J/ApJ/941/13 Proper motion and brightness changes of Cas A at 5GHz (Lei+, 2022)
A study of radio knots within supernova remnant Cassiopeia A.
Lei X., Zhu H., Zhang H., Tian W., Wu D.
<Astrophys. J., 941, 13 (2022)>
=2022ApJ...941...13L 2022ApJ...941...13L
ADC_Keywords: Supernova remnants ; Proper motions ; Radio sources
Keywords: Supernova remnants ; Proper motions
Abstract:
The study on the dynamic evolution of young supernova remnants (SNRs)
is an important way to understand the density structure of the
progenitor's circumstellar medium. We have reported the acceleration
or deceleration, proper motion, and brightness changes of 260 compact
radio features in the second-youngest known SNR Cas A at 5 GHz based
on the Very Large Array data of five epochs from 1987 to 2004. The
radio expansion center is located at α(1950)=23h21m9.7s±0.29s,
δ(1950)=+58°32'25.2"±2.2". Three-quarters of the compact
knots are decelerating; this suggests that there are significant
density fluctuations in the stellar winds of the remnant's progenitor.
We have verified that the acceleration or deceleration of compact
knots is not related with the distribution of brightness. The
brightening, fading, disappearing, or new appearing of compact radio
features in Cas A suggests that the magnetic field in the remnant is
changing rapidly.
Description:
In this work, we use the VLA archival visibility observation data for
Cas A at 5 GHz including five epochs of 1987, 1994, 1997, 2000, and
2004. These data were observed in the A, B, C, and D configuration of
VLA, which has a high sensitivity and high resolution of 1.5".
The data used in this study are the VLA archival C-band (5GHz;
λ=6cm) standard-configuration data of Cas A. Each data was
obtained at several frequencies around the nominal observing frequency
of 5GHz, which improves the aperture coverage. In the VLA standard
configurations, the A configuration is the most diffuse, with a
maximum baseline of 36.4km and a resolution of 0.33" in the C band;
the D configuration is the most compact, with the shortest baseline of
0.035km. In order to sample the complex spatial structure of Cas A,
the aperture coverage has been maximized. See table1 for more details
of the data, section 2 for the data calibration procedure and section
3 for images analysis for measurement of proper motion and brightness
changes for the radio features.
Objects:
----------------------------------------------------------
RA (ICRS) DE Designation(s)
----------------------------------------------------------
23 23 24.00 +58 48 53.9 Cas A = NAME Cassiopeia A
----------------------------------------------------------
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table2.dat 125 260 Summary of VLA observations for Cas A from 1987 to
2005, λ=6cm (C-band)
--------------------------------------------------------------------------------
See also:
J/ApJ/441/307 : Proper motions and brightness of Cas A (Anderson+ 1995)
J/ApJ/456/234 : Cas A radio knots spectral indices (Anderson+ 1996)
J/ApJ/613/343 : Cas A knot and filament proper motions (Delaney+, 2004)
J/ApJS/179/195 : A catalog of outer ejecta knots in Cas A (Hammell+, 2008)
J/A+A/484/755 : Oxygen recombination lines from Cas A knots (Docenko+, 2008)
J/ApJ/837/118 : NIR knots in the Cas A supernova remnant (Lee+, 2017)
J/ApJ/866/139 : Knots in the deep [FeII]+[SiI] image of Cas A (Koo+, 2018)
J/A+A/612/A110 : Cas A LOFAR and VLA images (Arias+, 2018)
Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 I3 --- Knot [1/260] Knot number, this work
5- 7 I3 --- AR95 [2/304]? Knot number,
(Anderson & Rudinck 1995, J/ApJ/441/307;
<[AR95] NNN> in Simbad)
9- 14 F6.1 arcsec Xpos [-184.5/152.1] X offset from Epoch 1987
continuum (1)
16- 21 F6.1 arcsec Ypos [-153.2/173.0] Y offset from Epoch 1987
continuum (1)
23- 28 F6.1 arcsec BoxX1 [-195.3/149.7] Box size (2)
30- 35 F6.1 arcsec BoxX2 [-158.6/170.5] Box size (2)
37- 42 F6.1 arcsec BoxY1 [-181.4/157.7] Box size (2)
44- 49 F6.1 arcsec BoxY2 [-150.4/181.8] Box size (2)
51- 56 F6.3 arcsec/yr pmRA [-0.61/0.71] Knot proper motion in RA, Vx
58- 62 F5.3 arcsec/yr e_pmRA [0.004/0.2] Uncertainty in pmRA
64- 69 F6.3 arcsec/yr pmDE [-0.54/0.55] Knot proper motion in DE, Vy
71- 75 F5.3 arcsec/yr e_pmDE [0/0.2] Uncertainty in pmDE
77- 83 F7.4 arcsec/yr2 ax [-0.023/0.02] Knot acceleration in RA
85- 90 F6.4 arcsec/yr2 e_ax [0.0002/0.02] Uncertainty in ax
92- 98 F7.4 arcsec/yr2 ay [-0.017/0.033] Knot acceleration in DE
100-105 F6.4 arcsec/yr2 e_ay [0/0.02] Uncertainty in ay
107-112 F6.2 mJy/beam Peak [12.2/188] Peak Brightness in 1987 map
114-119 F6.3 %/yr DB/B [-0.063/0.37] Annual percentage of the
brightness change
121-125 F5.3 %/yr e_DB/B [0.001/0.1] Uncertainty in DB/B
--------------------------------------------------------------------------------
Note (1): Position of compact knots in the epoch 1987 continuum map,
measured in arcsec and reference to the optical expansion center
RA(1950)=23:21:11.4,DEC(1950)=+58:32:28.5
Note (2): Box size defined for each knot, in arcseconds and referenced to
the radio expansion center.
--------------------------------------------------------------------------------
History:
From electronic version of the journal
(End) Prepared by [AAS], Katia van der Woerd [CDS] 10-Oct-2024