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The recent paper by Jeltema & Profumo(2014) claims that contributions from ion{K}{18} and ion{Cl}{17} lines can explain the unidentified emission line found by Bulbul et al 2014 and also by Boyarsky et al, 2014a, 2014b. We show that their analysis relies upon incorrect atomic data and inconsistent spectroscopic modeling. We address these points and summarize in the appendix the correct values for the relevant atomic data from AtomDB.
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We present a comprehensive search for the 3.5 keV line, using $sim$51 Ms of archival Chandra observations peering through the Milky Ways Dark Matter Halo from across the entirety of the sky, gathered via the Chandra Source Catalog Release 2.0. We consider the datas radial distribution, organizing observations into four data subsets based on angular distance from the Galactic Center. All data is modeled using both background-subtracted and background-modeled approaches to account for the particle instrument background, demonstrating statistical limitations of the currently-available $sim$1 Ms of particle background data. A non-detection is reported in the total data set, allowing us to set an upper-limit on 3.5 keV line flux and constrain the sterile neutrino dark matter mixing angle. The upper-limit on sin$^2$(2$theta$) is $2.58 times 10^{-11}$ (though systematic uncertainty may increase this by a factor of $sim$2), corresponding to the upper-limit on 3.5 keV line flux of $2.34 times 10^{-7}$ ph s$^{-1}$ cm$^{-2}$. These limits show consistency with recent constraints and several prior detections. Non-detections are reported in all radial data subsets, allowing us to constrain the spatial profile of 3.5 keV line intensity, which does not conclusively differ from Navarro-Frenk-White predictions. Thus, while offering heavy constraints, we do not entirely rule out the sterile neutrino dark matter scenario or the more general decaying dark matter hypothesis for the 3.5 keV line. We have also used the non-detection of any unidentified emission lines across our continuum to further constrain the sterile neutrino parameter space.
I show that model dependencies in the analysis by Dessert, Rodd & Safdi (2020) relax their claimed constraint by a factor of ~20. After including conservative model choices, the derived limits are comparable to or slightly better than limits from previous searches. Further model tests and expansion of the data energy may enhance or relax sensitivity of the methodology.
The reported observations of an unidentified X-ray line feature at $sim$3.5 keV have driven a lively discussion about its possible dark matter origin. Motivated by this, we have measured the emph{K}-shell X-ray spectra of highly ionized bare sulfur ions following charge exchange with gaseous molecules in an electron beam ion trap, as a source of or a contributor to this X-ray line. We produce $mathrm{S}^{16+}$ and $mathrm{S}^{15+}$ ions and let them capture electrons in collision with those molecules with the electron beam turned off while recording X-ray spectra. We observed a charge-exchanged-induced X-ray feature at the Lyman series limit (3.47 $pm$ 0.06 keV). The inferred X-ray energy is in full agreement with the reported astrophysical observations and supports the novel scenario proposed by Gu and Kaastra (A & A textbf{584}, {L11} (2015)).
High-resolution X-ray spectroscopy with Hitomi was expected to resolve the origin of the faint unidentified E=3.5 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 Sxvi (E=3.44 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. A confirmation of this interesting feature has to wait for a more sensitive observation with a future calorimeter experiment.
Context. Recent findings of line emission at 3.5 keV in both individual and stacked X-ray spectra of galaxy clusters have been speculated to have dark matter origin. Aims. If the origin is indeed dark matter, the emission line is expected to be detectable from the Milky Way dark matter halo. Methods. We perform a line search in public Chandra X-ray observations of the region near Sgr A*. We derive upper limits on the line emission flux for the 2.0-9.0 keV energy interval and discuss their potential physical interpretations including various scenarios of decaying and annihilating dark matter. Results. While find no clear evidence for its presence, the upper flux limits are not inconsistent with the recent detections for conservative mass profiles of the Milky Way. Conclusions. The results depends mildly on the spectral modelling and strongly on the choice of dark matter profile.
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