Spitzer observations of Sgr A* and cloud G2
Abstract
The supermassive black hole at the center of our Galaxy is a fluctuating source of electromagnetic radiation derived from its accretion flow. For the past decade, the black hole’s ingestion has been modest, but its accretion rate and luminosity are predicted to surge as the cloud G2 swings by and feeds Sgr A* with a helping of fresh gas. We have started a program to monitor Sgr A* with Spitzer/IRAC at a wavelength of 4.5 microns as the anticipated elevated accretion episode proceeds. Near-infrared wavelengths are where the black hole’s emission has been best characterized in the past, and IRAC observations will complement planned observations with other observatories at X-ray, radio, and submillimeter wavelengths. The variability of Sgr A* is a random red-noise process, but the limited duration of continuous ground-based observations (<6 hr) has prevented direct measurement of the correlation timescale. This timescale corresponds to a thermal or viscous timescale associated with the inner radius of the accretion disk, and knowing it is critical for the black hole accretion physics.The Spitzer observing plan is to monitor Sgr A* continuously at 4.5 microns for >23.5 hours at each of six epochs. Epochs include one in 2013 Dec, three more in 2014 Jun-Jul, and two more in 2014 Nov-Dec. These will enable us to follow the initial stages of what has been predicted to be an extended accretion episode. In the 2013 Dec epoch we detected emission from Sgr A* in excess of the noise level for approximately 40% of the period observed, with individual maxima having peak levels of 1-10 milliJanskys.
- Publication:
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American Astronomical Society Meeting Abstracts #224
- Pub Date:
- June 2014
- Bibcode:
- 2014AAS...22421303H