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(Top:) MAXI lightcurve of J1621 plotted in the 2.0−10.0 keV (black points), 2.0−4.0 keV (S, blue squares), and 4.0−10.0 keV (H, orange diamonds) bands are plotted. Red vertical lines indicate the observation time of an X-ray burst from any instrument. (Bottom:) Hardness ratio = (H-S)/(H+S) for each point in the lightcurve. Credit: Gorgone et al., 2019.
An international team of astronomers has uncovered important insights about the recently discovered transient source known as MAXI J1621–501. Results of new observations conducted with NASA's NuSTAR spacecraft indicate that the object is a low-mass X-ray binary. The finding is detailed in a paper published August 9 on arXiv.org.
Binaries - Consist - Star - Dwarf - Mass
X-ray binaries consist of a normal star or a white dwarf transferring mass onto a compact a neutron star or a black hole. Based on the mass of the companion star, astronomers divide them into low-mass X-ray binaries (LMXB) and high-mass X-ray binaries (HMXB).
Some LMXBs exhibit transient outbursts, during which an increase in X-ray luminosities is observed. When these outbursts are characterized as Type I X-ray bursts—thermonuclear explosions taking place on the surface layers of neutron stars—they obviously confirm the presence of neutron stars in such binaries.
MAXI - J1621–501 - J1621 - Sources - Type
MAXI J1621–501 (J1621 for short) is one of the sources in which Type I X-ray bursts were identified. The transient was first detected by the Monitor of All-sky X-ray Image (MAXI) Nova Alert System on October 19, 2017.
Two months later, a follow-up observational campaign of this transient commenced using the Nuclear Spectroscopic Telescope Array (NuSTAR), resulting in the detection of two Type I X-ray bursts. Further monitoring of J1621 with ESA's INTEGRAL satellite, MAXI and the Neutron Star Interior Composition Explorer (NICER) revealed 22 more bursts of this type. All in all, these observations allowed...
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