"Slow" Radio Bursts from Galactic Magnetars?

Bing Zhang

Published 2020-11-19Version 1

Recently, one fast radio burst, FRB 200428, was detected from the Galactic magnetar SGR J1935+2154 during one X-ray burst. This suggests that magnetars can make FRBs. On the other hand, the majority of X-ray bursts from SGR J1935+2154 are not associated with FRBs. One possible reason of such rarity of FRB-SGR-burst associations is that the FRB emission is much more narrowly beamed than SGR burst emission. If such an interpretation is true, one would expect to detect radio bursts with viewing angle somewhat outside the narrow emission beam. These "slow" radio bursts (SRBs) would have broader widths and lower flux densities due to the smaller Doppler factor involved. The $2.2$-s long, 111 MHz radio burst detected from SGR J1935+2154 by the BSA LPI radio telescope may be such an SRB if the spectral slope is positive. If the FRB beam is narrow, there should be many more SRBs than FRBs from Galactic magnetars. Non-detection of these SRBs would disfavor the assumption that all SGR bursts are associated with narrow-beam FRBs.