Short-Term 0.3-10 keV Flare in the Epoch of Long-Term Enhanced X-Ray Activity of Markarian 501

ATel #15477; Bidzina Kapanadze (Ilia State University, Tbilisi, Gerogia; E. Kharadze National Astrophysical Observatory, Abastumani, Georgia)
on 28 Jun 2022; 09:15 UT
Credential Certification: Bidzina Kapanadze (bidzina_kapanadze@iliauni.edu.ge)

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Since 2021 March, the TeV-detected blazar Markarian 501 (z=0.034) shows a long-term X-ray flare (see, e.g., Kapanadze B., ATels #15059, #15124 and #15134), which should be related to the variations in the baseline X-ray level on timescales of several years (see also see Kapanadze et al. 2017, MNRAS, 469, 1655 and https://www.swift.psu.edu/monitoring/source.php?source=Mrk501). A general high 0.3--10 keV level is acompanied 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). Namely, the Target of Opportunity (TOO) observations with the X-Ray Telescope onboard Neil Gehrels Swift Observatory (Swift-XRT), triggered by us and David Paneque (Request Numbers 17483 and 17497, respectively), recorded a gradual increase in the 0.3-10 keV brightness by ~80% to 14.48+/-0.13 counts/sec during 2022 June 10-27. This event was characterize by the "harder-when-brighter" spectral evolution with the photon index at 1 keV $a$=1.85+/-0.02, position of the synchrotron SED peak position $E_p$=4.80+/-0.25 keV and de-absorbed 0.3-10 keV flux of (4.57+/-0.07)$\times$10^{-10} erg/cm^2/s during the last XRT visit to the source. Consequently, intense multiwavelength observations of the source are strongly encouraged for discerning the underlying emission mechanisms and instable processes in blazars. 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.