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Published October 1, 2014 | Submitted + Published
Journal Article Open

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

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.

Additional Information

© 2014 American Astronomical Society. Received 2014 May 30; accepted 2014 July 29; published 2014 September 15. This work is based on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. Support for this work was provided by NASA through an award issued by JPL/Caltech. A.G. acknowledges support from NSF grant AST 09-09218. G.W. acknowledges the European Union funded COST Action MP0905: Black Holes in a violent Universe and PECS project No. 98040. We thank the staff of the Spitzer Science Center for their help in planning and executing these demanding observations. We thank Keith Matthews and Arno Witzel for fruitful discussions. Facility: Spitzer/IRAC

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Published - 0004-637X_793_2_120.pdf

Submitted - 1408.1951v1.pdf

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Created:
August 22, 2023
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October 17, 2023