Search for pulsed gamma-ray emission from globular cluster M28

TL;DR

This study reports the detection of gamma-ray pulsations from the globular cluster M28, identifying a specific millisecond pulsar and analyzing its contribution to the cluster's gamma-ray emission.

Contribution

First detection of gamma-ray pulsations from M28 associated with MSP PSR B1821-24, providing insights into pulsar emission and cluster MSP populations.

Findings

Gamma-ray pulsations detected with 4.3-sigma significance.

Pulsed emission accounts for approximately 25% of total gamma-ray flux.

Constraints on MSP population and inverse Compton scattering scenarios.

Abstract

Using the data from the Large Area Telescope on board the Fermi Gamma-ray Space Telescope, we have searched for the gamma-ray pulsations from the direction of globular cluster M28 (NGC 6626). We report the discovery of a signal with the frequency consistent with that of the energetic millisecond pulsar (MSP) PSR B1821-24 in M28. A weighted H-test test statisic (TS) of 28.8 is attained which corresponds to a chance probability of ~1e-5 (4.3-sigma detection). With a phase-resolved analysis, the pulsed component is found to contribute ~25% of the total observed gamma-ray emission from the cluster. On the other hand, the unpulsed level provides a constraint for the underlying MSP population and the fundamental plane relations for the scenario of inverse Compton scattering. Follow-up timing observations in radio/X-ray are encouraged for further investigating this periodic signal candidate.