Swift observations of the Be X-ray binary 1A 1118-61
ATel #17627; Aru Beri (IIA, Bangalore)
on 24 Jan 2026; 18:17 UT
Credential Certification: Aru Beri (aru.beri8@gmail.com)
Subjects: X-ray, Binary, Neutron Star
We report results from a Swift/XRT observation of the Be/X-ray pulsar 1A 1118-61 obtained on 2026 January 23 at 13:08:56 UTC as part of our monitoring program following the onset of its recent outburst (GCN #43435; GCN #43442; ATel #17608).
The source is clearly detected in the 1-10 keV energy range. The XRT spectrum was fitted using an absorbed thermal Comptonization model. The fit provides an acceptable description of the data with a chi-squared value 529 for 510 degrees of freedom.
The best-fit hydrogen column density is (0.8 +/- 0.1) x 10^22 cm^-2. The Comptonization component yields a seed photon temperature of = 1.22 +/- 0.06 keV. The electron temperature and optical depth were fixed at 7.3 keV and 10, respectively, due to limited constraints within the Swift/XRT bandpass. All quoted uncertainties are at the 90% confidence level. The observed 1-10 keV flux is ~ 4e-09 erg cm^-2 s^-1. The spectral fit parameters are consistent with that reported in ATel #17626.
A timing analysis of the XRT light curve reveals coherent pulsations with a period of about 409.24 s, consistent with the known spin period of the system. No correction for orbital motion has been applied. The pulse profiles show double-peaked behavior.
These Swift/XRT results confirm that 1A 1118-61 is in an active outburst state. Continued Swift monitoring observations are planned.
We thank the Swift team for accepting the ToO request and for the quick execution of the observing program.
