Gamma-ray Flares of Flat Spectrum Radio Quasars: A statistical view
Luigi Pacciani
备注：
submitted to "Memorie della Società Astronomica Italiana"; Conference "8th Heidelberg International Symposium on High-Energy Gamma-Ray Astronomy (Gamma-2024)"
Based on a 10 years sample of gamma-ray flares of FSRQs collected with FERMI and AGILE, I report on this proceeding the advance on a statistical study of variability for a sample of more than 300 FSRQs. I will focus on waiting time between flares (defined as the time intervals between consecutive activity peaks (Pacciani 2022). The investigation revealed that gamma-ray activity can be modeled with overlapping bursts of flares, with flares uniformly distributed within each burst, and a typical burst rate of 0.6 y$^{-1}$. Moreover, a statistically relevant fast component with timescale of order of days is revealed. From these results, constraints on flares emission mechanisms were derived. I also discuss the preliminary results on an investigation of flares luminosity and duration in gamma-rays. A Simple fitting model is shown, correlating peak luminosity and duration of gamma-ray flares (paper in preparation).
The origin of gamma-ray flares observed from blazars is one of the major mysteries in jet physics. We have attempted to address this problem following a novel spectral energy distribution (SED) fitting technique that explored the flaring patterns identified in the broadband SEDs of two gamma-ray bright blazars 3C 279 (z=0.54) and 3C 454.3 (z=0.86), using near-simultaneous radio-to-gamma-ray observations. For both sources, the gamma-ray flux strongly correlates with the separation of the SED peaks and the Compton dominance. We propose that spectral hardening of the radiating electron population…
AGN in Gaia Alerts: from flares to Changing Look Quasars
Sorbonne University & CNRS, Institut d’Astrophysique de Paris (IAP)（索邦大学与法国国家科学研究中心，巴黎天体物理研究所）；Nordic Optical Telescope (NOT)（北欧光学望远镜）；University of Maryland, College Park（马里兰大学帕克分校）；Technical University of Denmark, DTU Space（丹麦技术大学）；University of Warwick（华威大学）；University of Tartu, Tartu Observatory（塔尔图大学）；University of Turku（图尔库大学）；CSIC, Inst. de Astrofisica de Andalucia（西班牙国家研究委员会，安达卢西亚天体物理研究所）；Universita di Bologna（博洛尼亚大学）；Trinity College Dublin（都柏林三一学院）；INAF-Osservatorio Astronomico di Roma（意大利国家天体物理研究所罗马天文台）
The physical scenario responsible for gamma-ray flaring activity and its location for Flat Spectrum Radio Quasars is still debated. The study of the statistical distribution of waiting-times between flares (the time intervals between consecutive activity peaks) can give information on the distribution of flaring times, and constrain the physical mechanism responsible for gamma-ray emission. We adopt here a Scan-Statistic driven clustering method (iSRS) to recognize flaring states within the FERMI-LAT data, and identify the time of activity-peaks. Results: Flares waiting times can be described …
GRB 131108A is a bright long Gamma-Ray Burst (GRB) detected by the Large Area Telescope and the Gamma-ray Burst Monitor on board the Fermi Gamma-ray Space Telescope. Dedicated temporal and spectral analyses reveal three $γ$-ray flares dominating above 100 MeV, which are not directly related to the prompt emission in the GBM band (10 keV - 10 MeV). The high-energy light curve of GRB 131108A (100 MeV - 10 GeV) shows an unusual evolution: a steep decay, followed by three flares with an underlying emission, and then a long-lasting decay phase. The detailed analysis of the $γ$-ray flares finds that…
In 2007 September, the Crab Nebula exhibited a bright gamma-ray flare in the GeV energy range that was detected by AGILE. The observed emission at >160 MeV indicates that the radiating electrons had energies above the classical synchrotron radiation-reaction limit, thus presenting a serious challenge to classical models for electron acceleration in astrophysical environments. In this paper, we apply our recently developed time-dependent self-similar analytical model describing electrostatic acceleration in the explosive reconnection region around the pulsar wind termination shock to the 2007 S…
Chandra, Keck and VLA Observations of the Crab Nebula during the 2011-April Gamma-ray Flare
本文介绍了对钱德拉X射线天文台、W。M. Keck天文台和Karl G. Jansky甚大阵（VLA）拍摄的蟹状星云图像，与2011年4月的伽马射线耀斑同时发生。尽管X射线数据中有一些暗示，但我们没有发现统计上显著的变化的证据，这些变化可以精确地确定星云内耀斑的具体位置。凯克的观察将这一结论扩展到“内结”，即，脉冲星的角秒内的特征。VLA观测结果支持这一结论。我们还讨论了伽玛射线耀斑的理论意义，并建议最戏剧性的伽玛射线耀斑是由于辐射反应限制同步辐射辐射与突发，耗散的变化，在当前系统持续的中央脉冲星。
PKS 0438$-$436 at a redshift of $z=2.856$ has been previously recognized as possessing perhaps the most luminous known synchrotron jet. Little is known about this source since the maximum elevation above the horizon is low for the Very Large Array (VLA). We present the first VLA radio image that detects the radio lobes. We use both the 151 MHz luminosity, as a surrogate for the isotropic radio lobe luminosity, and the lobe flux density from the radio image to estimate a long term, time averaged, jet power, $\overline{Q} =1.5\pm 0.7 \times 10^{47} \rm{ergs~s^{-1}}$. We analyze two deep optical …
