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Title: Spitzer/IRAC observations of the variability of Sgr A* and the object G2 at 4.5 μm

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, ∼100more » 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.« less
Authors:
; ; ; ;  [1] ; ; ; ; ;  [2] ; ;  [3]
  1. Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)
  2. University of California, Los Angeles, CA 90095 (United States)
  3. Spitzer Science Center, California Institute of Technology, Pasadena, CA 91125 (United States)
Publication Date:
OSTI Identifier:
22370549
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 793; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ACCRETION DISKS; BLACK HOLES; DENSITY; DETECTION; DISTRIBUTION; EMISSION; FLUX DENSITY; GALAXIES; INTERACTIONS; MILKY WAY; NOISE; ORBITS; SIMULATION; SPACE; STRUCTURE FUNCTIONS; TELESCOPES; VISIBLE RADIATION