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A Strong X-ray Flare in TeV-detected blazar 1ES 1959+650

ATel #10514; Bidzina Kapanadze (Abastumani Astrophysical Observatory at Ilia State University, Tbilisi, Georgia)
on 20 Jun 2017; 18:35 UT
Credential Certification: Bidzina Kapanadze (bidzina_kapanadze@iliauni.edu.ge)

Subjects: X-ray, Blazar

Referred to by ATel #: 10530

Since 2015 August, the nearby TeV-detected HBL source 1ES 1959+650 (z=0.048) is in a phase of enhanced X-ray activity compared to the previous years (Kapanadze et al. 2016, MNRAS, 461, L26; ATel #8014, #8289, #8342, #8468, #9121, #9205, #9694, #9949, #10430 and http://www.swift.psu.edu/monitoring/source.php?source=1ES1959+650 for the historical 0.3-10 keV light curve). The source has been observed four times by Swift-XRT since 2017 June 4 in the framework of our ToO observations of a medium urgency. During this campaign, 1ES 1959+650 has doubled its 0.3-10 keV brightness as follows: 2017 June 4: 8.85+/-0.11 cts/s 2017 June 12: 13.54+/-0.10 cts/s 2017 June 16: 14.75+/-0.10 cts/s 2017 June 20: 17.71+/-0.17 cts/s The latter value is by a factor of 2.25 higher than the weighted mean rate from all XRT observations of this source. It is evident that the source has underwent the fourth strong, prolonged X-ray flare since 2015 August. 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