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Browsing by Author "Gupta, Alok C."

Browsing by Author "Gupta, Alok C."

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  • Detection of a quasi-periodic oscillation in the optical light curve of the remarkable blazar AO 0235+164 
    Roy, Abhradeep ,et.al.; Gupta, Alok C. (Monthly Notices of the Royal Astronomical Society, 2022-07)
    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 ...
  • Detection of a quasi-periodic oscillation in γ -ray light curve of the high-redshift blazar B2 1520+31 
    Gupta, Alok C.; Tripathi, Ashutosh; Wiita, Paul J. (Monthly Notices of the Royal Astronomical Society, 2019-02)
    We detected a possible quasi-periodic oscillation (QPO) of ∼71 d in the 0.1–300 GeV γ-ray Fermi-Large Area Telescope light curve of the high-redshift flat spectrum radio quasar B2 1520+31. We identify and confirm that ...
  • Detection of Quasiperiodic Oscillations in the Blazar S4 0954+658 with TESS 
    Kishore, Shubham; Gupta, Alok C.; Wiita, Paul J. (The Astrophysical Journal, 2023-01)
    We report the detection of several quasiperiodicities around 0.6–2.5 days in the optical emission of the blazar S4 0954+658. The source was observed by the Transiting Exoplanet Survey Satellite in six sectors and it ...
  • Intra-night optical flux and polarization variability of BL Lacertae during its 2020–2021 high state 
    Bachev, Rumen; Tripathi, Tushar; Gupta, Alok C.; Kishore, Shubham; Gaur, Haritma; Dhiman, Vinit (Monthly Notices of the Royal Astronomical Society, 2023-06)
    In this work, we report the presence of rapid intra-night optical variations in both flux and polarization of the blazar BL Lacertae during its unprecedented 2020–2021 high state of brightness. The object showed significant ...
  • Investigating the origin of optical flares from the TeV blazar S4 0954+65 
    Pandey, Ashwani; Bachev, Rumen; Czerny, Bo˙zena; Wiita, Paul J.; Gupta, Alok C.; Strigachev, Anton; Popowicz, Adam (Astronomy & astrophysics, 2023-11)
    Aims. We aim to investigate the extreme variability properties of the TeV blazar S4 0954+65 using optical photometric and polarisation observations carried out between 2017 and 2023 using three ground-based telescopes. Methods. ...
  • Launching the VASCO Citizen Science Project 
    Villarroel, Beatriz, et.al.; Gupta, Alok C. (Universe, 2022-06)
    The Vanishing & Appearing Sources during a Century of Observations (VASCO) project investigates astronomical surveys spanning a time interval of 70 years, searching for unusual and exotic transients. We present herein ...
  • Long-term Multiband Near-infrared Variability of the Blazar OJ 287 during 2007–2021 
    Gupta, Alok C.; Kushwaha, Pankaj, et.al. (The Astrophysical Journal Supplement Series, 2022-06)
    We present the most extensive and well-sampled long-term multiband near-infrared (NIR) temporal and spectral variability study of OJ 287, considered to be the best candidate binary supermassive black hole blazar. ...
  • Multiband cross-correlated radio variability of the blazar 3C 279 
    Mohana A, Krishna; Gupta, Alok C.; Marscher, Alan P.; Sotnikova, Yulia V.; Jorstad, S. G.; Wiita, Paul J.; Cui, Lang; Aller, Margo F.; Aller, Hugh D.; Kovalev, Yu. A.; Kovalev, Y. Y.; Liu, Xiang; Mufakharov, T. V.; Popkov, A. V.; Mingaliev, M. G.; Erkenov, A. K.; Nizhelsky, N. A.; Tsybulev, P. G.; Tsybulev, P. G.; Zhao, Wei; Weaver, Z. R.; Morozova, D. A. (Monthly Notices of the Royal Astronomical Society, 2024-01)
    We present the results of our study of cross-correlations between long-term multiband observations of the radio variability of the blazar 3C 279. More than a decade (2008–2022) of radio data were collected at seven different ...
  • Multiband optical variability of a newly discovered 12 blazars sample from 2013 – 2019 
    Jovanovic, Miljana D.; Damljanovic, Goran; Taris, Francois; Gupta, Alok C.; Bhatta, Gopal (Monthly Notices of the Royal Astronomical Society, 2023-06)
    Here we present the first optical photometric monitoring results of a sample of 12 newly discovered blazars from the ICRF – Gaia CRF astrometric link. The observations were performed from April 2013 to August 2019 using ...
  • Multiband optical variability on diverse time-scales of the TeV blazar TXS 0506 + 056, the first cosmic neutrino source 
    Dhiman, Vinit; Gupta, Alok C.; Bachev, Rumen; Wiita, Paul J.; Cellone, Sergio A.; Strigachev, A.; Gaur, Haritma; Darriba, A.; Bisen, D. P.; Locatelli, G.; Mammana, L. A.; Semkov, E. (Monthly Notices of the Royal Astronomical Society, 2024-01)
    We report the first extensive optical flux and spectral variability study of the TeV blazar TXS 0506 + 056 on intranight to long-term time-scales using BVRI data collected over 220 nights between 2017 January 21 to 2022 ...
  • Multiwavelength Temporal Variability of the Blazar PKS 1510–089 
