Extreme Variability in a Broad Absorption Line Quasar
CRTS J084133.15+200525.8 is an optically bright quasar at z = 2.345 that has shown extreme spectral variability over the past decade. Photometrically, the source had a visual magnitude of V ~ 17.3 between 2002 and 2008. Then, over the following five years, the source slowly brightened by approximately one magnitude, to V ~ 16.2. Only ~1 in 10,000 quasars show such extreme variability, as quantified by the extreme parameters derived for this quasar assuming a damped random walk model. A combination of archival and newly acquired spectra reveal the source to be an iron low-ionization broad absorption line quasar with extreme changes in its absorption spectrum. Some absorption features completely disappear over the 9 years of optical spectra, while other features remain essentially unchanged. We report the first definitive redshift for this source, based on the detection of broad Hα in a Keck/MOSFIRE spectrum. Absorption systems separated by several 1000 km s^(−1) in velocity show coordinated weakening in the depths of their troughs as the continuum flux increases. We interpret the broad absorption line variability to be due to changes in photoionization, rather than due to motion of material along our line of sight. This source highlights one sort of rare transition object that astronomy will now be finding through dedicated time-domain surveys.
Additional Information© 2017 American Astronomical Society. Received 2017 January 13. Accepted 2017 February 15. Published 2017 April 21. We thank the anonymous referee for a prompt and helpful referee report. CRTS was supported by the NSF grants AST-1313422, AST-1413600, and AST-1518308. The work of D.S. and H.J. was carried out at Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA. D.S. also acknowledges support from NASA through ADAP award 12-ADAP12-0109. N.A. and C.C. acknowledge support from NSF through grant AST 1413319, and from NASA through STScI grants GO 11686 and GO 12022. Research by A.J.B. was supported by NSF grant AST-1412693. E.G. acknowledges the generous support of the Cottrell College Award through the Research Corporation for Science Advancement. H.J. is supported by an appointment to the NASA Postdoctoral Program at the Jet Propulsion Laboratory, administered by Universities Space Research Association under contract with NASA. The authors are grateful to the staff at the Palomar and Keck observatories, where some of the data presented here were obtained. The authors recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. Facilities: CRTS - , Keck (MOSFIRE) - , NEOWISE - , Palomar (DBSP) - , SDSS - , WISE - Wide-field Infrared Survey Explorer.
Published - Stern_2017_ApJ_839_106.pdf
Submitted - 1704.03923.pdf