NICER observation of LS V+44 17 during the record high outburst of 2022-2023

ATel #15848; Manoj Mandal (MCC), Sabyasachi Pal (MCC), Keith Gendreau (NASA/GSFC), Christian Malacaria (ISSI), Wataru Buz Iwakiri (Chiba U.), Deepto Chakrabarty (MIT), Zaven Arzoumanian (NASA/GSFC), Gaurava K. Jaisawal (DTU Space), Andrea Sanna (Univ. of Cagliari), Elizabeth C. Ferrara (UMCP, NASA/GSFC, CRESST)
on 5 Jan 2023; 19:07 UT
Credential Certification: Manoj Mandal (manojmandal@mcconline.org.in)

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The MAXI/GSC nova alert system detected X-ray brightening from the Be/X-ray binary pulsar LS V +44 17 (also known as BSD 24-491 and RX J0440.9+4431) on 2022 December 29 (ATel #15835). The X-ray flux from the source was seen to increase from December 24 (MJD 59937) and it is still increasing as detected in hard X-rays by Swift/BAT (15−50 keV), reaching a record high value of 572±43 mCrab on MJD 59948. MAXI/GSC (2−20 keV) flux has also been increasing since the trigger on December 29 and reached a maximum of nearly 230 mCrab on MJD 59948. LS V +44 17 was last seen in an outburst in April 2011.

NICER observed the source on December 29 beginning at 19:01:00 UTC (MJD 59942.79) with 26.6 ks exposure and recorded an average (0.5−10 keV) count rate of ∼325 cnts/s. A strong pulsation with a pulse period of ∼204.185 s is evident in the NICER data, with a multi-peak shape including an absorption structure in the pulse profile. The fractional amplitude of the pulse profile is ~25 percent (0.5−10 keV).

The NICER spectrum can be fitted with an absorbed cutoff power-law model together with a blackbody component. The best-fit results provide a photon index of −0.32±0.03 and a column density of (0.53±0.01) × 10²² cm^-2 (chi-squared/d.o.f. = 1198/937). The blackbody temperature is found to be 0.33±0.04 keV. A strong iron emission line is also detected at 6.4 keV. There are some spectral residuals in the 1−2 keV range, which is accounted for by adding a Gaussian component near 1.5 keV. The absorbed source flux is 3.25 × 10^-9 ergs/cm²/s in 0.5−10 keV. All reported uncertainties are 90% confidence limits.

Further NICER observations of the source are underway. We encourage multi-wavelength observations of the source.

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 light curves can be found on the following pages

Swift/BAT: https://swift.gsfc.nasa.gov/results/transients/weak/LSVp4417/

MAXI: http://maxi.riken.jp/pubdata/v7.7l/J0440+445/index.html

Fermi/GBM: https://gammaray.nsstc.nasa.gov/gbm/science/pulsars/lightcurves/rxj0440.html

BeXRB monitor page: http://integral.esac.esa.int/bexrbmonitor/Plots/sim_plot_LSV+4417.html