Rebrightening of 1 Crab from LS V+44 17 observed by Swift/BAT and NICER

ATel #15868; Sabyasachi Pal (MCC), Manoj Mandal (MCC), Keith Gendreau (NASA/GSFC), Christian Malacaria (ISSI), Wataru Buz Iwakiri (Chiba U.), Zaven Arzoumanian (NASA/GSFC), Gaurava K. Jaisawal (DTU Space), Andrea Sanna (Univ. of Cagliari), Michael T. Wolff (NRL), Elizabeth C. Ferrara (UMCP, NASA/GSFC, CRESST), Alexander Salganik (SPBU), Joel B. Coley (Howard University), Katja Pottschmidt (UMBC, NASA/GSFC, CRESST), James F. Steiner (CfA), Mason Ng (MIT), Paul S. Ray (NRL)
on 20 Jan 2023; 19:44 UT
Credential Certification: Manoj Mandal (manojmandal@mcconline.org.in)

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We report rebrightening from the Be/X-ray binary pulsar LS V +44 17 (also known as RX J0440.9+4431) detected by NICER, Swift/BAT and MAXI/GSC. The pulsar was recently reported to be in an X-ray outburst (ATel #15835, #15848).

The Swift/BAT X-ray flux from the source was seen to increase from December 24 (MJD 59937) and reached 572±43 mCrab on MJD 59948 (ATel #15835, #15848) before starting to decrease. From MJD 59958, the X-ray flux of LS V +44 17 began to increase again in Swift/BAT (15−50 keV). During the rebrightening phase, the X-ray flux has so far reached a record high of 1.086±0.06 Crab as observed by Swift/BAT (15−50 keV) on MJD 59964. MAXI/GSC (2−20 keV) flux has also been increasing and reached nearly 134 mCrab on MJD 59961.5.

NICER observed the source regularly beginning on December 29 at 19:01:00 UTC (MJD 59942.79). The pulse period reported in the earlier ATel# 15848 was incorrect. A strong pulsation with period ∼208±0.01 s (after barycentric correction) is evident in NICER data from December 29 (MJD 59942.79). The spin period decreased at a rate of nearly 0.016 s/d between MJD 59942 and MJD 59960. The pulse profile also shows a double-peak feature. The fractional amplitude of the profile is found to be ∼43±3% (0.5−10 keV).

The recent NICER observation of the source during the rebrightened phase on MJD 59963.507 recorded a peak count rate of ∼1000 cnts/s (0.5−10 keV). The NICER spectrum at MJD 59963.507 can be fitted with an absorbed cutoff power-law model together with a blackbody component. The best-fit results provide a photon index of −0.16±0.21 and a column density of (0.43±0.03) × 10²² cm^-2 (chi-squared/d.o.f. = 775/749). The blackbody temperature is found to be 0.38±0.05 keV. A strong iron emission line is also detected at 6.38 keV with an equivalent width of nearly 0.07 keV. The absorbed source flux is ∼6.1 × 10^-9 ergs/cm²/s in 0.5−10 keV. All reported uncertainties have 90% confidence limits.

NICER is continuing to monitor the source. We encourage additional multi-wavelength observations.

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: http://swift.gsfc.nasa.gov/results/transients/weak/LSVp4417/

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

Fermi/GBM: http://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.