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Modeling the Emission of the Galactic Very High Energy Gamma-Ray

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Modeling the Emission of the Galactic Very High Energy Gamma-Ray Modeling the Emission of the Galactic Very High Energy γ-Ray Sources G 1.9+0.3, G 330.2+1.0, HESS J1303 631 and PSR B1259 63/LS 2883 Observed with H.E.S.S.− − DISSERTATION zur Erlangung des akademischen Grades doctor rerum naturalium (Dr. rer. nat.) im Fach Physik eingereicht an der Mathematisch-Naturwissenschaftlichen Fakultät I Humboldt-Universität zu Berlin von M.Sc. Iurii Sushch Präsident der Humboldt-Universität zu Berlin: Prof. Dr. Jan-Hendrik Olbertz Dekan der Mathematisch-Naturwissenschaftlichen Fakultät I: Prof. Stefan Hecht, Ph.D. Gutachter: 1. Prof. Dr. rer. nat. habil. Thomas Lohse 2. Dr. rer. nat. Gernot Maier 3. Prof. Dr. Felix Aharonian Tag der mündlichen Prüfung: 19 Oktober 2012 Dedication I would like to thank Erasmus Mundus "External Cooperation Window" fellowship for the financial support without which this work would not be possible. I would like to thank my thesis supervisor Thomas Lohse for the chance to work in a fantastic scientific group with a great working environment. I also greatly appreciate the financial support which allowed me to finish my thesis after the end of my Erasmus Mundus grant. Lots of thanks to Ulli Schwanke for the supervision of the work presented in this thesis, lots of scientific discussions and proofreading which considerably improved the thesis. Many thanks to Manuel Paz Arribas for the collaboration and analysis crosschecks in work on SNRs G1.9+0.3 and G 330.2+1.0. I am also very grateful for his translation of the abstract of this thesis into German! I would like to thank Matt Dalton for the joint work on HESS J1303 631 and for being − my officemate for 2 years. It was a great time, Matt! I would also like to thank Ryan Chaves, Mathieu de Naurois, Bruno Khelifi, Matthieu Renauld, Pol Bordas and Felix Aharonian for our joint work and their internal refereeing of papers. I would like to thank all my collegues and all of the members of the group for a great atmosphere. Extra thanks to Veronika Fetting for helping with all burocratic stuff and Arne Schönwald who helped a lot in the process of getting a visa for my wife. Finally, thanks to my beloved neighbours Michelangelo Giorgi and Ena Bech for cooking lasagna every time I felt a lack of inspiration. þ ¸ ¸ º þ ý Á ¸ ¸ ¸ ¸ ¸ º ¸ º ¸ ¸ º ü ¸ ¹ ¸ º ¸ ý ¹ ¸ º ü ¸ ¸ ¸ º Á ¸ ¸ ¸ ¸ Thanks everybody! If anybody didn’t find his or her name here it means that you are in the category of everybody and I thank you too! iv Abstract Recently, imaging atmospheric Cherenkov telescopes (IACTs) have discov- ered numerous new sources representing various source classes in the very high energy (VHE; E > 100 GeV) sky. This work presents studies of representa- tives of three types of Galactic VHE emitters: the Supernova remnants (SNRs) G 1.9+0.3 and G330.2+1.0, the pulsar wind nebula (PWN) HESS J1303 631 and the binary system PSR B1259 63/LS 2883. The analysis of the H.E.S.S.− data and the broadband emission modeling− are presented. G 1.9+0.3 and G330.2+1.0 are synchrotron-dominated SNRs whose non-- thermal X-ray emission implies that intensive particle acceleration occurs at their shock fronts. This makes them promising candidates for the detection at VHEs. They were observed by the High Energy Stereoscopic System (H.E.S.S.) yielding no signs of significant VHE γ-ray emission from either SNR. The 99% confidence level upper limits on the TeV flux were determined. For an assumed spectral index of 2.5 the obtained upper limits are FG1.9(> 260 GeV) < 4.6 13 2 1 12 2 ×1 10− cm− s− for G 1.9+0.3 and FG330(> 380 GeV) < 1.6 10− cm− s− for G 330.2+1.0. Upper limits on the VHE emission provide constraints× on the interior magnetic field in the context of a leptonic scenario and on the inter- stellar medium (ISM) density and cosmic-ray (CR) efficiency in a hadronic sce- nario. Lower limits on the interior magnetic fields were estimated at 15 µG for G 1.9+0.3 and 14 µG for G 330.2+1.0. In the case of the hadronic scenario, the H.E.S.S. upper limits are two orders of magnitude greater than the flux pre- diction. Obtained upper limits on the ISM densities are compatible with other estimates of the densities (from the thermal X-ray emission for G 330.2+1.0 and from the expansion rate for G 1.9+0.3). The CR efficiency cannot be constrained with the current H.E.S.S. upper limits. HESS J1303 631 is an initially unidentified H.E.S.S. source which was re- cently