J/ApJ/853/68 Multi-epoch VLBA imaging of 20 Tev blazars (Piner+, 2018)
Multi-epoch VLBA imaging of 20 new TeV blazars: apparent jet speeds.
Piner B.G., Edwards P.G.
<Astrophys. J., 853, 68 (2018)>
=2018ApJ...853...68P 2018ApJ...853...68P
ADC_Keywords: BL Lac objects; Radio continuum; Redshifts; Proper motions
Keywords: BL Lacertae objects: general ; galaxies: active ; galaxies: jets ;
radio continuum: galaxies
Abstract:
We present 88 multi-epoch Very Long Baseline Array (VLBA) images (most
at an observing frequency of 8GHz) of 20TeV blazars, all of the
high-frequency-peaked BL Lac (HBL) class, that have not been
previously studied at multiple epochs on the parsec scale. From these
20 sources, we analyze the apparent speeds of 43 jet components that
are all detected at four or more epochs. As has been found for other
TeV HBLs, the apparent speeds of these components are relatively slow.
About two-thirds of the components have an apparent speed that is
consistent (within 2σ) with no motion, and some of these
components may be stationary patterns whose apparent speed does not
relate to the underlying bulk flow speed. In addition, a superluminal
tail to the apparent speed distribution of the TeV HBLs is detected
for the first time, with eight components in seven sources having a
2σ lower limit on the apparent speed exceeding 1c. We combine
the data from these 20 sources with an additional 18 sources from the
literature to analyze the complete apparent speed distribution of all
38 TeV HBLs that have been studied with very long baseline
interferometry at multiple epochs. The highest 2σ apparent speed
lower limit considering all sources is 3.6c. This suggests that bulk
Lorentz factors of up to about 4, but probably not much higher, exist
in the parsec-scale radio-emitting regions of these sources,
consistent with estimates obtained in the radio by other means such as
brightness temperatures. This can be reconciled with the high Lorentz
factors estimated from the high-energy data if the jet has velocity
structures consisting of different emission regions with different
Lorentz factors. In particular, we analyze the current apparent speed
data for the TeV HBLs in the context of a model with a fast central
spine and a slower outer layer.
Description:
The bulk of the observations come from the Very Long Baseline Array
(VLBA) experiments S6117 and S7017 during the years 2013 to 2015.
These two experiments together observed each of the 20 sources from
Table 2 at four epochs separated by about 6 months, for a total of 80
images. These observations were made at an observing frequency of
8.4GHz (4cm). We also obtained images at 15.3GHz during experiment
S7017 of the two sources 0033+595 and 0647+251.
In order to extend the measured time baseline for some sources, we
also included some earlier images from 2009 and 2010 recorded during
experiments BE055 and BE057 and originally published by Piner &
Edwards (2013EPJWC..6104021P 2013EPJWC..6104021P).
Altogether, these observations yield a final data set consisting of 88
images of 20 sources obtained over the years 2009-2015 and totaling
approximately 200hr of integration time on the VLBA.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 66 20 Observed sources
table5.dat 75 289 Gaussian models
table6.dat 62 43 Apparent component speeds
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See also:
J/ApJ/609/539 : Kinematics of parsec-scale radio jets (Kellermann+, 2004)
J/AJ/133/2357 : Relativistic jets in the RRFID database (Piner+, 2007)
J/ApJ/706/1253 : MOJAVE VII. Blazar jet acceleration (Homan+, 2009)
J/AJ/137/3718 : 15GHz monitoring of AGN jets with VLBA (Lister+, 2009)
J/AJ/138/1874 : MOJAVE. VI. Kinematic analysis of blazar jets (Lister+, 2009)
J/ApJ/742/27 : 15GHz and jet properties of MOJAVE blazars (Lister+, 2011)
J/ApJ/740/98 : Synchroton peak for blazars and radio galaxies (Meyer+, 2011)
J/A+A/545/A117 : Monitoring of Mrk 421 at 15 and 24 GHz (Lico+, 2012)
J/ApJ/758/84 : Relativistic jets in the RRFID database. II. (Piner+, 2012)
