Swift/XRT observation of the Be/X-ray binary pulsar GS 0834-430 during its 2026 outburst
ATel #18075; G. K. Jaisawal (DTU Space)
on 23 Sep 2026; 13:23 UT
Credential Certification: Gaurava Kumar Jaisawal (gaurava.jaisawal@gmail.com)
Subjects: X-ray, Binary, Transient, Pulsar
We report on a Swift/XRT observation of GS 0834-430, currently in outburst following the onset of X-ray activity seen by MAXI/GSC on 2026 August 29 (ATel #18031). Fermi/GBM subsequently detected coherent pulsations with a spin period of 12.2942 s (ATel #18054).
We observed the source with Swift/XRT for a net exposure of 814 s between 2026 September 19 02:35 UT and 2026 September 20 00:16 UT. The 0.5–10 keV spectrum is described by an absorbed power-law model, giving an equivalent hydrogen column density of (3.7 ± 0.8) × 1022 cm−2 and a photon index of 0.55 ± 0.23. The fit gives a χ2 of 20.7 for 23 degrees of freedom. The unabsorbed 0.5–10 keV flux is (1.1 ± 0.1) × 10−9 erg cm−2 s−1. Assuming a distance of 5 kpc (Miyasaka et al. 2013, ApJ, 775, 65), this corresponds to an X-ray luminosity of (3.3 ± 0.3) × 1036 erg s−1. Uncertainties on parameters are given at the 90% confidence level.
MAXI/GSC monitoring in the 2-20 keV range shows the source declining from a peak of 54 ± 5 mCrab around 2026 September 12 (MJD 61295) to 43 ± 4 mCrab on 2026 September 19 (MJD 61302), which was contemporaneous with our Swift observation. The hard photon index measured here is consistent with continued active accretion despite the ongoing flux decline. Given the rarity of activity from this source, continued X-ray and multi-wavelength monitoring is encouraged.
