Journal article · Preprint article
Discovery of thermonuclear (Type I) X-ray bursts in the X-ray binary Swift J1858.6–0814 observed with NICER and NuSTAR
University of Southampton1
Eureka Scientific, Inc.2
Tsinghua University3
University of Michigan4
University of California at Berkeley5
University of Cambridge6
University of Maryland, Baltimore7
Argentine Institute of Radio Astronomy8
Istanbul University9
National Space Institute, Technical University of Denmark10
Astrophysics and Atmospheric Physics, National Space Institute, Technical University of Denmark11
NASA Goddard Space Flight Center12
Massachusetts Institute of Technology13
CNRS14
...and 4 moreSwift J1858.6-0814 is a recently discovered X-ray binary notable for extremely strong variability (by factors $>100$ in soft X-rays) in its discovery state. We present the detection of five thermonuclear (Type I) X-ray bursts from Swift J1858.6-0814, implying that the compact object in the system is a neutron star.
Some of the bursts show photospheric radius expansion, so their peak flux can be used to estimate the distance to the system. The peak luminosity, and hence distance, can depend on several system parameters; for the most likely values, a high inclination and a helium atmosphere, $D=12.8_{-0.6}^{+0.8}$ kpc, although systematic effects allow a conservative range of $9-18$ kpc.
Before one burst, we detect a QPO at $9.6\pm0.5$ mHz with a fractional rms amplitude of $2.2\pm0.2$% ($0.5-10$ keV), likely due to marginally stable burning of helium; similar oscillations may be present before the other bursts but the light curves are not long enough to allow their detection. We also search for burst oscillations but do not detect any, with an upper limit in the best case of 15% fractional amplitude (over $1-8$ keV). Finally, we discuss the implications of the neutron star accretor and this distance on other inferences which have been made about the system.
In particular, we find that Swift J1858.6-0814 was observed at super-Eddington luminosities at least during bright flares during the variable stage of its outburst.
Language: | English |
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Year: | 2020 |
Pages: | 793-803 |
ISSN: | 13652966 and 00358711 |
Types: | Journal article and Preprint article |
DOI: | 10.1093/mnras/staa2749 |
ORCIDs: | Jaisawal, Gaurava Kumar , 0000-0001-5472-0554 , 0000-0002-5870-0443 , 0000-0003-3105-2615 , 0000-0002-6449-106X , 0000-0002-9639-4352 , 0000-0002-0380-0041 , 0000-0002-1481-1870 and 0000-0001-5819-3552 |