    Yuan, Q.; Kushwaha, Pankaj; Gupta, Alok C.; Tripathi, Ashutosh; Wiita, Paul J.; Zhang, M.; Liu, X.; Lähteenmäki, Anne; Tornikoski, Merja; Tammi, Joni; Ramakrishnan, Venkatessh; Cui, L.; Wang, X.; Gu, M. F.; Bambi, Cosimo; Volvach, A. E. (The Astrophysical Journal, 2023-08)
    We perform correlation and periodicity search analyses on long-term multiband light curves of the flat-spectrum radio quasar PKS 1510−089 observed by the space-based Fermi-Large Area Telescope in γ-rays, the SMARTS and ...
  • Optical Flux and Spectral Variability of BL Lacertae during Its Historical High Outburst in 2020 
    Kalita, Nibedita, et.al.; Gupta, Alok C. (The Astrophysical Journal, 2023-02)
    BL Lacertae underwent a series of historical high flux activity over a year from 2020 August in the optical to VHE γ-rays. In this paper, we report on optical flux and spectral variability of the first historical maxima ...
  • Optical Flux and Spectral Variability of the TeV Blazar PG 1553+113 
    Pandey, Ashwani; Gupta, Alok C.; Wiita, Paul J.; Tiwari, S. N. (The Astrophysical Journal, 2019-02)
    We present the results of our optical (VRI) observations of the TeV blazar PG 1553+113 over eight nights in 2016 April. We monitored the blazar quasi-simultaneously in V and R bands each night and examined the light ...
  • Optical intraday variability of the blazar S5 0716+714 
    Tripathi, Tushar; Gupta, Alok C.; Takey, Ali; Bachev, Rumen; Vince, Oliver; Strigachev, Anton; Kushwaha, Pankaj; Elhosseiny, E. G.; Wiita, Paul J.; Damljanovic, G.; Dhiman, Vinit; Fouad, A.; Gaur, Haritma; Gu, Minfeng; Hamed, G. E.; Kishore, Shubham; Kurtenkov, A.; Rastogi, Shantanu; Semkov, E.; Zead, I.; Zhang, Zhongli (Monthly Notices of the Royal Astronomical Society, 2024-01)
    We present an extensive recent multiband optical photometric observations of the blazar S5 0716+714 carried out over 53 nights with two telescopes in India, two in Bulgaria, one in Serbia, and one in Egypt during 2019 ...
  • Quasi-periodic oscillation detected in γ-rays in blazar PKS 0346−27 
    Prince, Raj; Banerjee, Anuvab; Sharma, Ajay; das, Avik Kumar; Gupta, Alok C.; Bose, Debanjan (Astronomy & astrophysics, 2023-10)
    Aims. We present a variability study of the blazar PKS 0346−27 conducted between December 2018 and January 2022 using archival γ-ray observations from Fermi-LAT. Methods. We used Lomb–Scargle periodogram and weighted ...
  • Quasi-simultaneous Optical Flux and Polarization Variability of the Binary Super Massive Black Hole Blazar OJ 287 from 2015 to 2023: Detection of an Anticorrelation in Flux and Polarization Variability 
    Gupta, Alok C.; Kushwaha, Pankaj; Valtonen, Mauri J.; Savchenko, Sergey S.; Jorstad, Svetlana G.; Imazawa, Ryo; Wiita, Paul J.; Gu, Minfeng; Marscher, Alan P.; Zhang, Zhongli; Bachev, Rumen; Borman, G. A.; Gaur, Haritma; Grishina, T. S.; Hagen-Thorn, V. A.; Kopatskaya, E. N.; Larionov, V. M.; Larionova, E. G.; Larionova, L. V.; Morozova, D. A.; Nakaoka, T; Strigachev, A; Troitskaya, Yulia V.; Troitsky, I. S.; Uemura, M.; Vasilyev, A. A.; Weaver, Z. R.; Zhovtan, A. V. (Astrophysical Journal Letters, 2023-11)
    We study the optical flux and polarization variability of the binary black hole blazar OJ 287 using quasi simultaneous observations from 2015 to 2023 carried out using telescopes in the USA, Japan, Russia, Crimea, ...
  • Rapid Optical Flares in the Blazar OJ 287 on Intraday Timescales with TESS 
    Kishore, Shubham; Gupta, Alok C.; Wiita, Paul J. (The Astrophysical Journal, 2024-01)
    We have analyzed the optical light curves of the blazar OJ 287 obtained with the Transiting Exoplanet Survey Satellite over about 80 days from 2021 October 13 to December 31, with an unprecedented sampling of 2 ...
  • Rapid quasi-periodic oscillations in the relativistic jet of BL Lacertae 
    Jorstad, S. G.,et.al.; Gupta, Alok C. (Nature, 2022-09)
    Blazars are active galactic nuclei (AGN) with relativistic jets whose non-thermal radiation is extremely variable on various timescales1–3 . This variability seems mostly random, although some quasi-periodic oscillations ...
  • Refining the OJ 287 2022 impact flare arrival epoch 
    Valtonen, Mauri J. , et.al.; Gupta, Alok C. (Monthly Notices of the Royal Astronomical Society, 2023-06)
    The bright blazar OJ 287 routinely parades high brightness bremsstrahlung flares, which are explained as being a result of a secondary supermassive black hole (SMBH) impacting the accretion disc of a more massive primary ...
  • A Search for Cosmic Ray Bursts at 0.1 PeV with a Small Air Shower Array 
    Clay, Roger,et.al.; Gupta, Alok C. (Symmetry, 2022-03)
    The Cosmic Ray Extremely Distributed Observatory (CREDO) pursues a global research strategy dedicated to the search for correlated cosmic rays, so-called Cosmic Ray Ensembles (CRE). Its general approach to CRE detection ...

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