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arXiv · 2508.16775

Characterising the short-orbital period X-ray transient Swift J1910.2-0546

J. M. Corral-Santana·P. Rodriguez-Gil·M. A. P. Torres·J. Casares·P. G. Jonker·A. Perdomo Garcia·D. T. Trelawny·J. A. Carballo-Bello·P. A. Charles·D. Mata Sanchez·T. Munoz-Darias·F. A. Ringwald·I. G. Martinez-Pais·R. L. M. Corradi·P. Saikia·D. M. Russell
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Abstract

SwiftJ1910.2-0546 is a Galactic X-ray transient discovered during a bright outburst in 2012. We use time-series optical photometry and spectroscopy to estimate the orbital period, characterise the donor star, determine the interstellar extinction, distance, and system geometry, and constrain the component masses. Multi-site r-band and clear-filter light curves and WHT/ACAM spectra from the 2012 outburst are combined with time-series spectroscopy from GTC/OSIRIS and VLT/FORS2 in quiescence. Period searches are conducted using generalised Lomb-Scargle, phase-dispersion minimisation, and analysis-of-variance algorithms. Diffuse interstellar bands constrain E(B-V), while empirical correlations involving H$α$ yield estimates of K2, q, and i. We detect a double-humped modulation with a period of $0.0941\pm0.0007$d ($2.26\pm0.02$h) during the outburst. Its morphology is consistent with an early superhump, suggesting that the true orbital period may be slightly shorter than 4.52h. The H$α$ radial velocity curves do not yield a definitive orbital period. In quiescence, TiO bands indicate an M3-M3.5 donor contributing 70% of the red continuum. Diffuse interstellar bands give E(B-V)=$0.60\pm0.05$ and N_H=$(3.9\pm1.3)$x10$^{21}$cm$^{-2}$, placing the system at a distance of 2.8-4.0 kpc. The H$α$ line width in quiescence (FWHM_0 =$990\pm45$km/s), via a FWHM-K_2 calibration, provides an estimate of K_2, while its double peaked profile gives q and i. Adopting the resulting K_2=$230\pm17$km/s and q=$0.032\pm0.010$, and two orbital period scenarios (2.25 and 4.50h), Monte Carlo sampling returns a compact object mass M_1=8-11M_sun and an inclination i=13-18 deg for plausible donor masses (M_2=0.25-0.35M_sun). We favour an orbital period of 4.5h. Further phase-resolved spectroscopy and photometry during quiescence are needed to better determine its fundamental parameters.

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J. M. Corral-Santana, P. Rodriguez-Gil, M. A. P. Torres, J. Casares, P. G. Jonker, A. Perdomo Garcia, D. T. Trelawny, J. A. Carballo-Bello, P. A. Charles, D. Mata Sanchez, T. Munoz-Darias, F. A. Ringwald, I. G. Martinez-Pais, R. L. M. Corradi, P. Saikia, D. M. Russell. 2025-08-26. Characterising the short-orbital period X-ray transient Swift J1910.2-0546. https://doi.org/10.1051/0004-6361%2F202556452

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