Che-Yen Chu (NTHU); C.-Y. Ng (HKU); Albert K. H. Kong (NTHU); Hsiang-Kuang Chang (NTHU)
Magnetars are isolated neutron stars with strong magnetic fields. Radio emission from magnetars is important to study neutron star physics. We investigated the radio spectra of two magnetars, PSR J1622-4950 and 1E 1547.0-5408, using observations from the Australia Telescope Compact 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 an order of magnitude 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 can provide a hint towards an understanding of the origin of radio emission and its connection with X-ray properties.