NICER detection of 376 Hz X-ray pulsations from IGR J17494-3030

M. Ng, P. S. Ray, Tod E. Strohmayer, P. M. Bult, D. Chakrabarty*, D. Altamirano, G. K. Jaisawal, C. Malacaria, S. Bogdanov, K. C. Gendreau, Z. Arzoumanian

*Corresponding author for this work

Research output: Other contributionNet publication - Internet publicationResearch

Abstract

Referred to by ATel #: 14126 Tweet In response to the recent report of renewed activity from the faint X-ray transient IGR J17494-3030 in INTEGRAL data (ATel #14119), NICER began monitoring observations of this source. We collected 4.1 ks of data between 2020 October 27 00:38 and 17:51 UTC, finding that the source is detected with an initial 1-10 keV count rate of about 16 c/s (including a background of < 1 c/s), with a slow decline to about 14 c/s. We detect highly significant coherent pulsations with a barycentric frequency of 376.05 Hz (2.66 ms period). The pulse frequency is modulated by a circular orbit having a period of 4509 s (75 minutes), and a projected semi-major axis of 0.0164 lt-s. Hence, this system is an ultracompact binary accreting millisecond X-ray pulsar with a minimum companion mass of 0.015 Msun. We find that the pulse profile has a 10% fractional sinusoidal amplitude in the 1-10 keV energy range, with a 2% second harmonic. We extracted the energy spectrum in the 0.5-10 keV range, finding that the continuum emission is well described by an absorbed power-law model. A preliminary fit provides a photon index of 1.84+/-0.04 and an absorption column density of (2.05+/-0.05)x1022 cm-2. The 0.5-10 keV unabsorbed flux is 1.68x10-10 erg cm-2 s-1. The NICER team is continuing the monitoring and analysis of this source. 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 date27 Oct 2020
Publication statusPublished - 27 Oct 2020
SeriesThe Astronomer's telegram
NumberATel #14124

Keywords

  • X-ray
  • Neutron Star
  • Transient
  • Pulsar

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