The 2006 Explosion of the Recurrent Nova RS Ophiuchi

1
The 2006 Explosion of the Recurrent Nova RS
Ophiuchi

• Tim OBrien
• Jodrell Bank Observatory, University of Manchester

• Bode, Harman (Liverpool), Porcas (MPIfR),
• Muxlow, Beswick, Garrington, Vaytet, Davis
  (Manchester),
• Eyres, Rushton (Central Lancs), Gawronski, Feiler
  (Torun),
• Anupama (Bangalore), Kantharia (Pune),
• Osborne, Page, Beardmore, Goad (Leicester),
• Evans (Keele), Starrfield, Ness (Arizona State),
• Burrows (Penn State), Schwarz (West Chester),
• Krautter (Heidelberg), Drake (Harvard CfA),
• Gehrels (Goddard)

2
Vital Statistics

• Recurrent Nova previous outbursts 1898, (1907),
  1933, 1958, 1967, 1985

Brightens from 11th mag to 4th mag in less than
a day.
Before after 2006
3
High-mass white dwarf (1.2-1.4 M?) Red Giant
(M2III), P 455 days
Outbursts due to thermonuclear runaway (TNR) on
WD surface
4
1985 Outburst First multi-wavelength campaign

• X-rays EXOSAT, 6 epochs from t 55d. Indicative
  of gas at several million degrees. Mason et al
  (1987)
• Radio Jodrell BBI from t 18d, VLA, EVNPadin
  et al (1985), Hjellming et al (1986), Porcas et
  al (1987), Taylor et al (1989)
• Models of shock interaction similar to SNR. Bode
  Kahn (1985), OBrien Kahn (1987), OBrien,
  Bode Kahn (1992)
• Led to estimates of various parametersd 1.6
  0.3 kpc, NH 2.4 0.6 cm-2 , Mej 1.1 x 10-6
  M, MW 2 x 10-7 M yr-1 , E 1.1 x 1043 erg

5
2006 Outburst

• Discovered Feb 12.83 UT (t 0)
• Within a few days, ToOs granted on Swift, XMM,
  Chandra, MERLIN, VLA, VLBA, EVN, Liv Tel, UKIRT,
  plus HST, GMRT, OCRA and Spitzer later.
• Thanks!

6
Radio Observations

• Monitoring from day 4.5 onwards with MERLIN, VLA,
  GMRT, OCRA, VLBA and EVN.

7
L/C-Band Lightcurve
Eyres et al (2006)
8
L/C-Band Lightcurve
1985
New component
9
VLBI Imaging
EVN
VLBA
VLBA
VLBA
EVN
10
First VLBI image Day 13.8
VLBA image revealsthe shock wave for thefirst
time. Earliest resolution of structure in any
such explosion. Resn 3 mas Peak Tb
5x107K Significant contribution from synchrotron.
6 cm
OBrien et al (2006)
11
Three epochs of VLBI imaging
VLBA
EVN
VLBA
6 cm
Day 13.8
Day 28.7
Day 21.5
18 cm
Day 13.8
Day 20.5
Day 28.7
12
Expansion velocity

• 0.63 mas day-1
• 1750 km s-1
• at 1600 pc.
• Consistent with
• Swift X-ray
• temperatures.

13
Three epochs of VLBI imaging
The second component
6 cm
Day 13.8
Day 28.7
Day 21.5
18 cm
Day 13.8
Day 20.5
Day 28.7
14
MERLIN imaging

• Second component clearly visible from day 21
  onwards.
• Third component to west visible around day 50.
• Source evolves into E-W structure.

15
VLBI Sequence
VLBA 14d
VLBA 63d
VLBA 49d
EVN 22d
6 cm
18 cm
VLBA 29d
6 cm
18 cm
6 cm
16
Swift X-ray Observations

• Two components
• Shock providing higher-energy emission visible at
  early and late times.
• Bright soft component from nuclear burning on
  white dwarf.

Bode et al (2006), Osborne et al (2006)
17
A model
Bipolar shell viewed at the (known) inclination
of the binary orbit and partially obscured by the
overlying red giant wind.
Binary orbit
18
A model
Synthetic images
Early
Late
As the source expands the overlying free-free
absorption is reduced and it becomes symmetrical.
19
Summary

• Direct imaging of shock wave for first time.
  Properties consistent with X-ray emission.
• Develops into E-W structure similar to the 1985
  image of Porcas et al despite doubters!
• Radio monitoring reveals double-peaked light
  curve related to these multiple components.
• X-rays reveal shock and nuclear burning (BTW
  proving part of my own PhD thesis wrong!).
• Hydro modelling in progress to determine whether
  ejection in form of jets.
• Will RS Oph explode as a Type Ia SN?