J/ApJ/953/32 AT 2021loi photometry & sp. follow-up (Makrygianni+, 2023)
AT 2021loi: a Bowen fluorescence flare with a rebrightening episode occurring in
a previously known AGN.
Makrygianni L., Trakhtenbrot B., Arcavi I., Ricci C., Lam M.C., Horesh A.,
Sfaradi I., Bostroem K.A., Hosseinzadeh G., Howell D.A., Pellegrino C.,
Fender R., Green D.A., Williams D.R.A., Bright J.
<Astrophys. J., 953, 32 (2023)>
=2023ApJ...953...32M 2023ApJ...953...32M
ADC_Keywords: Transient; Photometry, ugriz; Spectra, optical
Keywords: Supermassive black holes ; Active galactic nuclei ; Transient sources
Abstract:
The optical-ultraviolet transient AT 2021loi is located at the center
of its host galaxy. Its spectral features identify it as a member of
the Bowen fluorescence flare (BFF) class. The first member of this
class was considered to be related to a tidal disruption event, but
enhanced accretion onto an already active supermassive black hole was
suggested as an alternative explanation. Having occurred in a
previously known unobscured active galactic nucleus, AT 2021loi
strengthens the latter interpretation. Its light curve is similar to
those of previous BFFs, showing a rebrightening approximately 1yr
after the main peak (which was not explicitly identified but might be
the case in all previous BFFs). An emission feature around 4680Å,
seen in the preflare spectrum, strengthens by a factor of ∼2 around
the optical peak of the flare and is clearly seen as a double-peaked
feature then, suggesting a blend of NIIIλ4640 with
HeIIλ4686 as its origin. The appearance of OIIIλ3133 and
possible NIIIλλ4097,4103 (blended with Hδ) during
the flare further support a Bowen fluorescence classification. Here we
present ZTF, ATLAS, Keck, Las Cumbres Observatory, NEOWISE-R, Swift
AMI, and Very Large Array observations of AT 2021loi, making it one of
the best-observed BFFs to date. It thus provides some clarity on the
nature of BFFs but also further demonstrates the diversity of nuclear
transients.
Description:
We retrieved point-spread function (PSF)-fit photometry of
reference-subtracted images from the ZTF forced photometry service
from MJD=58194 to MJD=59975 and the Asteroid Terrestrial-impact Last
Alert System (ATLAS) forced photometry service from MJD=57232 to
MJD=59975 at the position of the transient AT 2021loi.
We also obtained optical photometry in the gri bands starting on
2021-Jul-01 with the Las Cumbres Observatory network of 1m telescopes.
The location of AT 2021loi was repeatedly observed in the mid-infrared
(MIR) regime by the Wide-Field Infrared Survey Explorer (WISE) and its
extensions, NEOWISE and the NEOWISE reactivation mission survey
(NEOWISE-R; Mainzer+ 2014, J/ApJ/792/30). The measurements were
conducted in both the W1 and W2 bands (3.4 and 4.6um, respectively).
We initiated near-UV (NUV) follow-up observations (PI: L. Makrygianni)
with the Neil Gehrels Swift Observatory Optical/UV Telescope (UVOT).
We obtained 23 Swift epochs from 2021 June 21 to 2022 October 11 in
all six UVOT filters (uvw2, uvm2, uvw1, U, B, and V).
We also used the archival NUV flux measurement from GALEX observations
taken on 2006 November 9.
The X-ray observations with the X-Ray Telescope (XRT) on Swift were
obtained simultaneously with the UVOT observations.
We also initiated radio measurements with the Arcminute Microkelvin
Imager-Large Array (AMI-LA) and the Karl G. Jansky Very Large Array
(VLA). The AMI-LA is a radio interferometer comprised of eight 12.8m
diameter antennas producing 28 baselines that extend from 18m up to
110m in length and operate with a 5GHz bandwidth divided into eight
channels around a central frequency of 15.5GHz.
See Section 3.1.2.
We retrieved an archival spectrum of WISEA J010039.62+394230.3, the
host galaxy of AT 2021loi, from the fifth data release of the LAMOST
survey (LAMOST/DR5) obtained on 2013 December 22. The LAMOST spectrum
covers the range 3500-9000Å with a resolution of R=1800.
The classification spectrum of AT 2021loi was obtained with the LRIS
on Keck I, which covers the wavelength range between 3400 and 10300Å
with a resolution of R=600-1000, on 2021 June 7.
We initiated a spectroscopic monitoring campaign for AT 2021loi using
the FLOYDS spectrograph mounted on the robotic 2m telescope at
Haleakala Hawaii (which is also part of the Las Cumbres Observatory
network). During the 16 months of spectroscopic monitoring, we
obtained 20 spectra. FLOYDS covers the 3500-10000Å range in a
single exposure by capturing two spectral orders simultaneously,
yielding a spectral resolution of R∼400. The exposure time of the
spectra varies between 1500 and 1800s, and we have used a slit width
of 2".
