Elevated X-Ray State in the TeV-Detected Blazar 1ES 1218+304
ATel #16626; Bidzina Kapanadze (Ilia State University, Tbilisi, Georgia; National Astrophysical Observatory, Abastumani, Georgia)
on 18 May 2024; 14:38 UT
Credential Certification: Bidzina Kapanadze (bidzina_kapanadze@iliauni.edu.ge)
The TeV-detected BL Lac object 1ES 1218+304 (z=0.184) has been observed 165 times by Neil Gehrels Swift Laboratory between 2005 October 30 and 2023 August 1 with a net exposure of 186 ks. These observations revealed a strong X-ray variability in the 0.3-10 keV count rate between 0.47+/-0.02 cts/s and 7.18+/-0.18 cts/s with more than 10 flares by a factor of 2-4 during the densely-sampled Swift campaigns (see https://www.swift.psu.edu/monitoring/source.php?source=1ES1218+304). The last visit of the X-Ray Telescope onboard Swift to the source (performed on 2024 May 15 in the framework of our Target of Opportunity Request Number 20509) revealed an elevated X-ray state corresponding to the 0.3-10 keV count rate of 2.80+/-0.07 cts/s ((8.57+/-0.27)x10^{-11} erg/cm^2/s in terms of the unabsorbed 0.3-10 keV flux). The latter is about 20\% higher than the mean rate from all Swift-XRT observations of 1ES 1218+304. 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 astronomical 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.
