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Very Strong 0.3-10 keV Flare in the HBL Source 1ES 1959+650

ATel #10622; Bidzina Kapanadze (Abastumani Astrophysical Observatory at Ilia State University, Tbilisi, Georgia)
on 7 Aug 2017; 13:03 UT
Credential Certification: Bidzina Kapanadze (bidzina_kapanadze@iliauni.edu.ge)

Subjects: X-ray, Blazar

Referred to by ATel #: 10743, 11059

Since 2017 June 12, the nearby TeV-detected HBL source 1ES 1959+650 (z=0.048) is showing another cycle of a very strong X-ray flaring activity, which is the fourth since 2015 August (see Kapanadze B. et al. "A recent strong X-ray flaring activity of 1ES 1959+650 with possibly less efficient stochastic acceleration"; ATel#9949,9694,9205,9121,8468,8342, 8289,8014,10439; see http://www.swift.psu.edu/monitoring/source.php?source=1ES1959+650 ). In this period, the source has shown an extreme flux variability and the 0.3--10\,keV count rate attained to the value of 34.0+/-0.20 cts/s during the first orbit of the June 24 pointing (the brightest blazar in the X-ray sky at that moment!) which is the highest historical value for this source. Afterwards, the source underwent a gradual decline to 10.41+/-0.12 cts/s (July 25) and then has shown an increase by a factor to 27.91+/-0.18 cts/s yesterday, observed in the framework of our ToO request Number 9582 (five Swift observations with 3-d separations; ). The latter value is 61% higher than the previous value recorded on August 3, and higher rates were recorded only on June 24. Possibly, 1ES 1959+650 has become the brightest blazar in the X-ray sky (compared to the last XRT observation of Mrk 421 on June 27. Note that this source was showing a prolonged lower X-ray state and currently it is not observed due to the Sun constraint). During to the yesterday's pointing, our target exhibited extreme spectral properties. The 03--10\,keV spectrum fits with the logparabola model with the photon index a=1.64+/-0.02, curvature parameter b=0.28+/-0.03, the position of the synchrotron SED peak Ep=4.40+/-0.38 keV, the reduced Chi-squared of 0.971 with 412 d.o.f. The unabsorbed 0.3-10 keV flux amounts to (1.13+/-0.07)\times 10^9 erg/cm$2/s. Note that the spectrum is very hard: the 0.3--10 keV spectra are uncommon even for HBLs, and they are explained more easily within the hadronic blazar scenarios than with the leptonic ones while their generation within the leptonic models is more demanding(Shukla et al. 2015, ApJ, 798, 2). Due to the extreme behaviour of 1ES 1959+650, its intensive multiwavelength observations 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.