📰 Publications | Arkadipta

Performance study update of observations in divergent mode for the Cherenkov Telescope Array

A. Donini, I Burelli, O Gueta, F Longo, E Pueschel, D Tak, A Vigliano, T Vuillamme, O Sergijenko, A Sarkar. Abstract: Due to the limited field of view (FoV) of Cherenkov telescopes, the time needed to achievetarget sensitivity for surveys of the extragalactic and Galactic sky is large. To optimize the timespent to perform such surveys, a so-called “divergent mode” of the Cherenkov Telescope ArrayObservatory (CTAO) was proposed as an alternative observation strategy to the traditional parallel pointing....

Variability studies of active galactic nuclei from the long-term monitoring program with the Cherenkov Telescope Array

G. Grolleron, J.B. González, J. Biteau, M. Cerruti, R. Grau, L. Gréaux, T. Hovatta, J. Lenain, E. Lindfors, W. Max-Moerbeck, D. Miceli, A. Moralejo, K. Nilsson, E. Pueschel, A. Sarkar, S. Suutarinen. Abstract: Blazars are active galactic nuclei (AGN) with a relativistic jet oriented toward the observer. This jet is composed of accelerated particles which can display emission over the entire electromagnetic spectrum. Spectral variability has been observed on short- and long-time scales in AGN, with a power spectral density (PSD) that can show a break at frequencies below the well-known red-noise process....

Analog signal processing for large area SiPM in Cherenkov telescope camera

S.K. Rao, K.S. Gothe, S.S. Upadhya, N.K. Parmar, R.L. Deshmukh, B.B. Singh, S. Kumar, M. Ranjan, A. Sarkar, S.R. Patel, V.R. Chitnis. Abstract: We have developed a preamplifier which processes signals from large area pixel sensors each comprising a 4 × 4 array of SiPMs. These amplifiers constitute a front-end portion of 256 pixel camera for an Imaging Atmospheric Cherenkov Telescope (IACT). The camera would be mounted at the focal plane of the 4-m class telescope....

Development of 256-Pixel SiPM-Based Imaging Camera and Its Status

S.S. Upadhya, A. Chatterjee, V.R. Chitnis, R.L. Deshmukh, P. Dorjey, N. Dorji, S. Duhan, K.S. Gothe, A.P.K. Kutty, B.K. Nagesh, V.A. Nikam, N.K. Parmar, S.R. Patel, M. Ranjan, S.K. Rao, A. Roy, M.N. Saraf, A. Sarkar, B.B. Singh, P. Verma. Abstract: A 256-pixel imaging Camera based on SiPM is being developed for a 4m class Cherenkov telescope would be the first of its kind in India that uses SiPM as a pixel sensor in place of photomultipliers....

Development of Front-End Electronics for an SiPM-Based Cherenkov Telescope Camera

K.S. Gothe, S.K. Rao, S.S. Upadhya, S. Duhan, B.K. Nagesh, N.K. Parmar, M. Ranjan, B.B. Singh, A. Sarkar. Abstract: A prototype 64-pixel camera for a 4 m class Imaging Atmospheric Cherenkov Telescope is in its final stage of development. The camera is based on 4 (\times ) 4 array of SiPMs as a pixel sensor and would be mounted on the focal plane of the telescope. Eventually, the camera would be expanded to 256 pixels....

Detection of a quasi-periodic oscillation in the optical light curve of the remarkable blazar AO 0235+164

A. Roy, V.R. Chitnis, A.C. Gupta, P.J. Wiita, G.E. Romero, S.A. Cellone, A. Chatterjee, J.A. Combi, C.M. Raiteri, A. Sarkar, M. Villata Abstract: We present a long term optical R band light-curve analysis of the gravitationally lensed blazar AO 0235+164 in the time span 1982-2019. Several methods of analysis lead to the result that there is a periodicity of ~8.13 yr present in these data. In addition, each of these five major flares are apparently double-peaked, with the secondary peak following the primary one by ~2 yr....

SiPM Based Imaging Camera for 4m Class Telescope

V. Chitnis, S.S. Upadhya, K. Gothe, S. Duhan, S.K. Rao, B.B. Singh, M. Ranjan, N.K. Parmar, A. Chatterjee, R.L. Deshmukh, P. Dorjey, N. Dorji, A.P.K. Kutty, B.K. Nagesh, V.A. Nikam, S.R. Patel, A. Roy, M.N. Saraf, A. Sarkar, P. Verma, K.K. Yadav, N. Chouhan, V.K. Dhar, P. Chandra and K. Venugopal Abstract: In last few years, SiPMs have emerged as a viable alternative to PMTs used in the imaging atmospheric Cherenkov telescopes....

Transient quasi-periodic oscillations at γ-rays in the TeV blazar PKS 1510-089.

A. Roy, A. Sarkar, A. Chatterjee, A.C. Gupta, V.R. Chitnis, P.J. Wiita Abstract: We present periodicity search analyses on the γ-ray light curve of the TeV blazar PKS 1510-089 observed by the Fermi Large Area Telescope. We report the detection of two transient quasi-periodic oscillations: A 3.6-d QPO during the outburst in 2009 that lasted five cycles (MJD 54906–54923); and a periodicity of 92 d spanning over 650 d from 2018 to 2020 (MJD 58200–58850), which lasted for seven cycles....

Multiwaveband Quasi-periodic Oscillation in the Blazar 3C 454.3

A. Sarkar, A.C. Gupta, V.R. Chitnis, P.J. Wiita Abstract: We report the detection (>4σ) of a quasi-periodic oscillation (QPO) in the gamma-ray light curve of 3C 454.3 along with a simultaneous marginal QPO detection (>2.4σ) in the optical light curves. Periodic flux modulations were detected in both of these wavebands with a dominant period of ∼47 d. The gamma-ray QPO lasted for over 450 d (from MJD 56800 to 57250), resulting in over nine observed cycles which is among the highest number of periods ever detected in a blazar light curve....

Temporal and spectral study of PKS B1222+ 216 flares in 2014.

A. Chatterjee, A. Roy, A. Sarkar, V.R. Chitnis. Abstract: We report on a temporal and spectral study of a flat-spectrum radio quasar, PKS B1222 + 216, in a flare state to get insight into the acceleration and emission mechanisms inside the jet. It is one of the brightest and highly active blazars in the MeV–GeV regime. The long-term multiwaveband light curves of this object showed flaring activity in 2014, with two distinct flares....