J/ApJ/820/90 4yr 1.3mm VLBI observations of SgrA* with EHT (Fish+, 2016)
Persistent asymmetric structure of Sagittarius A* on Event Horizon scales.
Fish V.L., Johnson M.D., Doeleman S.S., Broderick A.E., Psaltis D.,
Lu R.-S., Akiyama K., Alef W., Algaba J.C., Asada K., Beaudoin C.,
Bertarini A., Blackburn L., Blundell R., Bower G.C., Brinkerink C.,
Cappallo R., Chael A.A., Chamberlin R., Chan C.-K., Crew G.B., Dexter J.,
Dexter M., Dzib S.A., Falcke H., Freund R., Friberg P., Greer C.H.,
Gurwell M.A., Ho P.T.P., Honma M., Inoue M., Johannsen T., Kim J.,
Krichbaum T.P., Lamb J., Leon-Tavares J., Loeb A., Loinard L., MacMahon D.,
Marrone D.P., Moran J.M., Moscibrodzka M., Ortiz-Leon G.N., Oyama T.,
Ozel F., Plambeck R.L., Pradel N., Primiani R.A., Rogers A.E.E.,
Rosenfeld K., Rottmann H., Roy A.L., Ruszczyk C., Smythe D.L., Soohoo J.,
Spilker J., Stone J., Strittmatter P., Tilanus R.P.J., Titus M.,
Vertatschitsch L., Wagner J., Wardle J.F.C., Weintroub J., Woody D.,
Wright M., Yamaguchi P., Young A., Young K.H., Zensus J.A., Ziurys L.M.
<Astrophys. J., 820, 90 (2016)>
=2016ApJ...820...90F 2016ApJ...820...90F (SIMBAD/NED BibCode)
ADC_Keywords: Interferometry ; Millimetric/submm sources ; Milky Way
Keywords: Galaxy: center; submillimeter: general;
techniques: high angular resolution; techniques: interferometric
Abstract:
The Galactic Center black hole Sagittarius A* (Sgr A*) is a prime
observing target for the Event Horizon Telescope (EHT), which can
resolve the 1.3mm emission from this source on angular scales
comparable to that of the general relativistic shadow. Previous EHT
observations have used visibility amplitudes to infer the morphology
of the millimeter-wavelength emission. Potentially much richer source
information is contained in the phases. We report on 1.3mm phase
information on Sgr A* obtained with the EHT on a total of 13 observing
nights over four years. Closure phases, which are the sum of
visibility phases along a closed triangle of interferometer baselines,
are used because they are robust against phase corruptions introduced
by instrumentation and the rapidly variable atmosphere. The median
closure phase on a triangle including telescopes in California,
Hawaii, and Arizona is nonzero. This result conclusively demonstrates
that the millimeter emission is asymmetric on scales of a few
Schwarzschild radii and can be used to break 180° rotational
ambiguities inherent from amplitude data alone. The stability of the
sign of the closure phase over most observing nights indicates
persistent asymmetry in the image of Sgr A* that is not obscured by
refraction due to interstellar electrons along the line of sight.
Description:
The Event Horizon Telescope (EHT) obtained detections of Sgr A* on
closed triangles of baselines among stations in Arizona, California,
and Hawaii in 2009, 2011, 2012, and 2013. In all cases, two 480MHz
bands, centered at 229.089GHz and 229.601GHz (hereafter, low and high
bands, respectively), were observed.
One or more telescopes from each of three sites in Arizona,
California, and Hawaii participated in each set of observations. The
Arizona Radio Observatory (ARO) Submillimeter Telescope (SMT) on
Mt. Graham, Arizona, was used in all cases. Over the years of data
analyzed here, the configuration of VLBI recording at these sites
evolved as described in section 2.1.
Objects:
--------------------------------------------------
RA (ICRS) DE Designation(s)
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17 45 40.04 -29 00 28.2 Sgr A* = NAME Sgr A*
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 83 414 Detected closure phases
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See also:
J/ApJ/802/69 : VLA, ALMA and SMA monitoring of Sgr A* (Bower+, 2015)
J/ApJ/727/L36 : 1.3mm VLBI observations of Sagittarius A* (Fish+, 2011)
J/ApJ/707/L114 : The orbit of S2 star around Sgr A* (Gillessen+, 2009)
J/ApJ/697/1741 : Warped disks of YSOs in Galactic center (Bartko+, 2009)
J/AJ/127/3399 : Sgr A* variability at cm wavelengths (Herrnstein+, 2004)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 4 I4 yr Obs.Y [2009/2013] Year
6- 7 I2 d Obs.D [80/97] Day of Year
9- 15 F7.4 h Obs.H UT Time (hours)
17 A1 -- Band [HL] Observing Band ("H" or "L") (1)
19- 23 A5 -- Tri Triangle (2)
25- 29 F5.1 deg CPhase [-21.4/36.3] Closure Phase
31- 35 F5.2 -- S/N [3/52] Bispectral Signal-to-Noise Ratio
37- 43 F7.1 -- u12 [-2797/0] u_12, in units of Megaλ (3)
45- 51 F7.1 -- v12 [-1692/0.1] v_12, in units of Megaλ (3)
53- 59 F7.1 -- u23 [-2797/3403] u_23, in units of Megaλ (3)
61- 67 F7.1 -- v23 [-1645/1592] v_23, in units of Megaλ (3)
69- 75 F7.1 -- u31 [-3402/2797] u_31, in units of Megaλ (3)
77- 83 F7.1 -- v31 [-1502/1646] v_31, in units of Megaλ (3)
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Note (1): Low (229.089GHz) or High (229.601GHz) band
Note (2): Triangle Station codes, from Table 1 of this article as follows:
C = CARMA (single antenna), Left-circular polarization (LCP)
D = CARMA (single antenna), Left-circular polarization (LCP)
E = CARMA (single antenna), Right-circular polarization (RCP)
F = CARMA (phased array), Left-circular polarization (LCP)
G = CARMA (phased array), Right-circular polarization (RCP)
J = JCMT, Left-circular polarization (LCP) for 2009-2011 data;
RCP for 2012-2013
O = CSO, Left-circular polarization (LCP)
P = SMA (phased array), Left-circular polarization (LCP)
S = SMT, Left-circular polarization (LCP)
T = SMT, Right-circular polarization (RCP)
Note (3): In units of Mega-λ where λ is the observational
wavelength.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 01-Jun-2016