Markarian 501 is Still Keeping a Long-Term X-Ray Flaring State

ATel #15753; Bidzina Kapanadze (E. Kharadze National Astrophysical Observatory; Ilia State University, Tbilisi, Georgia; INAF-OAB, Merate, Italy)
on 11 Nov 2022; 06:30 UT
Credential Certification: Bidzina Kapanadze (bidzina_kapanadze@iliauni.edu.ge)

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The nearby (z=0.034), X-ray bright, TeV-detected blazar Markarian 501 is one of the "favourite" Targets: 925 observations with a net exposure time of 958 ks during the 17.5 yr period. Owing to this effort, a wide range of the variability timescales (a few minutes to several years) are revealed and a number of the strong 0.3-10 keV flares recorded. Since 2021 March, the source shows a long-term X-ray flare (see, e.g., Kapanadze B., ATels #15059, #15124, #15134 and #15477), 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 superimposed by short-term flaring activity on timescales of 2-3 weeks, to be yielded by some instable processes occurring in the relativistic jet closely aligned to our line-of-sight (Kapanadze et al. 2017, doi:10.1093/mnras/stx891). Although the last run of the TOO observations (triggered by us and performed during 2022 October 19 -- November 9) shows a slight long-term decline in the X-ray brightness, the 0.3-10 keV count rate recorded during the last XRT visit to the source (7.31+/-0.08 cts/s) was still ~20% higher than the weighted mean rate from the aforementioned 925 XRT observations. Note that another run of the Swift TOO observations has been approved by the Swift Science Operations Team (to be performed during November 16 - December 6), and the intense multiwavelength observations of Markarian 501 are strongly encouraged for discerning the underlying emission mechanisms and instable processes. 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.