Discovery of High-Energy Gamma-Ray Pulsations from PSR J2021+3651 with AGILE

TL;DR

This paper reports the discovery of gamma-ray pulsations from PSR J2021+3651 using AGILE data, confirming it as the source of high-energy gamma rays and providing insights into pulsar emission models.

Contribution

First detection of gamma-ray pulsations from PSR J2021+3651 with AGILE, linking it to the previously unidentified gamma-ray source and supporting outer-gap emission models.

Findings

Gamma-ray pulsations detected in 100-1500 MeV range.

Gamma-ray peaks separated by 0.47 cycles.

Radio pulse leads gamma-ray peak by 0.165 cycles.

Abstract

Discovered after the end of the Compton Gamma-Ray Observatory mission, the radio pulsar PSR J2021+3651 was long considered a likely counterpart of the high-energy gamma-ray source 2CG 075+00 = 3EG J2021+3716 = GeV J2020+3658, but it could not be confirmed due to the lack of a contemporaneous radio pulsar ephemeris to fold the sparse, archival gamma-ray photons. Here, we report the discovery of gamma-ray pulsations from PSR J2021+3651 in the 100-1500 MeV range using data from the AGILE satellite gathered over 8 months, folded on a densely sampled, contemporaneous radio ephemeris obtained for this purpose at the Green Bank Telescope. The gamma-ray pulse consists of two sharp peaks separated by 0.47+/-0.01 cycles. The single radio pulse leads the first gamma-ray peak by 0.165+/-0.010 cycles. These properties are similar to those of other gamma-ray pulsars, and the phase relationship of the peaks can be interpreted in the context of the outer-gap accelerator model for gamma-ray emission. Pulse-phase resolved images show that there is only one dominant source, AGL J2020.5+3653 = PSR J2021+3651 in the region previously containing confused sources 3EG J2021+3716 and 3EG J2016+3657.