📰 Publications

A. Roy, S.R. Patel, A. Sarkar, A. Chatterjee, V.R. Chitnis Abstract: The regular monitoring of flat-spectrum radio quasars (FSRQs) in γ-rays by Fermi-LAT (Large Area Telescope) since past 12 yr indicated six sources who exhibited extreme γ-ray outbursts crossing daily flux of 10-5 photons cm-2 s-1. We obtained nearly simultaneous multiwavelength data of these sources in radio to γ-ray waveband from OVRO (Owens Valley Radio Observatory), Steward Observatory, SMARTS (Small and Moderate Aperture Research Telescope System), Swift-UVOT (UV/Optical Telescope), Swift-XRT (X-ray Telescope), and Fermi-LAT....

P. Kushwaha, A. Sarkar, A.C. Gupta, A. Tripathi, P.J. Wiita Abstract: We report the detection of a probable γ-ray quasi-periodic oscillation (QPO) of around 314 d in the monthly binned 0.1–300 GeV γ-ray Fermi-Large Area Telescope light curve of the well-known BL Lacertae blazar OJ 287. To identify and quantify the QPO nature of the γ-ray light curve of OJ 287, we used the Lomb–Scargle periodogram (LSP), REDFIT, and weighted wavelet Z-transform (WWZ) analyses....

A. Sarkar, P. Kushwaha, A.C. Gupta, V.R. Chitnis, P.J. Wiita Abstract: Context. Quasi-periodic fluctuations in the light curves of blazars can provide insight into the underlying emission process. This type of flux modulation hints at periodic physical processes that result in emission. CTA 102, a flat spectrum radio quasar at a redshift of 1.032, has displayed significant activity since 2016. The multi-waveband light curve of CTA 102 shows signs of quasi-periodic oscillations during the 2016–2017 flare....

A. Sarkar, V.R. Chitnis, A.C. Gupta, H. Gaur, S.R. Patel, P.J. Wiita, A.E. Volvach, M. Tornikoski, W. Chamani, S. Enestam, A. Lähteenmäki, J. Tammi, R.J.C Vera and L.N. Volvach Abstract: We performed a long-term optical (B, V, R bands), infrared (J and K bands), and radio band (15, 22, 37 GHz band) study of the flat spectrum radio quasar, 3C 454.3, using data collected over a period of more than 8 yr (MJD 54500–57500)....