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Title: Hitomi Constraints on the 3.5 keV Line in the Perseus Galaxy Cluster

High-resolution X-ray spectroscopy with Hitomi was expected to resolve the origin of the faint unidentified $$E\approx 3.5\,\mathrm{keV}$$ emission line reported in several low-resolution studies of various massive systems, such as galaxies and clusters, including the Perseus cluster. We have analyzed the Hitomi first-light observation of the Perseus cluster. The emission line expected for Perseus based on the XMM-Newton signal from the large cluster sample under the dark matter decay scenario is too faint to be detectable in the Hitomi data. However, the previously reported 3.5 keV flux from Perseus was anomalously high compared to the sample-based prediction. We find no unidentified line at the reported high flux level. Taking into account the XMM measurement uncertainties for this region, the inconsistency with Hitomi is at a 99% significance for a broad dark matter line and at 99.7% for a narrow line from the gas. We do not find anomalously high fluxes of the nearby faint K line or the Ar satellite line that were proposed as explanations for the earlier 3.5 keV detections. We do find a hint of a broad excess near the energies of high-n transitions of S xvi ($$E\simeq 3.44\,\mathrm{keV}$$ rest-frame)—a possible signature of charge exchange in the molecular nebula and another proposed explanation for the unidentified line. While its energy is consistent with XMM pn detections, it is unlikely to explain the MOS signal. In conclusion, a confirmation of this interesting feature has to wait for a more sensitive observation with a future calorimeter experiment.
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Publication Date:
Report Number(s):
SLAC-PUB-17171
Journal ID: ISSN 2041-8213
Grant/Contract Number:
AC02-76SF00515; NNX15AM19G; AC52-07NA27344; 15H02070; 15K05107; 23340071; 26109506; 24103002; 25400236; 25800119; 25400237; 25287042; 24540229; 25105516; 23540280; 25400235; 25247028; 26800095; 25400231; 26220703; 24105007; 23340055; 15H00773; 23000004; 15H02090; 15K17610; 15H05438; 15H00785; 24540232; ST/J003697/2
Type:
Accepted Manuscript
Journal Name:
The Astrophysical Journal. Letters
Additional Journal Information:
Journal Volume: 837; Journal Issue: 1; Journal ID: ISSN 2041-8213
Publisher:
Institute of Physics (IOP)
Research Org:
SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Org:
USDOE; Japan Society for the Promotion of Science (JSPS); National Aeronautic and Space Administration (NASA); Canadian Space Agency
Contributing Orgs:
Hitomi Collaboration
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS; dark matter; galaxies; clusters; X-rays
OSTI Identifier:
1353206