Since 2007, the blazar 3C 454.3 has become the most active and the brightest gamma-ray source of the sky, deserving the nickname of "Crazy Diamond". The short-term variability in the gamma-ray energy band and the extremely high peak fluxes reached during intense flaring episodes make 3C 454.3 one of the best targets to investigate the blazar jet properties. We review almost four years of observational properties of this remarkable source, discussing both short- and long-term multi-wavelength campaigns, with particular emphasis on the recent flaring episode which occurred on 2010 November 20, when 3C 454.3 reached on a daily time-scale a gamma-ray flux (E>100 MeV) higher than 6.5E-5 ph/cm2/s, about six times the flux of the brightest gamma-ray steady source, the Vela Pulsar.
Outbursts from gamma-ray quasars provide insights on the relativistic jets of active galactic nuclei and constraints on the diffuse radiation fields that fill the Universe. The detection of significant emission above 100 GeV from a distant quasar would show that some of the radiated gamma rays escape pair-production interactions with low-energy photons, be it the extragalactic background light (EBL), or the radiation near the supermassive black hole lying at the jet's base. VERITAS detected gamma-ray emission up to 200 GeV from PKS 1441+25 (z=0.939) during April 2015, a period of high activity…
Galactic cosmic rays are believed to be accelerated at supernova remnant shocks. Gamma-ray observations of both supernova remnants and associated molecular clouds have been used in several occasions to test (so far quite successfully) this popular hypothesis. Despite that, a conclusive solution to the problem of cosmic ray origin is still missing, and further observational and theoretical efforts are needed. In this paper, the current status of these investigations is briefly reviewed.
Although it has been established observationally beyond doubt that broad-line stripped envelope supernovae (SNe) of type Ic produce long duration gamma ray bursts (GRBs), that neutron star mergers produce short hard GRBs (SHBs), and that phase transition of neutron stars in high mass X-ray binaries (HMXBs) may produce SN-Less GRBs, their production mechanism is still debated. The two leading theoretical models of GRBs and their afterglows, the fireball model and the cannonball model, have been widely confronted with the mounting observational data on GRBs and SHBs during the last two decades. …
Context. We have presented a numerical model for the non-thermal emission of gamma-ray binaries in a pulsar-wind driven scenario. Aims. We apply this model to one of the best-observed gamma-ray binaries, the LS 5039 system. Methods. The model involves a joint simulation of the pulsar- and stellar-wind interaction and the transport of electronic pairs from the pulsar wind accelerated at the emerging shock structure. We compute the synchrotron and inverse Compton emission in a post-processing step, while consistently accounting for relativistic beaming and $γγ$-absorption in the stellar radiatio…
Unexpected gamma-ray signal in the vicinity of 1ES 0229+200
我们报告在BL Lac天体1 ES 0229+200周围区域发现的一个身份不明的伽马射线信号。我们在分析距耀变体不到3°的6.2年费米-LAT数据时偶然发现了它。观察到的计数过量本身表现为检验统计量图中的非预期局部最大值。虽然在这一区域已经确定了几个费米LAT源，但我们无法将它们与该残留信号的位置联系起来。与其他波段可见光源的明确关联也不成功。我们简要地讨论了这种未解决的现象的特点。我们的研究结果表明，陡峭的能谱和点状的性质，这个候选人的伽马射线发射器。
The observation of cosmic gamma-rays from the ground is based upon the detection of gamma-ray initiated air showers. At energies between approximately $10^{11}$ eV and $10^{13}$ eV, the imaging air Cherenkov technique is a particularly successful approach to observe gamma-ray sources with energy fluxes as low as $\approx 10^{-13}$ erg\,cm$^{-2}\,$s$^{-1}$. The observations of gamma-rays in this energy band probe particle acceleration in astrophysical plasma conditions and are sensitive to high energy phenomena beyond the standard model of particle physics (e.g., self-annihilating or decaying d…
Long-duration gamma-ray bursts (GRBs) have been often considered as the natural evolution of some core-collapse supernovae (SNe). While GRBs with relativistic jets emit an electromagnetic signal, GRBs with mildly relativistic jets are opaque to photons and, therefore, could be detectable through neutrinos only. We discuss the possibility that successful GRBs and mildly relativistic jets belong to the same class of astrophysical transients with different Lorentz factor Gamma_b and study the production of high-energy neutrinos as a function of Gamma_b, by including both proton-photon and proton-…
The detection of GRB 180722B and GRB 190114C in sub-TeV gamma-rays has opened up a new window to study gamma-ray bursts in high energy gamma-rays. Recently it is shown that the synchrotron and inverse Compton processes are responsible for the production of these high energy gamma-rays during the afterglow. Here, for the first time we demonstrate that, the photohadronic scenario which is successful in explaining the multi-TeV flaring in high energy blazars is also applicable for gamma-ray bursts. We show that the sub-TeV spectra of GRB 190114C and GRB 180720B are due to the interaction of high …
Follow-up on the Supermassive Black Hole Binary Candidate J1048+7143: Successful Prediction of the Next Gamma-ray Flare and Refined Binary Parameters in the Framework of Jet Precession Model
Long duration gamma-ray bursts (GRBs) have often been considered as the natural evolution of some core-collapse supernova (CCSN) progenitors. However, the fraction of CCSNe linked to astrophysical jets and their properties are still poorly constrained. While any successful astrophysical jet harbored in a CCSN should produce high energy neutrinos, photons may be able to successfully escape the stellar envelope only for a fraction of progenitors, possibly leading to the existence of high-luminosity, low-luminosity and not-electromagnetically bright ("choked") GRBs. By postulating a CCSN-GRB conn…
Gamma rays, electrons and positrons up to 3 TeV with the Fermi Gamma-ray Space Telescope
费米伽马射线太空望远镜（英语：Fermi Gamma-ray Space Telescope），原名伽马射线大面积太空望远镜（Gamma-ray Large Area Space Telescope，GLAST），于2008年6月11日发射升空。它的主要仪器是大面积望远镜（LAT），可探测20 MeV至300 GeV以上的伽马射线。它是一台成对转换望远镜，有16个相同的塔（跟踪器和热量计），覆盖着反符合探测器以拒绝带电粒子。量热计是CsI（Tl）晶体的速观阵列，排列在8个交替的正交层中，具有8.6辐射长度的总厚度。在本文中，我们将介绍LAT的性能，特别注意量热计，它提供了一个很好的能量测量高达3 TeV。我们还将审查其运行4年后的一些科学成果，重点是延伸到极高能量的测量，如河外漫发射光谱、宇宙电子光谱和正电子分数。
The most popular model for short gamma-ray bursts (sGRBs) involves the coalescence of binary neutron stars. Because the progenitor is actually hidden from view, we must consider under which circumstances such merging systems are capable of producing a successful sGRB. Soon after coalescence, winds are launched from the merger remnant. In this paper, we use realistic wind profiles derived from global merger simulations in order to investigate the interaction of sGRB jets with these winds using numerical simulations. We analyze the conditions for which these axisymmetric winds permit relativisti…
