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This is the homepage of the of the weekly Astrophysics journal club at the Division of Particle physics and astrophysics at the University of Helsinki.
The meetings are of an unofficial nature and the main driver is to get together and discuss recent interesting papers. This meeting differs from the
Seminar series in that people are not expected to talk about their own research and in that no credits will be awarded to students. The meetings are
open to everyone and the aim is to stimulate discussion about recent results and provide the possibility to
 learn about research that is not necessarily
connected to one's own field of expertise.

All topics are welcome ranging from planetary science to larger scales involving stellar
 astrophysics, Milky Way studies, galaxies and cosmology.
The only requirement is that the
 presented papers should be interesting to a wider audience and that they should be presented 
in such a way that also
a non-expert can follow the presentation. In the meetings we discuss one paper each week for about 45 minutes.
 All meetings are in English.

Location: Conference room C310 on the third floor.

Time: Thursdays at 10.15-11.00am during term time.

Speakers: Please contact Peter Johansson, Mikael Granvik or Clif Kirkpatrick if you want to present a paper.

Present Program: The next talk will be on the 14th of September

Presenter: Clif Kirkpatrick:
Paper title: Hitomi Constraints on the 3.5 keV Line in the Perseus Galaxy Cluster
Authors: Hitomi collaboration, Aharonian, F. A. et al.
Reference: 2017, ApJ, 837, 15

Abstract: 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 S xvi (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.

Present program:

  • 28.09.2017 Peter Johansson:
  • 05.10.2017 Mikael Granvik:
  • 12.10.2017
  • 19.10.2017 Ghassem Gozaliasl:
  • 26.10.2017 Veli-Matti Pelkonen:
  • 02.11.2017 Elisabetta Micelotta:
  • 09.11.2017
  • 16.11.2017 Till Sawala:
  • 23.11.2017
  • 30.11.2017
  • 07.12.2017 Mika Juvela:
  • 14.12.2017


Past program:

Autumn 2017:

Spring 2017:

Autumn 2016:

Spring 2016:

Autumn 2015:

Spring 2015:

Autumn 2014:

Spring 2014:

Autumn 2013:

Spring 2013:

Autumn 2012:

Spring 2012:

Autumn 2011:

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