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Testing the relativistic Doppler boost hypothesis for the binary candidate quasar PG1302-102 with multiband Swift data

Xin, Chengcheng and Charisi, Maria and Haiman, Zoltán and Schiminovich, David and Graham, Matthew J. and Stern, Daniel and D’Orazio, Daniel J. (2020) Testing the relativistic Doppler boost hypothesis for the binary candidate quasar PG1302-102 with multiband Swift data. Monthly Notices of the Royal Astronomical Society, 496 (2). pp. 1683-1696. ISSN 0035-8711.

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The bright quasar PG1302-102 has been identified as a candidate supermassive black hole binary from its near-sinusoidal optical variability. While the significance of its optical periodicity has been debated due to the stochastic variability of quasars, its multiwavelength variability in the ultraviolet (UV) and optical bands is consistent with relativistic Doppler boost caused by the orbital motion in a binary. However, this conclusion was based previously on sparse UV data that were not taken simultaneously with the optical data. Here, we report simultaneous follow-up observations of PG1302-102 with the Ultraviolet Optical Telescope on the Neil Gehrels Swift Observatory in six optical + UV bands. The additional nine Swift observations produce light curves roughly consistent with the trend under the Doppler boost hypothesis, which predicts that UV variability should track the optical, but with a ∼2.2 times higher amplitude. We perform a statistical analysis to quantitatively test this hypothesis. We find that the data are consistent with the Doppler boost hypothesis when we compare the the amplitudes in optical B-band and UV light curves. However, the ratio of UV to V-band variability is larger than expected and is consistent with the Doppler model, only if either the UV/optical spectral slopes vary, the stochastic variability makes a large contribution in the UV, or the sparse new optical data underestimate the true optical variability. We have evidence for the latter from comparison with the optical light curve from All-Sky Automated Survey for Supernovae. Additionally, the simultaneous analysis of all four bands strongly disfavours the Doppler boost model whenever Swift V band is involved. Additional, simultaneous optical + UV observations tracing out another cycle of the 5.2-yr proposed periodicity should lead to a definitive conclusion.

Item Type:Article
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URLURL TypeDescription Paper
Charisi, Maria0000-0003-3579-2522
Haiman, Zoltán0000-0003-3633-5403
Graham, Matthew J.0000-0002-3168-0139
Stern, Daniel0000-0003-2686-9241
Additional Information:© 2020 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model ( Accepted 2020 June 2. Received 2020 May 5; in original form 2019 July 18. Published: 10 June 2020. We thank Michele Vallisneri for useful suggestions and Tingting Liu for providing the best-fitting parameters of their models. MC acknowledges support from the National Science Foundation (NSF) North American Nanohertz Observatory for Gravitational Waves (NANOGrav) Physics Frontier Center, award number 1430284. ZH acknowledges support from the National Aeronautics and Space Administration(NASA), grants NNX17AL82G and 80NSSC19K0149 and NSF grant 1715661. The work of DS was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA. We acknowledge the use of public data from the Swift data archive.
Funding AgencyGrant Number
Subject Keywords:quasars: individual: PG1302-102 – quasars: supermassive black holes
Issue or Number:2
Record Number:CaltechAUTHORS:20200903-095005268
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Official Citation:Chengcheng Xin, Maria Charisi, Zoltán Haiman, David Schiminovich, Matthew J Graham, Daniel Stern, Daniel J D’Orazio, Testing the relativistic Doppler boost hypothesis for the binary candidate quasar PG1302-102 with multiband Swift data, Monthly Notices of the Royal Astronomical Society, Volume 496, Issue 2, August 2020, Pages 1683–1696,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:105236
Deposited By: Tony Diaz
Deposited On:08 Sep 2020 22:54
Last Modified:08 Sep 2020 22:54

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