Orbital Solution from NICER monitoring of the newly discovered accreting millisecond pulsar SRGA J144459.2-604207
ATel #16480; P. S. Ray (NRL), T. E. Strohmayer (NASA GSFC), A. Sanna (University of Cagliari), M. Ng (MIT), Z. Arzoumanian, K. C. Gendreau (NASA GSFC), E. C. Ferrara (University of Maryland, NASA GSFC, CRESST II), J. B. Coley (Howard University, NASA GSFC, CRESST II), S. Bogdanov (Columbia), on behalf of the NICER team
on 24 Feb 2024; 02:00 UT
Credential Certification: Paul S. Ray (paul.ray@nrl.navy.mil)
Subjects: X-ray, Neutron Star, Transient, Pulsar
Following the discovery of the X-ray transient SRGA J144459.2-604207 (ATel #16464, #16469, #16470, #16471), and the detection of millisecond X-ray pulsations (ATel #16474), we performed a timing analysis of the NICER dataset collected starting from 19:58 UTC on February 21 for a total exposure of 8.7 ks.
The data were barycenter-corrected using the Swift/XRT localization (ATel #16471). Pulsations are significantly detected in a large fraction of the data segments and exhibit a clear sinusoidal Doppler shift. The best-fitting orbital solution obtained has a period of 5.2231(1) hours, a projected semi-major axis a*sin(i) of 0.6513(1) lt-s, a time of ascending node TASC 60361.64126(3) MJD (TDB), and a barycentric pulse frequency of 447.871717(3) Hz. Note that this solution is not fully phase connected so is preliminary and may not be unique, but the inferred orbital properties are robust. The mass function is 0.006263(1) M_sun. Under the hypothesis of a neutron star of mass 1.4 M_sun, this would imply a mass greater than 0.255 M_sun for the companion star. The mean pulsed fraction registered during the NICER observations is relatively constant at approximately 3%.
NICER will continue to observe SRGA J144459.2-604207 during the outburst as visibility allows. We encourage further multiwavelength observations with other facilities.
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.
