphere. The temperature distribution was also calculated from the white-light data, and we found the lower-layer emission to have a higher temperature. This indicates that high-energy particles penetrated down to near the photosphere, and deposited heat into the ambient lower layers of the atmosphere.

Milagro Limits on the Rate-Density of Primordial Black Holes

Primordial Black Holes (PBHs) created early in the universe are dark matter candidates. One method of detecting these PBHs is through their Hawking radiation. PBHs created with an initial mass of 5.0 x 10^14 g should be evaporating today with bursts of high-energy particles, including gamma radiation in the GeV – TeV energy range. The Milagro high energy observatory, which operated from 2000 to 2008, is sensitive to the high end of the PBH evaporation gamma ray spectrum. Due to its large field-of-view, more than 90% duty cycle and sensitivity up to 100 TeV gamma rays, the Milagro observatory is ideally suited for the direct search of PBH bursts. Based on a search in Milagro data, we report PBH upper limits according to the standard model.

A Comparison of the Galactic Cosmic Ray H, He and C/O Nuclei Spectra Measured Between ~5 and 500 MeV/nuc Beyond 122 AU at Voyager 1 with the Predictions of a Diffusion Model for Propagation in the Galaxy [Cross-Listing]

After the disappearance of lower energy heliospheric particles at Voyager 1 starting on August 25th, 2012, spectra of H, He and C/O nuclei were revealed that resembled those to be expected for galactic cosmic rays. These spectra had intensity peaks in the range of 30-60 MeV, decreasing at both lower energies down to a few MeV and at higher energies up to several hundred MeV. We have modeled the propagation of these particles in the galaxy using an updated Leaky Box Diffusion model which determines the spectra of these components from ~2 MeV to >200 GeV. The key parameters used in the model are a galactic input spectrum ~P^-2.24, the same for all components and independent of rigidity, and a diffusion coefficient that is ~P^0.5 above a lower rigidity and increases ~beta^-1.0 below a lower rigidity ~0.56 GV. These same parameters also fit the high energy H and He data from ~10-200 GeV/nuc from the PAMELA and BESS experiments. The new Voyager spectra for all three nuclei are thus consistent with rigidity spectra ~P^-2.24 from the lowest energies to at least 100 GeV. Deviations from this spectrum can reasonably be attributed to propagation effects. Some deviations between the calculated and newly observed spectra are noted, however, below ~30 MeV/nuc, particularly for C/O nuclei, that could be significant regarding the propagation and sources of these particles.

Studying flux variability of the BL Lac object 1ES0806+524 with MAGIC in a multi-wavelength context

We present results of multi-wavelength (MWL) observations of the high-frequency-peaked BL Lacertae (HBL) object 1ES 0806+524 (z=0.138). Triggered by a high optical state, very high energy (VHE; E > 100 GeV) observations were carried out with the MAGIC stereoscopic system from January to March 2011. During the observations a relatively short VHE gamma-ray flare was detected that lasted no longer than one night. To complement the VHE observations, simultaneous MWL data were collected in high energy gamma-rays using the \textit{Fermi Large Area Telescope (HE, 300 MeV – 100 GeV), in the X-ray and UV band with the \textit{Swift} satellite, in the optical R–band through observations with the KVA telescope and in the radio band using the OVRO telescope. This constitutes the first time that such a broad band coverage has been obtained for this source. We study the source properties through the characterization of the spectral energy distribution (SED) and its evolution through two different VHE flux states. The SED can be modeled with a simple one-zone SSC model, resulting in parameters that are comparable to those obtained for other HBLs.

EUV Non-thermal Line Broadening and High-energy particles during Solar Flares

We have studied the relationship between the location of EUV nonthermal broadening and high-energy particles during the large flares by using EUV imaging spectrometer onboard {\it Hinode}, Nobeyama Radio Polarimeter, Nobeyama Radioheliograph, and Atmospheric Imaging Assembly onboard {\it Solar Dynamic Observatory}. We have analyzed the five large flare events which contain thermal rich, intermediate, and thermal poor flares classified by the definition discussed in the paper. We found that, in the case of thermal rich flares, the nonthermal broadening of \ion{Fe}{24} occurred at the top of the flaring loop at the beginning of the flares. The source of the 17 GHz microwave is located at the footpoint of the flare loop. On the other hand, in the case of intermediate/thermal poor flares, the nonthermal broadening of \ion{Fe}{24} occurred at the footpoint of the flare loop at the beginning of the flares. The source of the 17 GHz microwave is located at the top of the flaring loop. We discussed the difference between thermal rich and intermediate/thermal poor flare based on the spatial information of nonthermal broadening, which may give a clue for the presence of turbulence playing an important role in the pitch angle scattering of the high-energy electron.

High-energy neutrino production from photo-hadronic interactions of gamma rays from Active Galactic Nuclei at source

Recent astronomical observations reveal that Active Galactic Nuclei (AGN) are sources of high-energy radiation. For example, the Fermi-LAT and Hess telescopes have detected gamma-ray emissions from the cores of several types of AGN’s. Even more, the Pierre Auger observatory has found a correlation of ultra-high energy cosmic ray events with the position of Active Galactic Nuclei, such as Centaurus A. In this way, according to particle physics, a flux of high-energy neutrinos should be expected from the interactions of cosmic and gamma-rays with the ambient matter and radiation at the source. In this work, estimations of the diffuse neutrino flux from AGN’s arising from interactions of the gamma radiation with the gas and dust of the sources will be presented.

