Fermi Discovery of Gamma-ray Emission from the Globular Cluster Terzan 5
Abstract
We report the discovery of gamma-ray emission from the Galactic globular cluster (GC) Terzan 5 using data taken with the Fermi Gamma-ray Space Telescope, from 2008 August 8 to 2010 January 1. Terzan 5 is clearly detected in the 0.5-20 GeV band by Fermi at ~27σ level. This makes Terzan 5 the second gamma-ray-emitting GC seen by Fermi after 47 Tuc. The energy spectrum of Terzan 5 is best represented by an exponential cutoff power-law model, with a photon index of ~1.9 and a cutoff energy at ~3.8 GeV. By comparing Terzan 5 to 47 Tuc, we suggest that the observed gamma-ray emission is associated with millisecond pulsars and is either from the magnetospheres or inverse Compton scattering between the relativistic electrons/positrons in the pulsar winds and the background soft photons from the Galactic plane. Furthermore, it is suggestive that the distance to Terzan 5 is less than 10 kpc and >10 GeV photons can be seen in the future.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- March 2010
- DOI:
- 10.1088/2041-8205/712/1/L36
- arXiv:
- arXiv:1002.2431
- Bibcode:
- 2010ApJ...712L..36K
- Keywords:
-
- gamma rays: stars;
- globular clusters: individual: Terzan 5;
- pulsars: general;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- 4 pages, 2 figures