J/ApJ/951/93 Submillimeter light curves of 7 low-luminosity AGNs (Chen+, 2023)
Testing the linear relationship between black hole mass and variability
timescale in low-luminosity AGNs at submillimeter wavelengths.
Chen B.-Y., Bower G.C., Dexter J., Markoff S., Ridenour A., Gurwell M.A.,
Rao R., Wallstrom S.H.J.
<Astrophys. J., 951, 93 (2023)>
=2023ApJ...951...93C 2023ApJ...951...93C
ADC_Keywords: Photometry, millimetric/submm; Active gal. nuclei
Keywords: Low-luminosity active galactic nuclei ; Radio cores ;
Radio active galactic nuclei ; Supermassive black holes ;
Time series analysis
Abstract:
The variability of submillimeter emission provides a useful tool to
probe the accretion physics in low-luminosity active galactic nuclei.
We accumulate four years of observations using the Submillimeter Array
for Centaurus A, NGC 4374, NGC 4278, and NGC 5077, and one year of
observations for NGC 4552 and NGC 4579. All sources are variable. We
measure the characteristic timescale at which the variability is
saturated by modeling these sources' light curves as a damped random
walk. We detect a timescale for all the sources except NGC 4552. The
detected timescales are comparable to the orbital timescale at the
event horizon scale for most sources. Combined with previous studies,
we show a correlation between the timescale and the black hole mass
over 3 orders of magnitude. This discovery suggests the submillimeter
emission is optically thin with the emission originating from the
event horizon. The mass scaling relationship further suggests that a
group of radio sources with a broadband spectrum that peaks at
submillimeter wavelengths have similar inner accretion physics.
Sources that follow this relationship may be good targets for high-
resolution imaging with the Event Horizon Telescope.
Description:
We designed a monitoring observation toward six nearby low-luminosity
active galactic nuclei (LLAGNs) on a small patch of sky (RA∼1hr) in a
weekly-to-daily observation frequency. Six LLAGNs, Centaurus A,
NGC4374, NGC 4552, NGC 4579, NGC 4278, and NGC 5077, were selected.
Six targets were monitored using the Submillimeter Array (SMA) from
2015 June to 2019 January. We adopted the "piggybacked" observation on
the full-track schedule to collect the light curve; therefore,
observational frequency varied around 230GHz. Note that the angular
resolution varies from ∼1" to ∼10", which is related to the array
configuration schedule.
In addition to the monitoring observation, we compiled data from the
SMA calibrator database and ALMA archive for M87, Cen A, NGC 4552, and
NGC 4579. See Section 2.2.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 67 7 Information of full light curve
table2.dat 53 394 Table of unpublished SMA (the Submillimeter Array)
data
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See also:
J/ApJ/698/895 : Variations in QSOs optical flux (Kelly+, 2009)
J/ApJS/187/135 : SEDs of weak AGNs associated with LINERs (Eracleous+, 2010)
J/ApJ/869/106 : SMARTS & Euler R-band obs. of WFI J2033-4723 (Morgan+, 2018)
J/other/Sci/373.789 : optical variability of AGNs (Burke+, 2021)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 7 A7 --- Name Target name
9- 15 F7.1 d MJDSt [52379/57174] Start date, MJD
17- 23 F7.1 d MJDEnd [58484/59789] End date, MJD
25- 52 A28 --- Consist Consist (#)
54- 58 F5.3 Jy Flux [0.02/7.8] Mean flux
60- 64 F5.3 Jy e_Flux [0.005/1.8] Flux uncertainty
66- 67 I2 % Var [15/84] Mean fraction of variation (1)
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Note (1): The mean fraction of variation is defined as
Var=(σ2-δ2)0.5/,
where σ2 is the variance of the light curve,
δ2=1/NΣiNδi2 is the mean square of
flux uncertainties, and is the mean of flux.
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 7 A7 --- Name Source name
9- 18 A10 "Y/M/D" Epoch Observation time
20- 24 F5.1 GHz Freq [202/264] Observation frequency
26- 30 F5.3 Jy Flux [0.012/9.6] Flux Density
32- 36 F5.3 Jy e_Flux [0.001/0.4] The 1σ uncertainty in Flux
38- 42 F5.2 arcsec Maj [0.98/14] Size of beam major axis
44- 47 F4.2 arcsec Min [0.4/6.2] Size of beam minor axis
49- 53 F5.1 deg PA [-90/90] Position angle
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 21-Aug-2025