Identification and characterisation of the gamma-ray counterpart of the transitional pulsar candidate CXOU J110926.4-650224

TL;DR

This study confirms the gamma-ray counterpart of the transitional pulsar candidate CXOU J110926.4-650224 by analyzing Fermi-LAT data, establishing spatial association and characterizing its spectral properties, thus supporting its classification as a tMSP.

Contribution

The paper provides the first precise localization and spectral characterization of the gamma-ray emission from CXOU J110926.4-650224, confirming its association with a known X-ray source.

Findings

Gamma-ray source localized with 95% confidence to match X-ray position.

Gamma-ray emission described by a power-law with photon index 2.5.

Measured gamma-ray flux in 0.1-300 GeV range is (3.7±0.9)×10⁻¹² erg cm⁻² s⁻¹.

Abstract

Transitional millisecond pulsars (tMSPs) represent a crucial link between the rotation-powered and accretion-powered states of binary pulsars. During their active X-ray state, tMSPs are the only low-mass X-ray binary systems detected up to GeV energies by the Fermi Large Area Telescope (LAT). CXOU J110926.4-650224 is a newly discovered tMSP candidate in an active X-ray state, potentially spatially compatible with a faint gamma-ray source listed in the latest Fermi-LAT point-source catalogue as 4FGL J1110.3-6501. Confirming the association between CXOU J110926.4-650224 and the Fermi source is a key step toward validating its classification as a tMSP. In this study, we analyse Fermi-LAT data collected from August 2008 to June 2023 to achieve a more accurate localisation of the gamma-ray source, characterise its spectral properties, and investigate potential time variability. By thoroughly reconstructing the gamma-ray background around the source using a weighted likelihood model, we obtain a new localisation that aligns with the position of the X-ray source at the 95% confidence level, with a Test Statistic value of $\sim 42$. This establishes a spatial association between the gamma-ray source and CXOU J110926.4-650224. The gamma-ray emission is adequately described by a power-law model with a photon index of $\Gamma = 2.5 \pm 0.1$ and a corresponding flux of $(3.7\pm0.9) \times 10^{-12}$ erg cm$^{-2}$ s$^{-1}$ in the 0.1-300 GeV range.