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The Onset of Another Very Strong X-Ray Flare in the HBL Source 1ES 1959+650

ATel #11059; Bidzina Kapanadze (Abastumani Astrophysical Observatory at Ilia State University, Tbilisi, Georgia; INAF-OAB, Merate, Italy)
on 14 Dec 2017; 18:51 UT
Credential Certification: Bidzina Kapanadze (bidzina_kapanadze@iliauni.edu.ge)

Subjects: X-ray, Blazar

Since 2015 August, the nearby TeV-detected HBL source 1ES 1959+650 (Z=0.048) is showing a phase of significantly enhanced X-ray flaring activity compared to the previous years (Kapanadze et al. 2016, MNRAS, 461, L26; Kapanadze et al. 2017, MNRAS, 473, 2542; ATel #9949, # 9694, #9205, #9121, #8468, # 8342, # 8289, #8014, #10439, #10622). Note the flares detected in this epoch are mostly revealed by means of our Target of Opportunity (ToO) observations with X-Ray Telescope onboard the satellite Swift. During 2017 December 13-14, the source has been pointed twice in the framework of our recent ToO request, and it is found in a strong flaring state: during these two pointings, the 0.3-10 keV count rate increased by 22% in 13.7 hr to 29.10+/-0.18 cts/s which is by a factor 3.7 higher than the weighted mean rate from all XRT observations of our target during 2005--2017. The spectra extracted from these observations are very hard with the photon index smaller than 1.80 (predicted in the case of the Proton Blazar Model; see Mannheim 1993). 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 unstable 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.