J/A+A/688/A157 The awakening of SDSS J133519.91+072807.4 (Sanchez-Saez+, 2024)
SDSS1335+0728: The awakening of a ∼106 M☉ black hole.
Sanchez-Saez P., Hernandez-Garcia L., Bernal S., Bayo A.,
Calistro Rivera G., Bauer F.E., Ricci C., Merloni A., Graham M.J.,
Cartier R., Arevalo P., Assef R.J., Concas A., Homan D., Krumpe M.,
Lira P., Malyali A., Martinez-Aldama M.L., Munoz Arancibia A.M., Rau A.,
Bruni G., Forster F., Pavez-Herrera M., Tubin-Arenas D., Brightman M.
<Astron. Astrophys. 688, A157 (2024)>
=2024A&A...688A.157S 2024A&A...688A.157S (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies ; Spectra, optical ; Spectra, infrared
Keywords: accretion, accretion discs - galaxies: active -
galaxies: individual: SDSS J133519.91+072807.4
Abstract:
The early-type galaxy SDSS J133519.91+072807.4 (hereafter
SDSS1335+0728), which had exhibited no prior optical variations during
the preceding two decades, began showing significant nuclear
variability in the Zwicky Transient Facility (ZTF) alert stream from
December 2019 (as ZTF19acnskyy). This variability behaviour, coupled
with the host-galaxy properties, suggests that SDSS1335+0728 hosts a
∼106M☉ black hole (BH) that is currently in the process of
'turning on'.
We present a multi-wavelength photometric analysis and spectroscopic
follow-up performed with the aim of better understanding the origin of
the nuclear variations detected in SDSS1335+0728.
We used archival photometry (from WISE, 2MASS, SDSS, GALEX, eROSITA)
and spectroscopic data (from SDSS and LAMOST) to study the state of
SDSS1335+0728 prior to December 2019, and new observations from Swift,
SOAR/Goodman, VLT/X-shooter, and Keck/LRIS taken after its turn-on to
characterise its current state. We analysed the variability of
SDSS1335+0728 in the X-ray/UV/optical/mid-infrared range, modelled its
spectral energy distribution prior to and after December 2019, and
studied the evolution of its UV/optical spectra.
From our multi-wavelength photometric analysis, we find that: (a)
{since 2021, the UV flux (from Swift/UVOT observations) is four times
brighter than the flux reported by GALEX in 2004; (b) since June
2022, the mid-infrared flux has risen more than two times, and the
W1-W2 WISE colour has become redder; and (c) since February 2024, the
source has begun showing X-ray emission. From our spectroscopic
follow-up, we see that (i) the narrow emission line ratios are now
consistent with a more energetic ionising continuum; (ii) broad
emission lines are not detected; and (iii) the [OIII] line increased
its flux ∼3.6 years after the first ZTF alert, which implies a
relatively compact narrow-line-emitting region.
We conclude that the variations observed in SDSS1335+0728 could be
either explained by a ∼106M☉ AGN that is just turning on or by
an exotic tidal disruption event (TDE). If the former is true,
SDSS1335+0728 is one of the strongest cases of an AGN observed in the
process of activating. If the latter were found to be the case, it
would correspond to the longest and faintest TDE ever observed (or
another class of still unknown nuclear transient). Future observations
of SDSS1335+0728 are crucial to further understand its behaviour.
Description:
In this work, we study the source galaxy SDSS J133519.91+072807.4,
which started presenting an unusual variable behaviour in December
2019. Here we provide the optical spectra of SDSS J133519.91+072807.4,
obtained using SOAR/Goodman (1 arcsec slit) and Keck/LRIS
(0.7 and 1.5 arcsec slits).
Objects:
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RA (2000) DE Designation(s)
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13 35 19.91 +07 28 07.4 SDSS J133519.91+072807.4 = LEDA 3091738
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 244 4 List of fits files
fits/* . 4 Individual fits files
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Byte-by-byte Description of file: list.dat
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Bytes Format Units Label Explanations
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1- 2 I2 h RAh Right Ascension of center (J2000)
4- 5 I2 min RAm Right Ascension of center (J2000)
7- 11 F5.2 s RAs Right Ascension of center (J2000)
12 A1 --- DE- Declination sign of center (J2000)
13- 14 I2 deg DEd Declination of center (J2000)
16- 17 I2 arcmin DEm Declination of center (J2000)
19- 22 F4.1 arcsec DEs Declination of center (J2000)
24- 28 I5 --- Nx Number of pixels along X-axis
30- 34 I5 --- Ny Number of pixels along Y-axis
36- 37 I2 Kibyte size Size of FITS file
39- 91 A53 --- FileName Name of FITS file, in subdirectory fits
92-244 A153 --- Title Title of the FITS file
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Acknowledgements:
Paula Sanchez-Saez, paula.sanchezsaez(at)eso.org
(End) Patricia Vannier [CDS] 29-May-2024