Elizabeth Lovegrove. Los Alamos National Laboratory

Transcription

1 Elizabeth Lovegrove Los Alamos National Laboratory

2 OUTLINE VLE SNe & Shock Breakout Theory CASTRO Simulations Prospects for Observations Conclusions & Future Work

3 IN CASE YOU HAVE TO LEAVE EARLY Observations (or null detections) of VLE SNe would provide a new window into CCSNe behavior How often does core-collapse go wrong? The shock breakouts of VLE SNe are a viable means to observe these otherwise dim events Shock breakout in VLE SNe behaves differently than in standard CCSNe VLE SNe breakouts will be substantially cooler than standard-energy breakouts and even brighter in optical & IR

4 Nucleosynthesis + observed SNR require at least 50% of progenitors to explode (Kochanek 2008, Brown & Woosley 2013) Observed progenitor masses range from 8-20 M (Smartt 2009, 2015) So far the observed SNR does not match the rate predicted by the observed SFR Selection effects, dim supernovae, and dust may account for some, but not all missing explosions (Horiuchi+ 2011) Horiuchi+ (2011)

5 VERY-LOW-ENERGY SUPERNOVAE (VLE SNE) Define failure as: no outgoing explosion produced directly by collapse of the iron core Define a very-low-energy supernova as: transient produced by a massive, evolved star, that has a final KE significantly < 0.6 B, generally < 0.3 B Sukhbold et al. 2015: some mechanism must routinely eject the H envelope before black hole formation Can t match SMBH population statistics otherwise Many possible ways for a massive evolved star to produce a low energy transient Neutrino-mediated mass loss, unstable burning, LBV outbursts

6 SHOCK BREAKOUTS Bright pulse emitted when a shockwave reaches the surface of a star Breakout begins when radiation behind the hydrodynamic shock can stream out ahead of the shock Can be much brighter & harder than rest of light curve Luminosity, spectral temperature, and duration carry information about the progenitor star & explosion In most cases it is very hard to recover this information any other way

7 RSG15 PROGENITOR ZAMS mass 15 M, final mass M Solar metallicity

8 RSG15 BOLOMETRIC LIGHTCURVES 15 M red supergiant tested with energies erg: Also tested 25 M red supergiant with energies erg

9 LATE-TIME LIGHTCURVES

10 ANALYTIC PREDICTIONS Piro 2013 considered the specific case of VLE SNe KE f (erg) L p (erg/s) L p, Kep Pred. L T eff (K) T eff, Kep Pred T eff 9.50e e e e3 6.93e3 6.29e3 3.89e e e e4 1.99e4 1.84e4 8.39e e e e4 4.02e4 3.71e4 5.43e e e e4 6.36e4 6.02e4 2.13e e e e4 8.34e4 8.15e4 8.25e e e5 1.31e5 1.68e e e5 1.77e

11 COLOR TEMPERATURE VS. EFFECTIVE TEMPERATURE Effective temperature is defined by luminosity L = 4πR 2 σ SB T eff 4 Set at photosphere Color temperature T col is defined by spectral form (Wien s Law) Set at chromosphere Spectral form is therefore a dilute blackbody

12 WHAT IS THE RATIO T COL /T EFF? T col /T eff set by difference between chromosphere & photosphere depth T eff based on total opacity, T col based on absorptive opacity Klein & Chevalier 78, Ensman & Burrows 92, Tolstov et al. 12 all give values of 2 3 Nakar & Sari 10, Rabinak & Waxman 13, predict values Not set by fundamental physics function of temperature, density, opacity

13 OPACITY PROCESSES IN VLE SNE If absorptive opacity dominates the total opacity, expect T col and T eff to converge The dominant opacity source sets the photosphere Absorptions set the color & chromosphere If absorptive opacity sets the photosphere, then the photosphere is also the chromosphere So what? Scattering (non-absorptive) dominates the total opacity Except it doesn t in VLE SNe!

14 OPACITY PROCESSES IN VLE SNE High-energy breakout: T ~ 1e5 1e7 K VLE breakout: T ~ 4.5e4 5e5 K Density regimes in both: 1e-8 1e-12 g/cc Opacity tables for stellar evolution codes do not generally consider the high-t, low-rho regime Different opacity processes can dominate in the VLE SNe regime

15 FREE-FREE ABSORPTION Comptonization depends on kt/hν Less efficient as T drops Inverse bremsstrahlung: photon strikes electron moving in field of ion Temperature dependence makes inv. bremsstrahlung much more significant in low-t breakout

16 BOUND-FREE ABSORPTION Individual photoionization cross-sections are very sensitive to frequency If H and He are assumed ionized, can be represented by a Kramer s Law form Opacity assumed to come only from metal fraction Z Same temperature dependence as bremsstrahlung Becomes much more significant at low T

17 OPACITY PROCESSES VS. BREAKOUT ENERGY Solid: Total opacity Absorptive opacity B15, 1.54e48 erg Dashed: Compton scattering bremsstrahlung photoionization G15, 1.2e51 erg

18 HOW IS COLOR TEMPERATURE SET? Chromosphere set at τ abs τ tot =1 τ chr = 1/τ abs Photosphere set at τ tot = c/v s = τ ph But chromosphere can t be after the photosphere τ chr can t be lower than τ ph Gives criterion for T col = T eff : SN1987A: v s = 15,000 km/s, v s /c = 5e-2, τ abs ~ 1e-3 VLE SNe: v s = 1,500 km/s, v s /c = 5e-3, τ abs ~ 1e

19 COMPARING KEPLER RESULTS TO KEPLER RESULTS KEPLER calculation for VLE SNe breakout, assuming T col = T eff, mapped into the Kepler satellite bandpass ( microns) In the IR, the low-energy breakout is brighter & longer than the highenergy one!

20 VLE SNE IN IR

21 OBSERVING PROSPECTS Looking for blue, >1e4 K transients, t ~ 3 70h L bol ~ 1e40 1e44 erg/s L IR ~ 3e39 4e41 erg/s Kepler satellite already optimized for spotting luminosity changes in a wide field of view Kepler2 observing program has already reported 2 breakouts UV transient satellite ULTRASAT (proposed) Unfortunately, bolometric brightness & duration are inversely correlated Cadence is a problem

22 CONCLUSIONS Observations (or null detections) of VLE SNe would provide a new window into CCSNe behavior How often does core-collapse go wrong? The shock breakouts of VLE SNe are a viable means to observe these otherwise dim events Shock breakout in VLE SNe behaves differently than in standard CCSNe Dim bolometric magnitudes compensated-for by lower spectral temperatures VLE SNe breakouts may actually appear brighter than standard counterparts in optical and IR windows

23 Q&A Elizabeth Lovegrove Los Alamos National Lab Thanks to: Stan Woosley, Weiqun Zhang, Daniel Kasen