The GALEX Time Domain Survey. II. Wavelength-Dependent Variability of Active Galactic Nuclei in the Pan-STARRS1 Medium Deep Survey
Abstract
We analyze the wavelength-dependent variability of a sample of spectroscopically confirmed active galactic nuclei selected from near-UV (NUV) variable sources in the GALEX Time Domain Survey that have a large amplitude of optical variability (difference-flux S/N > 3) in the Pan-STARRS1 Medium Deep Survey (PS1 MDS). By matching GALEX and PS1 epochs in five bands (NUV, g_(P1), r_(P1), i_(P1), z_(P1)) in time, and taking their flux difference, we create co-temporal difference-flux spectral energy distributions (ΔƒSEDs) using two chosen epochs for each of the 23 objects in our sample, on timescales of about a year. We confirm the "bluer-when-brighter" trend reported in previous studies, and measure a median spectral index of the ΔƒSEDs of ɑ_⋋ = 2.1 that is consistent with an accretion disk spectrum. We further fit the ΔƒSEDs of each source with a standard accretion disk model in which the accretion rate changes from one epoch to the other. In our sample, 17 out of 23 (~74%) sources are described well by this variable accretion-rate disk model, with a median average characteristic disk temperature T^* of 1.2 x 10^5 K that is consistent with the temperatures expected, given the distribution of accretion rates and black hole masses inferred for the sample. Our analysis also shows that the variable accretion rate model is a better fit to the ΔƒSEDs than a simple power law.
Additional Information
© 2016 American Astronomical Society. Received 2016 June 27. Accepted 2016 September 20. Published 2016 December 19. We thank the anonymous referee for valuable comments and suggestions that helped to improve this paper. S.G. was supported in part by NSF CAREER grant 1454816. Some of the observations reported here were obtained at the MMT Observatory, a joint facility of the Smithsonian Institution and the University of Arizona. We thank R. Foley for his contribution to the PS1 transients program. The Pan-STARRS1 Surveys (PS1) have been made possible through contributions of the Institute for Astronomy, the University of Hawaii, the Pan-STARRS Project Office, the Max-Planck Society and its participating institutes, the Max Planck Institute for Astronomy, Heidelberg and the Max Planck Institute for Extraterrestrial Physics, Garching, The Johns Hopkins University, Durham University, the University of Edinburgh, Queen's University Belfast, the Harvard-Smithsonian Center for Astrophysics, the Las Cumbres Observatory Global Telescope Network Incorporated, the National Central University of Taiwan, the Space Telescope Science Institute, the National Aeronautics and Space Administration under Grant No. NNX08AR22G issued through the Planetary Science Division of the NASA Science Mission Directorate, the National Science Foundation under Grant No. AST-1238877, and the University of Maryland.Attached Files
Published - Hung_2016_ApJ_833_226.pdf
Submitted - 1609.06307v1.pdf
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Additional details
- Eprint ID
- 72968
- Resolver ID
- CaltechAUTHORS:20161220-093154418
- AST-1454816
- NSF
- Institute for Astronomy
- University of Hawaii
- Pan-STARRS Project Office
- Max-Planck Society
- Max Planck Institute for Astronomy (MPIA)
- Max Planck Institute for Extraterrestrial Physics
- Johns Hopkins University
- Durham University
- University of Edinburgh
- Queen's University Belfast
- Harvard-Smithsonian Center for Astrophysics
- Las Cumbres Observatory Global Telescope Network Incorporated
- National Central University of Taiwan
- NNX08AR22G
- NASA
- AST-1238877
- NSF
- University of Maryland
- Created
-
2016-12-20Created from EPrint's datestamp field
- Updated
-
2021-11-11Created from EPrint's last_modified field
- Caltech groups
- Space Astrophysics Laboratory