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

Here, we perform a systematic search for long-term extreme variability quasars (EVQs) in the overlapping Sloan Digital Sky Survey (SDSS) and 3-Year Dark Energy Survey (DES) imaging, which provide light curves spanning more than 15 years. We also identified 1000 EVQs with a maximum g band magnitude change of more than 1 mag over this period, about 10% of all quasars searched. The EVQs have L bol 10 45 - 10 47 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.22 quasars over a baseline of 15 years. These EVQs are good candidates for so-called “changing-look quasars”, where a spectral transition between the two types of quasars (broad-line and narrow-line) is observed between the dim and bright states. We performed detailed multi-wavelength, spectral and variability analyses for the EVQs and compared 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 formore » EVQs suggest that internal processes associated with accretion are the main driver for the observed extreme long-term variability. In spit of 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 accretion rates, where the accretion flow is more likely to experience instabilities that drive the factor of few changes in flux on multi-year timescales.« less
  1. National Center for Supercomputing Applications, Urbana, IL (United States). et al
Publication Date:
Report Number(s):
Journal ID: ISSN 1538-4357
Grant/Contract Number:
SC0012704; AC02-76SF00515; AST-1138766; AYA2012-39559; ESP2013-48274; FPA2013-47986; 240672; 291329; 306478; AC05-00OR22725
Accepted Manuscript
Journal Name:
The Astrophysical Journal (Online)
Additional Journal Information:
Journal Name: The Astrophysical Journal (Online); Journal Volume: 854; Journal Issue: 2; Journal ID: ISSN 1538-4357
Institute of Physics (IOP)
Research Org:
Brookhaven National Laboratory (BNL), Upton, NY (United States); SLAC National Accelerator Lab., Menlo Park, CA (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org:
USDOE Office of Science (SC), High Energy Physics (HEP) (SC-25)
Contributing Orgs:
DES Collaboration
Country of Publication:
United States
79 ASTRONOMY AND ASTROPHYSICS; black hole physics; galaxies: active; line: profiles; quasars: general; surveys
OSTI Identifier:
Alternate Identifier(s):
OSTI ID: 1389253; OSTI ID: 1435204