Infrared Time Lags for the Periodic Quasar PG 1302-102
The optical light curve of the quasar PG 1302-102 at z = 0.278 shows a strong, smooth 5.2 year periodic signal, detectable over a period of ~20 years. Although the interpretation of this phenomenon is still uncertain, the most plausible mechanisms involve a binary system of two supermassive black holes with a subparsec separation. At this close separation, the nuclear black holes in PG 1302-102 will likely merge within ~ 10^5 years due to gravitational wave emission alone. Here, we report the rest-frame near-infrared time lags for PG 1302-102. Compiling data from WISE and Akari, we confirm that the periodic behavior reported in the optical light curve from Graham et al. is reproduced at infrared wavelengths, with best-fit observed-frame 3.4 and 4.6 µm time lags of (2219 ± 153, 2408 ± 148) days for a near face-on orientation of the torus, or (4103 ± 153, 4292 ± 148) days for an inclined system with relativistic Doppler boosting in effect. The periodicity in the infrared light curves and the light-travel time of the accretion disk photons to reach the dust glowing regions support that a source within the accretion disk is responsible for the optical variability of PG 1302-102, echoed at the farther out dusty regions. The implied distance of this dusty, assumed toroidal region is ~1.5 pc for a near face-on geometry or ~1.1 pc for the relativistic Doppler-boosted case.
Additional Information© 2015 American Astronomical Society. Received 2015 August 13; accepted 2015 November 2; published 2015 November 19. We thank the anonymous referee for the comments that greatly improved the paper, as well as Daniel D'Orazio, Moshe Elitzur, Saavik Ford, Zoltan Haiman, Barry McKernan, and Robert Nikutta for helpful discussions. This research was supported by an appointment to the NASA Postdoctoral Program at the Jet Propulsion Laboratory, administered by Oak Ridge Associated Universities through a contract with NASA. This publication makes use of data products from the Wide-field Infrared Survey Explorer, which is a joint project of the University of California, Los Angeles, and the Jet Propulsion Laboratory/California Institute of Technology, funded by the National Aeronautics and Space Administration. This publication makes use of data products from NEOWISE, which is a project of the Jet Propulsion Laboratory/California Institute of Technology. NEOWISE is funded by the National Aeronautics and Space Administration. CRTS was supported by the NSF grants AST-1313422 and AST-1413600. D.S. acknowledges support from NASA through ADAP award 12-ADAP12-0109. Facilities: - WISE - Wide-field Infrared Survey Explorer - .
Published - Jun_2015.pdf
Submitted - 1511.01515v1.pdf