Radio continuum emission from the magnetar SGR J1745-2900

interaction with gas orbiting Sgr A∗

F. Yusef-Zadeh, R. Diesing, M. Wardle, L. O. Sjouwerman, M. Royster, W. D. Cotton, D. Roberts, C. Heinke

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Abstract

We present radio continuum light curves of the magnetar SGR J1745-2900 and Sgr A∗ obtained with multi-frequency, multi-epoch Very Large Array observations between 2012 and 2014. During this period, a powerful X-ray outburst from SGR J1745-2900 occurred on 2013 April 24. Enhanced radio emission is delayed with respect to the X-ray peak by about seven months. In addition, the flux density of the emission from the magnetar fluctuates by a factor of 2-4 at frequencies between 21 and 41 GHz and its spectral index varies erratically. Here, we argue that the excess fluctuating emission from the magnetar arises from the interaction of a shock generated from the X-ray outburst with the orbiting ionized gas at the Galactic center. In this picture, variable synchrotron emission is produced by ram pressure variations due to inhomogeneities in the dense ionized medium of the Sgr A West bar. The pulsar with its high transverse velocity is moving through a highly blueshifted ionized medium. This implies that the magnetar is at a projected distance of ∼0.1 pc from Sgr A∗ and that the orbiting ionized gas is partially or largely responsible for a large rotation measure detected toward the magnetar. Despite the variability of Sgr A∗ expected to be induced by the passage of the G2 cloud, monitoring data show a constant flux density and spectral index during this period.

Original languageEnglish
Article numberL35
Pages (from-to)1-7
Number of pages7
JournalAstrophysical Journal Letters
Volume811
Issue number2
DOIs
Publication statusPublished - 1 Oct 2015

Bibliographical note

Copyright 2015 The American Astronomical Society. Firstly published in the Astrophysical Journal Letters, 811(2), L35, 2015, published by IOP Publishing. The original publication is available at http://www.doi.org/10.1088/2041-8205/811/2/L35. Version archived for private and non-commercial use with the permission of the author/s and according to publisher conditions. For further rights please contact the publisher.

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    Yusef-Zadeh, F., Diesing, R., Wardle, M., Sjouwerman, L. O., Royster, M., Cotton, W. D., ... Heinke, C. (2015). Radio continuum emission from the magnetar SGR J1745-2900: interaction with gas orbiting Sgr A∗. Astrophysical Journal Letters, 811(2), 1-7. [L35]. https://doi.org/10.1088/2041-8205/811/2/L35