Unidentified emission line in Galaxy Clusters

  1. I could not find a thread about this (and I hope I don't start a duplicate one :smile:).
    I got a mail from a friend today about this:

    Detection of An Unidentified Emission Line in the Stacked X-ray spectrum of Galaxy Clusters
    Esra Bulbul, Maxim Markevitch, Adam Foster, Randall K. Smith, Michael Loewenstein, Scott W. Randall
    A paper was published in the July 1st issue of The Astrophysical Journal.
    Arxiv link: http://arxiv.org/abs/1402.2301
    (Submitted on 10 Feb 2014 (v1), last revised 9 Jun 2014)

    We detect a weak unidentified emission line at E=(3.55-3.57)+/-0.03 keV in a stacked XMM spectrum of 73 galaxy clusters spanning a redshift range 0.01-0.35. MOS and PN observations independently show the presence of the line at consistent energies. When the full sample is divided into three subsamples (Perseus, Centaurus+Ophiuchus+Coma, and all others), the line is significantly detected in all three independent MOS spectra and the PN "all others" spectrum. It is also detected in the Chandra spectra of Perseus with the flux consistent with XMM (though it is not seen in Virgo). However, it is very weak and located within 50-110eV of several known faint lines, and so is subject to significant modeling uncertainties. On the origin of this line, we argue that there should be no atomic transitions in thermal plasma at this energy. An intriguing possibility is the decay of sterile neutrino, a long-sought dark matter particle candidate. Assuming that all dark matter is in sterile neutrinos with m_s=2E=7.1 keV, our detection in the full sample corresponds to a neutrino decay mixing angle sin^2(2theta)=7e-11, below the previous upper limits. However, based on the cluster masses and distances, the line in Perseus is much brighter than expected in this model. This appears to be because of an anomalously bright line at E=3.62 keV in Perseus, possibly an Ar XVII dielectronic recombination line, although its flux would be 30 times the expected value and physically difficult to understand. In principle, such an anomaly might explain our line detection in other subsamples as well, though it would stretch the line energy uncertainties. Another alternative is the above anomaly in the Ar line combined with the nearby 3.51 keV K line also exceeding expectation by factor 10-20. Confirmation with Chandra and Suzaku, and eventually Astro-H, are required to determine the nature of this new line.(ABRIDGED)

    Bonus material:
    Article 1: Mystery in the Perseus Cluster (NASA article)
    Article 2: Perseus Cluster: Mysterious X-ray Signal Intrigues Astronomers (Chandra article)
    Article 3: Mysterious signal from the center of the Perseus Cluster unexplained by known physics (The Watchers)
    Blogs: Links to some blogs that have written about it.

    Just wanted to let the forum readers know about it. It got me a little excited...:tongue2:
    Last edited: Jul 26, 2014
  2. jcsd
  3. Greg Bernhardt

    Staff: Admin

    Thanks for sharing! What part are you most excited about?
  4. Chronos

    Chronos 9,758
    Science Advisor
    Gold Member

    1 person likes this.
  5. This thing :smile::
    But I'm not even remotely qualified to say very much about it, haha!

    Excellent! :thumbs: I had a feeling it ought to have appeared on the forum :smile:. I'll make a new post in that very thread, and request for this thread to be closed.

    EDIT: I've added the info in the thread by Chronos here now instead.
    Last edited: Aug 6, 2014
  6. Drakkith

    Staff: Mentor

    Thread closed at the request of the OP. Any responses to the topic can be made in the threads linked in the posts above.
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