Understanding How a Black Hole Feeds: Sgr A*
Abstract
The Galactic center supermassive black hole is by far the closest example for studying the mechanisms of accretion onto such objects. Sgr A* is the fluctuating source of electromagnetic radiation derived from the accretion flow or perhaps a related jet. The variable radiation has been detected at radio, submillimeter (submm), near infrared (NIR), and X-ray wavelengths. Recent numerical general relativistic magneto-hydrodynamic (GRMHD) flare models across the electromagnetic spectrum indicate that variability may be connected to a tilted inner disk or to the black hole gravitationally lensing a bright spot in the accretion flow. Different models predict different amplitudes of flaring, and observations can therefore distinguish between strong-mean-magnetization accretion and weak magnetization. Disentangling the power source and emission mechanisms of the flares is a central challenge to our understanding of the Sgr A* accretion flow. Following our successful observations of the variability of Sgr A* with IRAC in 2013 and 2014, we propose simultaneous IRAC (4.5 micron) and Chandra (2-10 keV) observations to (1) probe the accretion physics of Sgr A* on event-horizon scales via multi-wavelength monitoring and (2) detect any effect of the object G2 on Sgr A*. Specifically, we propose two epochs of observation, each of 24 uninterrupted hours (86.4 ks), in 2016 July. Independent of this proposal we will also request NuSTAR (3-79 keV), SMA/ALMA/APEX (0.8 mm), and Keck/Magellan NIR (2.2 micron) observations during the two IRAC/Chandra epochs. Only such long-duration, continuous, multi-wavelength observations can achieve a comprehensive view of the dominant emission process(es) and quantify the physical properties near the event horizon. Theoretical models are increasing in physical sophistication, and our study will provide essential constraints for the next generation of models.
- Publication:
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Spitzer Proposal
- Pub Date:
- October 2015
- Bibcode:
- 2015sptz.prop12034F