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LEIA detected a new X-ray outburst from MAXI J1810-222, and several outbursts from nearby sources in the Galactic center region

ATel #16108; H. N Yang, M. J Liu, Y. Liu, Z. X. Ling, C. Zhang, H. Q. Cheng, C. Z. Cui, D. W. Fan, H. B. Hu, J. W.Hu, M. H. Huang, C. C. Jin, D. Y. Li, H. Y. Liu, M. Sugizaki, H. Sun, H. W. Pan, W. X. Wang, Y. L. Wang, Q. Y. Wu, X. P. Xu, Y. F. Xu, M. Zhang, W. D.Zhang, D. H. Zhao and W. Yuan (NAOC, CAS), on behalf of the LEIA and Einstein Probe team
on 30 Jun 2023; 15:42 UT
Credential Certification: Yuan Liu (liuyuan@bao.ac.cn)

Subjects: X-ray, Binary, Black Hole

Referred to by ATel #: 16124

We report on a new X-ray outburst from the X-ray transient MAXI J1810-222 detected by LEIA (Lobster Eye Imager for Astronomy). The position of the LEIA source is R.A. = 273.168 deg, DEC = -22.317 deg with an uncertainty of 1.5 arcmin (radius, 90%C.L. statistical and systematic), which is 25.5 arcseconds away from the improved position of MAXI J1810-222 obtained by Swift UVOT. The source was observed several times by LEIA on 2023-06-22 and 2023-06-25. The spectrum of the last observation at 2023-06-25T10:00:19 can be fitted with an absorbed powerlaw with N_H fixed at 6.0e21 cm^-2 (according to the Swift observation on 2023-06-11) and a photon index of 1.59+/-0.34, giving an unabsorbed 0.5 - 4.0 keV flux of 9.0(+/-1.5)e-10 erg/s/cm^2. Before that, the source was detected by LEIA once at 2023-05-19T09:58:38 with a lower unabsorbed flux of 1.1(+/-0.6)e-10 erg/s/cm^2. However, the source was not detected on 2023-05-29, 2023-06-05 and 2023-06-07 at a flux limit of a few times e-11 erg/s/cm^2. Thus, we suggest that the source is likely to enter a new outburst period.

Aside from MAXI J1810-222, several outbursts from known X-ray sources near the Galactic center region were also detected by LEIA in June, including GRS 1739-278, GRS 1747-312, 1RXS J173546.9-302859, and 4U 1722-30. The outburst of GRS 1739-278 detected with LEIA was reported by Li et al. (ATel #16102). The highest unabsorbed fluxes of others detected with LEIA are 2.1(+/-1.3)e-10 erg/s/cm^2 for GRS 1747-312 (with N_H=0.86+/-0.64 e22 cm^-2 and a photon index of 1.93+/-1.43), 1.5(+/-0.8)e-9 erg/s/cm^2 for 1RXS J173546.9-302859 (with N_H=1.37+/-0.51 e22 cm^-2 and a photon index of 1.77+/-0.83), and 5.0(+/-2.4)e-9 erg/s/cm^2 for 4U 1722-30 (with N_H=1.82+/-0.30 e22 cm^-2 and a photon index of 2.52+/-0.46).

LEIA(Zhang et al. 2022, ApJL, 941, 2) is a soft X-ray Lobster-eye imager (0.5 - 4.0keV) with a FoV of 340 square degrees aboard the experimental satellite SATech-01 of the CAS, launched on July 27, 2022. The above result is preliminary and the final result will be published elsewhere.