Multiwavelength Evidence for Quasi-periodic Modulation in the Gamma-Ray Blazar PG 1553+113

Creators: Ackermann, M.; Max-Moerbeck, W.; Pearson, T. J.; Readhead, A.

Abstract

We report for the first time a γ-ray and multiwavelength nearly periodic oscillation in an active galactic nucleus. Using the Fermi Large Area Telescope we have discovered an apparent quasi-periodicity in the γ-ray flux (E > 100 MeV) from the GeV/TeV BL Lac object PG 1553+113. The marginal significance of the 2.18 ± 0.08 year period γ-ray cycle is strengthened by correlated oscillations observed in radio and optical fluxes, through data collected in the Owens Valley Radio Observatory, Tuorla, Katzman Automatic Imaging Telescope, and Catalina Sky Survey monitoring programs and Swift-UVOT. The optical cycle appearing in ~10 years of data has a similar period, while the 15 GHz oscillation is less regular than seen in the other bands. Further long-term multiwavelength monitoring of this blazar may discriminate among the possible explanations for this quasi-periodicity.

Additional Information

© 2015 American Astronomical Society. Received 2015 September 7; accepted 2015 October 4; published 2015 November 10. We thank the anonymous referee for useful and constructive comments. We extend special thanks to Prof. C. Done of Durham University, UK, and Prof. R. W. Romani of Stanford University, USA, for useful comments during the course of this work. The Fermi-LAT Collaboration acknowledges support for LAT development, operation and data analysis from NASA and DOE (United States); CEA/Irfu and IN2P3/CNRS (France); ASI and INFN (Italy); MEXT, KEK, and JAXA (Japan); and the K.A. Wallenberg Foundation, the Swedish Research Council, and the National Space Board (Sweden). Science analysis support in the operations phase from INAF (Italy) and CNES (France) is also gratefully acknowledged. The Tuorla blazar monitoring program has been partially supported by the Academy of Finland grant 127740. The KAIT telescope program is supported by Katzman Foundation and the National Science Foundation. The CSS survey is funded by the National Aeronautics and Space Administration under grant No. NNG05GF22G issued through the Science Mission Directorate Near-Earth Objects Observations Program. The CRTS survey is supported by the U.S. National Science Foundation under grants AST-0909182. The OVRO 40 m program is supported in part by NASA grants NNX08AW31G and NNX11A043G and NSF grants AST-0808050 and AST-1109911. The MOJAVE program is supported under NASA-Fermi grant NNX12A087G. The National Radio Astronomy Observatory (NRAO) is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. The NASA Swift γ-ray burst explorer is a MIDEX Gamma Ray Burst mission led by NASA with participation of Italy and the UK. This research has made use of the Smithsonian/NASA's ADS bibliographic database. This research has made use of the NASA/IPAC NED database (JPL CalTech and NASA, USA). This research has made use of the archives and services of the ASI Science Data Center (ASDC), a facility of the Italian Space Agency (ASI Headquarters, Rome, Italy). This research has made use of the XRT Data Analysis Software (XRTDAS) developed under the responsibility of the ASDC. This work is a product of the ASDC Fermi team developed in the frame of the INAF Senior Scientists project and the foreign visiting scientists program of ASDC. Facilities: Fermi Gamma-ray Space Telescope, Swift, OVRO:40m, KAIT.

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