J/A+A/649/A153 BL Lac 86GHz images (Casadio+, 2021)
The jet collimation profile at high resolution in BL Lacertae.
Casadio C., MacDonald N.R., Boccardi B., Jorstad S.G., Marscher A.P.,
Krichbaum T.P., Hodgson J.A., Kim J-Y., Traianou E., Weaver Z.R.,
Gomez Garrido M., Gonzalez Garcia J., Kallunki J., Lindqvist M.,
Sanchez S., Yang J., Zensus J.A.
<Astron. Astrophys. 649, A153 (2021)>
=2021A&A...649A.153C 2021A&A...649A.153C (SIMBAD/NED BibCode)
ADC_Keywords: BL Lac objects
Keywords: instrumentation: interferometers -
instrumentation: high angular resolution - galaxies: active -
galaxies: jets - BL Lacertae objects: individual: BL Lacertae
Abstract:
Controversial studies on the jet collimation profile of BL Lacertae
(BL Lac), the eponymous blazar of the BL Lac objects class, complicate
the scenario in this already puzzling class of objects. Understanding
the jet geometry in connection with the jet kinematics and the
physical conditions in the surrounding medium is fundamental for
better constraining the formation, acceleration, and collimation
mechanisms in extragalactic jets.
With the aim of investigating the jet geometry in the innermost
regions of the BL Lac jet, and resolving the controversy, we explore
the radio jet in this source using high-resolution millimeter-wave
VLBI data.
We collect 86GHz GMVA and 43 GHz VLBA data to obtain stacked images
that we use to infer the jet collimation profile by means of two
comparable methods. We analyze the kinematics at 86GHz, and we
discuss it in the context of the jet expansion. Finally, we consider a
possible implication of the Bondi sphere in shaping the jet of BL Lac.
The jet in BL Lac expands with an overall conical geometry. A higher
expanding rate region is observed between ∼5 and 10pc (de-projected)
from the black hole. Such a region is associated with the decrease in
brightness usually observed in high frequency VLBI images of BL Lac.
The jet retrieves the original jet expansion around 17pc, where the
presence of a recollimation shock is supported by both the jet profile
and the 15GHz kinematics (MOJAVE survey). The change in the jet
expansion profile occurring at ∼5pc could be associated with a change
in the external pressure at the location of the Bondi radius
(∼3.3x105RS)/
Description:
We analyzed 86GHz Global Millimeter VLBI Array (GMVA) data of BL Lac
obtained from May 2009 to April 2017 (11 observing epochs) and 43 GHz
VLBA data from the VLBABU-BLAZAR program covering 10 years of
observations (94epochs), obtained between May 2009 and March 2019. The
GMVA data are part of an ongoing monitoring program (PI: A. Marscher)
of a sample of gamma-ray bright blazars and radio galaxies.
Objects:
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RA (2000) DE Designation(s)
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22 02 43.29 +42 16 40.0 BL Lac = QSO B2200+420
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 109 10 List of fits images
fits/* . 10 Individual fits images
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See also:
J/AZh/71/717 : Polarimetric Observations of BL Lac (Gagen-Torn+ 1994)
J/A+A/369/758 : VRI photometry of BL Lac (1997-1999) (Fan+, 2001)
J/A+A/385/55 : Long-Term Polarization of BL Lac (Hagen-Thorn+ 2002)
J/MNRAS/373/209 : BATC eim photometry of BL Lac (Hu+, 2006)
J/ApJ/787/151 : Fitted jet components in BL Lacertae (Cohen+, 2014)
J/ApJ/816/53 : Multiwavelength obs. of BL Lac in 2012-2013 (Wehrle+, 2016)
J/A+A/623/A175 : 2015 BL Lac VHE gamma-ray flare (MAGIC Collaboration, 2019)
Byte-by-byte Description of file: list.dat
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Bytes Format Units Label Explanations
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1- 9 F9.5 deg RAdeg Right Ascension of center (J2000)
10- 18 F9.5 deg DEdeg Declination of center (J2000)
20- 23 I4 --- Nx Number of pixels along X-axis
25- 28 I4 --- Ny Number of pixels along Y-axis
30- 39 A10 "datime" Obs.date Observation date
41- 47 F7.4 GHz Freq Observed frequency
49- 52 I4 Kibyte size Size of FITS file
54- 72 A19 --- FileName Name of FITS file, in subdirectory fits
74-109 A36 --- Title Title of the FITS file
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Acknowledgements:
Carolina Casadio, ccasadio(at)physics.uoc.gr
(End) Patricia Vannier [CDS] 21-May-2021