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The extended H.E.S.S. galactic plane survey [Elektronische Ressource] : discovering and identifying new sources of VHE γ-rays / put forward by Ryan Carlos Gonçalves Chaves

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Dissertationsubmitted to theCombined Faculties for the Natural Sciences and forMathematicsof theRuperto-Carola University of Heidelberg, Germanyfor the degree ofDoctor of Natural SciencesPut forward byDipl.-Phys.: Ryan Carlos Gonc¸alves Chavesborn in: Springfield, Massachusetts, USAOral examination: 4 February 2011The extendedH.E.S.S. Galactic Plane survey:Discovering and identifyingnew sources of VHE -raysReferees: Prof. Dr. Werner HofmannProf. Dr. Heinz Vo¨lkThe extended H.E.S.S. Galactic Plane Survey:Discovering and identifying new sources of VHE -raysThe extended H.E.S.S. Galactic Plane Survey:Discovering and identifying new sources of VHE -raysRyan Carlos Gonc¸alves ChavesPh.D. Thesis, Universita¨t Heidelberg, 19 December 2010ISBN: TBDContentsAbstract 1Preface 61 Observing VHE -rays with the H.E.S.S. telescope array 72 The extended H.E.S.S. Galactic Plane Survey 133 VHE -ray emission from PSR B1706 44 & SNR G 343.1 2.3 394 Discovery and multi-wavelength study of HESS J1503 582 675 Discovery of the pulsar wind nebula candidate HESS J1832 084 856 Discovery of VHE -ray emission from the direction of W 43 1017 Deep TeV -ray observations of young SNR G 1.9+0.3 1098 VHE counterparts of Galactic Fermi sources & spectral characterization 1239 Conclusions and outlook 153A H.E.S.S.

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Published 01 January 2011
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Dissertation
submitted to the
Combined Faculties for the Natural Sciences and for
Mathematics
of the
Ruperto-Carola University of Heidelberg, Germany
for the degree of
Doctor of Natural Sciences
Put forward by
Dipl.-Phys.: Ryan Carlos Gonc¸alves Chaves
born in: Springfield, Massachusetts, USA
Oral examination: 4 February 2011The extended
H.E.S.S. Galactic Plane survey:
Discovering and identifying
new sources of VHE -rays
Referees: Prof. Dr. Werner Hofmann
Prof. Dr. Heinz Vo¨lkThe extended H.E.S.S. Galactic Plane Survey:
Discovering and identifying new sources of VHE -raysThe extended H.E.S.S. Galactic Plane Survey:
Discovering and identifying new sources of VHE -rays
Ryan Carlos Gonc¸alves Chaves
Ph.D. Thesis, Universita¨t Heidelberg, 19 December 2010
ISBN: TBDContents
Abstract 1
Preface 6
1 Observing VHE -rays with the H.E.S.S. telescope array 7
2 The extended H.E.S.S. Galactic Plane Survey 13
3 VHE -ray emission from PSR B1706 44 & SNR G 343.1 2.3 39
4 Discovery and multi-wavelength study of HESS J1503 582 67
5 Discovery of the pulsar wind nebula candidate HESS J1832 084 85
6 Discovery of VHE -ray emission from the direction of W 43 101
7 Deep TeV -ray observations of young SNR G 1.9+0.3 109
8 VHE counterparts of Galactic Fermi sources & spectral characterization 123
9 Conclusions and outlook 153
A H.E.S.S. Galactic Plane Survey: Supplementary material 157
B Power-laws as indicators of desertification 161
References 167
Acknowledgements 181
Curriculum Vitae 182
12 CONTENTS
Publications 185Abstract
H.E.S.S. is an array of four imaging atmospheric-Cherenkov telescopes located in Namibia
and designed to detect -rays in the very-high-energy (VHE; 0:1 . E . 100 TeV) domain.
The full array has been in operation and observing the Galaxy since late 2003. The H.E.S.S.
array’s large field-of-view, high sensitivity, and location in the southern hemisphere have
made it well-suited for both systematic surveying and for deeply observing specific sources
of interest. The efforts of the H.E.S.S. Galactic Plane Survey (GPS), the first comprehen-
sive survey of the inner Galaxy (current ` 280 to ` 60 , b . 4 ) at TeV energies,
have contributed to the discovery of an unexpectedly large and diverse population of over 60
sources of VHE -rays. In this thesis, the latest dataset of the H.E.S.S. GPS is presented in
detail, providing the most complete view of the Galaxy in the VHE-ray regime to date. The
resulting discoveries of four previously unknown VHE -ray sources — HESS J1708 443,
HESS J1503 582, HESS J1832 084, and HESS J1848 018 — are reported in particular,
and their associations with astrophysical phenomena seen at lower energies are investigated
with the aid of both dedicated and archival multi-wavelength data, in an attempt to reveal
their physical nature. In addition, deep observations of the youngest Galactic supernova
remnant (SNR) G 1.9+0.3 are used to probe its VHE -ray emission in light of theoretical
predictions. Finally, the first study to correlate bright MeV–GeV-ray sources with VHE-
ray sources is presented. Although the current population of VHE -ray emitters is found to
be dominated by pulsar wind nebulae (PWNe) and SNRs, nearly a third still remain unidenti-
fied or confused, illustrating both the challenges and scientific potential that pervade Galactic
TeV astronomy.
12 CONTENTSPreface
Our Galaxy, the Milky Way, is brimming with electromagnetic radiation, from low-energy
radio waves to infrared radiation, through the visible light to which human eyes are sensitive,
all the way across the spectrum to X-rays and the highest-energy gamma-ray photons (-
rays). The Milky Way has been explored extensively at most energies, with the observations
of hundreds of telescope both on the ground and in space, but until recently virtually nothing
was known about the Galaxy at the highest energies, the domain now known as very-high-
energy (VHE) -ray astronomy.
Just six years ago, only a handful of objects in the Galaxy were known to emit VHE
1-rays (also called TeV -rays), compared to, for example, the billions of stars known to
emit visible light (with energies 1 eV). It was not clear which — or how many — objects
could actually emit VHE-ray photons, which are so energetic that only extreme astrophys-
ical processes could be responsible. In 2004, the H.E.S.S. telescope array (see Chapter 1
for a brief summary of its most important properties) in Namibia became fully operational
and began to investigate this VHE side of the Milky Way by systematically observing and
mapping our disc-shaped Galaxy.
H.E.S.S. is no ordinary telescope; it is actually an array of four so-called imaging atmo-
spheric Cherenkov telescopes (IACTs) which work in concert and employ very fast elec-
tronics, uniquely-designed cameras, and specialized detection techniques which have been
under development for decades. It is able to indirectly detect VHE -rays, which are them-
selves unable to reach the telescopes because they inevitably collide with air molecules in
the upper atmosphere, by imaging the complex cascade of particle decays and interactions
resulting from the initial collision. From its preferred vantage point in the southern hemi-
sphere, H.E.S.S. is well posed to search the inner Galaxy — not visible to IACTs in the
northern hemisphere — for evidence of new VHE -ray emitting objects and to piece to-
gether our first complete picture of the Galaxy. Not only will this answer the basic question
of “What does our Galaxy look like in VHE -rays?”, but it may also shed light on a similar
1A VHE -ray is a photon with energy E in the range 100 GeV . E . 100 TeV, where 1 GeV =
9 1210 electron volts (eV) and 1 TeV= 10 eV.
3