Short-Term X-ray Variability during Different Activity Phases of Blazars S5 0716+714 and PKS 2155-304
Abstract
We explored the statistical properties of short-term X-ray variability using long-exposure XMM-Newton data during high X-ray variability phases of blazars S5 0716+714 and PKS 2155-304. In general, the hardness ratio shows correlated variations with the source flux state (count rate), but in a few cases, mainly the bright phases, the trend is complex with both correlation and anti-correlation, indicating spectral evolution. Stationarity tests suggest the time series are non-stationarity or have trend stationarity. Except for one, none of the histogram fits resulted in a reduced-χ2∼1 for a normal and log-normal profile but a normal profile is favored in general. On the contrary, the Anderson–Darling test favors log-normal with a test-statistic value lower for log-normal over normal for all the observations, even if out of significance limits. None of the IDs show linear RMS-flux relation. The contrary inferences from different widely used statistical methods indicate that a careful analysis is needed while the complex behavior of count rate with hardness ratio suggests spectral evolution over a few 10 s of kilo-seconds during bright phases of the sources. In these cases, the spectrum extracted from whole observation may not be meaningful for spectral studies and certainly not a true representation of the spectral state of the source.
- Publication:
-
Galaxies
- Pub Date:
- September 2020
- DOI:
- 10.3390/galaxies8030066
- arXiv:
- arXiv:2009.06443
- Bibcode:
- 2020Galax...8...66K
- Keywords:
-
- galaxies;
- active galaxies;
- jets—radiation mechanisms;
- non-thermal gamma-rays;
- Astrophysics - High Energy Astrophysical Phenomena;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- 14 Pages, 4 figures, 2 Tables