High-frequency radio observations of two magnetars, PSR J1622 − 4950 and 1E 1547.0 − 5408

Abstract

We investigated the radio spectra of two magnetars, PSR J1622 − 4950 and 1E 1547.0 − 5408, using observations from the Australia Telescope Compact Array and the Atacama Large Millimeter/submillimeter Array obtained in 2017. Our observations of PSR J1622 − 4950 show a steep spectrum with a spectral index of −1.3 ± 0.2 in the range of 5.5–45 GHz during its reactivating X-ray outburst in 2017. By comparing the data taken in different epochs, we found a significant enhancement in the radio flux density. The spectrum of 1E 1547.0 − 5408 was inverted in the range of 43–95 GHz, suggesting a spectral peak at a few hundred gigahertz. Moreover, we obtained X-ray and radio data of the radio magnetars PSR J1622 − 4950 and SGR J1745 − 2900 from the literature and found two interesting properties. First, radio emission is known to be associated with X-ray outbursts but has a different evolution; furthermore, we found that the rise time of the radio emission is much longer than that of the X-ray emission during the outburst. Second, radio magnetars may have double-peak spectra at a few GHz and a few hundred GHz. This could indicate that the emission mechanism is different in the cm and the submm bands. These two phenomena could provide a hint towards an understanding of the origin of radio emission and its connection with X-ray properties.