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Axion constraints from quiescent soft gamma-ray emission from magnetars

Lloyd, Sheridan J. and Chadwick, Paula M. and Brown, Anthony M. and Guo, Huai-Ke and Sinha, Kuver (2021) 'Axion constraints from quiescent soft gamma-ray emission from magnetars.', Physical Review D, 103 (2). 023010.


Axion-like-particles (ALPs) emitted from the core of a magnetar can convert to photons in its magnetosphere. The resulting photon flux is sensitive to the product of (i) the ALP-nucleon coupling Gan which controls the production cross section in the core and (ii) the ALP-photon coupling gaγγ which controls the conversion in the magnetosphere. We study such emissions in the soft-gamma-ray range (300 keV to 1 MeV), where the ALP spectrum peaks and astrophysical backgrounds from resonant Compton up scattering are expected to be suppressed. Using published quiescent soft-gamma-ray flux upper limits in five magnetars obtained with CGRO COMPTEL and INTEGRAL SPI/IBIS/ISGRI, we put limits on the product of the ALP-nucleon and ALP-photon couplings. We also provide a detailed study of the dependence of our results on the magnetar core temperature. We further show projections of our result for future Fermi-GBM observations. Our results motivate a program of studying quiescent soft-gamma-ray emission from magnetars with the Fermi-GBM.

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Publisher statement:Reprinted with permission from the American Physical Society: Lloyd, Sheridan J., Chadwick, Paula M., Brown, Anthony M., Guo, Huai-Ke & Sinha, Kuver (2021). Axion constraints from quiescent soft gamma-ray emission from magnetars. Physical Review D 103(2): 023010. © 2021 by the American Physical Society. Readers may view, browse, and/or download material for temporary copying purposes only, provided these uses are for noncommercial personal purposes. Except as provided by law, this material may not be further reproduced, distributed, transmitted, modified, adapted, performed, displayed, published, or sold in whole or part, without prior written permission from the American Physical Society.
Date accepted:14 December 2020
Date deposited:23 September 2021
Date of first online publication:12 January 2021
Date first made open access:23 September 2021

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