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A new highest historical 0.3-10 keV brightness State of TeV-detected Blazar 1ES 1959+650

ATel #10743; Bidzina Kapanadze (Abastumani Astrophysical Observatory at Ilia State University, Tbilisi, Georgia; INAF-OAB, Merate, Italy)
on 13 Sep 2017; 21:00 UT
Credential Certification: Bidzina Kapanadze (bidzina_kapanadze@iliauni.edu.ge)

Subjects: X-ray, Blazar

Since 2017 June, the nearby TeV-detected HBL source 1ES 1959+650 (z=0.048) is showing another cycle of a strong X-ray flaring activity, which is the fourth since 2015 August ( 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", submitted to MNRAS; ATel #9949, # 9694, #9205, # 9121, #8468, # 8342, # 8289, #8014, #10439, #10622) and revealed mostly by means of our ToO observations. The last XRT pointing to this source, performed on September 12 (UTC 23:05 - 23:19), yielded a new highest historical 0.3-10 keV count rate amounting to 39.80+/-0.25 cts/s which is 17% higher than the previous highest value recorded during the first orbit of the June 24 observation, and 1ES 1959+650 possibly is the brightest blazar in the 0.3-10 keV band now (The potentially brighter source Mrk 421 can not be observed by Swift due to the Sun constrain). The corresponding spectrum fits well with the logparabolic model (the reduced Chi-Squared equals 1.123 with 408 d.o.f.) yielding the photon index at 1 keV a=1.63+/-0.02, the curvature parameter b=0.33+/-0.04, the position of the synchrotron SED peak Ep=3.64+/-0.23 keV, the unabsorbed 0.3-10 keV flux of (1.56+/-0.02)\times 10^{-9} erg/cm^2/s. The source showed a flux variability above 3 sigma within the 690 sec observational run that has been observed seldomly for BL Lac sources. The spectrum is very hard, rather expected in the framework of hadronic models than within the leptonic ones (see Shukla et al. 2015, ApJ, 798, 2). In the framework of one-zone SSC models, an enhanced activity 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.