MeerKAT follow-up observations of MAXI J1348-630 reveal bright radio flare at state transition

ATel #12497; Francesco Carotenuto, Evangelia Tremou, Stephane Corbel (CEA-Saclay), Rob Fender (Oxford, UCT), Patrick Woudt (UCT), James Miller-Jones (Curtin), on behalf of the ThunderKAT collaboration
on 12 Feb 2019; 10:58 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Evangelia Tremou (evangelia.tremou@cea.fr)

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Following the discovery of a new X-ray transient MAXI J1348-630 (ATel #12425) by the MAXI instrument aboard the International Space Station, intense follow-up has been conducted at all wavelengths with observations by Swift, INTEGRAL, Nicer, ATCA and optical telescopes (e.g. ATels #12434, #12439, #12441, #12447, #12456). As part of the ThunderKAT Large Survey Programme (Fender et al., 2017), we conducted radio observations with the new MeerKAT radio telescope located in the Karoo desert in South Africa. We report on three epochs: from 2019-01-29 00:31 UT to 2019-01-29 00:53 UT (MJD 58512.02) with 59 antennas, from 2019-02-01 03:45 UT to 2019-02-01 04:00 UT (MJD 58515.16) with 59 antennas, from 2019-02-09 05:08 UT to 2019-02-09 05:23 UT (MJD 58523.21) with 60 antennas. All observations were taken at a central frequency of 1.284 GHz with a total bandwidth of 860 MHz. The data were first calibrated with CASA, while imaging was carried out with the KillMS and DDFacet software (Tasse et al., 2018), with a Briggs robust parameter of -1 for weighting. In all observations, a radio source is detected at a position consistent with the location of MAXI J1348-630, displaying, on 2019-02-09, a preliminary flux density of 520.3 +/- 5.0 mJy. This is approximately 15 times brighter than MeerKAT observations taken one week earlier. The first two MeerKAT observations occurred during the initial hard state and are in agreement with the presence of self-absorbed compact jets, as outlined by the ATCA observations (ATel #12456). The strong radio brightening of MAXI J1348-630 between the second and third epoch is consistent with the expected radio flare following the transition from hard to soft state of X-ray binaries, as inferred from the INTEGRAL monitoring observations (ATel #12471). Further monitoring is ongoing and we encourage high resolution radio follow-up of the source during its outburst. ThunderKAT will run for 5 years and aims to monitor all bright, active, southern hemisphere X-ray binaries in the radio band. For further information on this programme please contact Rob Fender and/or Patrick Woudt. We thank the staff at the South African Radio Astronomy Observatory (SARAO) for scheduling these observations. The MeerKAT telescope is operated by SARAO, which is a facility of the National Research Foundation, an agency of the Department of Science and Technology.