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. =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 4.5{mu}m 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 3.6{mu}m flux of 13.9_-0.1_^+0.5^ days. The lags indicate that the dust emitting at 3.6 and 4.5{mu}m 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 4.5{mu}m reverberation radii fall above the K-band {tau}{propto}L^0.5^ size-luminosity relationship by factors <~2.8 and <~3.4, respectively, while the 4.5{mu}m reverberation radius is only 27% larger than the 3.6{mu}m 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: ------------------------------------------------------- RA (2000) DE Designation(s) ------------------------------------------------------- 17 38 09.31 +58 42 53.6 NGC 6418 = MCG+10-25-074 ------------------------------------------------------- File Summary: -------------------------------------------------------------------------------- FileName Lrecl Records Explanations -------------------------------------------------------------------------------- ReadMe 80 . This file ch1.dat 33 182 Spitzer 3.6{mu}m photometry ch2.dat 33 181 Spitzer 4.5{mu}m 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 -------------------------------------------------------------------------------- Byte-by-byte Description of file: *.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 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 -------------------------------------------------------------------------------- Acknowledgements: Billy Vazquez, bxv2548(at)rit.edu ================================================================================ (End) Billy Vazquez [RIT, Rochester, NY], Patricia Vannier [CDS] 19-Jun-2015