J/A+A/676/A114 Mini-cocoon in 3C84 RadioAstron discovery (Savolainen+, 2023)
RadioAstron discovery of a mini-cocoon around the restarted parsec-scale jet
in 3C 84.
Savolainen T., Giovannini G., Kovalev Y.Y., Perucho M., Anderson J.M.,
Bruni G., Edwards P.G., Fuentes A., Giroletti M., Gomez J.L., Hada K.,
Lee S.-S., Lisakov M.M., Lobanov A.P., Lopez-Miralles J., Orienti M.,
Petrov L., Plavin A.V., Sohn B.W., Sokolovsky K.V., Voitsik P.A.,
Zensus J.A.
<Astron. Astrophys. 676, A114 (2023)>
=2023A&A...676A.114S 2023A&A...676A.114S (SIMBAD/NED BibCode)
ADC_Keywords: Active gal. nuclei ; Galaxies, radio ; Radio sources ; VLBI
Keywords: galaxies: jets - galaxies: active - galaxies: individual: 3C 84 -
techniques: interferometric - techniques: high angular resolution
Abstract:
We present RadioAstron space-based very long baseline interferometry
(VLBI) observations of the nearby radio galaxy 3C84 (NGC1275) at the
centre of the Perseus cluster. The observations were carried out
during a perigee passage of the Spektr-R spacecraft on September
21-22, 2013 and involved a global array of 24 ground radio telescopes
observing at 5GHz and 22GHz, together with the Space Radio Telescope
(SRT). Furthermore, the Very Long Baseline Array (VLBA) and the phased
Very Large Array (VLA) observed the source quasi-simultaneously at 15
GHz and 43 GHz. Fringes between the ground array and the SRT were
detected on baseline lengths up to 8.1 times the Earth's diameter,
providing unprecedented resolution for 3C 84 at these wavelengths. We
note that the corresponding fringe spacing is 125uas at 5GHz and 27uas
at 22GHz. Our space-VLBI images reveal a previously unseen sub-
structure inside the compact ∼1pc long jet that was ejected about ten
years earlier. In the 5GHz image, we detected, for the first time,
low-intensity emission from a cocoon-like structure around the
restarted jet. Our results suggest that the increased power of the
young jet is inflating a bubble of hot plasma as it carves its way
through the ambient medium of the central region of the galaxy. Here,
we estimate the minimum energy stored in the mini-cocoon, along with
its pressure, volume, expansion speed, and the ratio of heavy
particles to relativistic electrons, as well as the density of the
ambient medium. About half of the energy delivered by the jet is
dumped into the mini-cocoon and the quasi-spherical shape of the
bubble suggests that this energy may be transferred to a significantly
larger volume of the interstellar medium than what would be
accomplished by the well-collimated jet on its own. The pressure of
the hot mini-cocoon also provides a natural explanation for the almost
cylindrical jet profile seen in the 22GHz RadioAstron image.
Description:
Space-VLBI and global-VLBI CLEAN images of 3C84 in FITS format. The
observations were made on 21-09-2013 and comprised four frequency
bands: 5GHz and 22GHz with RadioAstron space-VLBI satellite together
with a global VLBI ground array and 15GHz and 43GHz with the Very
Long Baseline Array together with the Very Large Array. The FITS files
include CLEAN images from several different (u,v) weighting schemes
and using several different restoring beam sizes.
These data were observed as a part of the RadioAstron Nearby AGN Key
Science program (global VLBI project code GS032A).
Objects:
-------------------------------------------
RA (2000) DE Designation(s)
-------------------------------------------
03 19 48.15 +41 30 42.1 3C84 = NGC 1275
-------------------------------------------
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
list.dat 219 16 List of fits images
fits/* . 16 Individual fits images
--------------------------------------------------------------------------------
See also:
J/A+A/622/A196 : GMVA 86GHz Stokes IQU images of 3C84 jet (Kim+, 2019)
J/A+A/669/A32 : 3C 84 multi-band study (Paraschos+, 2023)
Byte-by-byte Description of file: list.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
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- 51 E11.5 Hz Freq Observed frequency
53- 57 I5 Kibyte Size Size of the FITS file
59-119 A61 --- FileName Name of FITS file, in subdirectory fits
121-219 A99 --- Title Title of the FITS file
--------------------------------------------------------------------------------
Acknowledgements:
Tuomas Savolainen, tuomas.k.savolainen(at)aalto.fi
(End) Patricia Vannier [CDS] 21-Jun-2023