J/A+A/693/A196 Misaligned BL Lac object 3C 371 (Otero-Santos+, 2025)
Multi-wavelength picture of the misaligned BL Lac object 3C 371.
Otero-Santos J., Raiteri C.M., Tramacere A., Escudero Pedrosa J.,
Acosta-Pulido J.A., Carnerero M.I., Villata M., Agudo I., Rahimov I.A.,
Andreeva T.S., Ivanov D.V., Marchili N., Righini S., Giroletti M.,
Gurwell M.A., Savchenko S.S., Carosati D., Chen W.P., Kurtanidze S.O.,
Joner M.D., Semkov E., Pursimo T., Benitez E., Damljanovic G.,
Andreuzzi G., Apolonio G., Borman G.A., Bozhilov V., Galindo-Guil F.J.,
Grishina T.S., Hagen-thorn V.A., Hiriart D., Hsiao H.Y., Ibryamov S.,
Ivanidze R.Z., Kimeridze G.N., Kopatskaya E.N., Kurtanidze O.M.,
Larionov V.M., Larionova E.G., Larionova L.V., Minev M., Morozova D.A.,
Nikolashvili M.G., Ovcharov E., Sigua L.A., Stojanovic M., Troitskiy I.S.,
Troitskaya Y.V., Tsai A., Valcheva A., Vasilyev A.A., Vince O.,
Zaharieva E., Zhovtan A.V.
<Astron. Astrophys. 693, A196 (2025)>
=2025A&A...693A.196O 2025A&A...693A.196O (SIMBAD/NED BibCode)
ADC_Keywords: BL Lac objects ; VLBI
Keywords: galaxies: active - BL Lacertae objects: general -
BL Lacertae objects: individual: 3C 371 - galaxies: jets -
galaxies: nuclei
Abstract:
The BL Lac object 3C 371 is one of the targets regularly monitored by
the Whole-Earth Blazar Telescope (WEBT), a collaboration of observers
studying blazar variability on both short and long timescales.
We aim to evaluate the long-term multi-wavelength (MWL) behaviour of
3C 371, comparing it with results derived from its optical emission in
our previous study. For this, we make use of the multi-band campaigns
organised by the WEBT collaboration in optical and radio between
January 2018 and December 2020, and of public data from Swift and
Fermi satellites and the MOJAVE Very Large Interferometry programme.
We evaluated the variability shown by the source in each band by
quantifying the amplitude variability parameter, and also looked for a
possible inter-band correlation using the z-discrete correlation
function. We also present a deep analysis of the optical-UV, X-ray,
and gamma-ray spectral variability. With the MOJAVE data, we performed
a kinematics analysis, looking for components propagating along the
jet and calculating its kinematics parameters. We then used this set
of parameters to interpret the source MWL behaviour, modelling its
broadband spectral energy distribution (SED) with theoretical blazar
emission scenarios.
The MWL variability of the source in the UV, X-ray, and gamma-ray
bands is comparable to that in optical, especially considering the
lower coverage of the first two wavebands. On the other hand, the
radio bands show variability of much lower magnitude. Moreover, this
MWL emission shows a high degree of correlation, which is compatible
with zero lag, again with the exception of the radio emission. The
radio VLBI images reveal super-luminal motion of one of the identified
components, which we used to set constraints on the jet kinematics and
parameters, and to estimate a viewing angle of
{GAMMA}=(9.6±1.6)°, a Doppler factor of δ=6.0±1.1, and a
Lorentz factor of {GAMMA}=6.0±1.8. The polarised radio emission was
found to be anti-correlated with the total flux, and to follow the
same behaviour as the polarised optical radiation. The optical-UV
spectral behaviour shows a mild harder-when-brighter trend on long
timescales, and other trends such as redder-when-brighter on shorter
timescales. We successfully modelled the broadband emission with a
leptonic scenario, where we compared the low and high emission states
during the period of complete MWL coverage. The difference between
these two states can be ascribed mainly to a hardening of the
distribution of particles. The derived features of the source confirm
that 3C 371 is a BL Lac whose jet is not well aligned with the line of
sight.
Description:
In Table A.1 we compile the modelfit results obtained from our
analysis of the VLBI data during all epochs, for all identified
components. This table includes the information of the flux density
and the position of each identified component for the different epochs
included here.
Objects:
------------------------------------------------
RA (2000) DE Designation(s)
------------------------------------------------
18 06 50.68 +69 49 28.1 3C 371 = UGC 11130
------------------------------------------------
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
tablea1.dat 65 235 Modelfit results derived from the VLBI data analysis
for all epochs and each identified component
--------------------------------------------------------------------------------
Byte-by-byte Description of file: tablea1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 2 A2 --- Id Label of the identified feature (1)
4- 13 A10 "date" Date Date of the observation
15- 25 F11.8 Jy Flux VLBI 2cm flux density of the identified feature
27- 45 F19.16 mas Xpos X position of the identified feature
47- 65 F19.16 mas Ypos Y position of the identified feature
--------------------------------------------------------------------------------
Note (1): Components without an associated name correspond to those used for the
modelfitting but not included in our analysis due to high noise, making them
not suitable for the kinematic evaluation and for tracing their evolution and
continuity. More details on the modelfit results can be consulted in the
documentation of difmap
(http://www.ira.inaf.it/Computing/manuals/difmap/cookbook.ps).
--------------------------------------------------------------------------------
History:
Copied at https://zenodo.org/records/14281786
(End) Patricia Vannier [CDS] 21-May-2025