Strong X-Ray Flaring Activity in Markarian 421
ATel #16062; Bidzina Kapanadze (E. Kharadze National Astrophysical Observatory; Ilia State University, Tbilisi, Georgia; INAF-OAB, Merate, Italy)
on 29 May 2023; 20:51 UT
Credential Certification: Bidzina Kapanadze (bidzina_kapanadze@iliauni.edu.ge)
Subjects: X-ray, AGN, Blazar
The nearby TeV-detected high-energy peaked BL Lacertae object Markarian 421 (z=0.031) is one of the most frequently targeted blazars with the X-Ray Telescope onboard Swift (Swift-XRT; 1423 visits between 2005 March 1 and 2023 May 25), amounting a net exposure of 1822 ks. The observation-binned 0.3-10 keV count rate (CR) showed an extreme range between 1.89+/-0.05 cts/s and 173.61+/-0.19 cts/s (see, e.g., Kapanadze B. et al. 2016, 831, 102). A general high brightness and the presence of the synchrotron SED peak in the XRT energy range allows us to perform X-ray spectral analysis with a high accuracy for the spectra extracted from the short segments of the particular exposure (50-500 seconds, depending on the brightness state), reveal very fast spectral variability (on timescales of a few hundred seconds), draw conclusions about the particle acceleration processes in the relativistic jets, discern non-stationary processes in the jet and in the vicinity of the central supermassive black hole (SMBH), which are responsible for the extreme brightness and spectral variability. Since 2023 March 24, Markarian 421 has been another strong X-ray flaring activity (as revealed by means of the Swift-TOO observations triggered by us and David Paneque), showing a short-term flares by a factor of 2.7-3.5 with the peak flux values of ~75 cts/s (corresponding to about 2$\times$10^{-9}erg/cm^2/s). During the most Swift-XRT visits, the source demonstrated a very fast flux variability on timescales of ~1 ks and shorter. During the last XRT observation, Markarian 421 exhibited an onset of another short-term flare with CR=41.69+/-0.22 cts/s, corresponding to the brightness increase by ~20% compared to the previous minimum. Due to the opportunity of recording another strong X-ray flare and enhanced multiwavelength (MWL) activity is predicted also in other spectral ranges in the framework of one-zone SSC scenario, we strongly encourage intense MWL observations with the space and ground-based instruments. 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.
