The GALEX time domain survey. II. Wavelength-dependent variability of active galactic nuclei in the PAN-STARRS1 medium deep survey
- Department of Astronomy, University of Maryland, College Park, MD 20742 (United States)
- Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218 (United States)
- Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)
- Astrophysical Institute, Department of Physics and Astronomy, 251B Clippinger Lab, Ohio University Athens, OH 45701 (United States)
- Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)
- Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States)
- National Optical Astronomy Observatory, 950 North Cherry Avenue, Tucson, AZ 85719 (United States)
- Kavli Institute for Cosmological Physics, University of Chicago, Chicago, IL 60637 (United States)
- Cahill Center for Astrophysics, California Institute of Technology, 1216 East California Boulevard, Mail Code 278-17, Pasadena, California 91125 (United States)
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 {sub P1}, r {sub P1}, i {sub P1}, z {sub P1}) in time, and taking their flux difference, we create co-temporal difference-flux spectral energy distributions (ΔfSEDs) 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 ΔfSEDs of α{sub λ} = 2.1 that is consistent with an accretion disk spectrum. We further fit the ΔfSEDs 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-bar ∗ of 1.2×10{sup 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 ΔfSEDs than a simple power law.
- OSTI ID:
- 22869653
- Journal Information:
- Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 833; ISSN ASJOAB; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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