Short-Term X-ray Variability during Different Activity Phases of Blazars S5 0716+714 and PKS 2155-304

Galaxies

卷:8

Pankaj Kushwaha¹  Main Pal² 

[1] Aryabhatta Research Institute of Observational Sciences (ARIES), Manora Peak, Nainital 263001, India;

[2] Centre for Theoretical Physics, Jamia Millia Islamia, New Delhi 110025, India;

关键词: galaxies;    active galaxies;    jets—radiation mechanisms;    non-thermal gamma-rays;    galaxies;   

DOI  :  10.3390/galaxies8030066

来源: DOAJ

【 摘 要 】

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-${\chi }^2\sim 1$ 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.

【 授权许可】

Unknown