J/ApJ/859/60 Sgr A* 1.3mm VLBI observations with the EHT in 2013 (Lu+, 2018)
Detection of intrinsic source structure at ∼3 Schwarzschild radii with
millimeter-VLBI observations of Sagittarius A*.
Lu R.-S., Krichbaum T.P., Roy A.L., Fish V.L., Doeleman S.S., Johnson M.D.,
Akiyama K., Psaltis D., Alef W., Asada K., Beaudoin C., Bertarini A.,
Blackburn L., Blundell R., Bower G.C., Brinkerink C., Broderick A.E.,
Cappallo R., Crew G.B., Dexter J., Dexter M., Falcke H., Freund R.,
Friberg P., Greer C.H., Gurwell M.A., Ho P.T.P., Honma M., Inoue M., Kim J.,
Lamb J., Lindqvist M., Macmahon D., Marrone D.P., Marti-Vidal I.,
Menten K.M., Moran J.M., Nagar N.M., Plambeck R.L., Primiani R.A.,
Rogers A.E.E., Ros E., Rottmann H., SooHoo J., Spilker J., Stone J.,
Strittmatter P., Tilanus R.P.J., Titus M., Vertatschitsch L., Wagner J.,
Weintroub J., Wright M., Young K.H., Zensus J.A., Ziurys L.M.
<Astrophys. J., 859, 60 (2018)>
=2018ApJ...859...60L 2018ApJ...859...60L
ADC_Keywords: Galactic center; Millimetric/submm sources; Interferometry
Keywords: Galaxy: center ; submillimeter: general ;
techniques: high angular resolution ; techniques: interferometric
Abstract:
We report results from very long baseline interferometric (VLBI)
observations of the supermassive black hole in the Galactic center,
Sgr A*, at 1.3mm (230GHz). The observations were performed in 2013
March using six VLBI stations in Hawaii, California, Arizona, and
Chile. Compared to earlier observations, the addition of the APEX
telescope in Chile almost doubles the longest baseline length in the
array, provides additional uv coverage in the N-S direction, and leads
to a spatial resolution of ∼30 µas (∼3 Schwarzschild radii) for Sgr
A*. The source is detected even at the longest baselines with
visibility amplitudes of ∼4%-13% of the total flux density. We argue
that such flux densities cannot result from interstellar refractive
scattering alone, but indicate the presence of compact intrinsic
source structure on scales of ∼3 Schwarzschild radii. The measured
nonzero closure phases rule out point-symmetric emission. We discuss
our results in the context of simple geometric models that capture the
basic characteristics and brightness distributions of disk- and
jet-dominated models and show that both can reproduce the observed
data. Common to these models are the brightness asymmetry, the
orientation, and characteristic sizes, which are comparable to the
expected size of the black hole shadow. Future 1.3mm VLBI observations
with an expanded array and better sensitivity will allow more detailed
imaging of the horizon-scale structure and bear the potential for a
deep insight into the physical processes at the black hole boundary.
Description:
The Event Horizon Telescope (EHT) observations of Sgr A* at 230GHz
(1.3mm) were performed on March 21, 22, 23, 26, and 27 (days 80, 81,
82, 85, and 86, respectively) in 2013 with telescopes located at four
geographical sites: the Arizona Radio Observatory Submillimeter
Telescope (SMT) on Mount Graham in Arizona, USA; the phased Combined
Array for Research in Millimeter-wave Astronomy (CARMA) array and one
single CARMA comparison antenna in California, USA; The James Clerk
Maxwell Telescope (JCMT) and the phased Submillimeter Array (SMA) on
Maunakea in Hawaii, USA; and the APEX telescope in Chile.
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
--------------------------------------------------------------------------------
ReadMe 80 . This file
table2.dat 46 865 Gain-corrected visibility amplitudes of Sgr A*
table3.dat 26 262 Closure phases of Sgr A*
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See also:
J/AJ/128/1646 : The Galactic Center region at 330MHz (Nord+, 2004)
J/ApJ/727/L36 : 1.3mm VLBI observations of Sagittarius A* (Fish+, 2011)
J/other/Sci/338.355 : 1.3mm VLBI detections of M87 (Doeleman+, 2012)
J/ApJ/772/13 : VLBI observations of 3C 279 at 230GHz (Lu+, 2013)
J/ApJ/807/150 : 230GHz VLBI observations of M87 (Akiyama+, 2015)
J/ApJ/830/17 : Galactic Center secondary IR standards (Boehle+, 2016)
J/ApJ/820/90 : 4yr 1.3mm VLBI obs. of SgrA* with EHT (Fish+, 2016)
J/A+A/618/A35 : ALMA images of the CND and SgrA* (Goicoechea+, 2018)
J/A+A/621/A119 : SgrA* and NRAS530 86GHz images (Brinkerink+, 2019)
Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 I3 d Day [80/86] Day of the observation (G1)
5- 6 I2 h Obs.h UT Hour of the observation
8- 9 I2 min Obs.m UT Minute of the observation
11- 12 A2 --- Base Baseline (G2)
14- 22 F9.3 --- u [-5103/3384] u in units of Megaλ (1)
24- 32 F9.3 --- v [-1685/5395] v in units of Megaλ (1)
34- 38 F5.3 Jy Flux [0.1/3.5] Flux density
40- 44 F5.3 Jy e_Flux [0.01/0.7] Uncertainty in Flux
46- 46 A1 --- Band Band code; H=High & L=Low
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Note (1): Not corrected for blurring (see Section 3.1).
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Byte-by-byte Description of file: table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 I3 d Day [80/86] Day of the observation (G1)
5- 6 I2 h Obs.h UT Hour of the observation
8- 9 I2 min Obs.m UT Minute of the observation
11- 13 A3 --- Tri Triangle (G2)
15- 19 F5.1 deg CPhase [-20.4/56.9] Closure phase
21- 24 F4.1 deg e_CPhase [1.2/37.2] Uncertainty in CPhase
26- 26 A1 --- Band Band code; H=High & L=Low
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Global notes:
Note (G1): March 21, 22, 23, 26, and 27 = days 80, 81, 82, 85, and 86,
respectively (in 2013)
Note (G2): Stations, as indicated by one letter codes per polarization
(Table 1) as follows:
-----------------------------------------------------------------------------
Telescope ID Polarization Effective Note
aperture
(m)
-----------------------------------------------------------------------------
CARMA (single) D/E LCP/RCP 10.4 single dish (low band only)
CARMA (phased) F/G LCP/RCP 25.5/24.1 5x10.4m+3x6.1m (day 80);
4x10.4m+4x6.1m (days 81-86)
JCMT J RCP 15.0 JCMT standalone
SMA (phased) P/Q LCP/RCP 15.9 SMA (7x6.0m); Q for 30s scans
APEX A LCP 12.0 APEX standalone
SMT S/T LCP/RCP 10.0 SMT standalone
-----------------------------------------------------------------------------
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 28-May-2019