Cover Page The handle

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Cover Page

The handle http://hdl.handle.net/1887/45082 holds various files of this Leiden University dissertation.

Author: Franse, J.

Title: Hunting dark matter with X-rays

Issue Date: 2016-12-20

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Hunting Dark Matter with X-rays

Jeroen Franse

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Casimir PhD series, Delft-Leiden 2016-36

ISBN: 978-90-8593-279-6

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Hunting Dark Matter with X-Rays

Proefschrift

ter verkrijging van

de graad van Doctor aan de Universiteit Leiden, op gezag van Rector Magnificus prof. mr. C.J.J.M. Stolker,

volgens besluit van het College voor Promoties te verdedigen op dinsdag 20 December 2016

klokke 10.00 uur

door

Jeroen Franse

geboren te Maarssen

in 1988

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Promotor: Prof. dr. Ana Ach´ucarro Co-promotor: Dr. Alexey Boyarsky

Promotiecommissie: Prof. dr. I. Tkachev (Institute of Nuclear Research, Moscow, Russia) Prof. dr. E.R. Eliel

Prof. dr. H.J.A. R¨ottgering

Dr. O. Ruchayskiy (Niels Bohr Institute, Copenhagen, Denmark) Dr. J. Vink (Universiteit van Amsterdam)

An electronic version of this thesis can be found at openaccess.leidenuniv.nl

The work described in this thesis is part of the Leiden de Sitter Cosmology program that is funded by the Netherlands Organisation for Scientific Research (NWO).

Cover by Caroline Toxopeus

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Contents i

C ONTENTS

1 Introduction 1

1.1 The Case for Dark Matter . . . . 1

1.2 The Nature of the Dark Matter . . . . 3

1.2.1 Known Properties . . . . 3

1.2.2 Dark Matter Candidates . . . . 4

1.3 Decaying Dark Matter . . . . 6

1.3.1 Signal Properties of Decaying Dark Matter . . . . 6

1.3.2 Cosmological Effects of Decaying Dark Matter . . . . 6

1.3.3 Decaying Dark Matter Candidates . . . . 7

1.3.4 Sterile Neutrinos . . . . 7

1.4 X-Ray Astronomy . . . . 9

1.4.1 X-ray Instruments and Data Processing . . . . 9

1.4.2 Sources in the X-Ray Sky . . . . 11

1.5 Search Strategy . . . . 12

1.5.1 Single Objects . . . . 12

1.5.2 Holistic Approach . . . . 13

1.5.3 Previous Searches . . . . 14

1.6 Outline . . . . 15

2 Discovery of a Dark Matter Decay Candidate Signal at 3.5 keV 17 2.1 Introduction . . . . 17

2.2 Unidentified Signal in M31 and Perseus . . . . 19

2.2.1 Data Analysis . . . . 19

2.2.2 Analysis of M31 . . . . 19

2.2.3 Perseus Cluster . . . . 21

2.2.4 Interpretation . . . . 21

2.2.5 Discussion . . . . 22

2.3 Detection in the Galactic Center . . . . 32

2.3.1 Data and Analysis . . . . 32

2.3.2 Results . . . . 32

2.3.3 Discussion . . . . 34

2.3.4 Dark Matter Profiles of the Milky Way . . . . 37

2.3.5 Ion Abundances and Emission Lines . . . . 41

2.4 Literature Response . . . . 43

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ii Contents

3 Devoted Observations of the Draco Dwarf Spheroidal 47

3.1 Introduction . . . . 47

3.2 Data preparation and analysis . . . . 49

3.3 Results . . . . 50

3.3.1 Line detection in PN camera . . . . 54

3.3.2 MOS cameras . . . . 54

3.3.3 Common fit of MOS1, MOS2 and PN cameras . . . . 55

3.4 Discussion . . . . 56

3.4.1 Implications for dark matter decay lifetime . . . . 58

3.4.2 Comparison with the previous studies of the 3.5 keV line . . . . . 58

3.4.3 Comparison with another recent analysis of Draco extended dataset 60 4 Perseus out to R

200

with Suzaku 61 4.1 Introduction . . . . 61

4.2 Data Reduction and Analysis . . . . 63

4.2.1 Systematics . . . . 66

4.3 Results . . . . 68

4.3.1 Perseus Center . . . . 68

4.3.2 Perseus Outskirts . . . . 71

4.4 Discussion . . . . 73

4.4.1 Line Flux and Dark Matter Profiles . . . . 73

4.4.2 Discussion of Perseus’ Morphological and Dynamical State . . . 78

4.4.3 Literature Comparison . . . . 78

4.5 Conclusion . . . . 79

4.6 Appendix - Details of the Spectral Fits . . . . 80

5 Correlation Method for Weak Line Searches 87 5.1 Introduction . . . . 87

5.2 Formalism . . . . 88

5.2.1 (De)composition of the Correlation . . . . 90

5.3 Methodology . . . . 91

5.4 Data and Implementation . . . . 93

5.5 Error Estimation . . . . 96

5.6 Recovery of Injected Decay Signals . . . . 97

5.7 Conclusion and Summary . . . 104

5.8 Discussion . . . 105

5.8.1 Decomposition Reliability . . . 105

5.8.2 Independence of Calibration Uncertainties . . . 106

5.8.3 Flexibility and Robustness . . . 107

5.8.4 Sensitivity . . . 108

5.A Derivations . . . 108

5.A.1 Correlation (De)composition . . . 108

5.A.2 Calibration Independence . . . 110

5.B Null Tests . . . 113

5.C Weighted Correlations . . . 113

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Contents iii

6 Appendices 117

6.1 Charge Exchange . . . 117

6.2 Comment on Jeltema & Profumo 2015 . . . 119

6.3 Comment on Carlson et al. 2014 . . . 120

7 Nederlandse Samenvatting 123 7.1 Introductie . . . 123

7.2 Hoofdstuk 2 - Ontdekking van Kandidaat Donkere Materie Signaal op 3.5 keV . . . 125