Searching for radio emission from radio quiet magnetars with MeerKAT

Context. Magnetars are neutron stars that occupy the extreme end of the neutron star population, with magnetic field strengths greater than 10 12 G. They have been proposed as one of the most likely progenitor models for the phenomenon of energetic, millisecond-duration, extragalactic radio bursts (FRBs), which have been increased even further due to the FRB-like bursts emitted from the galactic Magnetar SGR 1935+2154. However, only a low fraction of the magnetars (six in total) have been detected in the radio regime, and thus most magnetars are radio quiet. Aims. We conducted regular observations of 13 radio quiet magnetars to probe the long-term radio quietness using the most sensitive telescope in the southern hemisphere: MeerKAT. These observations provide deep constraints on the radio emission of magnetars, relevant for the progenitor models of FRBs. Methods. Given that MeerKAT is an interferometer, we probe the magnetars for radio emission in both the imaging and time domain. We search in the time domain in the DM range of 20 pc/cm 3 10 000 pc/cm 3 for single pulses using a TransientX-based search pipeline (the FRB perspective), as well as from a pulsar perspective by folding the data using the X-ray ephemeris. On the other hand, we use the imaging domain to search for persistent radio emission in total intensity and circular polarisation, as well as to create light curves using snapshot imaging, which also has a long transient perspective. Results. We find no radio emission in the time domain for any of the observed magnetars. Nevertheless, we are providing deep limits of the mean flux density (52 μJy to 68 μJy) and the single pulse fluence 39 mJy ms to 52 mJy ms. From the image domain, we provide individual upper limits on the persistent radio emission and the light curve for the 13 magnetars. Additionally, an ultra-long period transient and an additional magnetar happened to be in the imaging beam, for which we provide lower limits as well. Conclusions. We provide an extensive series of deep upper limits in the time domain, but also as novelty limits from the imaging domain for magnetars. As the current magnetar radio emission models are based on a few radio loud magnetars, we encourage monitoring of radio quiet magnetars independent of their X-ray flux with high cadence for further insights into their potential for emitting in the radio regime.