J/A+A/710/A217 NGC 7213 ATCA 5.5 and 9GHz and Swift/XRT obs. (Bruni+, 2026)
Symmetric kiloparsec-scale radio knots in NGC 7213.
Evidence for a confined weak jet and recurrent nuclear activity
Bruni G., Panessa F., Kammoun E., Thakur A. L., Reynolds C., Ricci R.,
Wieringa M., Bianchi S., De Rosa A., Matt G., Nicastro F., Ursini F.
<Astron. Astrophys. 710, A217 (2026)>
=2026A&A...710A.217B 2026A&A...710A.217B (SIMBAD/NED BibCode)
ADC_Keywords: Active gal. nuclei ; Radio sources ; X-ray sources
Keywords: galaxies: active - galaxies: ISM - galaxies: individual: NGC 7213 -
galaxies: jets - galaxies: nuclei - galaxies: Seyfert
Abstract:
Low-luminosity active galactic nuclei (LLAGNs) often host weak radio
jets whose propagation and impact on their host galaxies are strongly
influenced by the surrounding interstellar medium. Constraining the
connection between nuclear activity, radio variability, and
large-scale radio structures in these systems remains a key
observational challenge.
We investigate the radio properties of the nearby LLAGN NGC 7213 to
assess its ability to launch collimated outflows beyond the nuclear
region and to characterise the nature, origin, and variability of
newly identified radio components on parsec to kiloparsec scales.
We present new radio observations obtained with MeerKAT, uGMRT, ATCA,
and the Australian Long Baseline Array (LBA), covering frequencies
from 300MHz to 9GHz. We analysed the morphology and spectra of the
radio emission on kiloparsec scales and performed a dedicated LBA
monitoring campaign to probe the parsec-scale core and its
variability.
We discovered a pair of compact radio knots located symmetrically at a
projected distance of ∼5 kpc north and south of the nucleus of NGC
7213. The two knots exhibit nearly identical flux densities and flat
radio spectra from 300MHz up to at least 5.5GHz, with no significant
spectral or geometric asymmetry. ATCA observations confirm the flat
spectra at higher frequencies. The LBA monitoring shows that the
nuclear radio source remains unresolved at all epochs, constraining
the 8 GHz emission to sub-parsec scales. Significant variability is
detected on both decade-long timescales, relative to archival LBA
data, and on month-long timescales during our monitoring, with a
flux-density increase of ∼40mJy over six months.
The symmetry, spectra, and physical properties of the kiloparsec-scale
knots strongly support their interpretation as compact termination
shocks of a weak or intermittent jet launched by the LLAGN in NGC 7213
and confined by the dense, disturbed interstellar medium of the host
galaxy. The unresolved yet variable parsec-scale core traced by the
LBA indicates that the observed high-frequency radio variability
originates in the innermost jet region, which is likely linked to the
recent increase in nuclear activity. NGC 7213 thus provides a nearby
example of how weak jets in low-accretion AGN can produce both compact
nuclear variability and symmetric kiloparsec-scale structures when
interacting with complex environments.
Description:
We report the discovery of two compact and symmetric radio knots
located at a projected distance of ∼5kpc from the nucleus of the
low-luminosity AGN NGC 7213. These structures are interpreted as
termination shocks of a weak or intermittent jet that is strongly
confined by the dense, merger-disturbed interstellar medium of the
host galaxy. We present new multi-frequency radio observations
(MeerKAT, uGMRT, ATCA, LBA) complemented by a dedicated 6-month
coordinated monitoring campaign of NGC7213 core, following an X-ray
flare, with ATCA at 5.5 and 9GHz and Swift/XRT observations in the
2-10keV band.
ATCA radio monitoring of NGC 7213 at 5.5 and 9.0GHz and Swift/XRT
spectral fitting results (2-10keV).
Objects:
---------------------------------------------------------------
RA (2000) DE Designation(s)
---------------------------------------------------------------
22 09 16.21 -47 10 00.1 NGC 7213 = 1eRASS J220916.5-470959
---------------------------------------------------------------
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
tablec1.dat 25 27 ATCA radio monitoring of NGC 7213 at 5.5 and 9.0GHz.
27 epochs from 2024 July to 2025 February
tabled1.dat 40 89 *Swift/XRT spectral fitting results (2-10 keV).
79 observations from 2024 March to 2025 December
--------------------------------------------------------------------------------
Note on tabled1.dat: Swift/XRT spectra were fitted with an absorbed power-law
model with only Galactic absorption (NH=1.08x1020cm-2).
--------------------------------------------------------------------------------
Byte-by-byte Description of file: tablec1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 2 I2 --- Epoch Epoch number (1-27)
4- 12 F9.3 d MJD Modified Julian Date
14- 16 I3 mJy S5.5GHz Flux density at 5.5GHz
18 I1 mJy e_S5.5GHz 1-sigma error on S5.5GHz (G1)
20- 22 I3 mJy S9.0GHz Flux density at 9.0GHz
24- 25 I2 mJy e_S9.0GHz 1-sigma error on S9.0GHz (G1)
--------------------------------------------------------------------------------
Byte-by-byte Description of file: tabled1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 7 F7.1 d MJD Modified Julian Date
9- 12 I4 s NetExp Net exposure time
14- 17 F4.2 10-14W/m2 F2-10 Absorbed 2-10 keV flux
(in 10-11erg/cm2/s)
19- 22 F4.2 10-14W/m2 e_F2-10 1-sigma error on F2-10
(in 10-11erg/cm2/s) (G1)
24- 27 F4.2 --- Gamma Photon index
29- 32 F4.2 --- e_Gamma 1-sigma error on Gamma (G1)
34- 40 A7 --- C/dof Cash statistic / degrees of freedom
--------------------------------------------------------------------------------
Global notes:
Note (G1): Uncertainties include both statistical image noise and a
conservative 5% flux-scale calibration error (ATCA).
--------------------------------------------------------------------------------
Acknowledgements:
Gabriele Bruni, gabriele.bruni(at)inaf.it
License: CC-BY-4.0
(End) Patricia Vannier [CDS] 12-May-2026