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ABSTRACT We present the results of a multiwavelength follow-up campaign for the luminous nuclear transient Gaia16aax, which was first identified in 2016 January. The transient is spatially consistent with the nucleus of an active galaxy at z = 0.25, hosting a black hole of mass $${\sim }6\times 10^8\, \mathrm{M}_\odot$$. The nucleus brightened by more than 1 mag in the Gaia G band over a time-scale of less than 1 yr, before fading back to its pre-outburst state over the following 3 yr. The optical spectra of the source show broad Balmer lines similar to the ones present in a pre-outburst spectrum. During the outburst, the H α and H β emission lines develop a secondary peak. We also report on the discovery of two transients with similar light-curve evolution and spectra: Gaia16aka and Gaia16ajq. We consider possible scenarios to explain the observed outbursts. We exclude that the transient event could be caused by a microlensing event, variable dust absorption or a tidal encounter between a neutron star and a stellar mass black hole in the accretion disc. We consider variability in the accretion flow in the inner part of the disc, or a tidal disruption event of a star $${\ge } 1 \, \mathrm{M}_{\odot }$$ by a rapidly spinning supermassive black hole as the most plausible scenarios. We note that the similarity between the light curves of the three Gaia transients may be a function of the Gaia alerts selection criteria.
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Resolving the inner accretion flow towards the central supermassive black hole in SDSS J1339+1310
We studied the accretion disc structure in the doubly imaged lensed quasar SDSS J1339+1310 using r -band light curves and UV-visible to near-IR spectra from the first 11 observational seasons after its discovery. The 2009−2019 light curves displayed pronounced microlensing variations on different timescales, and this microlensing signal permitted us to constrain the half-light radius of the 1930 Å continuum-emitting region. Assuming an accretion disc with an axis inclined at 60° to the line of sight, we obtained log( r 1/2 /cm) = 15.4 −0.4 +0.93 . We also estimated the central black hole mass from spectroscopic data. The width of the C IV , Mg II , and H β emission lines, and the continuum luminosity at 1350, 3000, and 5100 Å, led to log( M BH / M ⊙ ) = 8.6 ± 0.4. Thus, hot gas responsible for the 1930 Å continuum emission is likely orbiting a 4.0 × 10 8 M ⊙ black hole at an r 1/2 of only a few tens of Schwarzschild radii.
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- PAR ID:
- 10272180
- Date Published:
- Journal Name:
- Astronomy & Astrophysics
- Volume:
- 646
- ISSN:
- 0004-6361
- Page Range / eLocation ID:
- A165
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1051/0004-6361/202038770
