Radio spectrum of the AXP J1810−197 and of its profile components

As part of a European Pulsar Network (EPN) multitelescope observing campaign, we performed simultaneous multifrequency observations at 1.4, 4.9 and 8.4 GHz during 2006 July and quasi-simultaneous multifrequency observations from 2006 December until 2007 July at 2.7, 4.9, 8.4, 14.6 and 32 GHz, in order to obtain flux density measurements and spectral features of the 5.5 s radio-emitting magnetar AXP J1810−197. We monitored the spectral evolution of its pulse shape which consists of a main pulse (MP) and an interpulse (IP). We present the flux density spectrum of the average profile and of the separate pulse components of this first-known radio-emitting transient anomalous X-ray pulsar. We observe a decrease in the flux density by a factor of 10 within 8 m and follow the disappearance of one of the two main components. Although the spectrum is generally flat, we observe large fluctuations of the spectral index with time. For that reason, we have made some measurements of modulation indices for individual pulses in order to investigate the origin of these fluctuations.