Detection of the X-ray source likely associated with 4FGL J0031.5-564 by Einstein Probe

ATel #16704; M. J. Liu, X. P. Xu (NAOC, CAS), Y. J. Zhang (THU), H. W. Pan, C. C. Jin, Z. X. Ling, W. Yuan, Y. Liu, C. Zhang, W. Chen, H. Q. Cheng, C. Z. Cui, D. W. Fan, H. B. Hu, J. W. Hu, M. H. Huang, D. Y. Li, H. Y. Liu, Z. Z. Lv, T. Y. Lian, X. Mao, X. Pan, H. Sun, W. X. Wang, Y. L. Wang, S. X. Wen, Q. Y. Wu, Y. F. Xu, H. N. Yang, M. Zhang, W. D. Zhang, W. J. Zhang, Z. Zhang, D. H. Zhao (NAOC, CAS), Y. Chen, S. M. Jia, S. N. Zhang (IHEP, CAS), E. Kuulkers, A. Santovincenzo (ESA), P. O'Brien (Univ. of Leicester), K. Nandra, A. Rau (MPE), B. Cordier (CEA) on behalf of the Einstein Probe team
on 12 Jul 2024; 10:34 UT
Credential Certification: Yuan Liu (liuyuan@bao.ac.cn)

Tweet

We report on the detection of an X-ray source EP240709a at 2024-07-09T13:35:48 (UTC) by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP). The position of the source is R.A. = 7.910 deg, DEC = -56.760 deg (J2000) with an uncertainty of 3 arcmin (radius, 90% C.L. statistical and systematic). The emission of the source does not show significant flaring activity. The averaged 0.5-4 keV spectrum can be fitted by an absorbed power-law (with the column density fixed at the Galactic value of 1.2 x 10^20 cm^-2) with a photon index of 0.7(+0.6/-0.6). The derived unabsorbed 0.5-4 keV flux is 1.3(+0.6/-0.5) x 10^-11 erg/cm^2/s.

We performed the follow-up observation with Follow-up X-ray Telescope (FXT) on board EP starting from 2024-07-11T10:23:38 (UTC) with a total exposure time of about 3880 s. An X-ray source is detected at R.A. = 7.8976 deg, DEC = -56.7786 deg (J2000) with an uncertainty of 10 arcsec (radius, 90% C.L. statistical and systematic). The emission of the source does not show significant variability in this observation. The averaged X-ray spectrum can be fitted by an absorbed power law with the column density NH=1.5(+/-0.4) x 10^21 cm^-2 and a photon index of 2.3(+0.1/-0.2). The derived unabsorbed flux is 6.6(+/-0.3) x 10^-12 erg/cm^2/s in 0.5-10 keV. The 90 % uncertainties are given for the above parameters.

The FXT position is coincident with the known gamma-ray source 4FGL J0031.5-5648 (Abdollahi et al. 2020). This gamma-ray source was detected by Swift-XRT in 2019 with a flux of 4.3 x 10^-13 erg/cm2/s (0.3-10 keV) and by eROSITA with a flux of 3.6 x 10^-13 erg/cm2/s (0.6-2.3 keV). The separation of the X-ray source between FXT and Swift-XRT is 4.6''. That value is 4.8'' between FXT and eROSITA. We tend to suggest that EP240709a is likely associated with 4FGL J0031.5-564. Multi-band follow-up observations are encouraged.

The above observations were made with the WXT and FXT instruments. 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.