Objects:
----------------------------------------------------------
RA (ICRS) DE Designation(s)
----------------------------------------------------------
01 00 39.61 +39 42 30.3 AT 2021loi = ZTF20aanxcpf
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 36 679 Photometry of AT 2021loi
table4.dat 81 22 Optical spectroscopy of AT 2021loi
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See also:
II/328 : AllWISE Data Release (Cutri+ 2013)
VIII/65 : 1.4GHz NRAO VLA Sky Survey (NVSS) (Condon+ 1998)
J/ApJ/680/169 : SDSS DR5 virial black hole masses (Shen+, 2008)
J/ApJS/194/45 : QSO properties from SDSS-DR7 (Shen+, 2011)
J/ApJ/753/106 : QSO variability with SDSS and POSS imaging (MacLeod+, 2012)
J/MNRAS/429/3330 : AMI Galactic Plane Survey at 16GHz. I. (Perrott+, 2013)
J/ApJ/779/109 : Long-term monitoring of NGC 5548 (Peterson+, 2013)
J/ApJ/793/38 : Palomar Transient Factory photometric obs. (Arcavi+, 2014)
J/ApJ/788/159 : 17 Seyfert 1 galaxies light curves (Koshida+, 2014)
J/ApJ/792/30 : NEOWISE magnitudes for near-Earth objects (Mainzer+, 2014)
J/ApJ/805/122 : X-ray properties of PHL1811 analogs and WLQs (Luo+, 2015)
J/A+A/588/A103 : 2nd ROSAT all-sky survey (2RXS) source cat. (Boller+, 2016)
J/ApJ/819/154 : SDSS-DR7 QSOs with X-ray and UV luminosities (Lusso+, 2016)
J/MNRAS/459/3939 : Type II supernova light curves (Valenti+, 2016)
J/ApJ/844/46 : Phot. of the transient event iPTF16fnl (Blagorodnova+, 2017)
J/ApJS/233/17 : Swift/BAT AGN spectroscopic survey. V. X-ray (Ricci+, 2017)
J/ApJS/234/23 : The WISE AGN candidates catalogs (Assef+, 2018)
J/ApJ/854/160 : SDSS & DES long-term extreme var. QSOs (Rumbaugh+, 2018)
J/ApJ/874/8 : Follow-up sp. of SDSS changing-look QSOs (Macleod+, 2019)
J/ApJ/883/94 : Optical & UV follow-up of 1ES 1927+654 (Trakhtenbrot+, 2019)
J/ApJ/872/198 : UV-Opt LC of flare AT2018zr (van Velzen+, 2019)
J/MNRAS/491/4925 : Changing-state quasars with CRTS (Graham+, 2020)
J/ApJS/249/17 : SDSS QSO DR14 spectral properties (Rakshit+, 2020)
J/ApJS/261/5 : BASS. XXV. DR2 AGNs BH masses (Mejia-Restrepo+, 2022)
Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 F8.2 d MJD [59341.4/59969.2] Modified Julian Date (JD-2400000.5)
10- 13 A4 --- Filt Description of Filter
15- 19 F5.2 mag mag [16.3/19.52]? AB magnitude in Filt
21- 24 F4.2 mag e_mag [0/0.3]? Uncertainty in mag
26- 36 A11 --- Tel Source (Telescope) for mag (1)
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Note (1): Telescope as follows:
ZTF = The Zwicky Transient Facility (346 occurrences)
ATLAS = The Asteroid Terrestrial-impact Last Alert System
(144 occurrences)
Swift = The Swift UV/Optical Telescope (124 occurrences)
Las Cumbres = The Las Cumbres Observatory network of 1m telescopes
(65 occurrences)
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Byte-by-byte Description of file: table4.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 F8.2 d MJD [56648/59839.6] Modified Julian Date
(JD-2400000.5)
10- 29 A20 --- Tel Telescope/Instrument used
31- 34 I4 --- R [500/1800] Approximate resolving power of
the spectrum
36- 40 F5.2 10-18W/m2 FHb [10/79] Flux, Hβ, 10-15erg/s/cm2
42- 45 F4.2 10-18W/m2 e_FHb [0.5/9.2] Uncertainty in FHb
47- 51 F5.2 10-18W/m2 FBF [5.8/56] Flux, double peaked emission
feature, 10-15erg/s/cm2 (1)
53- 56 F4.2 10-18W/m2 e_FBF [0.2/3] Uncertainty in FBF (1)
58- 61 F4.2 10-18W/m2 FOIII [1/4.2] Flux, [O III] 5007 Angstroms,
10-15erg/s/cm2
63- 66 F4.2 10-18W/m2 e_FOIII [0.02/0.3] Uncertainty in FOIII
68- 72 F5.2 [10-7W] logL5100 [42.46/43.7] Log, Luminosity at 5100Å
continuum, erg/s
74- 77 I4 km/s FWHM [1917/3024] Full-width at half-max,
Hβ
79- 81 I3 km/s e_FWHM [31/528] Uncertainty in FWHM
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Note (1): The double peaked emission feature around ∼4680Å
originating from HeIIλ4686Å and NIIIλ4640Å
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 19-Sep-2025