Measurement of very high energy gamma-ray emission from four blazars using the MAGIC telescope and a comparative blazar study [Elektronische Ressource] / Robert Marcus Wagner

Robert Marcus Wagner

Sujets

• Astronomie

Informations

• Publié par: technische_universitat_munchen
• Publié le: 01 janvier 2006
• Nombre de lectures: 23
• Langue: English
• Poids de l'ouvrage: 9 Mo

Extrait

MPP 2006 245
¨Technische Universitat Munc¨ hen
Max Planck Institut fur¨ Physik
(Werner Heisenberg Institut)
Measurement of very high energy
gamma–ray emission from four blazars
using the MAGIC telescope and a
comparative blazar study
¨Dissertation an der Fakultat fur¨ Physik
¨der Technischen Universitat Munchen¨
vorgelegt von
Robert Marcus Wagner¨Technische Universitat Munc¨ hen
Max Planck Institut fur¨ Physik
(Werner Heisenberg Institut)
Measurement of very high energy
gamma–ray emission from four blazars
using the MAGIC telescope and a
comparative blazar study
Robert Marcus Wagner
Vollstandiger¨ Abdruck der von der Fakultat¨ fur¨ Physik der Technischen Universitat¨
Munchen¨ zur Erlangung des akademischen Grades eines
Doktors der Naturwissenschaften
genehmigten Dissertation.
Vorsitzender: Univ. Prof. Dr. A. J. Buras
Prufer¨ der Dissertation:
1. Hon. Prof. Dr. S. Bethke
2. Univ. Prof. Dr. F. von Feilitzsch
Die Dissertation wurde am 14. November 2006 bei der Technischen Universitat¨ Munchen¨
eingereicht und durch die Fakultat¨ fur¨ Physik am 19. Dezember 2006 angenommen.Measurement of very high energy
gamma–ray emission from four blazars
using the MAGIC telescope and a
comparative blazar study
Robert Marcus Wagner
November 2006Bibliografische Information Der Deutschen Bibliothek
Die Deutsche Bibliothek verzeichnet diese Publikation in der Deutschen Nationalbiblio
grafie; detaillierte bibliographische Daten sind im Internet uber¨ http://dnb.ddb.de/
abrufbar.
Frontispiece: On a rare foggy night, mysterious laser beams seem to play
across the MAGIC telescope at the Roque de los Muchachos on the Ca
nary Island of La Palma. The lasers are actually part of a system de
signed to automatically adjust the focusing of the innovative, seventeen
meter wide, multi mirrored instrument. The MAGIC (Major Atmospheric
Gamma Imaging Cherenkov) telescope itself is intended to detect gamma
rays—photons with over 100 billion times the energy of visible light. As
the gamma rays impact the upper atmosphere they produce air showers
of high energy particles. The MAGIC camera records in detail the brief
flashes of optical light, called Cherenkov light, created by the air shower
particles that ultimately correspond to cosmic sources of extreme gamma
rays. The dramatic picture shows the telescope in May 2004.
viSummary
The thesis reports on the measurement of very high energy (VHE) gamma–rays from
four Active Galactic Nuclei (AGN) with the Major Atmospheric Gamma–ray Imaging
Cherenkov telescope (MAGIC).
The AGN Mkn 501 was observed with the MAGIC telescope during six weeks in 2005. A
baseline flux of about 25% of the Crab nebula flux as well as high flux states of up to four
times the Crab nebula flux were found. Different flux states are defined and energy spectra
for these states are determined in the energy range between 100 GeV and 4 TeV. The
spectra show a clear spectral hardening with increasing flux level, ranging from baseline of
? ¶¡2:39§0:06
dF E¡9 ¡1 ¡2 ¡1=(0:56§ 0:04)£ 10 TeV cm s
dE 250 GeV
to high flux level spectra that can be described by
? ¶¡2:14§0:03
dF E¡9 ¡1 ¡2 ¡1=(4:11§ 0:16)£ 10 TeV cm s :
dE 250 GeV
When taking into account ray absorption by the extragalactic background light (EBL),
a hint for an inverse Compton peak is found with the peak energy moving from (0:3§
0:1) TeV to(1:4§ 0:7) TeV with increasing flux level. This evidence is strengthened by
the observation of a moving structure also in the measured spectra, which are free of
uncertainties of the EBL model used.
Unprecedented rapid flux variability with doubling times of• 5 minutes was found during
some of the observation nights. These fast flares are used to infer significant limits on the
¡1 12size of the acceleration region of R¢ d • 10 cm for homogeneous one–zone Self–