Blazars emit a highly-variable non-thermal spectrum. It is usually assumed that the same non-thermal electrons are responsible for the IR-optical-UV emission (via synchrotron) and the gamma-ray emission (via inverse Compton). Hence, the light curves in the two bands should be correlated. Orphan gamma-ray flares (i.e., lacking a luminous low-frequency counterpart) challenge our theoretical understanding of blazars. By means of large-scale two-dimensional radiative particle-in-cell simulations, we show that orphan gamma-ray flares may be a self-consistent by-product of particle energization in t…
Gamma-ray flare activity from PSR B1259-63 during 2014 periastron passage and comparison to its 2010 passage
PSR B1259-63/LS 2883是一个伽玛射线双星系统，其中包含一颗射电脉冲星，它围绕Be星运行在一个高椭圆轨道上，周期约3.4年。在其2010年的近星点通道中，观测到了从射电到TeV的多波长辐射，以及费米大面积望远镜（LAT）测量到的一个意想不到的GeV耀斑。在这里，我们报告了PSR B1259-63在其最近的2014年近星通过期间的LAT监测结果。我们比较了2010年和这次近星点的伽马射线行为，发现PSR B1259-63显示了一个周期性的GeV耀斑。这两个近星点通道的现象学的异同进行了讨论。
Afterglows of gamma-ray bursts often show flares, plateaus, and sudden intensity drops: these temporal features are difficult to explain as coming from the forward shock. We calculate radiative properties of early GRB afterglows with the dominant contribution from the reverse shock (RS) propagating in an ultra-relativistic (pulsar-like) wind produced by the long-lasting central engine. RS emission occurs in the fast cooling regime -- this ensures high radiative efficiency and allows fast intensity variations. We demonstrate that: (i) mild wind power, of the order of $\sim 10^{46}$ erg s$^{-1}$…
We develop a model to explain the flaring activity in gamma-ray burst X-ray afterglows within the framework of slightly misaligned observers to structured jets. We suggest that flares could be the manifestation of prompt dissipation within the core of the jet, appearing to a misaligned observer in the X-ray band because of less favorable Doppler boosting. These flares appear during the afterglow phase because of core--observer light travel delays. In this picture, the prompt emission recorded by this observer comes from material along their line of sight, in the lateral structure of the jet, o…
Gamma radiation from the Crab pulsar wind nebula (PWN) shows significant variability at $\sim100$ MeV energies, recently revealed with spaceborne gamma-ray telescopes. Here we report the results of a systematic search for gamma-ray flares using a 7.4-year data set acquired with the Fermi Large Area Telescope. Analyzing the off-pulse phases of the Crab pulsar, we found seven previously unreported low-intensity flares ("small flares"). The "small flares'' originate from the variable synchrotron component of the Crab PWN and show clearly different features from the steady component of the Crab PW…
The high-energy radiation from short period binaries containing a massive star with a compact relativistic companion was detected from radio to TeV gamma rays. We show here that PeV regime protons can be efficiently accelerated in the regions of collision of relativistic outflows of a compact object with stellar winds in these systems. The accelerated proton spectra in the presented Monte Carlo model have an upturn in the PeV regime and can provide very hard spectra of sub-PeV photons and neutrinos by photo-meson processes in the stellar radiation field. Recent report of a possible sub-PeV gam…
The flat spectrum radio quasar 3C 279 was observed in an extremely high activity state on June 16, 2015 (MJD 57189). In this paper, we investigate the properties of this flaring episode in the high energy $γ$-ray and optical bands using data from the \emph{Fermi}-LAT, SMARTS, and SPOL observations during the period June 1-30, 2015 (MJD 57174-57203). The highest emission state in the $γ$-ray band detected by the \emph{Fermi}-LAT exhibits a peak flux of $\sim$ 2$\times$10$^{-7}$ erg~cm$^{-2}$~s$^{-1}$ which is more than 25 times the flux level measured in the low activity state of the source. Th…
Distinct X-ray plateau and flare phases have been observed in the afterglows of gamma-ray bursts (GRBs), and most of them should be related to central engine activities. In this paper, we collect 174 GRBs with X-ray plateau phases and 106 GRBs with X-ray flares. There are 51 GRBs that overlap in the two selected samples. We analyze the distributions of the proportions of the plateau energy $E_{\rm plateau}$ and the flare energy $E_{\rm flare}$ relative to the isotropic prompt emission energy $E_{\rm γ,iso}$. The results indicate that they well meet the Gaussian distributions and the medians of…
