X-Ray Re-Flare in TeV-Detected BL Lacerate Object 1ES 1218+304

ATel #16112; Bidzina Kapanadze (Ilia State University, Tbilisi, Gerogia; E. Kharadze National Astrophysical Observatory, Abastumani, Georgia)
on 3 Jul 2023; 08:47 UT
Credential Certification: Bidzina Kapanadze (bidzina_kapanadze@iliauni.edu.ge)

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In ATel#15969 (posted on 2023 March 31), we notified a long-term gradual brightening by ~40% to the 0.3-10 keV count rate CR=3.65+/-0.11 cts/s. This detection was followed by 23 Swift visits to the source, performed in the framework of our target-of-opportunity observation (TOO) requests. During this monitoring, the source showed a gradual decline in the X-ray brightness by ~40\% (with some micro-oscillations with respect to the long-term trend), which was followed by re-brightening and the 0.3-10 keV flux attained to the aforementioned level during the last observation of the object performed with X-Ray Telescope onboard Swift (on June 28). The unabsorbed 0.3-10 keV flux amounted to (1.19+/-0.05)x10^{-10} erg/cm^2/s with the 0.3-10 keV photon index $\Gamma$=1.94+/-0.06 (by fixing the Hydrogen column density to the value 2.03$\times$10^2, derived from Willingale et al. 2013). Note that the hard power-law spectrum can be obtained via the relativistic magnetic reconnection, which, in turn, occurs when the jet plasmoid is relativistically magnetized (i.e. the magnetic field energy is higher than the matter rest energy; see Sironi & Spitkovsky 2014, Astrophys. J., 783, L21). Since the source is in X-ray flaring state and a further brightening may occur, as well as 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.