identified− as a PWN associated with the pulsar PSR J1301 6305. The broadband emission of the source was modeled within a one-zone− 1D station- ary model yielding a magnetic field of 1.4 0.2 µG and a total energy in elec- trons above 1 GeV of 2 1048 erg. This estimate± of the magnetic field is of the same magnitude as the× averaged line-of-sight magnetic field of 2 µG pro- vided by the measurement of the pulsar’s rotation measure. A magnetic∼ field in a PWN much lower than the averaged ISM magnetic field would be difficult to explain. A low magnetic field is also expected for evolved PWNe for which the magnetic field is believed to have decreased with time. The obtained total en- ergy in electrons yields an estimate for the pulsar birth period between 51 and 75 ms, which is in good agreement with estimations of birth periods for pulsars associated with composite SNRs. Possible extensions of the modeling towards more realistic scenarios which would take into account the time evolution and spatial distribution of the source emission are also discussed. The binary system PSR B1259 63/LS 2883 is the only TeV binary for which the compact companion is unambiguously− identified as a pulsar. It consists of a 48 ms pulsar orbiting around a massive Be star. PSR B1259 63/LS 2883 was monitored by H.E.S.S. around the periastron passage on 15th of− December 2010. The source was observed by H.E.S.S. in the period from 26 to 32 days after the periastron passage. A firm detection of the source was obtained. The observed v flux F(> 1 TeV) = (1.61 0.22 0.32 ) 10 12 cm 2s 1 and spectral in- ± stat ± syst × − − − dex Γ = 2.82 0.25stat 0.2syst are in good agreement with results obtained during previous± periastron± passages. The observations were performed at sim- ilar orbital phases as around the 2004 periastron, for the first time directly con- firming the repetitive behavior of the source at VHEs. H.E.S.S. observations were part of a joint multiwavelength (MWL) campaign including also radio, optical, X-ray and, for the first time, high energy (HE; E > 100 MeV) obser- vations. Fermi LAT detected a spectacular flare which had started within the period of H.E.S.S. observations. A statistical study shows that the HE flare does not have a counterpart at VHEs indicating that the HE and VHE emissions are produced in different physical processes. The modeling of the VHE emission with the model of emission generated via inverse Compton (IC) scattering of shock-accelerated electrons on the stellar photon field is done considering the HE flux as an upper limit for this emission. The modeling yields upper limits on the electron spectral parameters and the total energy in electrons depending on the assumed electron spectral index. It was shown that for indices in the range from 1.7 to 1.9 the time needed to accumulate the required total energy in electrons is smaller than the orbital period of the pulsar. vi Zusammenfassung Abbildende Cherenkov-Teleskope haben in den letzten Jahren eine große An- zahl neuer Gammastrahlungsquellen im Bereich sehr hoher Energien (VHE, ve- ry high energy, E > 100 GeV) entdeckt. Diese Studie behandelt Vertreter von drei unterschiedlichen Klassen von galaktischen Gammastrahlungsquellen: die Supernova-Überreste G 1.9+0.3 und G330.2+1.0, den Pulsarwind-Nebel HESS J1303 631 und das Binärsystem PSR B1259 63/LS 2883. Für alle Objekte wer- den die− Analyse der H.E.S.S.-Daten und die− Modellierung der Emission unter Einbeziehung von Daten aus anderen Wellenlängenbereichen dargestellt. G 1.9+0.3 und G330.2+1.0 sind Supernova-Überreste, deren nicht-thermi- sche Emission durch Synchrotron-Strahlung dominiert wird und so nahelegt, dass es in den Supernova-Schockfronten zur Beschleunigung von Teilchen auf sehr hohe Energien kommt. Daher sind beide Objekte für Beobachtungen im VHE-Bereich von Interesse. Beobachtungen mit dem High Energy Stereosco- pic System (H.E.S.S.) ergaben jedoch keine Hinweise auf signifikante Emission und es wurden daher obere Grenzen auf den Teilchenfluss berechnet. Die obe- ren Grenzen für ein Konfidenzniveau von 99% und eine angenommen Photon- 13 2 1 Index von 2,5 sind FG1.9(> 260 GeV) < 4.6 10− cm− s− für G 1.9+0.3 12 2 1× und FG330(> 380 GeV) < 1.6 10− cm− s− für G 330.2+1.0. Die Flussgren- zen auf die Emission im VHE-Bereich× schränken die möglichen Werte für das Magnetfeld in einem leptonischen Szenario bzw. die Dichte des interstellares Mediums im Fall eines hadronischen Szenarios ein. Die unteren Grenzen für das Magnetfeld in der Emissionsregion sind 15 µG für G 1.9+0.3 und 14 µG für G 330.2+1.0.
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