Further X-Ray Brightening and Hard Spectrum of 1ES 1218+304
ATel #16914; Bidzina Kapanadze (Space Research Center, Department of Astronomy and Astrophysics, School of Natural Sciences and Medicine, Ilia State University, Tbilisi, Georgia; National Astrophysical Observatory, Abastumani, Georgia)
on 20 Nov 2024; 09:36 UT
Credential Certification: Bidzina Kapanadze (bidzina_kapanadze@iliauni.edu.ge)
In ATel #16906 (Kapanadze B., posted on 2024 November 12), we reported about the onset of X-ray flare in the the TeV-detected high-energy peaked BL Lac object (HBL) 1ES 1218+304 (z=0.182). The last observation with the X-Ray Telescope (XRT) onboard Swift (performed in the framework of our Target of Opportunity Observations, Request Number 21356) revealed a further X-Ray brightening of the source: the 0.3-10 keV count rate attained to the value of 3.78+/0.06 cts/s (corresponding to the undabsorbed flux of 1.22$\times$10^{-10} erg/cm^2/s), which is ~30% higher than that reported in ATel #16906 and more than 50% higher than the mean rate from all 177 XRT visits to the source. The 0.3-10 keV spectrum is well-fit with the logparabolic model, yielding the photon-index at 1 keV $a$=1.82+/-0.04, curvature parameter $b$=0.12+/0.07 and the position of the synchrotron SED peak E_p=5.62+/-0.35 keV. Note that the latter is the most extreme value ever shown by the source (see Massaro et al. 2008, A&A 478, 395 for comparison). Since a further x-ray brightening of the source is expected (along with extreme spectral properties), as well as an 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.
