TeV-Detected Blazar 1ES 0033+595 in the lowest Historical X-Ray State

ATel #15384; Bidzina Kapanadze (Ilia State University, Tbilisi, Georgia; E. Kharadze National Astrophysical Observatory, Abastumani, Georgia)
on 19 May 2022; 07:48 UT
Credential Certification: Bidzina Kapanadze (bidzina_kapanadze@iliauni.edu.ge)

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The TeV-detected blazar 1ES 0033+595 (tentative redshift: z=0.467; Paiano et al. 2017, ApJ, 837, 134) has been observed 156 times with the Neihl Gehrels Swift Observatory since 2005 April with a net exposure of about 200 ks. During this monitoring, the 0.3-10 keV emission showed a strong variability, as recorded by the X-Ray Telescope onboard Swift (Swift-XRT). The source exhibited fast X-ray flares by a factor of 2.2-3.5 and the XRT-band count rate (CR) attained to the highest historical value of 9.24+/-0.13 cts/s in 2014 December (see http://www.swift.psu.edu/monitoring /source.php?source=1ES0033+595; Kapanadze B., ATel#8107, 10187,11494, ). During those flares, the source also showed a fast flux and spectral variability down to the sub-hour timescales (e.g., a flux doubling instance in about 1.5 hr). Furthermore, 1ES 0033+595 is characterized by the hardest X-ray spectra among blazars with the photon index at 1 keV frequently lower than $a$=1.5 and the position of the synchrotron SED peak sometimes shifted beyond 10 keV that has been rarely observed for blazars (our results, paper in preparation; see also Table 11 in Kapanadze et al. 2018, ApJ, 858, 68). 1ES 0033+595 also frequently shows very hard MeV-GeV spectra from the Fermi-LAT observations which is explained easier in the framework of hadronic models than via the leptonic scenarios (see, e.g., Sukla et al. 2015, ApJ, 798,2). The last run of the Target of Opportunity (TOO) observations with Swift-XRT (four visits to the source during April 29 --May 17, performed on the basis of our TOO Request Number 17232) has recorded a gradual decline in the X-ray brightness by a factor of 2.5 to the lowest historical value CR=0.51+/-0.03 cts/s, corresponding to the de-absorbed 0.3-10 keV flux of 3.63$\times$10$^{-11}$ erg/cm$^2}$/s. The next Swift visit to 1ES 0033+595 is tentatively planned on May 23. 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.