Fermi Variability Study of the Candidate Pulsar Binary 2FGL~J0523.3-2530

TL;DR

This study analyzes Fermi LAT data of the candidate millisecond pulsar binary 2FGL J0523.3-2530, revealing long-term variability, spectral features, and orbital modulation, supporting its pulsar binary nature.

Contribution

It provides the first detailed variability and spectral analysis of 2FGL J0523.3-2530, including detection of orbital modulation in high-energy emission.

Findings

Long-term flux variability with a factor of 4 in 1-300 GeV.

Detection of an extra spectral component at 2-3 GeV.

Orbital modulation observed in >2 GeV emission during last 1.5 years.

Abstract

The Fermi source 2FGL~J0523.3$-$2530 has recently been identified as a candidate millisecond pulsar binary with an orbital period of 16.5 hrs. We have carried out detailed studies of the source's emission properties by analyzing data taken with the Fermi Large Area Telescope in the 0.2--300 GeV energy range. Long-term, yearly variability from the source has been found, with a factor of 4 flux variations in 1--300 GeV. From spectral analysis, we find an extra spectral component at 2--3 GeV that causes the source brightening. While no orbital modulations have been found from the Fermi data over the whole period of 2008--2014, orbital modulation in the source's $>$2 GeV emission is detected during the last 1.5 yrs of the Fermi observation. Our results support the millisecond pulsar binary nature of 2FGL~J0523.3$-$2530. Multi-wavelength observations of the source are warranted in order to find any correlated flux variations and thus help determine the origin of the long-term variability, which currently is not understood.