Naslov
Characterization of very high energy gamma-radiation from active galactic nuclei observed by the MAGIC telescopes

Autori
Terzić, Tomislav

Vrsta, podvrsta i kategorija rada
Ocjenski radovi, doktorska disertacija

Fakultet
Prirodoslovno-matematički fakultet

Mjesto
Zagreb

Datum
13.07

Godina
2015

Stranica
234

Mentor
Dominis Prester, Dijana

Ključne riječi
active galactic nuclei; blazars; gamma-rays; imaging atmospheric Cherenkov telescopes; M87; PKS 1222+21; 4C +21.35; H1722+119

Sažetak
Active galactic nuclei (AGN) are bright compact regions in the centres of galaxies, that emit radiation across the entire electromagnetic spectrum. They are believed to be powered by supermassive black holes (SMBH), which actively accrete matter. Some of that matter is ejected in the form of collimated jets of ultrarelativistic particles. Jets are sources of electromagnetic radiation of all wavelengths. A significant portion of energy radiated by AGN is emitted in the form of gamma-rays. In addition, gamma-rays are produced through physical processes different from the ones responsible for lower energy radiation. Therefore, in order to understand how jets are formed and how particles are accelerated to ultrarelativistic energies, it is important to understand the mechanisms and locations of gamma-ray production within AGN. To reach closer to this goal here we study the very high energy (VHE) gamma-radiation from three sources belonging to different classes of AGN: M87 (radio galaxy), PKS 1222+21 (flat spectrum radio quasar) and H1722+119 (BL Lac object). For these sources we obtained VHE gamma-ray spectra and light curves using the MAGIC ground-based Cherenkov telescopes. We used long term monitoring of M87 to evaluate the level of low emission state. We propose a structured jet "spine-layer" scenario to explain the emission from M87. It places the VHE gamma-ray emission region in the vicinity of the SMBH, and suggests that, if viewed head on, the emission from M87 would resemble that from a typical BL Lac. PKS 1222+21 was first detected by the MAGIC telescopes. Very short variability timescale and absence of a cut-off in the VHE spectrum sets constraints on VHE gamma-ray emission region, and on emission models. We performed a multiwavelength study using contemporaneous data, concluding that the gamma-ray emission region is most probably located outside of the broad line region, and that it is possible to explain the emission using a simple one-zone emission scenario. H1722+119 is a source with unknown redshift, first detected by the MAGIC telescopes. We performed a multiwavelength study using contemporaneous data, and estimated the redshift of the source using gamma-rays to z = 0.4. As expected, different types of emission models are required to explain emission from different types of sources. However, we also find that the VHE γ-radiation originates in different locations in the sources we studied.

Izvorni jezik
Engleski

Znanstvena područja
Fizika

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