Synchrotron Compton models. Significant spectral hardening of Da = 0:4 within less
than 20 minutes could be observed. The well defined fast flares were also used to infer a
17lower limit on the quantum gravity energy scale of 1:5£ 10 GeV.
For the BL Lac object 1ES 2344+514 for the first time a differential energy spectrum
during a state of low ray activity is inferred, which between140 GeV and 5 TeV can be
vii
described by a power law of the form
? ¶¡2:95§0:12
dF E¡11 ¡1 ¡2 ¡1=(1:18§ 0:13)£ 10 TeV cm s
dE 500 GeV
The study of the 24 day VHE ray light curve of 1ES 2344+514 yields a low flux level
of 0:04• F • 0:11 times the Crab nebula flux. In combination with the all timeE>350 GeV
(1995–2005) light curve a low emission level of about…4% of the Crab nebula flux is
found.
Within the thesis, predictions for the detectability of BL Lac candidate objects in VHE
rays with the MAGIC telescope are presented. These predictions led to the discovery of
two new objects in this energy domain, PG 1553+113 and BL Lacertae. PG 1553+113 was
detected at a high significance level of 8:8s. The softest gamma ray spectrum observed
so far in VHE rays was found for this source. It can be described by a pure power law
between 95 GeV and 500 GeV:
? ¶¡4:21§0:25dF E¡9 ¡1 ¡2 ¡1=(0:18§ 0:03)¢ 10 £ TeV cm s :
dE 200 GeV
The spectrum is used to infer an upper limit of z< 0:78 on the yet undetermined redshift
of PG 1553+113 by imposing a maximum hardness of the intrinsic spectrum. While the
light curve does not show apparent short–term variability, simultaneously recorded optical
data feature a substantial flare, which leaves room for interpretation of the non existing
correlations.
BL Lacertae, the prototype of the BL Lac objects, was detected at a significance level of
5:6s. This object is the first low–frequency peaked BL Lac object seen in VHE rays.
A preliminary spectrum hints at a steep slope of…¡3:7 between 100 GeV and 1 TeV.
For the first time a synoptic study of all high–frequency peaked BL Lac type objects de
tected as VHE gamma ray emitters is performed. The intrinsic properties of the observed
emission are compared and correlated among each other and with the individual estimated
black hole masses. Key findings are (1) that all currently known VHE ray blazars host
8supermassive black holes with masses exceeding 10 solar masses, (2) that in the current
VHE blazar sample no obvious correlations of the VHE emission properties with the
black hole masses of the blazars are found, (3) that a weak correlation of the intrinsic
spectral hardness and the source distance is likely due to an EBL overprediction by the
current EBL models, and (4) that there is a general trend of an increase of the VHE
luminosity with the hardness of the intrinsic source spectra. The latter behavior is also
found for sources that were observed in different emission states. Furthermore, the found
luminosity distribution of the VHE blazar sample is used to constrain the distance of
PG 1553+113. Depending on the strength of the assumptions taken, the limit varies be
tween z• 0:43 and z• 0:68.
viii
The technical part of the thesis deals with the implementation of a telescope drive system
that permits the fast follow–up of gamma ray bursts. For measuring the tracking accuracy
of the telescope, a starfield monitoring system has been commissioned. Further, the im
plementation of the flux and light curve calculation within the framework of the MAGIC
Analysis and Reconstruction Software is discussed. The application of the analysis chain
is exemplified on the first large data sample taken on the Crab nebula with the MAGIC
telescope. The observations were performed in 2004/5 to understand and calibrate the We find a light curve that is compatible with a constant ray emission of
¡10 ¡2 ¡1F =(2:16§ 0:07)£ 10 cm s and a differential ray spectrum that canE>200 GeV
be described by a curved power law
? ¶ E(¡2:35§0:09)¡(0:09§0:07)log ( )10 250 GeVdF E¡10 ¡1 ¡2 ¡1=(7:8§ 0:4)¢10 £ TeV cm s
dE 250 GeV
in the energy range of 95 GeV¡ 6:5 TeV. The results are well compatible with that of
other experiments and with model predictions.
ix