EP-WXT detected two X-ray flares EP J0433.6+3255 and EP J0452.7-0541

ATel #16915; S. K. Yang (WHU), Q. C. Shui (IHEP, CAS), H. Z. Wu (HUST), X. P. Xu, M. J. Liu (NAO, CAS), H. He (WHU), Y. L. Hua (PMO, CAS), W. D. Zhang, W. Yuan (NAO, CAS) on behalf of the Einstein Probe team
on 21 Nov 2024; 14:46 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Yuan Liu (liuyuan@bao.ac.cn)

Tweet

We report on the detection of two X-ray flares, designated EP J0433.6+3255 and EP J0452.7-0541, by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP).

The X-ray flare EP J0433.6+3255 was first detected by WXT at 2024-11-20T07:56:57 (UTC) with the duration longer than 2000 s. The source position of R.A. = 68.4 deg, Dec. = 32.917 deg (J2000; with an uncertainty of 2.7 arcmin in radius; 90% C.L. statistical and systematic) is around 30 arcsec away from a ROSAT X-ray source, 1RXS J043335.1+325432 that is spatially consistent with a nearby M-type star Gaia DR3 172042272322881792. The seperation between the star and 1RXS J043335.1+325432 is 11 arcsec. It is possible that the outburst is associated with both of the M star and the X-ray source. If this is the case, the X-ray flux of 1RXS J043335.1+325432 would have increased by about 2 orders of magnitude compared to the flux measured by ROSAT (2.2 x 10^-13 erg/s/cm^2). The WXT spectrum can be fitted by an absorbed power-law with a photon index of 2.5(-1.7/+1.8) (with the column density fixed at the Galactic value of 2.3 x 10^21 cm^-2). The unabsorbed 0.5-4 keV flux of the WXT source is 3.0 (+1.7/-1.3) x 10^-11 erg/s/cm^2. If this transient is indeed associated with Gaia DR3 172042272322881792, its luminosity is around 6.4 x 10^30 erg/s in the 0.5-4 keV range. (The quoted errors of the parameters derived above are at the 90% C.L.).

EP J0452.7-0541 was detected by WXT at 2024-11-20 22:14:07 (UTC) at R.A. = 73.176 deg, DEC = -5.687 deg (J2000), with an uncertainty of 2.3 arcmin (radius, 90% C.L. statistical and systematic). The source position is consistent with that of a faint X-ray source, 1eRASS J045241.6-054101, which was detected in the first six months of the eROSITA all-sky survey (Merloni et al. 2024). The 0.2-2.3 keV flux of 1eRASS J045241.6-054101 was 3.0 x 10^-13 erg/s/cm^2. A star, Gaia DR3 3188422199717067648, is only 1.4 arcsec away from the 1eRASS source. The WXT spectrum can be fitted with an absorbed apec model with a temperature of 2.8(+3.7/-1.0) keV, where the column density was fixed at the Galactic value of 3.8 x 10^20 cm^-2. The unabsorbed 0.5-4 keV flux of the WXT source is 4.3 (+1.4/-1.1) x 10^-11 erg/s/cm^2, which is 2 orders of magnitude higher than the previous flux measured by eROSITA. If this transient is indeed associated with the star Gaia DR3 3188422199717067648, its luminosity is around 3.9 x 10^31 erg/s in the 0.5-4 keV range. (The quoted errors of the parameters derived above are at the 90% C.L.).

Multi-wavelength follow-up observaitons are encouraged.

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.