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dc.contributor.authorDomček, V
dc.contributor.authorVink, J
dc.contributor.authorHernández Santisteban, J V
dc.contributor.authorDeLaney, T
dc.contributor.authorZhou, P
dc.identifier.citationDomček , V , Vink , J , Hernández Santisteban , J V , DeLaney , T & Zhou , P 2021 , ' Mapping the spectral index of Cassiopeia A : evidence for flattening from radio to infrared ' , Monthly Notices of the Royal Astronomical Society , vol. 502 , no. 1 , pp. 1026-1040 .
dc.identifier.otherPURE: 272951551
dc.identifier.otherPURE UUID: 979e4035-33ec-4d05-87fa-153be509d761
dc.identifier.otherJisc: 15cb28cc6260415087d6650a15629b12
dc.identifier.otherORCID: /0000-0002-6733-5556/work/89178816
dc.identifier.otherWOS: 000649423200068
dc.identifier.otherScopus: 85117310429
dc.descriptionFunding: The work of VD is supported by a grant from the NWO graduate programme/GRAPPA-PhD programme. JVHS acknowledges support from the STFC grant ST/R000824/1.en
dc.description.abstractSynchrotron radiation from supernova remnants is caused by electrons accelerated through diffusive shock acceleration (DSA). The standard DSA theory predicts an electron spectral index of p = 2, corresponding to a radio spectral index of α = −0.5. An extension of DSA theory predicts that the accelerated particles change the shock structure, resulting in a spectrum that is steeper than p > 2 (α < −0.5) at low energies and flattens with energy. For Cassiopeia A, a synchrotron spectral flattening was previously reported for a small part of the remnant in the mid-infrared regime. Here, we present new measurements for spectral flattening using archival radio (4.72 GHz) and mid-infrared (3.6 μm) data, and we produce a complete spectral index map to investigate the spatial variations within the remnant. We compare this to measurements of the radio spectral index from L-band (1.285 GHz) and C-band (4.64 GHz) maps. Our result shows overall spectral flattening across the remnant (αR-IR ∼ −0.5 to −0.7), to be compared with the radio spectral index of αR = −0.77. The flattest values coincide with the locations of most recent particle acceleration. In addition to overall flattening, we detect a relatively steeper region in the south-east of the remnant (αR-IR ∼ −0.67). We explore whether these locally steeper spectra could be the result of synchrotron cooling, which provides constraints on the local magnetic field strengths and the age of the plasma, suggesting B ≲ 2 mG for an age of 100 yr, and even B ≲ 1 mG using the age of Cas A, in agreement with other estimates.
dc.relation.ispartofMonthly Notices of the Royal Astronomical Societyen
dc.rightsCopyright © 2021 The Author(s). Published by Oxford University Press on behalf of Royal Astronomical Society. This work has been made available online in accordance with publisher policies or with permission. Permission for further reuse of this content should be sought from the publisher or the rights holder. This is the final published version of the work, which was originally published at
dc.subjectAcceleration of particlesen
dc.subjectRadiation mechanisms: non-thermalen
dc.subjectISM: individual objects: Cassiopeia Aen
dc.subjectISM: supernova remnantsen
dc.subjectQB Astronomyen
dc.subjectQC Physicsen
dc.titleMapping the spectral index of Cassiopeia A : evidence for flattening from radio to infrareden
dc.typeJournal articleen
dc.description.versionPublisher PDFen
dc.contributor.institutionUniversity of St Andrews.School of Physics and Astronomyen
dc.description.statusPeer revieweden

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