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arXiv · 2508.20178

The orbital period and inclination of the neutron star X-ray transient MAXI J1807+132

E. A. Saavedra·T. Muñoz-Darias·M. A. P. Torres·I. V. Yanes-Rizo·M. Armas Padilla·A. Álvarez-Hernández·J. Casares·D. Mata Sánchez·S. K. Rout·S. Navarro
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Abstract

The neutron star X-ray transient MAXI J1807+132 has undergone outbursts in 2017, 2019, and 2023. We conducted an $R$-band time series photometry campaign using the Isaac Newton Telescope during the 2022 quiescent state. We detected a periodic variation in the light curve, consistent with ellipsoidal modulation, which allowed us to determine an orbital period of $P_{\rm orb} = 4.258 \pm 0.008$ hr. By modelling the light curve, we obtained a binary inclination of $ i = 72\pm5 \, \deg $ and a mass ratio $q = 0.24^{+0.19}_{-0.14}$ ($68$ per cent confidence level). Furthermore, our analysis supports an early M-dwarf companion that contributes between 30 and 50 per cent to the total flux in the $R$-band. We extend the previously established absolute magnitude versus orbital period correlation for black hole X-ray transients to neutron star systems. We applied the correlation to MAXI J1807+132, estimating its distance as $6.3 \pm 0.7$ kpc and its height above the Galactic plane to be $1.6 \pm 0.2$ kpc.

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E. A. Saavedra, T. Muñoz-Darias, M. A. P. Torres, I. V. Yanes-Rizo, M. Armas Padilla, A. Álvarez-Hernández, J. Casares, D. Mata Sánchez, S. K. Rout, S. Navarro. 2025-08-27. The orbital period and inclination of the neutron star X-ray transient MAXI J1807+132. https://doi.org/10.1051/0004-6361%2F202555321

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