NICER follow-up observations of 1A 1744-361
ATel #15424; M. Ng (MIT), J. M. Miller (Univ. Michigan), T. E. Strohmayer, K. C. Gendreau, P. M. Bult, Z. Arzoumanian (NASA/GSFC), C. Malacaria (ISSI), D. J. K. Buisson (Southampton), S. Guillot (IRAP/CNRS), D. Chakrabarty (MIT), E. C. Ferrara (UMCP, NASA/GSFC), on behalf of the NICER team
on 8 Jun 2022; 22:23 UT
Credential Certification: Mason Ng (masonng@mit.edu)
Subjects: X-ray, Neutron Star, Transient, Pulsar
Referred to by ATel #: 15429
MAXI/GSC detected an outburst from the field including 1A 1744-361 on 2022 May 30 (ATel #15407). Swift/XRT subsequently confirmed the outburst to originate from the known neutron star low-mass X-ray binary 1A 1744-361 (ATel #15408). Previous outbursts of the source have shown Type I X-ray bursts, thus it is a neutron star low-mass X-ray binary system (Bhattacharyya et al. 2006, ApJ, 639, 31). NICER began observations of the source over 2022 June 03 and 2022 June 08, for a total of 5.5 ks exposure. The 0.3-10.0 keV count rate is 778.2 +/- 0.4 counts/s.
Pulsation searches over 0.3-2.0 keV and 2.0-10.0 keV via acceleration searches and averaged power spectra do not show any significant coherent periodicity. The 0.5-10 keV stacked power spectrum (32 s segments) shows power-law noise below about 10 Hz with a fractional rms amplitude of 7%.
The time-averaged 0.5-10.0 keV spectrum is well-fitted by an absorbed cutoff power law and blackbody component with a Gaussian absorption line component. We find a decent fit with a chi-squared value of 253 with 146 degrees of freedom. We find an absorption column density of 0.435 (+0.011, -0.012) × 1022cm-2, a photon index of 0.83 (+0.10, -0.13), high energy cutoff of 2.7 (+0.5, -0.6) keV, and a blackbody temperature of 1.50 (+0.07, -0.12) keV. The Gaussian absorption line has centroid energy 6.988 (+0.012, -0.015) keV and width 0.0040 (+0.0302, -0.0015) keV. The spectral model implies a 0.3-10.0 keV absorbed flux of F = 2.913 (+0.010, -0.112) × 10-10 erg/s/cm2, or a 0.3-10.0 keV unabsorbed flux of 3.6 × 10-10 erg/s/cm2. These are consistent with the values reported by Swift/XRT (ATel #15408). All uncertainties reported are to the 90% confidence level.
We also found a strong dip in the 0.3-10.0 keV light curve, similar to the absorption dips that have been reported on this source in previous outbursts (Bhattacharyya et al. 2006, ApJ, 639, 31).
NICER will continue to observe 1A 1744-361. We encourage further observations of this source in other wavelengths.
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.
