J/A+A/634/A112 TXS 2013+370 gamma-ray emitting region (Traianou+, 2020)
Localizing the gamma-ray emitting region in the blazar TXS 2013+370.
Traianou E., Krichbaum T.P., Boccardi B., Angioni R., Rani B., Liu J.,
Ros E., Bach U., Sokolovsky K.V., Lisakov M.M., Kiehlmann S., Gurwell M.,
Zensus J.A.
<Astron. Astrophys. 634, A112 (2020)>
=2020A&A...634A.112T 2020A&A...634A.112T (SIMBAD/NED BibCode)
ADC_Keywords: BL Lac objects ; Gamma rays ; VLBI
Keywords: magnetic fields - techniques: interferometric - galaxies: active -
gamma rays: galaxies - relativistic processes - galaxies: jets
Abstract:
The gamma-ray production mechanism and its localization in blazars are
still a matter of debate. The main goal of this paper is to constrain
the location of the high-energy emission in the blazar TXS 2013+370
and to study the physical and geometrical properties of the inner jet
region on sub-pc scales.
TXS 2013+370 was monitored during 2002-2013 with VLBI at 15, 22, 43,
and 86GHz, which allowed us to image the jet base with an angular
resolution of ≥0.4pc. By employing CLEAN imaging and Gaussian
model-fitting, we performed a thorough kinematic analysis at multiple
frequencies, which provided estimates of the jet speed, orientation,
and component ejection times. Additionally, we studied the jet
expansion profile and used the information on the jet geometry to
estimate the location of the jet apex. VLBI data were combined with
single-dish measurements to search for correlated activity between the
radio, mm, and gamma-ray emission. For this purpose, we employed a
cross-correlation analysis, supported by several significance tests.
The high-resolution VLBI imaging revealed the existence of a spatially
bent jet, described by co-existing moving emission features and
stationary features. New jet features, labeled as A1, N, and N1, are
observed to emerge from the core, accompanied by flaring activity in
radio/mm- bands and rays. The analysis of the transverse jet width
profile constrains the location of the mm core to lie ≤2pc downstream
of the jet apex, and also reveals the existence of a transition from
parabolic to conical jet expansion at a distance of ∼54pc from the
core, corresponding to ∼1.5x106 Schwarzschild radii. The
cross-correlation analysis of the broad-band variability reveals a
strong correlation between the radio-mm and gamma-ray data, with the
1mm emission lagging 49 days behind the rays. Based on this, we infer
that the high energy emission is produced at a distance of the order
of ∼1pc from the VLBI core, suggesting that the seed photon fields for
the external Compton mechanism originate either in the dusty torus or
in the broad-line region.
Description:
Our VLBI data set includes observations at 15, 22, 43, and 86GHz.
The 86GHz observations were performed with the Global
Millimeter VLBI Array (GMVA1) and the 43GHz observations with the
Global VLBI array; four epochs were observed in 2007-2009 and three
epochs in 2009-2010, respectively.
For a single epoch, the RadioAstron space antenna, in combination with
the VLBI ground array performed simultaneous observations at two
frequencies, 22GHz and 5GHz, to facilitate fringe search at the
space-ground baselines. In this article we consider the 22GHz data.
At 15GHz we re-analyzed fifteen epochs of Very Long Baseline Array
(VLBA) observations that cover a period from 2002 to 2012 and are
publicly available at the MOJAVE data archive
(https://www.physics.purdue.edu/MOJAVE/sourcepages/2013+370.shtml)
(see Lister et al. 2009, Cat. J/AJ/137/3718, 2011, Cat. J/ApJ/742/27,
2018, Cat. J/ApJS/234/12, and references therein).
Objects:
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RA (2000) DE Designation(s)
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20 15 28.73 +37 10 59.5 TXS 2013+370 = QSO J2015+371
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 151 23 List of fits images
fits/* . 23 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- 23 I4 --- Nx Number of pixels along X-axis
25- 28 I4 --- Ny Number of pixels along Y-axis
30- 39 A10 "date" Obs.date Observation date
41- 47 F7.4 GHz Freq Observed frequency
49- 55 F7.2 yr Epoch Observing year (from table B1)
57- 82 A26 --- Array Participating antennas (from table B1) (1)
84- 87 F4.2 mas bmaj Major axis of the convolving beam
(from table B1)
89- 92 F4.2 mas Bmin Minor axis of the convolving beam
(from table B1)
94- 99 F6.2 deg PA [] Position angle (from table B1)
101-105 F5.3 Jy Speak Image peak flux density (from table B1)
107-110 F4.2 mJy/beam rms Noise level (from table B1)
112-115 F4.2 Jy/beam Stot Image total flux density (from table B1)
117-120 I4 Kibyte size Size of FITS file
122-151 A30 --- FileName Name of FITS file, in subdirectory fits
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Note (1): Abbreviations used:
EB = Eelsberg
JB = Jodrell Bank
RO = Radioastronomical Observatory
YS = Yebes
RA = RadioAstron
ON = Onsala
GB = Green Bank
NT = Noto
PV = Pico Veleta
PB = Plateau de Bure
MH = Metsahovi
VLBA = Very Long Baseline Array
Individual notes:
a = Saint Croix did not participate in the observations
b = Ovro did not participate in the observations
c = Hancock and Saint Croix do not have 3mm receivers
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Acknowledgements:
Efthalia Traianou, etraianou(at)mpifr-bonn.mpg.de
(End) Patricia Vannier [CDS] 13-Dec-2019