J/A+A/668/A107 A399-401 144MHz images (de Jong+, 2022)
A deep study of A399-401: Application for wide-field facet calibration.
de Jong J.M.G.H.J., van Weeren R.J., Botteon A., Oonk J.B.R., Brunetti G.,
Shimwell T.W., Cassano R., Roettgering H.J.A., Tasse C.
<Astron. Astrophys. 668, A107 (2022)>
=2022A&A...668A.107D 2022A&A...668A.107D (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, galaxy ; Radio sources
Keywords: techniques: image processing - turbulence -
radiation mechanisms: non-thermal -
galaxies: clusters: intracluster medium - cosmic rays -
galaxies: clusters: general
Abstract:
Diffuse synchrotron emission pervades numerous galaxy clusters,
indicating the existence of cosmic rays and magnetic fields throughout
the intra-cluster medium. The general consensus is that this emission
is generated by shocks and turbulence that are activated during
cluster merger events and cause a (re-)acceleration of particles to
highly relativistic energies. Similar emission has recently been
detected in megaparsec-scale filaments connecting pairs of premerging
clusters. These instances are the first in which diffuse emission has
been found outside of the main cluster regions.
We aim to examine the particle acceleration mechanism in the
megaparsec-scale bridge between Abell 399 and Abell 401 and assess in
particular whether the synchrotron emission originates from first- or
second-order Fermi reacceleration. We also consider the possible
influence of active galactic nuclei (AGNs).
To examine the diffuse emission and the AGNs in Abell 399 and Abell
401, we used deep (∼40h) LOw-Frequency ARray (LOFAR) observations
with an improved direction-dependent calibration to produce radio
images at 144MHz with a sensitivity of σ=79uJy/beam at a
5.9°x10.5°resolution. Using a point-to-point analysis, we
searched for a correlation between the radio and X-ray brightness from
which we would be able to constrain the particle reacceleration
mechanism.
Our radio images show the radio bridge between the radio halos at high
significance. We find a trend between the radio and X-ray emission in
the bridge. We also measured the correlation between the radio and
X-ray emission in the radio halos and find a strong correlation for
Abell 401 and a weaker correlation for Abell 399. On the other hand,
we measure a strong correlation for the radio halo extension from A399
in the northwest direction. With our deep images, we also find
evidence for AGN particle injection and reenergized fossil plasma in
the radio bridge and halos.
We argue that second-order Fermi reacceleration is currently the most
favored process to explain the radio bridge. In addition, we find
indications for a scenario in which past AGN particle injection might
introduce significant scatter in the relation between the radio and
X-ray emission in the bridge, but may also supply the fossil plasma
needed for in situ reacceleration. The results for Abell 401 are also
clearly consistent with a second-order Fermi reacceleration model. The
relation between the thermal and nonthermal components in the radio
halo in Abell 399 is affected by a recent merger. However, a strong
correlation toward its northwest extension and the steep spectrum in
the radio halo support an origin of the radio emission in a
second-order Fermi reacceleration model as well. The evidence that we
find for reenergized fossil plasma near Abell 399 and in the radio
bridge supports the reacceleration of the fossil plasma scenario.
Description:
For the study of A399-A401, we used 6x8h of observations from
LOFAR from project LC9_015 (PI: van Weeren).
Every observation has a pointing center at a right ascension of
02:58:21 and a declination of +13:17:10 (J2000 equinox). The data
cover the frequency range from 120-168MHz and were observed only
with high-band antennas. We only used the stations located in the
Netherlands. L626692 used 60 stations, while the other observations
all used 62 stations.
Objects:
-----------------------------------------
RA (2000) DE Designation(s)
-----------------------------------------
02 57 56.4 +13 00 59 A399 = ACO 399
02 58 56.9 +13 34 56 A401 = ACO 401
-----------------------------------------
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 150 5 List of fits images
fits/* . 5 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- 50 A21 "datime" Obs.date Observation date
52- 58 F7.3 MHz Freq Observed frequency
60- 65 I6 Kibyte size Size of FITS file
67- 89 A23 --- FileName Name of FITS file, in subdirectory fits
91-150 A60 --- Title Title of the FITS file
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Acknowledgements:
Jurjen de Jong, jurjendejong(at)strw.leidenuniv.nl
(End) Patricia Vannier [CDS] 27-Sep-2022