Indian astronomers have studied the low-mass X-ray binary GX 3+1, revealing a thermonuclear flare. The results of the observation are reported in a preprint on arXiv.org.

X-ray binaries consist of an ordinary star or white dwarf transferring mass to a compact neutron star or 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).

GX 3+1 is a persistently bright double X-ray source that has been classified as an LMXB.

LMXBs can exhibit short bursts during which an increase in X-ray luminosity is observed. Some of these bursts are characterized as Type I X-ray bursts, thermonuclear explosions occurring in the surface layers of neutron stars. The first type I burst from GX 3+1 was discovered in 1983, and since then this source has been found to be a very active X-ray burster.

The new observations recorded a single Type I thermonuclear explosion lasting approximately 15 seconds. Analyzing the data, the astronomers noticed a double peak in the light curve of the flare at higher energies (8–12 keV, 12–20 keV). It was a relatively fast event, lasting about two seconds, during which the outburst exhibited a double peak, indicating the expansion phase of the star’s radius.

Bursters are flaring galactic X-ray sources, which are accreting neutron stars with orbital periods ranging from several hours to several days.