The second strong X-ray flare and multifrequency variability of 1ES 1959+650 in 2016 January-August
Date Issued
2018
Author(s)
Kapanadze, B.
•
Dorner, D.
•
•
•
Hughes, P.
•
Aller, M.
•
Aller, H.
•
Reynolds, M.
•
Kapanadze, S.
•
Tabagari, L.
Abstract
The X-ray variability of the BL Lacertae source 1ES 1959+650 was studied intensively with X-ray telescope (XRT) onboard Swift during 2016 January-August. In this paper, we present the results obtained during this campaign. A long-term high X-ray state was superimposed by shorter-term flares by a factor of 1.9-4.7. We found 35 instances of intra-day variability which showed very fast flux changes by 14-21 per cent occurring within 1 ks and a decline by a factor of 2.3 in 17.2 ks. Similarly to the previous years, this period sometimes was characterized by a lack of correlated X-ray and TeV variability, indicating that the high-energy emission in 1ES 1959+650 was generated in the emission region more complex than a single zone. The source showed a significant X-ray - high-energy flux correlation, while the former was not correlated with the optical-UV fluxes. The best fits of the 0.3-10 keV spectra were mainly obtained using the log-parabola model. Strong spectral variability was detected, shifting the peak of the spectral energy distribution by more than 10 keV that happens rarely in blazars. During some strong short-term flares, the photon index at 1 keV frequently became harder than 1.70, and the spectral evolution was characterized by a harder-when-brighter behaviour.
Volume
473
Issue
2
Start page
2542
Issn Identifier
0035-8711
Ads BibCode
2018MNRAS.473.2542K
Rights
open.access
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