Detection of gamma-ray emission from globular clusters M 15, NGC 6397, NGC 5904, NGC 6218 and NGC 6139 with Fermi-LAT

TL;DR

This paper reports the detection of gamma-ray emission from several globular clusters using Fermi-LAT data, supporting millisecond pulsars as the emission source, but finds no pulsation or variability evidence.

Contribution

First detection of gamma-ray emission from multiple globular clusters with Fermi-LAT, confirming MSPs as the likely origin.

Findings

Gamma-ray emission detected from M 15, NGC 6397, NGC 5904, NGC 6218, and NGC 6139.

MSPs found in some clusters support their role in gamma-ray emission.

No evidence of gamma-ray pulsation or flux variability observed.

Abstract

In the third Fermi catalogue (3FGL) there are sixteen gamma-ray globular clusters. After analyzing the recent released Pass 8 data of Fermi Large Area Telescope (LAT), we report the discovery of significant gamma-ray emission from M 15 and NGC 6397, confirm that NGC 5904 is a gamma-ray emitter and find evidence of gamma-ray emission from NGC 6218 and NGC 6139. Inter- estingly, in the globular clusters M 15, NGC 6397 and NGC 5904, millisecond pulsars (MSPs) have been found in radio or X-rays, which are strongly in support of the MSP origin of the gamma-ray emission. However, due to the relative low luminosity of the gamma-ray emission we do not find any evidence for the gamma-ray pulsation or flux variability of these sources.