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We present the first detection from the Spitzer Space Telescope of 4.5 micronvariability from Sgr A*, the emitting source associated with the Milky Way'scentral black hole. The >23 hour continuous light curve was obtained with theIRAC instrument in 2013 December. The result characterizes the variability ofSgr A* prior to the closest approach of the G2 object, a putative infalling gascloud that orbits close to Sgr A*. The high stellar density at the location ofSgr A* produces a background of ~250 mJy at 4.5 microns in each pixel with alarge pixel-to-pixel gradient, but the light curve for the highly variable SgrA* source was successfully measured by modeling and removing the variations dueto 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 thenoise level ~34% of the time. The light curve characteristics, including theflux density distribution and structure function, are consistent with thosepreviously derived at shorter infrared wavelengths. We see no evidence in thelight curve for activity attributable to the G2 interaction at the observingepoch, ~100 days before the expected G2 periapsis passage. The IRAC light curveis more than a factor of two longer than any previous infrared observation,improving constraints on the timescale of the break in the power spectraldistribution of Sgr A* flux densities. The data favor the longer of the twopreviously published values for the timescale.

Spitzer/IRAC Observations of the Variability of Sgr A* and the Object G2 at 4.5 microns