2011A&A...525A..76L


Query : 2011A&A...525A..76L

2011A&A...525A..76L - Astronomy and Astrophysics, volume 525A, 76-76 (2011/1-1)

Multiwavelength VLBI observations of Sagittarius A*.

LU R.-S., KRICHBAUM T.P., ECKART A., KOENIG S., KUNNERIATH D., WITZEL G., WITZEL A. and ZENSUS J.A.

Abstract (from CDS):

The compact radio, NIR, and X-ray source SagittariusA* (SgrA*), associated with the super massive black hole at the center of the Galaxy, has been studied with Very Long Baseline Interferometry (VLBI) observations performed on 10 consecutive days and at mm-wavelength. SgrA* varies in the radio through X-ray bands and occasionally shows rapid flux density outbursts. We monitor SgrA* with VLBI, aiming at the detection of related structural variations on the submilliarcsecond scale and variations of the flux density occurring after NIR-flares. We observed SgrA* with the Very Long Baseline Array (VLBA) at 3 frequencies (22, 43, 86GHz) on 10 consecutive days in May 2007 during a global multiwaveband campaign. From this we obtained accurate flux densities and sizes of the VLBI structure, which is partially resolved at mm-wavelength. The total VLBI flux density of SgrA* varies from day to day. The variability is correlated at the 3 observing frequencies with higher variability amplitudes appearing at the higher frequencies. For the modulation indices, we find 8.4% at 22GHz, 9.3% at 43GHz, and 15.5% at 86GHz. The radio spectrum is inverted between 22 and 86GHz, suggesting inhomogeneous synchrotron self-absorption with a turnover frequency at or above 86GHz. The radio spectral index correlates with the flux density, which is harder (more inverted spectrum) when the source is brighter. The average source size (FWHM) does not appear to be variable over the 10-day observing interval. However, we see a tendency for the sizes of the minor axis to increase with increasing total flux, whereas the major axis remains constant. Towards higher frequencies, the position angle of the elliptical Gaussian increases, indicative of intrinsic structure, which begins to dominate the scatter broadening. At cm-wavelength, the source size varies with wavelength as λ2.12±0.12, which is interpreted as the result of interstellar scatter broadening. After removal of this scatter broadening, the intrinsic source size varies as λ^1.4 ... 1.5^. The VLBI closure phases at 22, 43, and 86GHz are zero within a few degrees, indicating a symmetric or point-like source structure. In the context of an expanding plasmon model, we obtain an upper limit of the expansion velocity of about 0.1c from the non-variable VLBI structure. This agrees with the velocity range derived from the radiation transport modeling of the flares from the radio to NIR wavelengths.

Abstract Copyright:

Journal keyword(s): Galaxy: center - galaxies: individual: Sgr A* - scattering - techniques: interferometric - galaxies: nuclei

Simbad objects: 9

goto Full paper

goto View the references in ADS

Number of rows : 9
N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2024
#notes
1 3C 279 Bla 12 56 11.16657958 -05 47 21.5251510   18.01 17.75 15.87   ~ 3076 2
2 QSO B1730-130 QSO 17 33 02.70578907 -13 04 49.5482119   18 19.50 18.78 17.39 ~ 1149 1
3 NAME Sgr A Region reg 17 45 12 -28 48.3           ~ 939 0
4 NAME Galactic Center reg 17 45 39.60213 -29 00 22.0000           ~ 14643 0
5 NAME Sgr A* X 17 45 40.03599 -29 00 28.1699           ~ 4449 3
6 4C 09.57 BLL 17 51 32.81857326 +09 39 00.7284066   17.46 16.78 15.57   ~ 960 1
7 V* VX Sgr s*r 18 08 04.0442790744 -22 13 26.600899044 11.72 9.41 6.52 3.90 2.11 M8.5Ia 598 0
8 PSR B1849+00 Psr 18 52 27.42 +00 32 02.0           ~ 69 0
9 3C 446 BLL 22 25 47.25929101 -04 57 01.3907626   18.83 18.39 16.3   ~ 836 1

To bookmark this query, right click on this link: simbad:objects in 2011A&A...525A..76L and select 'bookmark this link' or equivalent in the popup menu