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The highest historical X-ray brightness state in HBL source 1ES 1959+650

ATel #8468; Bidzina Kapanadze (Abastumani Astrophysical Observatory at Ilia State University, Tbilisi, Georgia)
on 27 Dec 2015; 20:35 UT
Credential Certification: Bidzina Kapanadze (bidzina_kapanadze@iliauni.edu.ge)

Subjects: X-ray, Blazar

Referred to by ATel #: 9010, 9070, 9148, 9949, 10430, 10514, 10743, 11059, 11538, 15433, 16087, 16162

The nearby TeV-detected HBL object 1ES 1959+650 (z=0.047) has been monitored intensively by Swift since 2015 August 1 (mostly in the framework of out ToO requests) revealing its prolonged flaring activity. The source showed its highest historical X-ray brightness state during the last pointing performed on December 26 (corresponding to 0.3-10 keV count rate of 22.97 cts/s). Note that "record-breaking" count rate has been amended three times since the start of the aforementioned flare. The spectrum is extremely hard (described well with the logparabola model) with the photon index at 1 keV a=1.56+/-0.03, curvature parameter b=0.40+/-0.06, synchrotron SED peak location Ep=3.55+/-0.15 keV, hardness ratio HR=1.23, unabsorbed 0.3-10 keV flux of 9.35\times10^{-10} erg/cm^2/s. While the X-ray flux has been almost doubled after the previous Swift-XRT pointing performed on 2015 December 23, the contemporaneous UVOT observations showed practically the same brightness level in all optical and UV bands during the 3 d interval (within the error ranges). However, an increasing activity is expected in the UV-radio and gamma-ray parts of the spectrum in the framework of one-zone SSC models. Therefore, intensive multiwavelength observations of 1ES 1959+650 are strongly encouraged to study instable processes and emission mechanisms in this source.