Extreme Variability Quasars from the Sloan Digital Sky Survey and the Dark Energy Survey

Rumbaugh, N and Desai, Shantanu and et al, . (2018) Extreme Variability Quasars from the Sloan Digital Sky Survey and the Dark Energy Survey. Astrophysical Journal, 854 (2). ISSN 0004-637X

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Abstract

We perform a systematic search for long-term extreme variability quasars (EVQs) in the overlapping Sloan Digital Sky Survey and 3 Year Dark Energy Survey imaging, which provide light curves spanning more than 15 years. We identified ~1000 EVQs with a maximum change in g-band magnitude of more than 1 mag over this period, about 10% of all quasars searched. The EVQs have L bol ~ 1045–1047 erg s−1 and L/L Edd ~ 0.01–1. Accounting for selection effects, we estimate an intrinsic EVQ fraction of ~30%–50% among all $g\lesssim 22$ quasars over a baseline of ~15 yr. We performed detailed multi-wavelength, spectral, and variability analyses for the EVQs and compared them to their parent quasar sample. We found that EVQs are distinct from a control sample of quasars matched in redshift and optical luminosity: (1) their UV broad emission lines have larger equivalent widths; (2) their Eddington ratios are systematically lower; and (3) they are more variable on all timescales. The intrinsic difference in quasar properties for EVQs suggests that internal processes associated with accretion are the main driver for the observed extreme long-term variability. However, despite their different properties, EVQs seem to be in the tail of a continuous distribution of quasar properties, rather than standing out as a distinct population. We speculate that EVQs are normal quasars accreting at relatively low rates, where the accretion flow is more likely to experience instabilities that drive the changes in flux by a factor of a few on multi-year timescales.

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IITH Creators:
IITH CreatorsORCiD
Desai, Shantanuhttp://orcid.org/0000-0002-0466-3288
Item Type: Article
Subjects: Physics
Divisions: Department of Physics
Depositing User: Library Staff
Date Deposited: 25 Jan 2019 08:41
Last Modified: 25 Jan 2019 08:41
URI: http://raiith.iith.ac.in/id/eprint/4760
Publisher URL: http://dx.doi.org/doi:10.3847/1538-4357/aaa9b6/pdf
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