A study of gamma-ray emission from OJ 287 using Fermi-LAT from 2015-2023

TL;DR

This study analyzes gamma-ray emission from OJ 287 over 8 observing seasons from 2015 to 2023 using Fermi-LAT data, revealing consistent non-zero flux, a power-law spectrum, and a spectral cutoff at 20 GeV, with no correlation to optical or X-ray variability.

Contribution

First detailed gamma-ray analysis of OJ 287 over multiple seasons with Fermi-LAT, including spectral fitting and multiwavelength comparison.

Findings

Detected significant gamma-ray flux in all segments.

Gamma-ray spectrum fitted with a power law of slope 2.12.

Observed spectral cutoff at around 20 GeV.

Abstract

We search for gamma-ray emission from OJ287 in the energy range from 0.1-300 GeV during 2015-2023, in coincidence with an extensive observing campaign to monitor the optical flux variability and polarization, as discussed in arXiv:2311.02372. We present results for eight segments in the aforementioned period, with each segment corresponding to an observing season. We report non-zero gamma-ray flux (with $>10\sigma$ significance) for all the eight segments. The photon and energy flux observed during this period is $\sim 5.2 \times 10^{-8} \rm{ph~cm^{-2}~s^{-1}}$ and $2.75 \times 10^{-5} \rm{MeV~cm^{-2}~s^{-1}}$, respectively, while the SED can be fitted with a power law with a slope of $2.12 \pm 0.02$. The observed luminosity is between $10^{45}-10^{46}$ ergs/sec. Similar to previous works we find a hard cutoff in the gamma-ray spectrum at around 20 GeV. We do not observe any correlations between the peaks in the gamma ray light curves and corresponding optical light cuves in $I$ and $R$ bands, as well as the X-ray light curves from SWIFT between 0.3-10 keV.