J/A+A/602/A78 NGC1068 interferometric mid-IR measurements (Lopez-Gonzaga+, 2017)
NGC 1068: No change in the mid-infrared torus structure despite X-ray
variability.
Lopez-Gonzaga N., Asmus D., Bauer F.E., Tristram K.R.W., Burtscher L.,
Marinucci A., Matt G., Harrison F.A.
<Astron. Astrophys. 602, A78 (2017)>
=2017A&A...602A..78L 2017A&A...602A..78L (SIMBAD/NED BibCode)
ADC_Keywords: Active gal. nuclei ; Interferometry
Keywords: galaxies: nuclei - galaxies: Seyfert -
techniques: high angular resolution - radiation mechanisms: thermal -
galaxies: active
Abstract:
Recent NuSTAR observations revealed a somewhat unexpected increase in
the X-ray flux of the nucleus of NGC 1068. We expect the infrared
emission of the dusty torus to react on the intrinsic changes of the
accretion disk.
We aim to investigate the origin of the X-ray variation by
investigating the response of the mid-infrared environment.
We obtained single-aperture and interferometric mid-infrared
measurements and directly compared the measurements observed before
and immediately after the X-ray variations. The average correlated and
single-aperture fluxes as well as the differential phases were
directly compared to detect a possible change in the structure of the
nuclear emission on scales of ∼2pc.
The flux densities and differential phases of the observations before
and during the X-ray variation show no significant change over a
period of ten years. Possible minor variations in the infrared
emission are ∼6%.
Our results suggest that the mid-infrared environment of NGC 1068
has remained unchanged for a decade. The recent transient change in
the X-rays did not cause a significant variation in the infrared
emission. This independent study supports previous conclusions that
stated that the X-ray variation detected by NuSTAR observations is due
to X-ray emission piercing through a patchy section of the dusty
region.
Description:
Single-aperture mid-infrared images and spectra were taken with the
VLT spectrometer and imager for the mid-infrared (VISIR).
Interferometric measurements were obtained with the instrument MIDI at
the ESO's VLTI facility.
Observations with intermediate AT baselines were requested and
observed during the nights of January, 10, 20, and 23, 2015 using
Director's discretionary time (DDT). We additionally included
published and unpublished interferometric data from our previous
campaigns with the requirement that they were observed (nearly)
contemporaneously to the period of X-ray variation or observed a few
years before. These include observations taken on the nights of
September, 21, 26, and 30, 2014, and November, 17, 2014, using
Guaranteed Time Observations (GTO). For our observations we used the
low-resolution NaCl prism with spectral resolution
R=λ/Δλ∼30 to disperse the light of the beams. A
log of the observations and instrument setup can be found in Appendix
A. The published data were taken from Lopez-Gonzaga et al.
(2014A&A...565A..71L 2014A&A...565A..71L, Cat. J/A+A/565/A71).
Objects:
---------------------------------------------
RA (2000) DE Designation(s)
---------------------------------------------
02 42 40.77 -00 00 47.8 NGC 1068 = M 77
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablea1.dat 59 34 Log of observations: NGC 1068
NGC1068ats2016.oifits 2880 46 NGC 1068 reduced data
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See also:
J/A+A/565/A71 : NGC1068 MIDI/VLTI observations (Lopez-Gonzaga+, 2014)
Byte-by-byte Description of file: tablea1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 5 A5 --- Baseline Baseline
7- 16 A10 "YYYY-MM-DD" Obs.date Observation date
18- 25 A8 "h:m:s" Obs.time Time of fringe track observation
27 I1 --- St [0/1] Stacked with the following
observation (yes: 1, no: 0)
29- 30 I2 m BL Projected baseline length
32- 34 I3 deg PA Position angle
36- 38 F3.1 --- AirMass Airmass of fringe track
40 I1 --- OK? [0/1] Goodness of observation
(good: 1, bad: 0)
42- 46 I5 --- Gframes ?=- Number of good frames
48- 55 A8 "h:m:s" Caltime ?=- Time of the calibrator fringe track
observation
57- 59 F3.1 --- Dam ?=- Difference in airmass with calibrator,
Δam
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Acknowledgements:
Noel Lopez-Gonzaga,, nlopez.gonzaga(at)gmail.com
(End) Patricia Vannier [CDS] 22-Jun-2017