Identification of gamma-ray emission from 3C345 and NRAO512

TL;DR

This study identifies gamma-ray emission from the blazar 3C 345 and the quasar NRAO 512 using Fermi-LAT data combined with multiwavelength observations, revealing their contributions and activity over 20 months.

Contribution

It is the first to associate gamma-ray emission with 3C 345 and NRAO 512, clarifying their roles in gamma-ray sources and their activity timelines.

Findings

3C 345 is the main gamma-ray emitter in the region.

NRAO 512 showed increasing gamma-ray activity after November 2009.

No gamma-ray emission was detected from B3 1640+396.

Abstract

For more than 15 years, since the days of the Energetic Gamma-Ray Experiment Telescope (EGRET) on board the Compton Gamma-Ray Observatory (CGRO; 1991-2000), it has remained an open question why the prominent blazar 3C 345 was not reliably detected at gamma-ray energies <=20 MeV. Recently a bright gamma-ray source (0FGL J1641.4+3939/1FGL J1642.5+3947), potentially associated with 3C 345, was detected by the Large Area Telescope (LAT) on Fermi. Multiwavelength observations from radio bands to X-rays (mainly GASP-WEBT and Swift) of possible counterparts (3C 345, NRAO 512, B3 1640+396) were combined with 20 months of Fermi-LAT monitoring data (August 2008 - April 2010) to associate and identify the dominating gamma-ray emitting counterpart of 1FGL J1642.5+3947. The source 3C 345 is identified as the main contributor for this gamma-ray emitting region. However, after November 2009 (15 months), a significant excess of photons from the nearby quasar NRAO 512 started to contribute and thereafter was detected with increasing gamma-ray activity, possibly adding flux to 1FGL J1642.5+3947. For the same time period and during the summer of 2010, an increase of radio, optical and X-ray activity of NRAO 512 was observed. No gamma-ray emission from B3 1640+396 was detected.