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Broadband variability and correlation study of 3C 279 during flare of 2017-2018

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 نشر من قبل Raj Prince
 تاريخ النشر 2020
  مجال البحث فيزياء
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 تأليف Raj Prince




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A multiwavelength temporal and spectral analysis of flares of 3C 279 during November 2017--July 2018 are presented in this work. Three bright gamma-ray flares were observed simultaneously in X-ray and Optical/UV along with a prolonged quiescent state. A harder-when-brighter trend is observed in both gamma-rays and X-rays during the flaring period. The gamma-ray light curve for all the flares are binned in one-day time bins and a day scale variability is observed. Variability time constrains the size and location of the emission region to 2.1$times$10$^{16}$ cm and 4.4$times$10$^{17}$ cm, respectively. The fractional variability reveals that the source is more than 100% variable in gamma-rays and it decreases towards the lower energy. A cross-correlation study of the emission from different wavebands is done using the textit{DCF} method, which shows a strong correlation between them without any time lags. The zero time lag between different wavebands suggest their co-spatial origin. This is the first time 3C 279 has shown a strong correlation between gamma-rays and X-rays emission with zero time lag. A single zone emission model was adopted to model the multiwavelength SEDs by using the publicly available code GAMERA. The study reveals that a higher jet power in electrons is required to explain the gamma-ray flux during the flaring state, as much as, ten times of that required for the quiescent state. However, more jet power in magnetic field has been observed during the quiescent state compared to the flaring state.



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66 - Raj Prince 2018
In this work, I have presented a multi-frequency variability and correlation study of the blazar Ton 599, which was observed first time in flaring state at the end of 2017. Data from textit{Fermi}-LAT, Swift-XRT/UVOT, Steward Observatory, and OVRO (1 5 GHz) is used, and it is found that the source is more variable in $gamma$-ray and optical/UV than X-ray and radio. Large variations in the degree of polarization (DoP) and position angle (PA) is noticed during the flaring period. Maximum flux during $gamma$-ray flare is found to be 12.63$times$10$^{-7}$ at MJD 58057.5 from the 1-day bin light curve (LC), which is the maximum flux ever achieved by this source. It is further found that all the peaks of flare are very symmetric, which suggests the cooling time of electrons is much smaller than light crossing time. Using 1-day as a fast variability time, the size of the $gamma$-ray emission region is estimated as 1.88$times$10$^{16}$ cm. Two 42 GeV of photons are detected during the flare which puts a constraint on the location of the emission region, and it is found that the $gamma$-ray emitting blob is located at the outer edge or outside the broad line region (BLR). A trend of increasing fractional variability towards higher energies is also seen. Strong correlations were seen between $gamma$-ray, optical/UV, X-ray, and radio (15 GHz) emission. A small time lag between $gamma$-ray and optical/UV suggest their emission to be co-spatial while lag of 27 days between $gamma$-ray and OVRO (15 GHz) suggest two different emission zone separated by a distance of $sim$ 5 pc.
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The flat spectrum radio quasar 3C 279 is a known $gamma$-ray variable source that has recently exhibited minute-scale variability at energies $>100$ MeV. One-zone leptonic models for blazar emission are severely constrained by the short timescale var iability that implies a very compact emission region at a distance of hundreds of Schwarzschild radii from the central black hole. Here, we investigate a hadronic scenario where GeV $gamma$-rays are produced via proton synchrotron radiation. We also take into account the effects of the hadronically initiated electromagnetic cascades (EMC). For a $gamma$-ray emitting region in rough equipartition between particles and kG magnetic fields, located within the broad-line region (BLR), the development of EMC redistributes the $gamma$-ray luminosity to softer energy bands and eventually leads to broad-band spectra that differ from the observed ones. Suppression of EMC and energy equipartition are still possible, if the $gamma$-ray emitting region is located beyond the BLR, is fast moving with Doppler factor ($>70$), and contains strong magnetic fields ($>100$ G). Yet, these conditions cannot be easily met in parsec-scale jets, thus disfavouring a proton synchrotron origin of the Fermi-LAT flare.
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