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Master's Dissertation
DOI
https://doi.org/10.11606/D.14.2016.tde-03122020-195723
Document
Author
Full name
Raniere Maciel de Menezes
E-mail
Institute/School/College
Knowledge Area
Date of Defense
Published
São Paulo, 2016
Supervisor
Committee
Silva, Rodrigo Nemmen da (President)
Almeida, Ulisses Barres de
Lima Neto, Gastao Cesar Bierrenbach
Santos, Edivaldo Moura
Title in Portuguese
Variabilidade de AGNs em raios gama no Universo local
Keywords in Portuguese
núcleos ativos de galáxias
raios gama
Abstract in Portuguese
Desde seu lancamento em 2008, o Fermi Gamma-ray Space Telescope abriu uma nova janela para o lado extremo do Universo e vem explorando aceleradores de partculas astrofsicos como buracos negros supermacicos em núcleos ativos de galáxias (AGNs), explosões de estrelas no Universo longínquo e vários outros fenômenos. Neste projeto, investigamos um conjunto de 15 AGNs de baixa luminosidade do Palomar survey nas proximidades da Via Láctea com base em mais de sete anos de dados do Large Area Telescope, a bordo do Fermi. Caracterizamos a variabilidade de suas curvas de luz em raios gama, restringindo, assim, a natureza de seus processos de altas energias (basicamente usando a escala de tempo de variabilidade para restringir o tamanho da região emissora de raios gama). Entretanto, descobrimos que a maior parte da nossa amostra não emite fótons o suficiente para ser detectada pelo Fermi-LAT. O curioso comportamento periódico de algumas fontes também foi explorado. Aplicamos técnicas de análise de séries temporais, como transformada de Fourier, periodograma de Lomb-Scargle e continuous wavelet transform, que nos trouxe algumas conclusões interessantes juntamente com algumas descobertas fortuitas. Em particular, encontramos evidência de QPO na NGC 1275, com um período de aproximadamente 570 dias, e um comportamento periódico não-estacionário no BL Lac PG 1553+113.
Title in English
Gamma-ray variability of AGNs in the local Universe
Keywords in English
active galactic nuclei
gamma-rays
Abstract in English
Since its launch in 2008, the Fermi Gamma-ray Space Telescope opened a new window into the extreme side of the universe and has been observing -rays from astrophysical particle accelerators such as supermassive black holes in active galactic nuclei (AGN), exploding stars in the distant universe and many others phenomena. In this project, we investigate a sample of 15 nearby low-luminosity AGNs from Palomar survey based on Fermi Large Area Telescope (LAT) data. We characterize the -ray variability of these sources in order to constrain the nature of its high-energy processes (basically using the variability timescales to constrain the size of the -ray emission region). However, most of our sample does not emit enough photons to be detected by Fermi -LAT. The odd periodic behavior in the light curve of some sources was also explored. We applied time-series analysis techniques, such as fast Fourier transform, Lomb-Scargle periodogram and continuous wavelet transform, which gave us some interesting conclusions besides some serendipitous discoveries. In particular we found evidence of QPO in NGC 1275 with a period around 570 days and a non-stationary periodic behavior in PG 1553+113.
 
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Publishing Date
2020-12-09
 
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