LEIA detected several outbursts from nearby sources in the Galactic center region

Several outbursts from known X-ray sources near the Galactic center region were detected by LEIA in late June, including GRS 1739-278, GRS 1747-312, 1RXS J173546.9-302859, 4U 1722-30, and MAXI J1810-222.

The outburst of GRS 1739-278 was reported by Negoro et al. (ATel #16097) on June 26, 2023 and later confirmed by Swift/XRT observation on June 27, 2023 (Kennea et al., ATel #16100). Around this position a source (RA=265.676, Dec=-27.73, 90% uncertainty=2 arcmin) was detected with LEIA at a flux of (4.6 +/- 2.0)E-9 erg/s/cm^2 at 2023-06-22T09:43:27, which is spatially consistent with GRS 1739-278. It is thus suggested that GRS 1739-278 has already been at an outburst state since June 22, 2023, and exhibits flux variations by a factor of ~3.

The new X-ray outburst from the X-ray transient MAXI J1810-222 was detected several times by LEIA on 2023-06-22 and 2023-06-25. 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 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, it is suggested that the source is likely to enter a new outburst period.

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).

Figure 1 Images of four separate orbits of observations in galactic center region.

Figure 2 Image of X-ray outburst from the MAXI J1810-222.

The preliminary results have been posted at Astronomer's Telegram as ATel 16105 and ATel 16108.  Click here for more EP/LEIA Astronomer's Telegrams.