NICER detection of two thermonuclear (Type I) X-ray bursts establishes that MAXI J1807+132 hosts a neutron star

Zaven Arzoumanian, Keith C. Gendreau*, Tod E. Strohmayer, Peter Bult, Tolga Güver, Jérôme Chenevez, Gaurava K. Jaisawal, Diego Altamirano, Michael Wolff, Deepto Chakrabarty

*Corresponding author for this work

Research output: Other contributionNet publication - Internet publicationResearch

Abstract

MAXI J1807+132 is an X-ray transient first discovered by MAXI/GSC in March 2017 (ATel #10208). Optical spectroscopy (ATel #10221) suggests the source is a low-mass X-ray binary. On 2019 September 10, MAXI/GSC detected a new outburst (ATel #13097). NICER has been regularly monitoring the outburst (ATel #13139), which shows strong variability on timescales of hours to days in the form of reflares (ATel #13173).

On 2019 October 28 at 14:50 UTC, NICER detected a sudden increase in flux, followed by an exponential decay. Results from time-resolved spectroscopy are consistent with this event being a thermonuclear (Type I) X-ray burst from the source, indicating that the compact object in this system is a neutron star. A second Type I X-ray burst was detected about a day later, on October 29 at 12:10 UTC.

Each burst had a duration of approximately 10 seconds and peak count rates of 2000 and 1000 cps in the 0.4-10 keV band, respectively. The bolometric peak flux of the first burst was measured to be 1.0x10^{-8} erg/s/cm^2 from time-resolved spectroscopy, with a peak blackbody temperature of 1.7 keV. Assuming an Eddington-limited peak flux and solar composition, we derive an upper limit of the distance to the source of 13 kpc. The first burst occurred during the rise of a reflare and the second burst occurred near the peak of the most recent reflare. The persistent source count rates were 57 and 138 cps in the 0.4-10 keV band, respectively.

Assuming that there is no other source within the NICER 30 arcmin^2 FOV, the detection of these bursts demonstrates that MAXI J1807+132 harbors a neutron star.

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 date29 Oct 2019
Publication statusPublished - 29 Oct 2019
SeriesThe Astronomer's telegram
NumberATel #13239

Keywords

  • X-ray
  • Neutron Star
  • Transient

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