J/A+A/631/A49 LOFAR images of blazar S5 0836+710 (Kappes+, 2019)
LOFAR measures the hotspot advance speed of the high-redshift blazar S5 0836+710
Kappes A., Perucho M., Kadler M., Burd P.R., Vega-Garcia L., Brueggen M.
<Astron. Astrophys. 631, A49 (2019)>
=2019A&A...631A..49K 2019A&A...631A..49K (SIMBAD/NED BibCode)
ADC_Keywords: QSOs ; Radio sources
Keywords: galaxies: active - galaxies: jets -
galaxies: individual: S5 0836+710 - radio continuum: galaxies -
techniques: high angular resolution - techniques: interferometric
Abstract:
The emission and proper motion of the terminal hotspots of active
galactic nucleus (AGN) jets can be used as a powerful probe of the
intergalactic medium. However, measurements of hotspot advance speeds
in active galaxies are difficult, especially in the young universe,
because of the low angular velocities and the low brightness of
distant radio galaxies.
Our goal is to study the termination of an AGN jet in the young
universe and to deduce physical parameters of the jet and the
intergalactic medium.
We used the LOw Frequency ARray (LOFAR) to image the long-wavelength
radio emission of the high-redshift blazar S5 0836+710 on arcsecond
scales between 120MHz and 160MHz. The LOFAR image shows a compact
unresolved core and a resolved emission region about 1.5 arcsec to the
southwest of the radio core. This structure is in general agreement
with previous higher-frequency radio observations with the
Multi-Element Radio-Linked Interferometer Network (MERLIN) and the
Very Large Array (VLA). The southern component shows a moderately
steep spectrum with a spectral index of about ≳-1,and the spectral
index of the core is flat to slightly inverted. In addition, we detect
for the first time a resolved steep-spectrum halo with a spectral
index of about -1 surrounding the core.
The arcsecond-scale radio structure of S5 0836+710 can be understood
as a Faranoff-Riley (FR) II radio galaxy observed at a small viewing
angle. The southern component can be interpreted as the region of the
approaching jet's terminal hotspot, and the halo like diffuse
component near the core can be interpreted as the counter-hotspot
region. From the differentialDoppler boosting of both features, we can
derive the hotspot advance speed to (0.01-0.036)c. Ata constant
advance speed, the derived age of the source would exceed the total
lifetime of such a powerful FR II radio galaxy substantially. Thus,
the hotspot advance speed must have been higher in the past, in
agreement with a scenario in which the originally highly relativistic
jet has lost collimation as a result of instability growth and has
transformed into an only mildly relativistic flow. Our data suggest
that the density of the intergalactic medium around this distant
(z=2.22) AGN could be substantially higher than the values typically
found in less distant FR II radio galaxies.
Description:
LOFAR HBA observation of S5 0836+710 on June 17, 2015 between 117.5MHZ
and 162.6MHZ. Flux calibrated with 3C 196. Observation duration: 4
hours
Objects:
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RA (2000) DE Designation(s)
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08 41 24.37 +70 53 42.2 S5 0836+710 = QSO J0841+7053
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 96 11 List of fits images
fits/* . 11 Individual fits images
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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- 22 I3 --- Nx Number of pixels along X-axis
24- 26 I3 --- Ny Number of pixels along Y-axis
28- 37 A10 "date" Obs.date Observation date
39- 49 E11.6 Hz Freq Observed frequency
51- 53 I3 Kibyte size Size of FITS file
55- 65 A11 --- FileName Name of FITS file, in subdirectory fits
67- 96 A30 --- Title Title of the FITS file
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Acknowledgements:
Alexander Kappes, alexander.kappes(at)uni-wuerzburg.de
(End) Alexander Kappes [JMU/Germany], Patricia Vannier [CDS] 24-Sep-2019