  As part of a European Pulsar Network (EPN) multi-telescope observing
campaign, we performed simultaneous multi-frequency observations at 1.4, 4.9
and 8.4 GHz during July 2006 and quasi-simultaneous multi-frequency
observations from Decem- ber 2006 until July 2007 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-sec 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 of the flux density by
a factor of 10 within 8 months 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 also
investigate the origin of these fluctuations.
