Search for High-energy Gamma-ray Emission from an Anomalous X-ray Pulsar, 4U 0142+61

Abstract

Until 2004, anomalous X-ray pulsars (AXPs) were known as strong emitters of soft X-rays only (<10 keV). The discovery of hard X-ray component from AXPs provided important insight about their emission properties while it posed a serious challenge to explain its origin. The physical mechanism of the hard emission component has still not been fully resolved. We investigate the high-energy gamma-ray properties of the brightest AXP, 4U 0142+61, using data collected with the Large Area Telescope on board the Fermi Gamma-ray Space Telescope to establish the spectral behavior of the source on a very broad energy span and search for pulsed emission. Here, we present our results of detailed search for the persistent and pulsed high-energy gamma-ray emission from 4U 0142+61 which result in no significant detection. However, we obtain upper limits to the persistent high-energy gamma-ray emission flux which helps us to constrain existing physical models.