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. =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 {alpha}(1950)=23h21m9.7s+/-0.29s, {delta}(1950)=+58{deg}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; {lambda}=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, {lambda}=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, V_x_ 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, V_y_ 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