Science 5 months ago

Exciting Find: White Dwarf in New X-ray System

New study finds CXOU J005245.0-722844, an X-ray binary with a white dwarf and OBe star, showed a rare outburst. Key insights on X-ray emission and orbital changes.

Astronomers from PenX-ray binary system knowCXOU J005245.0-722844. DX-ray outburst awhite dwarf star.arXiv.

X-ray binaries are synormal star or a **whwhite dwarf (WD) transfeneutron star or a **blablack hole. These slow-mass X-ray binaries (LMXBs) andhigh-mass X-ray binaries (HMXBs).

The subgroup of Be/X-ray binaries (Be/XRBs) represents a major category within HMXBs. These systems typically consist of Be stars and neutron stars, such as pulsars. Observations indicate that these systems often exhibit weak, continuous X-ray emission, which is occasionally interrupted by outbursts lasting several weeks.

CXOU J005245.0-722844 was first identified as an X-ray source in 2009. Subsequent observations determined it to be a Be/XRB located in the Small Magellanic Cloud (SMC), featuring an OBe main sequence star and a compact object.

Recently, a team led by PSU's Thomas Gaudin used NASA's Swift spacecraft along with several ground-based telescopes to further study CXOU J005245.0-722844. They detected a new, extremely fast, and highly-luminous X-ray outburst in late May 2024. The X-ray spectrum during this outburst was identified as supersoft.

Further analysis revealed that the system contains a white dwarf. The results suggest that this white dwarf is likely a massive carbon and oxygen (CO) WD, nearing the upper limit of its mass range at approximately 1.2 solar masses. The study confirmed that the other component is an early-type OBe star, making CXOU J005245.0-722844 only the seventh known Be/WD X-ray binary and the fifth such system identified in the SMC.

The authors proposed that the recent outburst might be the initial thermonuclear phase of a nova outburst on the white dwarf's surface. They noted that the rapid decline of the event suggests minimal mass was ejected.

Additionally, observations revealed that the orbital period of CXOU J005245.0-722844 decreased from 17.55 to 17.14 days over two years. This change remains unclear and may require detailed mass transfer dynamical modeling to fully understand.