Testing the Radiatively Inefficient Accretion Flow Model for Sagittarius A* Using the Size Measurements

Graduate School, Chinese Academy of Sciences, Peping, Beijing, China
The Astrophysical Journal (Impact Factor: 5.99). 12/2008; 642(1):L45. DOI: 10.1086/504475
Source: arXiv


Recent radio observations by the Very Long Baseline Array at 7 and 3.5 mm produced the high-resolution images of the compact radio source located at the center of our Galaxy (Sgr A*) and detected its wavelength-dependent intrinsic sizes at the two wavelengths. This provides us with a good chance of testing previously proposed theoretical models for Sgr A*. In this Letter, we calculate the size based on the radiatively inefficient accretion flow (RIAF) model proposed by Yuan, Quataert, & Narayan. We find that after taking into account the scattering of the interstellar electrons, the predicted sizes are consistent with the observations. We further predict an image of Sgr A* at 1.3 mm that can be tested by future observations.

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    • "All such theoretical interpretations have observational support as it was recently reported that both X-ray flares and the outflows are originated from the vicinity of the black hole (Junor et al. 1999; Biretta et al. 2002; Falcke 1999). The typical size of the post-shock flow which possibly responsible for various diverse phenomenon is reasonably coherent with the observational results (Yuan et al. 2006). "
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    ABSTRACT: We examine the behaviour of accretion flow around a rotating black hole in presence of cooling. We obtain global flow solutions for various accretion parameters that govern the accreting flow. We show that standing isothermal shock wave may develop in such an advective accretion flow in presence of cooling. This shocked solution has observational consequences as it successfully provides the possible explanations of energy spectra as well as generation of outflows/jets of various galactic and extra-galactic black hole candidates. We study the properties of isothermal shock wave and find that it strongly depends on the cooling efficiency. We identify the region in the parameter space spanned by the specific energy and specific angular momentum of the flow for standing isothermal shock as a function of cooling efficiencies and find that parameter space gradually shrinks with the increase of cooling rates. Our results imply that accretion flow ceases to contain isothermal shocks when cooling is beyond its critical value.
    Astrophysics and Space Science 05/2009; 321(2):109-122. DOI:10.1007/s10509-009-0014-x · 2.26 Impact Factor
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    ABSTRACT: In May 2007 the compact radio source Sgr A* was observed in a global multi-frequency monitoring campaign, from radio to X-ray bands. Here we present and discuss first and preliminary results from polarization sensitive VLBA observations, which took place during May 14-25, 2007. Here, Sgr A* was observed in dual polarization on 10 consecutive days at 22, 43, and 86 GHz. We describe the VLBI experiments, our data analysis, monitoring program and show preliminary images obtained at the various frequencies. We discuss the data with special regard also to the short term variability.
    Journal of Physics Conference Series 09/2008; 131(1). DOI:10.1088/1742-6596/131/1/012059
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    ABSTRACT: We investigate the X-ray origin in FRIs using the multi-waveband high resolution data of eight FR I sources, which have very low Eddington ratios. We fit their multi-waveband spectrum using a coupled accretion-jet model. We find that X-ray emission in the source with the highest L_X (~1.8*10^-4 L_Edd) is from the advection-dominated accretion flow (ADAF). Four sources with moderate L_X(~several*10^-6 L_Edd) are complicated. The X-ray emission of one FR I is from the jet, and the other three is from the sum of the jet and ADAF. The X-ray emission in the three least luminous sources (L_X<1.0*10^-6L_Edd) is dominated by the jet. These results roughly support the predictions of Yuan and Cui(2005) where they predict that when the X-ray luminosity of the system is below a critical value, the X-radiation will not be dominated by the emission from the ADAF any longer, but by the jet. We also find that the accretion rates in four sources must be higher than the Bondi rates, which implies that other fuel supply (e.g., stellar winds) inside the Bondi radius should be important. Comment: 6 pages. To published in Journal of Physics, in proceedings of "The Universe under the Microscope - Astrophysics at High Angular Resolution" (Bad Honnef, Germany, April 2008), eds. R. Schoedel, A. Eckart, S. Pfalzner, and E. Ros
    Journal of Physics Conference Series 09/2008; DOI:10.1088/1742-6596/131/1/012060
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