Long-Term X-ray Flaring Activity of the TeV-Detected Blazar H1426+428

ATel #14560; Bidzina Kapanadze (Ilia State University, Tbilisi, Gerogia; E. Kharadze National Astrophysical Observatory, Abastumani, Georgia)
on 19 Apr 2021; 10:29 UT
Credential Certification: Bidzina Kapanadze (bidzina_kapanadze@iliauni.edu.ge)

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Since January 2021, the TeV-detected BLazar H1426+428 (z=0.129) is showing a long-term X-ray flaring activity, detected with the X-Ray Telescope onboard Neil Gehrels Swift Observatory (Swift-XRT). Namely, the 0.3-10 keV count rate attained a level of ~6 cts/s on March 19 which is the second highest value during the Swift-XRT monitoring of the source (199 observations since 2004 December 22). The flare peak was followed by the brightness fluctuations by a factor of ~2 which is evident even on the hourly timescales. Namely, H1426+428 showed the flux halving instances during the observations performed on March 19 and April 18. The flux variability is accompanied by the significant spectral changes which are consistent with the "harder-when-brighter" behaviour (hinting at the dominance of the synchrotron cooling of ultra-relativistic electrons). With ATel#14501 (posted on 2021 April 1), the VERITAS team reported the detection of the target's enhanced TeV-band activity: the mean flux in 2021 is approximately double of its long-term average over the last decade. Some optical-UV enhancements are evident from the Swift-UVOT observations. Consequently, the intense multiwavelength observations of H1426+428 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.