J/ApJ/793/120 Spitzer/IRAC Sgr A* light curve data (Hora+, 2014)
Spitzer/IRAC observations of the variability of Sgr A* and the object G2
at 4.5 µm.
Hora J.L., Witzel G., Ashby M.L.N., Becklin E.E., Carey S., Fazio G.G.,
Ghez A., Ingalls J., Meyer L., Morris M.R., Smith H.A., Willner S.P.
<Astrophys. J., 793, 120 (2014)>
=2014ApJ...793..120H 2014ApJ...793..120H (SIMBAD/NED BibCode)
ADC_Keywords: Milky Way ; Photometry, infrared ; Accretion
Keywords: accretion, accretion disks - black hole physics - Galaxy: center -
techniques: photometric
Abstract:
We present the first detection from the Spitzer Space Telescope of
4.5 µm variability from Sgr A*, the emitting source associated with
the Milky Way's central black hole. The >23 hr continuous light curve
was obtained with the Infrared Array Camera (IRAC) instrument in 2013
December. The result characterizes the variability of Sgr A* prior to
the closest approach of the tidally deformed G2 object, a putative
infalling gas cloud that orbits close to Sgr A*. The high stellar
density at the location of Sgr A* produces a background of ∼250 mJy at
4.5 µm in each pixel with a large pixel-to-pixel gradient, but the
light curve for the highly variable Sgr A* source was successfully
measured by modeling and removing the variations due to pointing
wobble. The observed flux densities range from the noise level of
∼0.7 mJy rms in a 6.4 s measurement to ≳10 mJy. Emission was seen
above the noise level ∼34% of the time. The light-curve
characteristics, including the flux density distribution and structure
function, are consistent with those previously derived at shorter
infrared wavelengths. We see no evidence in the light curve for
activity attributable to the G2 interaction at the observing epoch,
∼100 days before the expected G2 periapsis passage. The IRAC light
curve is more than a factor of two longer than any previous infrared
observation, improving constraints on the timescale of the break in
the power spectral distribution of Sgr A* flux densities. The data
favor the longer of the two previously published values for the
timescale.
Description:
All observations in this Spitzer Space Telescope program (ID #10060)
used IRAC in subarray mode, which obtains 64 consecutive images
(a "frame set") of a 32x32 pixel region (1.21''/pixel) near the corner
of the 256x256 pixel array. The observations were conducted as three
custom "Instrument Engineering Requests" (IERs) because the standard
IRAC Astronomical Observation Template does not allow the observation
sequence we designed for this program. We used the "PCRS Peakup" mode
to position Sgr A* as close as possible to the center of the pixel
(16,16).
Objects:
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RA (ICRS) DE Designation(s)
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17 45 40.04 -29 00 28.2 Sgr A* = NAME Sagittarius A
17 45 40.04 -29 00 28.1 Object G2 = NAME G2 Dust Cloud
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 31 10002 Sgr A* Light Curve Data
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See also:
J/AJ/127/3399 : Sgr A* variability at cm wavelengths (Herrnstein+, 2004)
J/ApJ/809/10 : Compact radio sources within 30" of Sgr A*
(Yusef-Zadeh+, 2015)
J/A+A/589/A116 : Multiwavelength study of Sgr A* (Mossoux+, 2016)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 13 F13.7 d MJD Modified Julian Date of the observation (1)
15- 22 F8.5 Jy SgrA* Sgr A* Flux Density at IRAC 4.5um (2)
24- 31 F8.5 Jy Ref Reference pixel (18,19) Flux Density (2)
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Note (1): Solar system barycenter. The date specified is at the midpoint of
the 6.4s BCD coadd.
Note (2): The observation design and data reduction methods are described in
Section 2 and Appendix A of the paper.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Tiphaine Pouvreau [CDS] 20-Apr-2017