NICER observes increasing luminosity from XTE J1739-285

P. M. Bult*, K. C. Gendreau, T. E. Strohmayer, Z. Arzoumanian, P. S. Ray, I. A. Mereminskiy, R. M. Ludlam, J. Chenevez, G. K. Jaisawal, M. T. Wolff, C. Malacaria

*Corresponding author for this work

Research output: Other contributionNet publication - Internet publicationResearch


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.
Original languageEnglish
Publication date30 Sep 2019
Publication statusPublished - 30 Sep 2019
SeriesThe Astronomer's telegram
NumberATel #13148


  • X-ray
  • Neutron star
  • Transient


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