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The hadronic model predicts a low X-ray and TeV flux while the leptonic model predicts an observable flux in these two energy bands. The follow-up observations of the LMC B in X-ray or TeV band would distinguish the radiation models of gamma-rays from this region. Submitted 4 January, ; v1 submitted 12 December, ; originally announced December Astrophysics and Space Science, , Submitted 21 July, ; v1 submitted 17 June, ; originally announced June ApJ , 56 Evidence of a spectral break in the gamma-ray emission of the disk component of Large Magellanic Cloud: The pion-decay mechanism predicts a unique spectral signature in the gamma-ray spectrum, characterized by a fast rising spectrum and a spectral break below a few hundreds of MeV.
The break is well consistent with the pion-decay model for the gamma-ray emission, although leptonic models, such as the electron bremsstrahlung emission, cannot be ruled out completely. Submitted 17 May, ; v1 submitted 5 March, ; originally announced March ApJ , 42 Qing-Wen Tang , Kenny C.
Beacom , Annika H. The solar disk is a bright source of multi-GeV gamma rays, due to the interactions of hadronic cosmic rays with the solar atmosphere. However, the underlying production mechanism is not understood, except that its efficiency must be greatly enhanced by magnetic fields that redirect some cosmic rays from ingoing to outgoing before they interact.
To elucidate the nature of this emission, we perform a new analysis of solar atmospheric gamma rays with 9 years of Fermi-LAT data, which spans nearly the full year solar cycle. We find a clear anticorrelation between the solar cycle phase and the gamma-ray flux between GeV.
This was not predicted, is not understood, and may provide crucial clues to the gamma-ray emission mechanism. Submitted 18 April, ; originally announced April Supplemental Material includes an additional 12 pages, 14 figures.
Peter , Kenny C. Ng , Qing-Wen Tang. The observed multi-GeV gamma-ray emission from the solar disk sourced by hadronic cosmic rays interacting with gas, and affected by complex magnetic fields is not understood. Utilizing an improved analysis of the Fermi-LAT data that includes the first resolved imaging of the disk, we find strong evidence that this emission is produced by two separate mechanisms. Between the rise to and fall from solar maximum , the gamma-ray emission is dominated by a polar component.
Between solar minimum this component remains present, but the total emission is instead dominated by a new equatorial component with a brighter flux and harder spectrum. Most strikingly, although 6 gamma rays above GeV are observed during the 1. These features, along with a GeV spectral dip which will be discussed in a companion paper, were not anticipated by theory.
Submitted 14 March, ; originally announced March Supplemental Material includes an additional 10 pages, 8 figures. Search for high energy gamma-ray emission from tidal disruption events with the Fermi Large Area Telescope. Massive black holes at galaxy center may tear apart a star when the star passes occasionally within the disruption radius, which is the so-called tidal disruption event TDE.
Most TDEs radiate with thermal emission resulted from the accretion disk, but three TDEs have been detected in bright non-thermal X-ray emission, which is interpreted as arising from the relativistic jets.
In this paper, we report the search for high energy emission from the other two relativistic TDEs Swift J The non-detection of high-energy emission from relativistic TDEs could be due to that the high-energy emission is absorbed by soft photons in the source.
Submitted 27 April, ; v1 submitted 12 January, ; originally announced January Accepted by ApJ, 6 pages, 3 figures. Recent detection of high-energy gamma-ray emission from starburst galaxies M82 and NGC suggests that starburst galaxies are huge reservoirs of cosmic rays and these cosmic rays convert a significant fraction of their energy into gamma-rays by colliding with the dense interstellar medium.
In this paper, we report the search for high-energy gamma-ray emission from several nearby star-forming and starburst galaxies using the 68 month data obtained with the Fermi Large Area Telescope. Submitted 8 August, ; v1 submitted 12 July, ; originally announced July Accepted by ApJ, discussions revised following the referee report, results and conclusions unchanged. A 55 GeV photon compatible with the position of the burst was found at about 5 hours after the prompt phase.
The probability that this photon is associated with GRB A is higher than Modeling of the broad-band spectral energy distribution suggests that such high energy photons can be produced by the synchrotron self-Compton emission of the afterglow. Submitted 11 May, ; v1 submitted 2 May, ; originally announced May Measuring the bulk Lorentz factors of gamma-ray bursts with Fermi.
Gamma-ray bursts GRBs are powered by ultra-relativistic jets. The exact value, rather than a lower limit, of the Lorentz factor can be obtained if the spectral cutoff due to such absorption is detected. Assuming that these cutoffs are caused by pair-production absorption within the source, the bulk Lorentz factors of these GRBs are obtained. We further find that the Lorentz factors are correlated with the isotropic gamma-ray luminosity of the bursts, indicating that more powerful GRB jets move faster.
