Brightness Decline Phase of the Ongoing Long-Term X-Ray Flare in the TeV-Detected Blazar Markarian 501
ATel #15828; Bidzina Kapanadze (E. Kharadze National Astrophysical Observatory; Ilia State University, Tbilisi, Georgia; INAF-OAB, Merate, Italy)
on 27 Dec 2022; 11:33 UT
Credential Certification: Bidzina Kapanadze (bidzina_kapanadze@iliauni.edu.ge)
Since 2021 March, the TeV-detected blazar Markarian 501 (z=0.034) shows a long-term X-ray flare which is obviously the variations in the baseline X-ray level on timescales of several years
(Kapanadze B., ATels #15059, #15124, #15134, #15753 and https://www.swift.psu.edu/monitoring/source.php?source=Mrk501) and comparable to the flaring activity observed during 2013--2015 (Kapanadze et al. 2017, MNRAS, 469, 1655 ). On the other hand, such long-term baseline flux variations can be triggered by long-term increase in the jet matter collimation rate, related to some instable processes in the accretion disc (see, e.g., Kapanadze et al. 2018, ApJS, 238, 13). A general high 0.3--10 keV level is accompanied by short-term flaring activity on timescales of 2-3 weeks, explained as the instable processes occurring in the relativistic jet closely aligned to our line-of-sight (Kapanadze et al. 2017). During to the last Swift-TOO campaign (4 observations during December 13-27, performed in the framework of our Request Number 18216), the 0.3-10 keV count rate showed an oscillation around 6 cts/s (corresponding to the long-term declining phase of the aforementioned flare, although 3-4 factors higher than those shown by the source during the "quiescent" states). Markarian 501 varied even on hourly timescales (between the different Swift orbits) and showed a change in the spectral curvature from $b\sim$0.6 to $b\sim$0.3. This result can be interpreted as an increasing importance of the stochastic particle acceleration in the blazar emission zone (see, e.g., Massaro et al. 2011, ApJ, 742, L32; Kapanadze et al. 2020, ApJS, 247, 27).
XRT is one of the Swift instruments along with Burst Alert Telescope (BAT) and UV/Optical Telescope (UVOT). It is a JET-X Wolter I type telescope, developed jointly by Pennsylvania State University, Brera Astronomical Observatory (OAB) and University of Leicester. Thanks to the unique characteristics, good photon statistics and low background counts of this instrument (in combination with EEV CCD2 detector), we can investigate a flux variability on different time-scales from minutes to years, obtain high-quality spectra for the majority of the observations, derive different spectral parameters, and study their timing behaviour in the 0.3-10 keV range of the electromagnetic spectrum. The Swift Satellite is operated by Pennsylvania State University.
