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Investigating the variability of Swift-BAT blazars with NICER

Presentation #416.04 in the session AGN and Quasars VII.

Published onJun 29, 2022
Investigating the variability of Swift-BAT blazars with NICER

Blazars have historically been known to exhibit high-amplitude, rapid variations in flux and in their spectra across most timescales and energy bands. A time-domain variability analysis of 117 blazars in the Swift-BAT 105-month catalog (Mundo et al. in prep) reveals that a significant portion (~30%) exhibit little to no excess variance on a monthly timescale, which is deeply at odds with previous studies that show that blazars are highly variable in the X-rays on a wide range of timescales. However, the BAT data are not sensitive to changes on shorter timescales, or to low-amplitude variability (≲15%) on monthly timescales. In order to investigate this, we have acquired recent NICER observations of a subsample of 4 such “quiescent” BAT blazars over 5 months, allowing us to probe the variability on shorter timescales while also representing the timescales of the BAT catalog. Thanks to the higher sensitivity per unit time of NICER, we find through a preliminary analysis that variations in the 0.3-2 keV flux are detected on minute, ~weekly, and monthly timescales, but that the fractional variability on these timescales is <25% and decreases on longer timescales, implying low-amplitude variability overall and showing very little to no variability on monthly timescales. In addition, we find hints of a lack of spectral variability for some sources on timescales of a few days to a week. These results could change our understanding of the properties of blazars and beamed AGN, and can serve as an additional stepping stone towards our goal of characterizing the variability of blazars. We plan on combining these data with the BAT data for a variability analysis in the broadband, as well as utilizing them to further our analysis of the spectral variability.

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