Suchergebnisse

We present the results of a large multiwavelength follow-up campaign of the tidal disruption event (TDE) AT 2019dsg, focusing on low to high resolution optical spectroscopy, X-ray, and radio observations. The galaxy hosts a super massive black hole of mass (5.4±3.2)×106M⊙ and careful analysis finds no evidence for the presence of an active galactic nucleus, instead the TDE host galaxy shows narrow optical emission lines that likely arise from star formation activity. The transient is luminous in the X-rays, radio, UV, and optical. The X-ray emission becomes undetected after ∼100 d, and the radio luminosity density starts to decay at frequencies above 5.4 GHz by ∼160 d. Optical emission line signatures of the TDE are present up to ∼200 d after the light-curve peak. The medium to high resolution spectra show traces of absorption lines that we propose originate in the self-gravitating debris streams. At late times, after ∼200 d, narrow Fe lines appear in the spectra. The TDE was previously classified as N-strong, but after careful subtraction of the host galaxy's stellar contribution, we find no evidence for these N lines in the TDE spectrum, even though O Bowen lines are detected. The observed properties of the X-ray emission are fully consistent with the detection of the inner regions of a cooling accretion disc. The optical and radio properties are consistent with this central engine seen at a low inclination (i.e. seen from the poles). © 2021 The Author(s). ; GC and PGJ acknowledge support from European Research Council (ERC) Consolidator Grant 647208. TW is funded by ERC grant 320360 and by European Commission grant 730980. This research was made possible through the use of the AAVSO Photometric All-Sky Survey (APASS), funded by the Robert Martin Ayers Sciences Fund and NSFAST-1412587. We acknowledge the use of public data from the Swift data archive. We thank P. M. Vreeswijk for the data reduction of the UVES spectrum. This paper includes data obtained with the William Herschel Telescope (proposal IDs: W19B/P7, W19A/N3) as well as observations made with the Italian Telescopio Nazionale Galileo (TNG) operated on the island of La Palma by the Isaac Newton Group of Telescopes and the Fundación Galileo Galilei of the INAF (Istituto Nazionale di Astrofisica) at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO programmes 1103.D-0328 "advanced Public ESO Spectroscopic Survey for Transient Objects" (ePESSTO+). GL was supported by a research grant (19054) from VILLUM FONDEN. D.M.-S. acknowledges support from the ERC under the European Union's Horizon 2020 research and innovation programme (grant agreement no. 715051; Spiders). JM acknowledges financial support from the State Agency for Research of the Spanish MICIU through the "Center of Excellence Severo Ochoa" award to the Instituto de Astrofísica de Andalucía (SEV-2017-0709) and from the grant RTI2018-096228-B-C31 (MICIU/FEDER, EU). IA is a CIFAR Azrieli Global Scholar in the Gravity and the Extreme Universe Program and acknowledges support from that program, from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (grant agreement number 852097), from the Israel Science Foundation (grant numbers 2108/18 and 2752/19), from the United States – Israel Binational Science Foundation (BSF), and from the Israeli Council for Higher Education Alon Fellowship. TWC acknowledges the EU Funding under Marie Skłodowska-Curie grant H2020-MSCA-IF-2018-842471. TMB was funded by the CONICYT PFCHA / DOCTORADOBECAS CHILE/2017-72180113. MN is supported by a Royal Astronomical Society Research Fellowship. FO acknowledges the support of the GRAWITA/PRIN-MIUR project: The new frontier of the Multi-Messenger Astrophysics: follow-up of electromagnetic transient counterparts of gravitational wave sources. ; Peer reviewed

Facilities: Liverpool:2 m, FTN, OO:0.65, MLO:1 m, BAT, OAO:0.5 m, Swift, Mayall. Software: IRAF (v2.16.1; Tody 1993), Starlink (v2015B; Disney & Wallace 1982), APHOT (Pravec et al. 1994), HEASOFT (v6.16), XIMAGE (v4.5.1), XSPEC (v12.8.2; Arnaud 1996), XSELECT (v2.4c), R (R Development Core Team 2011). ; The Andromeda Galaxy recurrent nova M31N 2008-12a had been observed in eruption 10 times, including yearly eruptions from 2008 to 2014. With a measured recurrence period of Prec = 351 ± 13 days (we believe the true value to be half of this) and a white dwarf very close to the Chandrasekhar limit, M31N 2008-12a has become the leading pre-explosion supernova type Ia progenitor candidate. Following multi-wavelength follow-up observations of the 2013 and 2014 eruptions, we initiated a campaign to ensure early detection of the predicted 2015 eruption, which triggered ambitious ground- and space-based follow-up programs. In this paper we present the 2015 detection, visible to near-infrared photometry and visible spectroscopy, and ultraviolet and X-ray observations from the Swift observatory. The LCOGT 2 m (Hawaii) discovered the 2015 eruption, estimated to have commenced at August 28.28 ± 0.12 UT. The 2013–2015 eruptions are remarkably similar at all wavelengths. New early spectroscopic observations reveal short-lived emission from material with velocities ∼13,000 km s^−1, possibly collimated outflows. Photometric and spectroscopic observations of the eruption provide strong evidence supporting a red giant donor. An apparently stochastic variability during the early supersoft X-ray phase was comparable in amplitude and duration to past eruptions, but the 2013 and 2015 eruptions show evidence of a brief flux dip during this phase. The multi-eruption Swift/XRT spectra show tentative evidence of high-ionization emission lines above a high-temperature continuum. Following Henze et al. (2015a), the updated recurrence period based on all known eruptions is Prec = 174 ± 10 days, and we expect the next eruption of M31N 2008-12a to occur around 2016 mid-September. ; A.F.V., and V.P.G. acknowledge support from RFBR Grant No. 16 February 00758. J.F., J.J., and G.S. acknowledge support from Spanish Ministry of Economy and Competitiveness (MINECO) grant AYA2014-59084-P, the E.U. FEDER funds, and AGAUR/Generalitat de Catalunya grant SGR0038/2014. S.F. acknowledges support from the Russian Scientific Foundation (grant N 14-50-00043) and the Russian Government Program of Competitive Growth of Kazan Federal University. M. Henze acknowledges the support of the Spanish MINECO under grant FDPI-2013-16933. M. Hernanz acknowledges MINECO support under grant ESP2014-56003-R.K.H. was supported by the project RVO:67985815. J.P.O. and K.L.P. acknowledge funding from the UK Space Agency. VARMR acknowledges financial support from the Radboud Excellence Initiative. S.C.W. acknowledges a visiting research fellowship at LJMU. This work has been supported in part by NSF grant AST-1009566 and NASA grant HST-Go-14125.012. ; Peer-reviewed ; Post-print