Study of the muon content of very high-energy EAS measured with the KASCADE-Grande observatory

The KASCADE-Grande detector is an air-shower array devoted to the study of primary cosmic rays with very high-energies (E = 10^{16} – 10^{18} eV). The instrument is composed of different particle detector systems suitable for the detailed study of the properties of Extensive Air Showers (EAS) developed by cosmic rays in the atmosphere. Among the EAS observables studied with the detector, the charged number of particles, the muon content (at different energy thresholds), and the number of electrons are found. By comparing the measurements of these air-shower parameters with the expectations from MC simulations, different hadronic interaction models can be tested at the high-energy regime with the KASCADE-Grande experiment. In this work, the results of a study on the evolution of the muon content of EAS with zenith angle, performed with the KASCADE-Grande instrument, is presented. Measurements are compared with predictions from MC simulations based on the QGSJET II, QGSJET II-04, SIBYLL 2.1 and EPOS 1.99 hadronic interaction models. A mismatch between experiment and simulations is observed. A similar problem is found for the evolution of the lateral distribution function of muons in the atmosphere.

The effect of photon-photon absorption on Fermi-LAT light-curves of GRB afterglows

We investigate the effect that the absorption of high-energy (above 100 MeV) photons produced in GRB afterglow shocks has on the light-curves and spectra of Fermi-LAT afterglows. Afterglows produced by the interaction of a relativistic outflow with a wind-like medium peak when the blast-wave deceleration sets in, and the afterglow spectrum could be hardening before that peak, as the optical thickness to pair-formation is decreasing. In contrast, in afterglows produced in the interaction with a homogeneous medium, the optical thickness to pair-formation should increase and yield a light-curve peak when it reaches unity, followed by a fast light-curve decay, accompanied by a spectral softening. If energy is injected in the blast-wave, then the accelerated increase of the optical thickness yields a convex afterglow light-curve. Other features, such as a double-peak light-curve or a broad hump, can arise from the evolution of the optical thickness to photon-photon absorption. Fast decays and convex light-curves are seen in a few LAT afterglows, but the expected spectral softening is rarely seen in (and difficult to measure with) LAT observations. Furthermore, for the effects of photon-photon attenuation to shape the high-energy afterglow light-curve without attenuating it too much, the ejecta initial Lorentz factor must be in a relatively narrow range (50–200), which reduces the chance of observing those effects.

Catalogue of particle-accelerating colliding-wind binaries

Massive systems made of two or more stars are known to be the site for interesting physical processes — including at least in some cases — particle acceleration. Over the past decade, this topic motivated a particular effort to unveil the properties of these systems and characterize the circumstances responsible for the acceleration of particles and the potential role of pre-supernova massive stars in the production of high energy particles in our Galaxy. Although previous studies on this topic were mostly devoted to processes in general, or to a few individual objects in particular, a unified target-oriented census of particle-accelerating colliding-wind binaries (hereafter PACWBs) does not exist yet. This paper aims at making a general and unified census of these systems, emphasizing their main properties. A general discussion includes energetic considerations along with wind properties in relation with non-thermal emission processes that are likely at work in colliding-wind binaries. Finally, some guidelines for future observational and theoretical studies are drawn.

A lingering non-thermal component in the GRB prompt emission: predicting GeV emission from the MeV spectrum

The high energy GeV emission of gamma-ray bursts (GRBs), detected by \emph{Fermi}/LAT, has a significantly different morphology compared to the lower energy MeV emission, detected by \emph{Fermi}/GBM. Though the late time GeV emission is believed to be synchrotron radiation produced via an external shock, this emission as early as the prompt phase is puzzling. Meaningful connection between these two emissions can be drawn only by an accurate description of the prompt MeV spectrum. We perform a time-resolved spectroscopy of the GBM data of long GRBs having significant GeV emission, using a model consisting of 2 blackbodies and a power-law. We examine in detail the evolution of the spectral components and found that GRBs having high GeV emission (GRB 090902B and GRB 090926A) have a delayed onset of the power-law component, in the GBM spectrum, which lingers at the later part of the prompt emission. This behaviour mimics the flux evolution in LAT. In contrast, bright GBM GRBs with an order of magnitude lower GeV emission (GRB 100724B and GRB 091003) show a coupled variability of the total and the power-law flux. Further, by analyzing the data for a set of 17 GRBs, we find a strong correlation between the power-law fluence in the MeV and the LAT fluence (Pearson correlation: r=0.88 and Spearman correlation: $\rho=0.81$). We demonstrate that this correlation is not influenced by the correlation between the total and the power-law fluences at a confidence level of 2.3$\sigma$. We speculate the possible radiation mechanisms responsible for the correlation.

Revisiting SWJ2000.6+3210 : A persistent Be X-ray pulsar ?

We present a detailed timing and spectral analysis of the Be X-ray binary SWJ2000.6+3210 discovered by the BAT Galactic plane survey. Two Suzaku observations of the source made at six months interval, reveal pulsations at ~ 890s for both observations with a much weaker pulse fraction in the second one. Pulsations are clearly seen in the energy band of 0.3-10 keV of XIS for both observations and at high energies up to 40 keV for the second observation. The broad band X-ray spectrum is consistent with a powerlaw and high energy cutoff model along with a hot blackbody component. No change in spectral parameters is detected between the observations. We have also analyzed several short observations of the source with Swift/XRT and detected only a few percent variation in flux around a mean value of 3:5 *10^{-11} erg cm^{-2} s^{-1}. The results indicates that SWJ2000.6+3210 is a member of persistent Be X-ray binaries which have the same broad characteristics as this source.


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