Einstein Probe detection of the brightening of LMXB EXO 0748-676/UY Vol
ATel #16853; H. Sun, Q. Y. Wu (NAO, CAS), Y. J. Zhang (THU), W. F. WEN (SZTU), J. H. Wu (GZHU), H. W. Pan (NAO, CAS) on behalf of the Einstein Probe team
on 8 Oct 2024; 15:31 UT
Credential Certification: Yuan Liu (liuyuan@bao.ac.cn)
We report on the detection of the brightening of the neutron star low-mass X-ray binary EXO 0748-676/UY Vol by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission. Several Type I bursts of EXO 0748-676/UY Vol have been observed since June 2024 (GCN#36653, ATel#16646, #16648, #16649, #16651, #16654, #16655, #16673), indicating that the X-ray burst has returned to an active state after being in quiescence for 16 years since 2008 (ATel#1812). The source was detected by EP-WXT in a 26 ks long exposure observation on 9 July 2024. The spectrum cannot be well constrained due to the limited number of counts. Assuming an absorbed power-law model with the photon index of -2 and the Galactic column density of 1.5 x 10^21 cm^-2, the estimated flux is 2.2 x 10^-12 erg/cm2/s in the 0.5-4 keV band. The source location was covered by EP-WXT in the following observations in July and August, while the object remained undetected with a flux upper limit of 7.7 x 10^-12 erg/cm2/s. Recently, EP-WXT detected the source in the observation starting at 2024-10-04T22:42:34 UTC and in several subsequent observations, with an increase in the 0.5-4 keV flux from 2.4 x 10^-11 erg/cm2/s to 4.5 x 10^-11 erg/cm2/s. The flux is more than one order of magnitude brighter than that detected in July, suggesting a brightening in the soft X-ray band of this source.
We have triggered the EP-FXT observation to follow the evolution of this source in more detail.
Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). EP is a mission of the Chinese Academy of Sciences in collaboration with ESA, MPE and CNES.
