A TeV-Detected Blazar 1ES 1959+650 in a Strong 0.3-10 keV Flaring State
ATel #11538; Bidzina Kapanadze (Abastumani Astrophysical Observatory at Ilia State University, Tbilisi, Georgia; INAF-OAB, Merate, Italy)
on 17 Apr 2018; 07:07 UT
Credential Certification: Bidzina Kapanadze (bidzina_kapanadze@iliauni.edu.ge)
Since 2015 August, the nearby TeV-detected HBL source 1ES 1959+650 (z=0.048) is showing a phase of considerably enhanced X-ray flaring activity compared to the previous years (Kapanadze et al. "A recent strong X-ray flaring activity of 1ES 1959+650 with possibly less efficient stochastic acceleration", MNRAS, 461, L26; Kapanadze et al. 2017, "The second strong X-ray flare in 1ES 1959+650", MNRAS, 473, 2542; ATel #9949, # 9694, #9205, # 9121, #8468, # 8342, # 8289, #8014, #10439, #10622). Note the flares detected in this epoch are revealed mostly by means of our Target of Opportunity (ToO) observations with X-Ray Telescope (XRT) onboard Neil Gehrels Swift Observatory. The last Swift-XRT observation of 1ES 1959+650 was performed on 2017 April 15 which revealed the source in a strong flaring state: the 0.3-10 count rate showed an increase by 8% between two different segments of ObsID 00094153001 (separated by 0.8 day from each other). It reached the value of 20.5+/-0.17 cts/s which is by a factor of 2 higher than the weighted mean rate from all XRT observations of our target during 2005--2018. Currently, 1ES 1959+650 is the second brightest blazar in the 0.3-10 KeV energy range (after Mrk 421; see https://www.swift.psu.edu/monitoring/source.php?source=1ES1959+650). In the framework of one-zone SSC models, a flaring activity of 1ES 1959+650 is also expected in the UV-radio and gamma-ray parts of the spectrum, and intensive multiwavelength observations of 1ES 1959+650 are strongly encouraged to study instable processes and emission mechanisms in this source.
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.
