Radio Pulsation Search and Imaging Study of SGR J1935+2154

TL;DR

This study conducted radio imaging and pulsation searches for the magnetar SGR J1935+2154, setting upper limits on radio emissions and exploring its association with a supernova remnant, but did not detect significant radio signals.

Contribution

First high-resolution radio imaging of SGR J1935+2154's associated supernova remnant and the establishment of new upper limits on radio pulsations and emissions.

Findings

No significant periodic radio pulsations detected.

Upper limits on flux density at 326.5 and 610 MHz established.

Possible physical association between the magnetar and SNR G57.2+0.8 suggested.

Abstract

We present the results obtained from imaging observations, and search for radio pulsations towards the magnetar SGR J1935+2154 made using the Giant Metrewave Radio Telescope, and the Ooty Radio Telescope. We present the high resolution radio image of the supernova remnant (SNR) G57.2+0.8, which is positionally associated with SGR J1935+2154. We did not detect significant periodic radio pulsations from the magnetar, with 8$\sigma$ upper limits on its flux density of 0.4, and 0.2 mJy at 326.5, and 610 MHz, respectively, for an assumed duty cycle of 10\%. The corresponding 6$\sigma$ upper limits at the two frequencies for any burst emission with an assumed width of 10 ms are 0.5 Jy, and 63 mJy, respectively. No continuum radio point source was detected at the position of SGR J1935+2154 with a 3$\sigma$ upper limit of 1.2 mJy. We also did not detect significant diffuse radio emission in a radius of 70 arc seconds in coincidence with the diffuse X-ray emission reported recently, with a 3$\sigma$ upper limit of 4.5 mJy. Using the archival HI spectra, we estimate the distance of SNR G57.2+0.8 to be 11.7 $\pm$ 2.8 kpc. Based on measured HI column density (N$_H$) along this line of sight, we argue that the magnetar could be physically associated with SNR G57.2+0.8. Based on present data, we can not rule out either a pulsar wind nebula or a dust scattering halo origin for the diffuse X-ray emission seen around the magnetar.