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

doi:10.1051/0004-6361/202555321

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Volume 702 (October 2025)

A&A, 702 (2025) A103

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Issue		A&A Volume 702, October 2025


Article Number		A103
Number of page(s)		8
Section		Stellar structure and evolution
DOI		https://doi.org/10.1051/0004-6361/202555321
Published online		10 October 2025

A&A, 702, A103 (2025)

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

E. A. Saavedra¹^,2^⋆, T. Muñoz-Darias¹^,2, M. A. P. Torres¹^,2, I. V. Yanes-Rizo¹^,2, M. Armas Padilla¹^,2, A. Álvarez-Hernández¹^,2, J. Casares¹^,2, D. Mata Sánchez¹^,2, S. K. Rout³^,4 and S. Navarro¹^,2

¹ Instituto de Astrofísica de Canarias (IAC), Vía Láctea, La Laguna, E-38205 Santa Cruz de Tenerife, Spain
² Departamento de Astrofísica, Universidad de La Laguna, E-38206 Santa Cruz de Tenerife, Spain
³ New York University Abu Dhabi, PO Box 129188 Abu Dhabi, UAE
⁴ Center for Astrophysics and Space Science (CASS), New York University Abu Dhabi, PO Box 129188 Abu Dhabi, UAE

^⋆ Corresponding author: saavedra.enzo@iac.es

Received: 28 April 2025
Accepted: 27 August 2025

Abstract

The neutron star X-ray transient MAXI J1807+132 underwent 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 that is consistent with ellipsoidal modulation, which allowed us to determine an orbital period of P_orb = 4.258 ± 0.008 h. By modelling the light curve, we obtained a binary inclination of i = 72 ± 5 deg and a mass ratio q = 0.24^+0.19_−0.14 (68% confidence level). Furthermore, our analysis indicates the presence of an early M-dwarf companion that contributes between 30 and 50% to the total flux in the R band. We have extended 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 to be 6.3 ± 0.7 kpc and its height above the Galactic plane to be 1.6 ± 0.2 kpc.

Key words: binaries: general / stars: neutron

Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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