Disc reflection and a possible disc wind during a soft X-ray state in the neutron star low-mass X-ray binary 1RXS J180408.9-342058
Abstract
1RXS J180408.9-342058 is a transient neutron star low-mass X-ray binary that exhibited a bright accretion outburst in 2015. We present NuSTAR, Swift, and Chandra observations obtained around the peak brightness of this outburst. The source was in a soft X-ray spectral state and displayed an X-ray luminosity of LX ≃ (2-3) × 1037(D/5.8 kpc)2 erg s-1 (0.5-10 keV). The NuSTAR data reveal a broad Fe-K emission line that we model as relativistically broadened reflection to constrain the accretion geometry. We found that the accretion disc is viewed at an inclination of I ≃ 27°-35° and extended close to the neutron star, down to Rin ≃ 5-7.5 gravitational radii (≃11-17 km). This inner disc radius suggests that the neutron star magnetic field strength is B ≲ 2 × 108 G. We find a narrow absorption line in the Chandra/HEG data at an energy of ≃7.64 keV with a significance of ≃4.8σ. This feature could correspond to blueshifted Fe XXVI and arise from an accretion disc wind, which would imply an outflow velocity of vout ≃ 0.086c (≃25 800 km s-1). However, this would be extreme for an X-ray binary and it is unclear if a disc wind should be visible at the low inclination angle that we infer from our reflection analysis. Finally, we discuss how the X-ray and optical properties of 1RXS J180408.9-342058 are consistent with a relatively small (Porb ≲ 3 h) binary orbit.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- October 2016
- DOI:
- 10.1093/mnras/stw1593
- arXiv:
- arXiv:1607.01780
- Bibcode:
- 2016MNRAS.461.4049D
- Keywords:
-
- accretion;
- accretion discs;
- stars: individual: 1RXS J180408.9-342058- stars: neutron;
- stars: winds;
- outflows;
- X-rays: binaries;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- 10 pages, 3 tables, 5 figures, accepted for publication in MNRAS