Periodic Gamma-ray Modulation of the blazar PG 1553+113 Confirmed by Fermi-LAT and Multi-wavelength Observations

TL;DR

This study confirms a 7+ year gamma-ray periodic modulation in the blazar PG 1553+113, supported by multi-wavelength observations, suggesting a binary black hole system or other astrophysical processes as the cause.

Contribution

It provides the first robust 7+ year gamma-ray periodicity detection with multi-wavelength confirmation, supporting models of binary black hole systems in blazars.

Findings

Gamma-ray modulation confirmed with >7 cycles over 15 years.

Optical and radio data show correlations with gamma-ray periodicity.

Possible physical origins include binary black holes, jet precession, or instabilities.

Abstract

A 2.1-year periodic oscillation of the gamma-ray flux from the blazar PG 1553+113 has previously been tentatively identified in almost 7 year of data from the Fermi Large Area Telescope. After 15 years of Fermi sky-survey observations, doubling the total time range, we report >7 cycle gamma-ray modulation with an estimated significance of 4 sigma against stochastic red noise. Independent determinations of oscillation period and phase in the earlier and the new data are in close agreement (chance probability <0.01). Pulse timing over the full light curve is also consistent with a coherent periodicity. Multiwavelength new data from Swift X-Ray Telescope, Burst Alert Telescope, and UVOT, and from KAIT, Catalina Sky Survey, All-Sky Automated Survey for Supernovae, and Owens Valley Radio Observatory ground-based observatories as well as archival Rossi X-Ray Timing Explorer satellite-All Sky Monitor data, published optical data of Tuorla, and optical historical Harvard plates data are included in our work. Optical and radio light curves show clear correlations with the gamma-ray modulation, possibly with a nonconstant time lag for the radio flux. We interpret the gamma-ray periodicity as possibly arising from a pulsational accretion flow in a sub-parsec binary supermassive black hole system of elevated mass ratio, with orbital modulation of the supplied material and energy in the jet. Other astrophysical scenarios introduced include instabilities, disk and jet precession, rotation or nutation, and perturbations by massive stars or intermediate-mass black holes in polar orbit.