The increasing X-Ray Activity of PKS 2155-304
Bidzina Kapanadze (Abastumani Astrophysical Observatory at Ilia State University, Tbilisi, Georgia)
The southern TeV-detected HBL source PKS 2155-304 (z=0.116) is prominent with its very strong TeV/X-ray flaring behaviour (see, e.g., Aharonian et al. 2009, A&A, 502, 749; Abramowski et al. 2012, A&A, 539; Kapanadze et al. 2014, MNRAS, 444; 1076), and, therefore, it represents one of the frequent Swift targets (203 observations since 2005 November 17). In the framework of our Target of Opportunity (ToO) request Number 8344, the source was pointed nine time by X-Ray Telescope onboard the Swift satellite (Swift-XRT) since 2016 August 5 with one week intervals between the successive observations. During the last five observations, the 0.3-10 keV count rate has shown an increase by 85 per cent as follows: September 2 1.75+/-0.05 cts/s; September 9 2.15+/-0.05 cts/s; September 16 2.22+/-0.06 cts/s; September 23 2.47+/-0.06 cts/s; September 30 3.26+/0.07 cts/s; Note that the latter value is by 40 per cent larger than the weighted mean rate from all Swift-XRT pointings to this source. In the framework of one-zone SSC models, an increased activity is also expected in the UV-radio and gamma-ray parts of the spectrum, and intensive multiwavelength observations of PKS 2155-304 are strongly encouraged to study instable processes and emission mechanisms in this source. Note that we have submitted another ToO request incorporating the seven Swift observations of PKS 2155-304 separated by the 3-d intervals from each other. 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.
radio,optical,x-ray,gamma ray,tev,blazar