The Highest Historical 0.3-10 keV Flux in HBL Source Markarian 501
ATel #6167; Bidzina Kapanadze (E. Kharadze Astrophysical Observatory at Ilia State University, Tbilisi, Georgia)
on 24 May 2014; 08:48 UT
Credential Certification: Bidzina Kapanadze (bidzina_kapanadze@iliauni.edu.ge)
Subjects: X-ray, AGN, Blazar
We report the highest historical X-ray flux level from the nearby (z=0.034) high-energy peaked BL Lacertae source Mrk 501 in the 0.3-10 keV energy band, detected by the X-ray Telescope (XRT) onboard the Swift satellite which observed the source 8 times since May 1 (total exposure - about 7.5 ks). Using the data provided at http://www.swift.psu.edu/monitoring/ , we have found that the object exhibited a permanent increase in the 0.3-10 keV flux from 6.74+/-0.17 cts/s (May 1 pointing) to 19.62+/-0.16 cts/s in the case of the May 23 observation, although there was a dip with 3.5 % on May 12. The source has not shown a flux variability at 99.9 % confidence within any single pointing. The spectra are curved and the curvature parameter seems to be anticorrelated with the 03-10 keV model flux while the synchrotron peak basically shows an opposite trend. Note that Mrk 501 exhibited an extreme X-ray flare in 1997 April when the synchrotron peak shifted with two orders of the frequencies to about 100 keV (Pian et al. 1998, ApJ, 492, L17). Since the source shows the most strong flare since the beginning of Swift observations, we can not exclude a possibility of a further spectral behaviour similar to that observed in 1997. In the framework of one-zone SSC model, an increased activity is also expected in the UV-radio and gamma-ray bands and intensive multiwavelength observations of Mrk 501 are crucial to study instable processes and emission mechanisms in this source.
