NICER observes increasing luminosity from XTE J1739-285
ATel #13148; P. M. Bult, K. C. Gendreau, T. E. Strohmayer, Z. Arzoumanian (NASA/GSFC), P. S. Ray (NRL), I. A. Mereminskiy (Space Research Institute, Russian Academy of Sciences), R. M. Ludlam (CalTech), J. Chenevez, G. K. Jaisawal (DTU Space), M. T. Wolff (NRL), C. Malacaria (NASA-MSFC/USRA)
on 30 Sep 2019; 19:36 UT
Credential Certification: Peter Bult (p.m.bult@nasa.gov)
Subjects: X-ray, Neutron Star, Transient
On 2019 September 27, routine monitoring of the Galactic Center with INTEGRAL revealed renewed activity from the neutron star X-ray transient XTE J1739-285 (ATel #13138). Follow-up observations with NICER commenced on September 27, collecting 19 ks of exposure between Sep 27 22:41 UTC and Sep 30 12:54 UTC. During this timespan we observed the source count-rate increase steadily from 200 c/s to 540 c/s.
The 0.5-10 keV continuum emission could be reasonably well described using an absorbed blackbody plus power-law, for absorption column density of N_H = (2.5 +/ 0.1)e22 cm^-2. Over the course of our observations we see the 1-10 keV source flux increase from 1.9e-9 erg/cm^2/s to 5.0e-9 erg/cm^2/s. In parallel, we observe a modest but significant shift in spectral shape, with the blackbody temperature evolving from 0.960 +/- 0.013 keV to 1.113 +/- 0.009 keV; and the power-law photon index holding at Gamma = 1.84 +/- 0.02. Additionally, we observe complex residuals around 0.8 and 6.7 keV; however, more detailed spectral analysis is required to interpret these features.
The 0.5-10 keV power spectrum of the source shows very low frequency noise (<0.5 Hz), with an integrated 0.01-100 Hz fractional rms of about 2%. No high frequency (>10 Hz) power was observed. Additionally, an acceleration search did not reveal any significant coherent periodicities above 50 Hz.
No X-ray bursts have been observed thus far, but further NICER monitoring of this source is underway.
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.
