AstroSat/SXT confirms GX 339-4 to be in the low-hard state
ATel #15615; N. T. Thomas, L. Giridharan, S. Anirudh, S. B. Gudennavar (CHRIST - Deemed to be University), R. Misra (IUCAA) and S. G. Bubbly (CHRIST - Deemed to be University)
on 13 Sep 2022; 09:37 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Shivappa Gudennavar (shivappa.b.gudennavar@christuniversity.in )
Subjects: X-ray, Binary, Black Hole, Transient
GX 339−4 is a recurrent galactic black hole X‐ray transient located at a distance of 8.0 +/− 0.9 kpc (Parker, M. L., et al., 2016, ApJ, 821, L6). Since its discovery in 1973, the source has undergone outbursts in 2017 (ATels #10797, #10798, #10808, #10820, #10824, #10825), 2018 (ATels #11208, #12287, #12322), 2019 (ATels #12413, #12420, #13024, #13113), 2021 (ATels #14351, #14352, #14367, #14384, #14400, #14419, #14440, #14455, #14484, #14490, #14493, #14494, #14504, #14507, #14953)
On 29th August, 2022, MAXI/GSC detected a new X‐ray outburst from GX 339−4 (ATel #15577). Swift/XRT confirmed the on-going outburst, indicated by its gradual brightening (ATel #15578). Follow-up campaign by NICER and NuSTAR deem the source to be in the low-hard state (ATel #15585). Optical observations with LCO suggests that the peak of the outburst is yet to be reached (ATel #15598).
We report the AstroSat observation of GX 339−4 using the SXT instrument. The source was observed for ~22 ks from 7th September, 2022 08:06:44.0 UTC to 8th September, 2022 09:30:59.0 UTC at RA(J2000): 255.70 and Dec(J2000): −48.78. The spectrum of the source in 0.7 — 7.0 keV range could be well described with the model combination: tbabs*(diskbb+powerlaw), which yielded an inner disk temperature (kTin) of 0.42 +/− 0.11 keV and a photon index (Γ) of 1.36 +0.09/−0.07, with an absorption column density (NH) of 0.58 +0.05/−0.06 × 1022/cm2. The total absorbed flux in the 0.7 to 7.0 keV range was calculated to be 4.97 +/− 0.07 × 10-10 erg/cm2/sec. The best-fit spectral parameters suggest that GX 339−4 is currently in the low-hard state and will possibly undergo a spectral state transition in the coming days.
Follow-up multi-wavelength observations of GX 339−4 are encouraged.
Acknowledgement: We thank the AstroSat operations team for scheduling this ToO observation and the SXT POC for timely release of the data.
