J/ApJ/952/34 RadioAstron space VLBI imaging of the M87 jet. I. (Kim+, 2023)
RadioAstron space VLBI imaging of the jet in M87.
I. Detection of high brightness temperature at 22 GHz.
Kim J.-Y., Savolainen T., Voitsik P., Kravchenko E.V., Lisakov M.M.,
Kovalev Y.Y., Muller H., Lobanov A.P., Sokolovsky K.V., Bruni G.,
Edwards P.G., Reynolds C., Bach U., Gurvits L.I., Krichbaum T.P., Hada K.,
Giroletti M., Orienti M., Anderson J.M., Lee S.-S., Sohn B.W.,
Zensus J.A.
<Astrophys. J., 952, 34 (2023)>
=2023ApJ...952...34K 2023ApJ...952...34K
ADC_Keywords: Active gal. nuclei; Galaxies, radio; Interferometry; Radio lines
Keywords: Relativistic jets ; Active galactic nuclei ; Radio galaxies ;
Very long baseline interferometry
Abstract:
We present results from the first 22GHz space very long baseline
interferometric (VLBI) imaging observations of M87 by RadioAstron. As
a part of the Nearby AGN Key Science Program, the source was observed
in 2014 February at 22GHz with 21 ground stations, reaching projected
(u, v) spacings up to ∼11Gλ. The imaging experiment was
complemented by snapshot RadioAstron data of M87 obtained during
2013-2016 from the AGN Survey Key Science Program. Their longest
baselines extend up to ∼25Gλ. For all of these measurements,
fringes are detected only up to ∼2.8 Earth diameter or ∼3Gλ
baseline lengths, resulting in a new image with angular resolution of
∼150µas or ∼20 Schwarzschild radii spatial resolution. The new
image not only shows edge-brightened jet and counterjet structures
down to submilliarcsecond scales but also clearly resolves the VLBI
core region. While the overall size of the core is comparable to those
reported in the literature, the ground-space fringe detection and
slightly superresolved RadioAstron image suggest the presence of
substructures in the nucleus, whose minimum brightness temperature
exceeds TB,min∼1012K. It is challenging to explain the origin of
this record-high TB,min value for M87 by pure Doppler boosting
effect with a simple conical jet geometry and known jet speed.
Therefore, this can be evidence for more extreme Doppler boosting due
to a blazar-like small jet viewing angle or highly efficient particle
acceleration processes occurring already at the base of the outflow.
Description:
M87 was observed by the RadioAstron mission at 22.236GHz
(λ=1.3cm; K band) from 2014 Feb 4, 16:00 to 2014 Feb 5, 12:53
UT, as a part of the Nearby AGN Key Science Program (experiment code
raks03b; gs032; see Bruni+ 2020AdSpR..65..712B 2020AdSpR..65..712B). The ground array
consisted of in total 21 telescopes.