J/A+A/559/A75 : 43GHz observation of the blazar Mrk 421 (Blasi+, 2013)
J/AJ/146/120 : MOJAVE. X. Parsec-scale kinematics of AGNs (Lister+, 2013)
J/ApJ/787/151 : Fitted jet components in BL Lacertae (Cohen+, 2014)
J/MNRAS/438/796 : Local radio-galaxy population at 20GHz (Sadler+, 2014)
J/ApJ/798/134 : MOJAVE. XII. Acceleration of blazar jets (Homan+, 2015)
J/ApJ/810/L9 : 1.5Jy MOJAVE AGN sample and 3FGL data (Lister+, 2015)
J/AJ/152/12 : MOJAVE. XIII. 15GHz observations on 1994-2013 (Lister+, 2016)
J/ApJ/846/98 : Jet kinematics of blazars at 43GHz with VLBA (Jorstad+, 2017)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 21 A21 --- Name Name of the TeV high-frequency-peaked BL Lac
(HBL)
23- 30 A8 --- BName B1950 name (HHMM+ddd; B1950)
32- 36 F5.3 --- z [0.06/0.6] Redshift from TeVCat unless
otherwise indicated
38- 40 A3 --- r_z [a-d, ] Note(s) on z (1)
42 I1 --- Img [4/5] Number of VLBA images
44- 54 A11 "Y/M/D" Date1 First epoch of observation
56- 66 A11 "Y/M/D" Date2 Last epoch of observation
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Note (1): Note as follows:
a = The redshift is a lower limit from Pita et al. (2014A&A...565A..12P 2014A&A...565A..12P).
b = The redshift has been updated compared to that used in Table 7 of Paper I
(Piner and Edwards, 2014ApJ...797...25P 2014ApJ...797...25P).
c = The redshift is a lower limit from Nilsson et al. (2012A&A...547A...1N 2012A&A...547A...1N).
d = The redshift is from Ahnen et al. (2016MNRAS.459.3271A 2016MNRAS.459.3271A).
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Byte-by-byte Description of file: table5.dat
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Bytes Format Units Label Explanations
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1- 8 A8 --- BName B1950 Source Name
11- 17 F7.2 yr Epoch Epoch of observation
20- 23 F4.1 GHz Freq [8.4/15.3] Observing frequency
26- 27 I2 --- Comp [0/99] Component ID (1)
30- 34 F5.1 mJy Flux [0.6/119.3] Component flux density
37- 42 F6.3 mas Rad [0.002/22.3] Radial position of component center
45- 50 F6.1 deg PA [-180/179] Position angle of component center (2)
53- 58 F6.3 mas Axis [0/12.7] Full-width at half maximum of
component major axis
61- 65 F5.3 --- Ratio [0.5/1] Axial ratio of component
68- 72 F5.1 deg PAmaj [-85/88.4] Position angle of major axis (3)
75 I1 --- Type [0/1] Component type. 0: delta function, 1: Gaussian
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Note (1): An ID of "0" indicates the presumed core. An ID of "99" indicates a
flagged component not used in the analysis.
Note (2): All position angles are measured from north through east.
Note (3): If elliptical instead of circular component.
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Byte-by-byte Description of file: table6.dat
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Bytes Format Units Label Explanations
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1- 8 A8 --- BName B1950 name of the source
10 I1 --- m_BName [1/5] Component ID
12- 15 F4.1 mJy Savg [1/25] Mean flux density
17- 21 F5.2 mas ravg [0.3/22] Mean separation from core
23- 26 F4.2 mas e_ravg [0.01/0.4] ravg uncertainty
28- 33 F6.3 mas/yr pm [-0.3/0.8] Proper motion
35- 39 F5.3 mas/yr e_pm [0.005/0.4] pm uncertainty
41- 45 F5.2 --- beta [-4.2/8] Apparent speed in units of
the speed of light
47- 50 F4.2 --- e_beta [0.04/4.5] beta uncertainty
52 A1 --- f_beta [a] Flag on beta (1)
54- 57 F4.2 --- 1sig [0.1/4.9]? 1σ lower limit on the
apparent speed if greater than zero
59- 62 F4.2 --- 2sig [0.1/3.6]? 2σ lower limit on the
apparent speed if greater than zero
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Note (1):
a = Speed used for the histogram in Figure 4; see text for explanation.
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History:
From electronic version of the journal
References:
Piner and Edwards Paper I 2014ApJ...797...25P 2014ApJ...797...25P
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 03-Oct-2018