The bright unidentified gamma-ray source 1FGL J1227.9-4852: Can it be associated with an LMXB?

TL;DR

This study analyzes gamma-ray, radio, and X-ray data to identify the nature of the gamma-ray source 1FGL J1227.9-4852, suggesting it is likely associated with the low-mass X-ray binary XSS J12270-4859, possibly a millisecond pulsar.

Contribution

The paper presents multi-wavelength observations and proposes a new association between the gamma-ray source and the low-mass X-ray binary XSS J12270-4859, indicating it may be a millisecond pulsar.

Findings

Gamma-ray spectrum fits an exponentially cutoff power-law, similar to pulsars.

Discovery of a compact radio source within the error circle.

XSS J12270-4859 is a likely counterpart, possibly a millisecond pulsar.

Abstract

We present an analysis of high energy (HE; 0.1-300 GeV) gamma-ray observations of 1FGL J1227.9-4852 with the Fermi Gamma-ray Space Telescope, follow-up radio observations with the Australia Telescope Compact Array, Giant Metrewave Radio Telescope and Parkes radio telescopes of the same field and follow-up optical observations with the ESO VLT. We also examine archival XMM-Newton and INTEGRAL X-ray observations of the region around this source. The gamma-ray spectrum of 1FGL J1227.9-4852 is best fit with an exponentially cutoff power-law, reminiscent of the population of pulsars observed by Fermi. A previously unknown, compact radio source within the 99.7% error circle of 1FGL J1227.9-4852 is discovered and has a morphology consistent either with an AGN core/jet structure or with two roughly symmetric lobes of a distant radio galaxy. A single bright X-ray source XSS J12270-4859, a low-mass X-ray binary, also lies within the 1FGL J1227.9-4852 error circle and we report the first detection of radio emission from this source. The potential association of 1FGL J1227.9-4852 with each of these counterparts is discussed. Based upon the available data we find the association of the gamma-ray source to the compact double radio source unlikely and suggest that XSS J12270-4859 is a more likely counterpart to the new HE source. We propose that XSS J12270-4859 may be a millisecond binary pulsar and draw comparisons with PSR J1023+0038.