Gamma-Ray Emission from the Broad-Line Radio Galaxy 3C111

TL;DR

This study re-analyzed EGRET data and found probable gamma-ray emission from the galaxy 3C111, suggesting it as a potential gamma-ray source, but uncertainties remain due to positional offsets and lack of definitive X-ray associations.

Contribution

The paper provides a re-analysis of EGRET data that indicates possible gamma-ray emission from 3C111, refining the association with the gamma-ray source 3EGJ0416+3650.

Findings

Probable detection of gamma-ray emission above 1000MeV from 3C111.

Identification of a new nearby gamma-ray source GROJ0426+3747.

Uncertain association between X-ray and gamma-ray sources due to positional uncertainties.

Abstract

The broad-line radio galaxy 3C111 has been suggested as the counterpart of the gamma-ray source 3EGJ0416+3650. While 3C111 meets most of the criteria for a high-probability identification, like a bright flat-spectrum radio core and a blazar-like broadband SED, in the Third EGRET Catalog, the large positional offset of about 1.5 degrees put 3C111 outside the 99% probability region for 3EGJ0416+3650, making this association questionable. We present a re-analysis of all available data for 3C111 from the EGRET archives, resulting in probable detection of high-energy gamma-ray emission above 1000MeV from a position close to the nominal position of 3C111, in two separate viewing periods (VPs), at a 3-sigma level in each. A new source, GROJ0426+3747, appears to be present nearby. For >100MeV, one source seems to account for most of the EGRET-detected emission of 3EGJ0416+3650. A follow-up Swift UVOT/XRT observation reveals one moderately bright X-ray source in the error box of 3EGJ0416+3650, but because of the large EGRET position uncertainty, it is not certain that the X-ray and gamma-ray sources are associated. Another Swift observation, of GROJ0426+3747, detected no X-ray source nearby.