2015MNRAS.451L..50T

We report on simultaneous observations of the magnetar SGR J1745-2900 at frequencies ν=2.54-225GHz using the Nanay94-m equivalent, Effelsberg100-m, and IRAM30-m radio telescopes. We detect SGR J1745-2900 up to 225GHz, the highest radio frequency detection of pulsed emission from a neutron star to date. Strong single pulses are also observed from 4.85 up to 154GHz. At the millimetre band we see significant flux density and spectral index variabilities on time scales of tens of minutes, plus variability between days at all frequencies. Additionally, SGR J1745-2900 was observed at a different epoch at frequencies ν=296-472GHz using the APEX12-m radio telescope, with no detections. Over the period MJD56859.83-56862.93 the fitted spectrum yields a spectral index of <α> = -0.4±0.1 for a reference flux density <S154> = 1.1±0.2mJy (with Sν∝να), a flat spectrum alike those of the other radio-loud magnetars. These results show that strongly magnetized neutron stars can be effective radio emitters at frequencies notably higher to what was previously known and that pulsar searches in the Galactic Centre are possible in the millimetre band.