Abstract Details

Name: Krishna Mohana A
Affiliation: Aryabhatta Research Institute of Observational Sciences (ARIES) Manora Peak Nainital - 263001 Uttarakhand, India
Conference ID : ASI2023_358
Authors : Krishna Mohana A¹, Debbijoy Bhattacharya² ¹Aryabhatta Research Institute of Observational Sciences (ARIES), Manora Peak, Nainital - 263001, Uttarakhand, India ²Manipal Centre for Natural Sciences, Centre of Excellence, Manipal Academy of Higher Education, Manipal-576104, Karnataka,
Mode of Presentation: Oral
Abstract Category : Thesis
Abstract : Active galaxies are highly luminous astrophysical sources in the universe powered by “supermassive black holes” via processes known as “accretion”. Blazars are a class of active galaxies whose multi-band emission is dominated by non-thermal radiation originating from their relativistic jet pointing towards the Earth. They exhibit extreme variations ranging from all the time-scale from minutes to years across the electromagnetic band. Considering the time-scale of the observed flux variation, variability can be classified as short-term (time-scale of minutes to hours to days to weeks) and long-term variability (variations with months to years time-scale). These variations occur as flares or quiescent/low-activity states. Studies on long-term variations were limited in the past due to a lack of acquisition of longer good-quality multi-band observations. The origin and cause of short-term variability might not represent the underlying mechanism for the observed long-term variations. The cause for such long-term variations could have a more fundamental global origin. Therefore, studies related to long-term variability are essential. “Fermi γ-ray space telescope”, with its enhanced sensitivity and rapid scanning capability over the earlier γ-ray space telescopes, along with other space and ground-based observatories and associated theoretical modelling, is used in this thesis to study blazar physics. Some key findings of this thesis are (a) blazars could remain in a decade-long low γ-ray activity state, (b) there might be an active region in the relativistic jet at ~3 lightyears distance from the central black hole, from which emission blobs originate and propagate down the jet (c) presence of bents in the jets or deceleration of emitting region down the jet could give rise to long-term variations. Overall, this thesis work confirms presence of decade-long long-term low activity states in blazars. The detailed temporal and spectral study of few blazars supports existence of such long-term low activity states.