Diverse Energy Sources for Stellar Explosions. Lars Bildsten Kavli Institute for Theoretical Physics University of California Santa Barbara

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1 Diverse Energy Sources for Stellar Explosions Lars Bildsten Kavli Institute for Theoretical Physics University of California Santa Barbara

2 Traditional Energy Sources Core collapse to NS or BH depositing E sn ~10 51 ergs in a star of radius R o. Shocks and ejects envelope, creating an event of duration set by radiative diffusion. Trigger a thermonuclear explosion in a 1.3M WD to make ~ 0.6M of 56 Ni (rest burned to Si, Ca, Fe). Unbound material leaves at 10,000 km/sec. The small R o implies huge radiative losses, but these are powered by radioactive 56 Ni decay

3 Traditional Stellar Explosions All the stars in the Milky Way! Duration contrast is mostly from the x10 difference in mass.

4 Two New Regimes Ultra-bright Supernovae (Quimby et al. 05, 11) Radiated energies approaching ergs, peak luminosities >10 44 erg sec -1 (e.g. 2005ap, 2008es,...) Kasen & Bildsten 10 and Woosley 10 showed that these L s can be reached when core collapse makes a 2-5 ms neutron star with G < B < G. Detonation of < 0.1M He on WDs=>.Ia Faint and fast (~week) explosions (Bildsten et al. 07; Shen & Bildsten 09; Shen et al. 10) Poznanski et al. 09 reported first candidate: 2002bj Kasliwal et al. 10 have a prototype: PTF 10bhp

5 Palomar Transient Factory Lightcurves of Bright Ic s Quimby et al 11

6 PS1-10ky and PS1-10awh Chomiuk et al. 11 Radiated energy nearly ergs Nearly constant photospheric velocity

7 A new Class of Explosions Associated with actively star forming galaxies => massive stars.. All stripped of Hydrogen 100 times brighter than typical core collapse supernovae Rate < 10-4 of core collapse (Quimby et al. 11)

8 Births of Magnetars! Studies of AXPs and SGRs reveal that ~10% of NSs are born with G < B < G. If born spinning at P=10msP 10 spin-down will occur in: To substantially impact lightcurve, want this to occur before diffusion occurs, requiring In the range of magnetars (Kasen & L.B. 10; Woosley 10).

9 Resetting the Entropy The deposition from spin-down resets the entropy Where the available energy is the NS rotation As long as E p >E sn (R o /vt p ), the entropy is reset (Ostriker & Gunn 71), so don t need to have E p ~E sn to impact the lightcurve

10 Hot Bubble Formation Magnetar spin-down time = 1 day Kasen & L.B. 10 M ej =5 M E sn =10 51 ergs One month

11 M ej =5 M E sn =10 51 erg P i =5 ms Dashed line is 1 M of 56 Ni Expect to see swept up shell in the photospheric velocity time evolution=> Constant velocity phase Kasen & L.B. 10

12 Peak Luminosity and Duration imply Magnetar Properties M ej =5 M ( Ic scenario) Kasen & L.B. 10

13 Off the Shelf Model for PTF 10cwr=2010gx Pastorello et al. 2010, Quimby et al M ej =5 M E sn =10 51 erg P i =1.5 ms B=2x10 14 G

14 Chomiuk et al. 11 PS1-10ky and PS1-10awh Using KB s model, they infer ejected mass of 2-5 M, P i =1.6 ms, B=2.5 x10 14 G

15 Accreting White Dwarfs Donor star of pure He, initially <0.2 M White Dwarf of Carbon/Oxygen Or Oxygen / Neon Piro 05

16 MESA is open source: anyone can download the source code, compile it, and run it for their own research or education purposes.

17 MESA Calculations for an AM CVn scenario Series of weak He flashes: basically He Novae (e.g. V445 Puppis) Mass loss occurs due to Roche Lobe overflow during the Helium flashes Final flash has a minimum heating time of 10 seconds (Bildsten et al. 07; Shen & LB 09)

18 Open Theoretical Challenges Raised by this Result How does the 1D convectively burning shell transition to a potentially multi-dimensional problem? Will a detonation occur in the Helium, and if so, will it propagate? Bildsten et al. 07 assumed a detonation, Shen et al. 10 argued that deflagrations quickly reach conditions so turbulent that flame fronts get broken up Woosley & Kasen 11 investigated both detonations and deflagrations. Waldman et al. 10 performed simulations with larger He shell masses.

19 Sample Detonation Shen et al 10 Shock (blue arrow) goes into the C/O and a He detonation (red arrow) moves outward. The shocked C/O under the layer is not ignited. Underlying WD remains unless converging shocks detonate it (see Livne & Glasner; Fink et al 07, 09, Sim et al. 10)

20 .Ia Supernovae L. B., Shen, Weinberg & Nelemans 07 Shen et al 10 The He shell leaves the the WD at 10,000 km/sec, leading to brief events The radioactive decays of the freshly synthesized 48 Cr (21 hr), 52 Fe (8.3 hr) and 56 Ni (6.1 d) will provide power on this short timescale!! In 2007, no observed events looked like this!

21 2002bj: Poznanski et al. 09

22 PTF 10bhp=2010X Kasliwal et al. 10 Peaks at Decay time is 5 days Velocities of 10,000 km/second Spectra shows Ca, C, Ti, Fe Maybe He, Na and Al?

23 Comparisons to Predictions Comparison to.ia models from Shen et al. (2010) imply an ejected mass of ~ M with roughly 1/2 being 56 Ni, and the rest mostly Helium...

24 Fink shock plots

25 Fink shock plots

26 Reviving the Helium Detonation => C/O Detonation as Type Ia Motivated by Helium star donors, early double detonation calculations had massive ( M ) He shells. These dense shells completely burn to 56 Ni; and were spectroscopically ruled out for typical Ia. Piro 12 If thin He shell detonations lead to C/O detonations... the lightcurves of M C/O exhibit Phillips relation (Sim et al 11; Woosley & Kasen 11) BUT what about the Helium on surface

27 Propagating Helium Detonations (0.028 M He on a 1.0 M WD) Propagated at 9000 km/sec. Made mostly 44 Ti, 48 Cr, little 52 Fe and 56 Ni Townsley, Moore and LB, 2012, submitted to Ap J Letters Distance (10 8 cm) Distance (10 8 cm) Distance (10 8 cm) Distance (10 8 cm)

28 What s Next?????