The 2006 Explosion of the Recurrent Nova RS Ophiuchi

1. The 2006 Explosion of the Recurrent Nova RS Ophiuchi 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)… Tim O’Brien Jodrell Bank Observatory, University of Manchester

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. EVN 1985 Effelsberg, Jodrell, Westerbork, No fringes on JB-Wb 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), O’Brien & Kahn (1987), O’Brien, Bode & Kahn (1992) • Led to estimates of various parameters:d = 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, ToO’s 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 EVN VLBA VLBA

10. First VLBI image – Day 13.8 VLBA image revealsthe shock wave for thefirst time. Earliest resolution of structure in any such explosion. Res’n ~ 3 mas Peak Tb ~ 5x107K Significant contribution from synchrotron. 6 cm O’Brien et al (2006)

11. Expanding ring VLBA VLBA EVN Three epochs of VLBI imaging 6 cm Day 13.8 Day 21.5 Day 28.7 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. ? The “second” component Three epochs of VLBI imaging 6 cm Day 13.8 Day 21.5 Day 28.7 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?