ﻻ يوجد ملخص باللغة العربية
Due to its powerful radiation over the entire electromagnetic spectrum and its radio jet activity, the blazar 3C273 offers the opportunity to study the physics of $gamma$-ray emission from active galactic nuclei. Since a historically strong outburst in 2009, 3C273 showed relatively weak emission in the gamma-ray band over multiple years. However, recent Fermi-Large Area Telescope observations indicate elevated activity during 2015-2019. We aim at constraining the origin of the gamma-ray outbursts towards 3C273 and investigate their connection to the parsec-scale jet. We generate Fermi-LAT gamma-ray light curves with multiple binning intervals and study the spectral properties of the gamma-ray emission. Using a 3-mm ALMA light curve, we study the correlation between radio and gamma-ray emission. Relevant activity in the parsec-scale jet of 3C273 is investigated with 7-mm VLBA observations obtained close in time to notable gamma-ray outbursts. We find two prominent gamma-ray outbursts in 2016 (MJD 57382) and 2017 (MJD 57883) accompanied by mm-wavelength flaring activity. The gamma-ray photon index time series show a weak hump-like feature around the gamma-ray outbursts. The monthly gamma-ray flux-index plot indicates a transition from softer-when-brighter to harder-when-brighter at $1.03times10^{-7}rm,ph,cm^{-2},s^{-1}$. A significant correlation between the gamma-ray and mm-wavelength emission is found, with the radio lagging the gamma-rays by about 105-112 days. The 43-GHz jet images reveal the known stationary features (i.e., the core, S1, and S2) in a region upstream of the jet. We find indication for a propagating disturbance and a polarized knot between the stationary components around the times of both gamma-ray outbursts.
We analyze the multifrequency behavior of the quasar 3C 454.3 during three prominent gamma-ray outbursts: 2009 Autumn, 2010 Spring, and 2010 Autumn. The data reveal a repeating pattern, including a triple flare structure, in the properties of each ga
The observed association between supernovae and gamma-ray bursts represents a cornerstone in our understanding of the nature of gamma-ray bursts. The collapsar model provides a theoretical framework for this connection. A key element is the launch of
Relativistic jets are one of the most powerful manifestations of the release of energy related to the supermassive black holes at the centre of active galactic nuclei (AGN). Their emission is observed across the entire electromagnetic spectrum, from
We present the analysis of the radio jet evolution of the radio galaxy 3C 120 during a period of prolonged gamma-ray activity detected by the Fermi satellite between December 2012 and October 2014. We find a clear connection between the gamma-ray and
After 25 years of quiescence, the microquasar V404 Cyg entered a new period of activity in June 2015. This X-ray source is known to undergo extremely bright and variable outbursts seen at all wavelengths. It is therefore an object of prime interest t