Astronomers explain X-ray flares of pulsar in BP Crucis system — Live Science
Astronomers have determined the cause of powerful X-ray flares from the neutron star GX 301-2 in the binary system BP Crucis, located about 13,000 light-years from Earth. As Live Science reports, the flares occur when the pulsar passes through a dense plasma plume ejected by its companion star, Wray 977.
The pulsar and the blue hypergiant
BP Crucis consists of the blue hypergiant Wray 977, which is approximately 60 times larger than the Sun, and the neutron star GX 301-2. The neutron star has a mass comparable to that of the Sun, but its size is about 20 kilometers.
GX 301-2 is a pulsar with a strong magnetic field that rotates rapidly and emits a beam of electromagnetic radiation into space, including X-rays. This beam wobbles, and when it is directed toward Earth, telescopes detect a signal about once every 11 minutes. In addition to regular pulses, GX 301-2 periodically produces much brighter X-ray flares.
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XRISM observations
Scientists used the XRISM space mission, jointly operated by NASA and the Japan Aerospace Exploration Agency. During a 16-hour observation that coincided with one of the flares, the instrument obtained detailed X-ray spectra of the system. They revealed rapid changes in emission and absorption lines, making it possible to trace the interaction of plasma with the neutron star.
Wray 977 ejects a concentrated plasma plume at a speed of about 540,000 kilometers per hour. GX 301-2 orbits its companion in 41.5 days and flares near the closest and farthest points of its orbit. The most powerful flares occur during the closest passage.
According to the team's modeling, stellar wind material falls onto the neutron star and accumulates on its surface. When enough material builds up, it causes bright X-ray flares. The study's first author, Roi Rahin, said that scientists had not previously seen such clear evidence of stellar-wind plasma falling onto a compact object. The team plans to continue observing the next flares of the BP Crucis system.
