NICER observation of Be/X-ray binary pulsar XTE J1946+274 during its 2024 outburst
ATel #16744; Manoj Mandal (MCC), Gaurava K. Jaisawal (DTU Space), Sabyasachi Pal (MCC), Keith Gendreau (NASA/GSFC), Sebastien Guillot (IRAP/CNRS), Andrea Sanna (UniCA), Mason Ng (MIT), Katja Pottschmidt (UMBC, NASA/GSFC, CRESST II)
on 30 Jul 2024; 17:06 UT
Credential Certification: Manoj Mandal (manojmandal@mcconline.org.in)
Subjects: X-ray, Neutron Star, Star, Transient, Pulsar
Referred to by ATel #: 16766
The transient Be/X-ray binary pulsar XTE J1946+274 recently went into an X-ray outburst as reported by MAXI/GSC (ATel #16717). After inactivity of a few years since 2021 (ATel #14936), the source is detected in the X-rays by SVOM/ECLAIRs and Einstein Probe WXT (ATel #16719, #16723) and in the optical by KAIT and SVOM/C-GFT (ATel #16720, #16722) in July 2024. The X-ray flux from the source was seen to increase by MAXI/GSC (2−20 keV) from 0.78 mCrab (MJD 60505) to a peak value of ~24 mCrab (close to MJD 60512). Monitoring by MAXI/GSC and Swift/BAT indicates the source may have crossed the peak of the outburst and entered into a decline phase.
NICER observed the source on 2024-07-24 (MJD 60515) with a total exposure of ~6.7 ks, recording an average count rate of roughly 17 c/s in the 0.5−10 keV energy band. The barycentric-corrected light curve shows X-ray pulsations at a period of 15.76±0.01 s. The pulse profile shows a double-peak feature with a pulsed fraction of nearly 30%.
The NICER spectra (0.7−10 keV) can be modelled with an absorbed power-law model. The best-fit results provide a photon index of 0.65±0.01 and a hydrogen column density of (1.20±0.02) × 1022 cm-2. The absorbed source flux is (2.30±0.03) × 10-10 ergs cm-2 s-1 in the 0.7−10 keV energy band. The corresponding luminosity is estimated to be ~2 × 1036 erg/s assuming a source distance of 8.7 kpc. All reported uncertainties have 90% confidence limits.
We thank the NICER team for making the ToO observation possible. NICER will keep monitoring the source in the following days.
NICER is a 0.2−12 keV X-ray telescope operating on the International Space Station. The NICER mission and portions of the NICER science team activities are funded by NASA.
The latest X-ray monitoring light curves can be found on the following pages:
Swift/BAT: https://swift.gsfc.nasa.gov/results/transients/weak/XTEJ1946p274/
MAXI: http://maxi.riken.jp/star_data/J1945+273/J1945+273.html
Fermi/GBM: https://gammaray.nsstc.nasa.gov/gbm/science/pulsars/lightcurves/xtej1946.html
BeXRB monitor page: http://integral.esac.esa.int/bexrbmonitor/Plots/sim_plot_XTEJ1946+274.html
