University of Hertfordshire

From the same journal

From the same journal

By the same authors

Can the Local Bubble explain the radio background?

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  • stab131

    Accepted author manuscript, 630 KB, PDF document

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Original languageEnglish
Article numberstab131
JournalMonthly Notices of the Royal Astronomical Society
Early online date16 Jan 2021
DOIs
Publication statusE-pub ahead of print - 16 Jan 2021

Abstract

The ARCADE 2 balloon bolometer along with a number of other instruments have detected what appears to be a radio synchrotron background at frequencies below about 3 GHz. Neither extragalactic radio sources nor diffuse Galactic emission can currently account for this finding. We use the locally measured Cosmic ray electron population, demodulated for effects of the Solar wind, and other observational constraints combined with a turbulent magnetic field model to predict the radio synchrotron emission for the Local Bubble. We find that the spectral index of the modelled radio emission is roughly consistent with the radio background. Our model can approximately reproduce the observed antenna temperatures for a mean magnetic field strength B between 3-5 nT. We argue that this would not violate observational constraints from pulsar measurements. However, the curvature in the predicted spectrum would mean that other, so far unknown sources would have to contribute below 100 MHz. Also, the magnetic energy density would then dominate over thermal and cosmic ray electron energy density, likely causing an inverse magnetic cascade with large variations of the radio emission in different sky directions as well as high polarisation. We argue that this disagrees with several observations and thus that the magnetic field is probably much lower, quite possibly limited by equipartition with the energy density in relativistic or thermal particles (B = 0.2-0.6 nT). In the latter case, we predict a contribution of the Local Bubble to the unexplained radio background at most at the per cent level.

Notes

© 2021 The Author(s). This is the accepted manuscript version of an article which has been published in final form at https://dx.doi.org/10.1093/mnras/stab131.

ID: 24360658