J/ApJ/801/127 3.6um, 4.5um, B and V light curves of NGC 6418 (Vazquez+, 2015)
Spitzer Space Telescope measurements of dust reverberation lags in the
Seyfert 1 galaxy NGC 6418.
Vazquez B., Galianni P., Richmond M., Robinson A., Axon D.J., Horne K.,
Almeyda T., Fausnaugh M., Peterson B.M., Bottorff M., Gallimore J.,
Eltizur M., Netzer H., Storchi-Bergmann T., Marconi A., Capetti A.,
Batcheldor D., Buchanan C., Stirpe G., Kishimoto M., Packham C., Perez E.,
Tadhunter C., Upton J., Estrada-Carpenter V.
<Astrophys. J., 801, 127 (2015)>
=2015ApJ...801..127V 2015ApJ...801..127V
ADC_Keywords: Galaxies, Seyfert ; Photometry, UBV ; Photometry, infrared
Keywords: galaxies: active - galaxies: individual: NGC 6418 - galaxies: nuclei -
galaxies: Seyfert
Abstract:
We present results from a 15 month campaign of high-cadence (∼3 days)
mid-infrared Spitzer and optical (B and V) monitoring of the Seyfert 1
galaxy NGC 6418, with the objective of determining the characteristic
size of the dusty torus in this active galactic nucleus (AGN). We find
that the 3.6 and 4.5µm flux variations lag behind those of the
optical continuum by 37.2-2.2+2.4-days and 47.1-3.1+3.1-days,
respectively. We report a cross-correlation time lag between the 4.5
and 3.6µm flux of 13.9-0.1+0.5 days. The lags indicate that the
dust emitting at 3.6 and 4.5µm is located at a distance
∼1-light-month (∼0.03pc) from the source of the AGN UV-optical
continuum. The reverberation radii are consistent with the inferred
lower limit to the sublimation radius for pure graphite grains at
1800K, but smaller by a factor of ∼2 than the corresponding lower
limit for silicate grains; this is similar to what has been found for
near-infrared (K-band) lags in other AGNs. The 3.6 and 4.5µm
reverberation radii fall above the K-band τ∝L0.5
size-luminosity relationship by factors ≲2.8 and ≲3.4, respectively,
while the 4.5µm reverberation radius is only 27% larger than the
3.6µm radius. This is broadly consistent with clumpy torus models,
in which individual optically thick clouds emit strongly over a broad
wavelength range.
Description:
Photometric measurements of NGC 6418 with the Spitzer Space Telescope
3.6 and 4.5 micron bands, ground-based B/V measurements with the
Fountainwood Observatory, Liverpool Telescope and Faulkes Telescope
North. The observations span the time range of 08-01-2011 to
01-04-2013.
Objects:
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RA (2000) DE Designation(s)
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17 38 09.31 +58 42 53.6 NGC 6418 = MCG+10-25-074
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
ch1.dat 33 182 Spitzer 3.6µm photometry
ch2.dat 33 181 Spitzer 4.5µm photometry
lt.dat 33 55 Liverpool Telescope Bessel B photometry
ftn.dat 33 57 Faulkes Telescope North Bessel B photometry
su_b.dat 33 21 Fountainwood Observatory Cousins B photometry
su_v.dat 33 21 Fountainwood Observatory Cousins V photometry
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Byte-by-byte Description of file: *.dat
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Bytes Format Units Label Explanations
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1- 11 F11.5 d MJD Modified Julian Date
13- 21 F9.7 mJy S Flux density
24- 33 F10.8 mJy e_S rms uncertainty on S
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Acknowledgements:
Billy Vazquez, bxv2548(at)rit.edu
(End) Billy Vazquez [RIT, Rochester, NY], Patricia Vannier [CDS] 19-Jun-2015