Onset of the 0.3-10 keV flare in TeV-Detected Blazar H1426+428

ATel #16871; Bidzina Kapanadze (Ilia State University, Tbilisi, Georgia; National Astrophysical Observatory, Abastumani, Georgia)
on 21 Oct 2024; 17:23 UT
Credential Certification: Bidzina Kapanadze (bidzina_kapanadze@iliauni.edu.ge)

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The TeV-detected BLazar H1426+428 (z=0.129) has been observed nine times with the X-Ray Telescope onboard Neil Gehrels Swift Observatory (Swift-XRT) since 2024 September 2, in the framework of our Target of Opportunity request Number#21040. The last observation, performed on October 20, revealed the source to be in elevated X-ray state: the observation-binned 0.3-10 keV count rate amounted to 2.53+/-0.09 cts/s which is ~20% higher that the mean rate from all 217 XRT observations to the source carried out since 2004 December 22. Note that the current 0.3-10 keV level is by more than 60% higher than that recorded during the first observation of the current campaign, achieved withing a long-term gradual brightness increase, and the source showed a similar behaviour in the first half of 2021 (see https://www.swift.psu.edu/monitoring/source.php?source=H1426+428 and Kapanadze B., ATel#14560). H1426+428 exhibited a very hard spectrum during the latest observation, with the photon-index at 1 keV $a$=1.77+/-0.04, the curvature parameter $b$=0.17+/-0.10 and the position of the synchrotron SED peak E_p=4.75+/-0.21 keV. This may serve as an indication of the significant contribution of the photons produced within different hadronic cascades (see, e.g., Kapanadze 2023, Universe, 9, 344). Since the source has shoving an X-ray flaring activity and a similar behaviour is expected in the framework of one-zone synchrotron self-Compton scenarios, 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.