Signatures of supernovae powered by neutron stars and black holes

Jason Dexter (with Dan Kasen)UC Berkeley

The Structure and Signals of Neutron Stars 2

Super-luminous supernovae

core collapse supernovae

after M. Kasliwal, D. Kasen

Type

Ia

2002bjptf10bhp

2008ha

2008es2007bi

2005ap scp06f6

2006gyptf09cnd

The Structure and Signals of Neutron Stars 3

Super-luminous supernovae

> 1044 ergs / s

Gal-Yam (2012)

The Structure and Signals of Neutron Stars 4

Models

• Magnetar spindown (Kasen & Bildsten 2010)

• Fallback accretion (Dexter & