A NuSTAR Observation of the Rapid Outburst of X-ray Binary XTE J1901+014

ATel #15958; Paul Draghis (University of Michigan), Jon M. Miller (University of Michigan)
on 22 Mar 2023; 14:09 UT
Credential Certification: Paul Draghis (pdraghis@umich.edu)

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The MAXI/GSC nova alert system detected an outburst of the X-ray binary XTE J1901+014 on February 14 2023 (ATEL #15904). We observed the system using NuSTAR on February 17 2023 under ObsID 80802345001 for an effective exposure of 34 ks. By the time of the NuSTAR observation, the flux had decreased from 658 ± 75 mCrab (4.0-10.0keV, 1σ error - ATEL #15904), or 1.58 ± 0.18 ×10$$^-8 erg/s/cm$$², to roughly 1mCrab, or 2.4 ± 0.15 ×10$$^-11 erg/s/cm$$².

The NuSTAR FPMA and FPMB spectra were background dominated at energies higher than 30keV. We rebinned the spectra from the two detectors using the optimal binning scheme described by Kaastra & Bleeker (2016) and fit them in the 3-30 keV band using a disk blackbody component and a power law component, while accounting for galactic absorption. In XSPEC parlance, the model used was TBabs×(diskbb+powerlaw). The model produces a good fit, returning χ$$²/dof.=205.74/185. The measured galactic column density was 2.0 +1.3/-0.8 cm$$^-2, the diskbb temperature and normalization were kT_in=0.92 ± 0.16 keV and norm_diskbb=0.95 +2.48/-0.60, while the power law index and normalizations were Γ=2.04 ± 0.03 and norm_powerlaw=1.7 +/- 0.1 ×10$$^-2. When removing the effects of the galactic absorption, the unabsorbed flux of the source during the observation in the 2-10 keV band corresponds to 4.2×10$$^-11 erg/s/cm$$². Assuming that the compact object in the system is a black hole with a mass of 10 solar masses, located at a distance of 10 kpc, this flux corresponds to an Eddington fraction of 0.04%. No signs of relativistic reflection are present in the NuSTAR spectra of this observation owing to its modest sensitivity.

We thank the NuSTAR team for quickly executing this observation.

References: Kaastra & Bleeker, 2016; A&A 587, A151.
Kawamuro et al, 2023; ATEL #15904.