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  1. Home
  2. Browse by Author

Browsing by Author "Chavushyan, V."

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    AT 2021hdr: A candidate tidal disruption of a gas cloud by a binary super massive black hole system
    (EDP Sciences, 2024) Hernández-García, L.; Muñoz-Arancibia, A. M.; Lira, P.; Bruni, G.; Cuadra, J.; Arévalo, P.; Sánchez-Sáez, P.; Bernal, S.; Bauer, Franz Erik; Catelan, Márcio; Panessa, F.; Pávez-Herrera, M.; Ricci, C.; Reyes-Jainaga, I.; Ailawadhi, B.; Chavushyan, V.; Dastidar, R.; Deconto-Machado, A.; Forster, F.; Gangopadhyay, A.; García-Pérez, A.; Márquez, I.; Masegosa, J.; Misra, K.; Patiño-Alvarez, V. M.; Puig-Subira, M.; Rodi, J.; Singh, M.
    With a growing number of facilities able to monitor the entire sky and produce light curves with a cadence of days, in recent years there has been an increased rate of detection of sources whose variability deviates from standard behavior, revealing a variety of exotic nuclear transients. The aim of the present study is to disentangle the nature of the transient AT 2021hdr, whose optical light curve used to be consistent with a classic Seyfert 1 nucleus, which was also confirmed by its optical spectrum and high-energy properties. From late 2021, AT 2021hdr started to present sudden brightening episodes in the form of oscillating peaks in the Zwicky Transient Facility (ZTF) alert stream, and the same shape is observed in X-rays and UV from Swift data. The oscillations occur every ≈60-90 days with amplitudes of ≈0.2 mag in the g and r bands. Very Long Baseline Array (VLBA) observations show no radio emission at milliarcseconds scale. It is argued that these findings are inconsistent with a standard tidal disruption event (TDE), a binary supermassive black hole (BSMBH), or a changing-look active galactic nucleus (AGN); neither does this object resemble previous observed AGN flares, and disk or jet instabilities are an unlikely scenario. Here, we propose that the behavior of AT 2021hdr might be due to the tidal disruption of a gas cloud by a BSMBH. In this scenario, we estimate that the putative binary has a separation of ≈0.83 mpc and would merge in ≈7 × 104 years. This galaxy is located at 9 kpc from a companion galaxy, and in this work we report this merger for the first time. The oscillations are not related to the companion galaxy.
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    BL Lacertae identifications in a ROSAT-selected sample of Fermi unidentified objects
    (2013) Masetti, N.; Sbarufatti, B.; Parisi, P.; Jimenez-Bailon, E.; Chavushyan, V.; Vogt, F. P. A.; Sguera, V.; Stephen, J. B.; Palazzi, E.; Bassani, L.; Bazzano, A.; Fiocchi, M.; Galaz, G.; Landi, R.; Malizia, A.; Minniti, D.; Morelli, L.; Ubertini, P.
    The optical spectroscopic followup of 27 sources belonging to a sample of 30 high-energy objects selected by positionally cross correlating the first Fermi/LAT Catalog and the ROSAT All-Sky Survey Bright Source Catalog is presented here. It has been found or confirmed that 25 of them are BL Lacertae objects (BL Lacs), while the remaining two are Galactic cataclysmic variables (CVs). This strongly suggests that the sources in the first group are responsible for the GeV emission detected with Fermi, while the two CVs most likely represent spurious associations. We thus find an 80% a posteriori probability that the sources selected by matching GeV and X-ray catalogs belong to the BL Lac class. We also show suggestions that the BL Lacs selected with this approach are probably high-synchrotron-peaked sources and in turn good candidates for the detection of ultra-high-energy (TeV) photons from them.
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    Searching for active galactic nuclei among unidentified INTEGRAL sources
    (2011) Maiorano, E.; Landi, R.; Stephen, J. B.; Bassani, L.; Masetti, N.; Parisi, P.; Palazzi, E.; Parma, P.; Bird, A. J.; Bazzano, A.; Ubertini, P.; Jimenez-Bailon, E.; Chavushyan, V.; Galaz, G.; Minniti, D.; Morelli, L.
    We report on a new method to identify active galactic nuclei (AGNs) among unidentified INTEGRAL sources. This method consists of cross-correlating unidentified sources listed in the fourth Imager on Board the INTEGRAL Satellite (IBIS) Survey Catalogue first with infrared and then with radio catalogues and a posteriori verifying, by means of X-ray and optical follow-up observations, the likelihood of these associations. In order to test this method, a sample of eight sources has been extracted from the fourth IBIS catalogue. For seven sources of the sample, we obtained an identification, whereas the last one (IGR J03103+5706) has insufficient information for a clear classification and deserves more in-depth study. We identified three objects (IGR J08190-3835, IGR J17520-6018 and IGR J21441+4640) as AGNs and suggest that three more (IGR J00556+7708, IGRJ17219-1509 and IGR J21268+6203) are likely active galaxies on the basis of their radio spectra, near-infrared photometry and location above the Galaxy plane. One source (IGR J05583-1257) has been classified as a starburst galaxy, but it might have been spuriously associated with the INTEGRAL detection.
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    The nature of 50 Palermo Swift-BAT hard X-ray objects through optical spectroscopy
    (2017) Rojas, A. F.; Masetti, N.; Minniti, D.; Jiménez Bailón, E.; Chavushyan, V.; Hau, G.; McBride, V. A.; Bassani, L.; Bazzano, A.; Galaz, Gaspar; Rojas, A. F.; Masetti, N.; Minniti, D.; Jiménez Bailón, E.; Chavushyan, V.; Hau, G.; McBride, V. A.; Bassani, L.; Bazzano, A.; Galaz, Gaspar

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