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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 (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: ---------------------------------------------------------- RA (ICRS) DE Designation(s) ---------------------------------------------------------- 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 ---------------------------------------------------------- File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table1.dat 31 10002 Sgr A* Light Curve Data
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
Bytes Format Units Label Explanations
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)
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.
History: From electronic version of the journal
(End) Prepared by [AAS], Tiphaine Pouvreau [CDS] 20-Apr-2017
The document above follows the rules of the Standard Description for Astronomical Catalogues.From this documentation it is possible to generate f77 program to load files into arrays or line by line

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