Che-Yen Chu (Institute of Astronomy, National Tsing Hua University); C.-Y. Ng (Department of Physics, The University of Hong Kong); Albert K. H. Kong (Institute of Astronomy, National Tsing Hua University); Hsiang-Kuang Chang (Institute of Astronomy, National Tsing Hua University)
We investigated the radio spectra of two magnetars, 1E 1547.0-5408 and PSR J1622-4950, using observations from the Australia Telescope Compact Array and the Atacama Large Millimeter/submillimeter Array taken in 2017. 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. Our observations of PSR J1622-4950 show a steep spectrum with a spectral index of -1.3 in the range of 5.5-45 GHz during its re-activating X-ray outburst in 2017. By comparing the data taken at different epochs, we found significant enhancement in the radio flux density. Moreover, we obtained the X-ray and radio light curves of radio magnetars from literature and found two interesting properties. First, the 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 sub-mm bands. Second, radio emission is known to be associated with X-ray outburst but has different evolution. We further suggest that the rising time of the radio emission is much longer than the X-ray during the outburst. This phenomenon could provide a hint to understand the origin of radio emission and its connection with the X-ray properties.