NICER detects pulsations from Swift J1749.4-2807

ATel #14428; P. M. Bult (NASA/GSFC), D. Altamirano, A. C. Albayati (Univ. of Southampton), T. E. Strohmayer (NASA/GSFC), P. S. Ray (NRL), D. Chakrabarty, M. Ng (MIT), K. C. Gendreau, Z. Arzoumanian (NASA/GSFC), A. Sanna (Univ. Cagliari)
on 2 Mar 2021; 04:42 UT
Credential Certification: Peter Bult (p.m.bult@nasa.gov)

Tweet

In response to the report of an INTEGRAL/JEM-X detection of the eclipsing accreting millisecond pulsar Swift J1749.4-2807 (ATel #14427), we began monitoring this source with the Neutron Star Interior Composition Explorer (NICER). Pointed observations were collected between 2021-03-01 14:51 UTC and 22:55 UTC, yielding a total good time exposure of 8.8 ks. The target is clearly detected at a total 1-10 keV count rate of 26 ct/s over an estimated background rate of <1 ct/s in the same energy band, but drops down to 5 ct/s during eclipse.

The 1-10 keV continuum emission is reasonably well described (chi² / dof = 308 / 211) as an absorbed blackbody plus power law, yielding an absorption column density of 4x10²² cm^-2, a blackbody temperature of 0.56 keV, and a power law photon index of 1.3. Using this model, we measure the current unabsorbed 1-10 keV X-ray flux at 3.52 +- 0.07 x 10^-10 erg / s / cm². Assuming a 7 kpc distance (Wijnands+ 2009; MNRAS 393, 1), this converts to an X-ray luminosity of 2 x10³⁶ erg / s.

Folding the barycentered data on the best-known timing solution (Altamirano+, 2011; ApJL 727 L18), we recover the 518 Hz pulsations at greater than 8 sigma significance after optimizing the local time of ascending node. The pulse fundamental amplitude is measured at 2% rms, while the second harmonic has a 0.7% rms amplitude. This preliminary timing analysis yields a time of ascending node of MJD 59274.12691 +/- 2x10^-5 TDB, which is sufficiently accurate to predict the ingress and egress times of the eclipses. A more detailed analysis of the binary ephemeris is in progress.

Continued high cadence NICER observations of this source are currently underway. Additional multiwavelength follow-up is encouraged.

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.