Search for Pulsed γ-Ray Emission from Globular Cluster M28
Abstract
Using the data from the Large Area Telescope on board the Fermi Gamma-ray Space Telescope, we have searched for γ-ray pulsations from the direction of the globular cluster M28 (NGC 6626). We report the discovery of a signal with a frequency consistent with that of the energetic millisecond pulsar (MSP) PSR B1821-24 in M28. A weighted H-test test statistic of 28.8 is attained, which corresponds to a chance probability of ~10-5 (4.3σ detection). With a phase-resolved analysis, the pulsed component is found to contribute ~25% of the total observed γ-ray emission from the cluster. However, 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 to further investigate this periodic signal candidate.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- March 2013
- DOI:
- 10.1088/2041-8205/765/2/L47
- arXiv:
- arXiv:1302.0610
- Bibcode:
- 2013ApJ...765L..47W
- Keywords:
-
- gamma rays: stars;
- globular clusters: individual: M28 NGC 6626;
- pulsars: individual: PSR B1821–24 PSR J1824–2452A;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- 8 pages, 2 figures, 2 tables, accepted for publication in ApJ Letter