Continued X-ray Monitoring of LS V +44 17 with NICER, Swift/BAT, and MAXI

ATel #15907; Joel B. Coley (Howard University, NASA/GSFC, CRESST II), Keith Gendreau (NASA/GSFC), Katja Pottschmidt (UMBC, NASA/GSFC, CRESST II), Sabyasachi Pal (MCC), Alexander Salganik (Saint Petersburg State University, IKI RAS), Manoj Mandal (MCC), Peter Kretschmar (ESA/ESAC), Gaurava K. Jaisawal (DTU Space), C. Malacaria (ISSI)
on 17 Feb 2023; 18:44 UT
Credential Certification: Joel Coley (joel.coley@howard.edu)

Tweet

NICER, Swift/BAT, and MAXI have continued to monitor the outburst of the Be/X-ray binary pulsar LS V +44 17 (also known as RX J0440.9+4431). The source peaked at a pulse-phase averaged count rate of ~1500 c/s in the NICER energy band and is now slowly decreasing in count rate. Swift/BAT (15–50 keV) recorded a peak X-ray flux of 2.25 Crab on MJD 59976, and MAXI/GSC (2–20 keV) measured a peak flux of 0.65 Crab. The flux started to decrease in both bands after MJD 59981. The flux in the 15–50 keV range dropped to 1.3 Crab on MJD 59988 as observed by Swift/BAT.

LS V +44 17 was easily detected by NICER at roughly 200 c/s on December 29, 2022 when NICER first observed the source (ATel #15848; see also ATel #15835, #15868, #15874, #15880). LS V +44 17 has reached peak brightness in NICER at roughly 1500 c/s in the 0.25 - 15.0 keV energy range. From the beginning of its observations (MJD 59942.79) NICER observed a relatively steady hardness for the source. However, at approximately MJD 59971 the source made a dramatic spectral transition as the luminosity increased, going into a significantly softer state in the NICER energy range below 2 keV. We encourage continued hard X-ray observations of this source as the outburst begins to fade.

The hardness ratio at higher energies, between the Swift/BAT (15-50 keV) and the MAXI (2-20 keV) bands, however, indicates hardening with increasing flux over both flux peaks of the current activity episode, see FLASHES (http://integral.esac.esa.int/flashes-plots/RX%20J0440.9+4431_plot.html).

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

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.