Objects:
----------------------------------------------------------
RA (ICRS) DE Designation(s)
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12 30 49.42 +12 23 28.0 M87 = NAME Virgo Galaxy
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table5.dat 70 191 Upper limits on the flux densities of M87 at 22GHz
for space baselines to RadioAstron, in the order
of increasing baseline length
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See also:
J/MNRAS/313/469 : Streaming motions of galaxy clusters. I. (Smith+, 2000)
J/AJ/130/2473 : Fine-scale structure at 15GHz (Kovalev+, 2005)
J/AJ/136/159 : 86GHz VLBI survey of compact radio sources (Lee+, 2008)
J/AJ/138/1874 : MOJAVE. VI. Kinematics of blazar jets (Lister+, 2009)
J/AJ/142/35 : The VLBA Galactic Plane Survey (VGaPS) (Petrov+, 2011)
J/A+A/545/A113 : MOJAVE IX. Core shift effects (Pushkarev+, 2012)
J/ApJ/846/98 : Jet kinematics of blazars at 43GHz (Jorstad+, 2017)
J/MNRAS/468/4992 : MOJAVE XIV. AGN jets & opening angles (Pushkarev+, 2017)
J/A+A/616/A188 : M87 jet VLBI images (Kim+, 2018)
J/ApJ/866/137 : Bright blazars var. brightness temp. (Liodakis+, 2018)
J/ApJS/234/12 : MOJAVE XV. 15GHz obs. of AGN jets 1996-2016 (Lister+, 2018)
J/A+A/622/A92 : Ultracompact extragal. radio sources at 86GHz (Nair+, 2019)
J/MNRAS/485/1822 : AGN core shift measurements (Plavin+, 2019)
J/ApJS/247/57 : Compact bright radio-loud AGNs. III. 43GHz (Cheng+, 2020)
J/A+A/640/A69 : 3C 279 Event Horizon Telescope imaging (Kim+, 2020)
J/ApJ/893/68 : RadioAstron. III. S5 0716+71 (Kravchenko+, 2020)
J/A+A/641/A40 : S50836+710 Ground and Space VLBI images (Vega Garcia+, 2020)
J/ApJ/923/67 : MOJAVE. XIX. Brightness temperatures of jets (Homan+, 2021)
J/ApJS/260/12 : Jet kinematics of blazars at 43GHz (Weaver+, 2022)
J/A+A/672/A130 : Blazar 3C 454.3 time variability (Chamani+, 2023)
Byte-by-byte Description of file: table5.dat
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Bytes Format Units Label Explanations
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1- 19 A19 "datime" Tobs starting time of the scans, ISO8601 format UTC
21- 28 A8 --- Code Experiment code for each observation (1)
30- 35 A6 --- Station Name of the ground station (2)
37- 40 I4 s Tsol [559/1200] Solution interval used in the
estimates of the S/N
42- 45 F4.2 --- SN-obs [4/6.3] observed signal-noise ratio
47- 50 F4.2 --- SN-det [6.1/7] detection-threshold signal-noise ratio
52- 57 F6.3 --- Baseline [0.26/25.3] Baseline length in 10+6*λ
59- 64 F6.1 deg PA [-177/179] baseline position angle, east of north
66- 70 F5.3 Jy Fup [0.07/2.9] Upper limit on flux density
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Note (1): Experiment code for each observation. "gs032" for the
imaging experiment and other codes to access the RadioAstron data
archive for the AGN survey observations using be
http://opendata.radioastron.ru/
Note (2): Name of the ground station as follows:
AT = ATCA (5x22m), 49m diameter, SEFD
(system equivalent flux density):101Jy;
BD = Badary, 32m, SEFD=1000Jy;
DSS63 = Deep Space Station 63 antenna (Robledo 70m; geodetic code RO);
EF = Effelsberg, 100m, SFED=160Jy;
FD = VLBA--Fort Davis, 25m, SEFD=730Jy;
GB = Green Bank, 100m, SEFD=23Jy;
HH = Hartebeesthoek, 26m, SEFD=4500Jy;
HN = VLBA--Hancock, 25m, SEFD=1087Jy;
KP = VLBA--Kitt Peak, 25m, SEFD=667Jy;
KZ = Kalyazin, 64m;
MP = Mopra, 22m, SEFD=1000Jy;
OV = VLBA--Owens Valley, 25m, SEFD=926Jy;
PT = VLBA--Pie Town, 25m, SEFD=642Jy;
SV = Svetloe, 32m, SEFD=1250Jy;
TR = Torun, 32m, SEFD=880Jy;
VLA-N8 = phased JVLA (Y27, N8 for the phase center location);
YS = Yebes, 40m, SEFD=1152Jy;
ZC = Zelenchukskaya, 32m, SEFD=877Jy.
Additional stations that participated in the AGN survey but not in
the imaging observation (Table 1) are DSS63 and VLA-N8.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 26-Aug-2025