Soft X-ray Excess in the Coma Cluster from a Cosmic Axion Background
We show that the soft X-ray excess in the Coma cluster can be explained by a cosmic background of relativistic axions converting into photons in the cluster magnetic field. We provide a detailed self-contained review of the cluster soft X-ray excess, the proposed astrophysical explanations and the p...
| Main Authors: | , , , , |
|---|---|
| Format: | Journal article |
| Language: | English |
| Published: |
Institute of Physics Publishing
2013
|
| _version_ | 1797055655031341056 |
|---|---|
| author | Angus, S Conlon, J Marsh, M Powell, A Witkowski, LT |
| author_facet | Angus, S Conlon, J Marsh, M Powell, A Witkowski, LT |
| author_sort | Angus, S |
| collection | OXFORD |
| description | We show that the soft X-ray excess in the Coma cluster can be explained by a cosmic background of relativistic axions converting into photons in the cluster magnetic field. We provide a detailed self-contained review of the cluster soft X-ray excess, the proposed astrophysical explanations and the problems they face, and explain how a 0.1-1 keV axion background naturally arises at reheating in many string theory models of the early universe. We study the morphology of the soft excess by numerically propagating axions through stochastic, multi-scale magnetic field models that are consistent with observations of Faraday rotation measures from Coma. By comparing to ROSAT observations of the 0.2-0.4 keV soft excess, we find that the overall excess luminosity is easily reproduced for $g_{a\gamma\gamma} \sim 2 \times 10^{-13}$ GeV$^{-1}$. The resulting morphology is highly sensitive to the magnetic field power spectrum. For Gaussian magnetic field models, the observed soft excess morphology prefers magnetic field spectra with most power in coherence lengths on ${\cal O}(3 {\rm ~kpc})$ scales over those with most power on ${\cal O}(12 {\rm ~kpc})$ scales. Within this scenario, we bound the mean energy of the axion background to $50\, {\rm eV}\lesssim \langle E_a \rangle \lesssim 250\, {\rm eV}$, the axion mass to $m_a \lesssim 10^{-12}\,\hbox{eV}$, and derive a lower bound on the axion-photon coupling $g_{a\gamma\gamma} \gtrsim \sqrt{0.5/\Delta N_{\rm eff}}\, 1.4 \times 10^{-13}$ GeV$^{-1}$. |
| first_indexed | 2024-03-06T19:12:52Z |
| format | Journal article |
| id | oxford-uuid:175901f4-9ce3-4443-857b-819ecf196d69 |
| institution | University of Oxford |
| language | English |
| last_indexed | 2024-03-06T19:12:52Z |
| publishDate | 2013 |
| publisher | Institute of Physics Publishing |
| record_format | dspace |
| spelling | oxford-uuid:175901f4-9ce3-4443-857b-819ecf196d692022-03-26T10:36:45ZSoft X-ray Excess in the Coma Cluster from a Cosmic Axion BackgroundJournal articlehttp://purl.org/coar/resource_type/c_dcae04bcuuid:175901f4-9ce3-4443-857b-819ecf196d69EnglishSymplectic Elements at OxfordInstitute of Physics Publishing2013Angus, SConlon, JMarsh, MPowell, AWitkowski, LTWe show that the soft X-ray excess in the Coma cluster can be explained by a cosmic background of relativistic axions converting into photons in the cluster magnetic field. We provide a detailed self-contained review of the cluster soft X-ray excess, the proposed astrophysical explanations and the problems they face, and explain how a 0.1-1 keV axion background naturally arises at reheating in many string theory models of the early universe. We study the morphology of the soft excess by numerically propagating axions through stochastic, multi-scale magnetic field models that are consistent with observations of Faraday rotation measures from Coma. By comparing to ROSAT observations of the 0.2-0.4 keV soft excess, we find that the overall excess luminosity is easily reproduced for $g_{a\gamma\gamma} \sim 2 \times 10^{-13}$ GeV$^{-1}$. The resulting morphology is highly sensitive to the magnetic field power spectrum. For Gaussian magnetic field models, the observed soft excess morphology prefers magnetic field spectra with most power in coherence lengths on ${\cal O}(3 {\rm ~kpc})$ scales over those with most power on ${\cal O}(12 {\rm ~kpc})$ scales. Within this scenario, we bound the mean energy of the axion background to $50\, {\rm eV}\lesssim \langle E_a \rangle \lesssim 250\, {\rm eV}$, the axion mass to $m_a \lesssim 10^{-12}\,\hbox{eV}$, and derive a lower bound on the axion-photon coupling $g_{a\gamma\gamma} \gtrsim \sqrt{0.5/\Delta N_{\rm eff}}\, 1.4 \times 10^{-13}$ GeV$^{-1}$. |
| spellingShingle | Angus, S Conlon, J Marsh, M Powell, A Witkowski, LT Soft X-ray Excess in the Coma Cluster from a Cosmic Axion Background |
| title | Soft X-ray Excess in the Coma Cluster from a Cosmic Axion Background |
| title_full | Soft X-ray Excess in the Coma Cluster from a Cosmic Axion Background |
| title_fullStr | Soft X-ray Excess in the Coma Cluster from a Cosmic Axion Background |
| title_full_unstemmed | Soft X-ray Excess in the Coma Cluster from a Cosmic Axion Background |
| title_short | Soft X-ray Excess in the Coma Cluster from a Cosmic Axion Background |
| title_sort | soft x ray excess in the coma cluster from a cosmic axion background |
| work_keys_str_mv | AT anguss softxrayexcessinthecomaclusterfromacosmicaxionbackground AT conlonj softxrayexcessinthecomaclusterfromacosmicaxionbackground AT marshm softxrayexcessinthecomaclusterfromacosmicaxionbackground AT powella softxrayexcessinthecomaclusterfromacosmicaxionbackground AT witkowskilt softxrayexcessinthecomaclusterfromacosmicaxionbackground |