Simultaneous Multi-band Radio & X-ray Observations of the Galactic Center Magnetar SGR 1745−2900

Pennucci, Timothy Thomas and Possenti, A. and Esposito, P. and Rea, N. and Haggard, D. and Baganoff, F. K. and Burgay, M. and Zelati, F. C. and Israel, G. L. and Minter, A. (2015) Simultaneous Multi-band Radio & X-ray Observations of the Galactic Center Magnetar SGR 1745−2900. ASTROPHYSICAL JOURNAL, 808 (1). ISSN 1538-4357

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Abstract

We report on multi-frequency, wideband radio observations of the Galactic Center magnetar (SGR 1745-2900) with the Green Bank Telescope for similar to 100 days immediately following its initial X-ray outburst in 2013 April. We made multiple simultaneous observations at 1.5, 2.0, and 8.9 GHz, allowing us to examine the magnetar's flux evolution, radio spectrum, and interstellar medium parameters (such as the dispersion measure (DM), the scattering timescale, and its index). During two epochs, we have simultaneous observations from the Chandra X-ray Observatory, which permitted the absolute alignment of the radio and X-ray profiles. As with the two other radio magnetars with published alignments, the radio profile lies within the broad peak of the X-ray profile, preceding the X-ray profile maximum by similar to 0.2 rotations. We also find that the radio spectral index gamma is significantly negative between similar to 2 and 9 GHz; during the final similar to 30 days of our observations gamma similar to -1.4, which is typical of canonical pulsars. The radio flux has not decreased during this outburst, whereas the long-term trends in the other radio magnetars show concomitant fading of the radio and X-ray fluxes. Finally, our wideband measurements of the DMs taken in adjacent frequency bands in tandem are stochastically inconsistent with one another. Based on recent theoretical predictions, we consider the possibility that the DM is frequency-dependent. Despite having several properties in common with the other radio magnetars, such as L-X,L-qui/L-rot less than or similar to 1, an increase in the radio flux during the X-ray flux decay has not been observed thus far in other systems.

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