MeerKAT radio non-detection of MAXI J1752-45
ATel #16923; J. Crook-Mansour (University of Oxford), E. Tremou (NRAO), A. Hughes (University of Alberta), R. Fender (University of Oxford and University of Cape Town), on behalf of the XKAT team.
on 25 Nov 2024; 22:02 UT
Credential Certification: Evangelia Tremou (etremou@nrao.edu)
Subjects: Radio, X-ray, Transient
As part of the X-KAT programme on the MeerKAT radio telescope, we observed the field of the new X-ray transient MAXI J1752-457, 5.55 days after its initial detection by MAXI/GSC at 18:23 UT on 9 November 2024 (ATel #16898). In this telegram, we report on its radio non-detection.
Soon after MAXI J1752-457 was initially detected, a further report (ATel #16902) noted that the possible tidal disruption event EP240809a (ATel #16765, #16767) is located within the MAXI error circle. After further observations by NuSTAR at 06:30 UTC on 12 November and 00:50 UTC on 13 November (ATel #16910), an updated position of (R.A., Dec) = (268.269, -45.866) (J2000) was obtained for MAXI J1752-45. This position is offset by about 9 arcsec from the Swift XRT position for EP240809a, reported as (R.A., Dec) = (268.2688 deg, -45.8635 deg) with an estimated uncertainty of 3.7 arcsec (ATel #16765). Given that this falls well within NuSTAR's PSF of 18 arcsec (FWHM), it was concluded that EP240809a and MAXI J1752-457 are the same source.
Our radio observations of the field were carried out at 07:30:08.8 UTC on 15 November (MJD 60629.313 ± 0.005), and at 10:13:22.4 UTC on 16 November (MJD 60630.426 ± 0.005), using 59 and 61 antennas of the MeerKAT radio telescope, respectively. For each observation, we observed the phase calibrator J1744-5144 for 2 minutes, both before and after a 15-minute scan on the target field. J1939-6342 was used as the primary flux and bandpass calibrator. The data were taken at a central frequency of 1.28 GHz, with a bandwidth of 856 MHz over 4096 channels. Calibration and imaging were performed using standard techniques.
In both epochs, no significant radio emission is detected at the NuSTAR/Swift position of MAXI J1752-457. We obtain 3-sigma upper limits of ~87 uJy/beam and ~73 uJy/beam, respectively, calculated using a 1' by 1' square region centered on the NuSTAR position.
The nearest radio source, offset by ~40 arcsec, is a slightly extended uncatalogued object, which is located at (R.A., Dec) = (268.2664, -45.8536) (J2000) with an estimated uncertainty of 1.2 arcsec (radius, 90% C.L. statistical and systematic). Its modest integrated flux density of 513 ± 64 uJy (with a peak flux density of 333 ± 27 uJy/beam) would have been undetected by recent all-sky radio surveys at comparable frequencies (e.g., the Rapid ASKAP Continuum Survey, which has a median 1-sigma RMS noise of 250 uJy/beam). Due to this source being located at a significant distance outside the error circles on the NuSTAR/Swift positions of MAXI J1752-457, it is unlikely to be related.
Multi-wavelength observations are encouraged to confirm the nature of MAXI J1752-457. We will continue our radio monitoring of the source over the next few weeks. Unfortunately, due to the Sun angle constraint, the source is currently not observable using Swift XRT.
X-KAT is a large MeerKAT open-time programme to observe X-ray binaries in the radio band, in coordination with large X-ray and optical monitoring programmes. It performs weekly radio monitoring of bright, active systems, with a capacity for higher cadence observations. Swift follow-up of X-ray binaries is largely performed as part of the SwiftKAT programme, which provides quasi-simultaneous X-ray coverage of the X-KAT targets. For further information about this programme, contact Rob Fender.
MeerKAT is operated by the South African Radio Astronomy Observatory (SARAO), a facility of South Africa's National Research Foundation. We thank the SARAO staff for carrying out our observations. For data processing, we acknowledge the use of the data-intensive research cloud of the Inter-University Institute for Data Intensive Astronomy (IDIA). IDIA is a South African university partnership involving the University of Cape Town, the University of Pretoria, and the University of the Western Cape.
