X-Ray Flare in the TeV-Detected Blazar 1ES 1218+304

ATel #16906; Bidzina Kapanadze (Ilia State University, Tbilisi, Georgia; National Astrophysical Observatory, Abastumani, Georgia)
on 12 Nov 2024; 20:13 UT
Credential Certification: Bidzina Kapanadze (bidzina_kapanadze@iliauni.edu.ge)

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The TeV-detected high-energy peaked BL Lac object (HBL) 1ES 1218+304 (z=0.182) has been observed 175 times with the Neil Gehrels Swift Observatory since 2005 October 30. The last Swift visit to the source (November 11; performed in the framework of our TOO Request Number 21356) revealed it to be in a X-ray flaring state: the 0.3-10 keV observation of 1.2 ks duration carried out with the X-Ray Telescope (XRT) onboard Swift recorded the count rate of 2.95+/-0.09 cts/s which is ~40% higher than that from the XRT observation of the target performed on November 7 and more than 20% higher than the mean rate from all XRT visits to the source. The 0.3-10 keV spectrum retrieved from the last observation is hard with the photon index at 1 keV $a$=1.87+/-0.04, the curvature parameter $b$=0.20+/-0.08 and synchrotron SED peak position E_p=2.11+/-0.18 keV. 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.