Discovery of the radio counterpart of MAXI J1744-294 with MeerKAT

ATel #17045; Noa Grollimund, Stephane Corbel (Universite Paris Cite & CEA Saclay), Arash Bahramian (Curtin University), Francesco Carotenuto (INAF-OAR), Ian Heywood, Fraser Cowie, Andrew Hughes, Rob Fender (Oxford University), Sara Motta (INAF-OAB), on behalf of the X-KAT collaboration
on 19 Feb 2025; 21:28 UT
Credential Certification: S. CORBEL (stephane.corbel@cea.fr)

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ATel #16975 reported the discovery of a new X-ray transient near the galactic center detected by MAXI/GSC from 2025-01-02 and tentatively named MAXI J1744-294. Further MAXI observations of the bright X-ray outburst allowed to determine a new error region which included the position of Sgr A* (ATel #16983). NinjaSat, NuSTAR and NICER follow-up observations confirmed activity from the new source (ATels #17009, #17031, #17040), while Swift/XRT provided an enhanced position of 17:45:41.93, -29:00:35, with 6.4" uncertainty (ATel #17010).

Following the X-ray trigger, we initiated follow-up radio observations with the MeerKAT radio telescope as part of the X-KAT programme. Radio observations were carried out at a central frequency of 1.284 GHz, with a total bandwidth of 856 MHz. We used J1939-6342 for flux and bandpass calibration, and J1830-3602 for complex gain calibration.

MAXI J1744-294 was observed for 15 minutes on 2025-01-25 05:15:20.3 UTC (MJD 60700.22). We find a point-like source ~18” from Sgr A*, but offset by ~23” from the Swift/XRT position (ATel #17010). In order to check the X-ray position, we performed localization analysis of the same Swift observation (obs. ID 00019513001), and find an enhanced position of 17:45:40.33, -29:00:49.2 (error radius of 2.6”). The latter is consistent with the radio source we have detected. Besides, when comparing our radio map with the L-band MeerKAT Galactic Center Mosaic (Heywood et al. 2022), we do not find any point-like source at this position. We thus consider the new source detected with MeerKAT as the radio counterpart of MAXI J1744-294.

We detected MAXI J1744-294 in three other observations. Fitting for a point source in the image plane, we improve the localisation to RA (J2000) = 17:45:40.45, Dec (J2000) = -29:00:46.6 (averaging over the four observations), with an uncertainty of ~0.5". MAXI J1744-294 is very close to Sgr A* in the plane of the sky and its surroundings are dominated by strong extended emission (Sgr A complex), thus measuring an accurate flux density can be difficult. While the peak brightness of the source (on 2025-01-25) is ~0.3 Jy/beam, we measure a preliminary flux density excess (with respect to the background emission) of 0.11 ± 0.05 Jy.

Multi-wavelength observations are encouraged to study the evolution of the outburst. Further radio monitoring is planned, as well as weekly Swift observations of the target.

X-KAT is a large MeerKAT open-time programme to observe X-ray binaries in the radio band, performing weekly monitoring of bright, active systems, with capacity for higher cadence observations, and in coordination with large X-ray and optical monitoring programmes. For further information on this programme contact Rob Fender. The Swift follow-up of X-ray binaries is largely performed as part of the SwiftKAT program, which provides quasi simultaneous X-ray coverage of the X-KAT targets.