Submitted 15 April, ; v1 submitted 10 December, ; originally announced December Accepted by ApJ, 10 pages, 2 figures. First detection of GeV emission from an ultraluminous infrared galaxy: Arp as seen with the Fermi Large Area Telescope. Cosmic rays CRs in starburst galaxies produce high energy gamma-rays by colliding with the dense interstellar medium ISM.
Arp is the nearest ultra luminous infrared galaxy ULIRG that has star-formation at extreme levels, so it has long been predicted to emit high-energy gamma-rays. However, no evidence of gamma-ray emission was found despite intense efforts of search. The gamma-ray emission shows no significant variability over the observation period and it is consistent with the quasi-linear scaling relation between the gamma-ray luminosity and total infrared luminosity for star-forming galaxies, suggesting that these gamma-rays arise from CR interactions.
As the high density medium of Arp makes it an ideal CR calorimeter, the gamma-ray luminosity can be used to measure the efficiency of powering CRs by supernova SN remnants given a known supernova rate in Arp Submitted 1 April, ; v1 submitted 21 March, ; originally announced March Accepted by ApJL, 6 pages, 3 figures.
Well-sampled optical lightcurves of gamma-ray bursts GRBs are complied from the literature. Multiple optical emission components are extracted with power-law function fits to these lightcurves.
We present a systematical analysis for statistical properties and their relations to prompt gamma-ray emission and X-ray afterglow for each component. We show that peak luminosity in the prompt and late flares are correlated and the evolution of the peak luminosity may signal the evolution of the accretion rate. Assuming that they are due to a long-lasting wind injected by a compact object, we show that the injected behavior favors the scenarios of a long-lasting wind after the main burst episode.
The peak luminosity of the afterglow onset is tightly correlated with Eiso, and it is dimmer as peaking later. Optical re-brightening is observed in 30 GRBs in our sample. It shares the same relation between the width and the peak time as found in the onset bump, but no clear correlation between the peak luminosity and Eiso as observed in the onset bumps is found. Although its peak luminosity also decays with time, the slope is much shallower than that of the onset peak. The late re-brightening may signal another jet component.
Mixing of different emission components may be the reason for the observed chromatic breaks in different energy bands. Submitted 13 March, ; originally announced March An evolving GeV spectrum from prompt to afterglow: We present the high-energy emission properties of GRB A, from its prompt mission to late afterglow phase.
GRB A contains two emission episodes: The existence of very energetic photons, e. GRB A represents the latest example where inverse Compton emission has to be taken into account in explaining the afterglow GeV emission, which had been suggested long before the launch of Fermi LAT. Submitted 18 June, ; originally announced June Discovery of an extra hard spectral component in the high-energy afterglow emission of GRB A. We characterize the time-resolved spectra of the GeV emission from the GRB onset to the afterglow phase.
By performing time-resolved spectral fits of GRB A, we found a strong evidence of an extra hard spectral component that exists in the extended high-energy emission of this GRB. We argue that this hard component may arise from the afterglow inverse Compton emission. Submitted 24 May, ; v1 submitted 14 May, ; originally announced May ApJL, , L13 The external forward shock EFS models have been the standard paradigm to interpret the broad-band afterglow data of gamma-ray bursts GRBs.
One prediction of the models is that some afterglow temporal breaks at different energy bands should be achromatic. In this paper, we perform a systematic study to address the question: Our sample includes 85 GRBs well-monitored X-ray and optical lightcurves.
Based on how well the data abide by the EFS models, we categorize them as: They show evidence of, or are consistent with having, an achromatic break. They are also consistent with having an achromatic break, even though one or more afterglow segments do not comply with the closure relations.
These are included in the Bad sample. Overall, we conclude that the simplest EFS models can account for the multi-wavelength afterglow data of at least half of the GRBs. When more advanced modeling e. Submitted 5 June, ; v1 submitted 11 March, ; originally announced March We study an extensive sample of 87 GRBs for which there are well sampled and simultaneous optical and X-ray light-curves. We extract the cleanest possible signal of the afterglow component, and compare the temporal behaviors of the X-ray light-curve, observed by Swift XRT, and optical data, observed by UVOT and ground-based telescopes for each individual burst.
Only 9 cases have afterglow light-curves that exactly match the standard fireball model prediction, having a single power law decay in both energy bands which are observed during their entire duration.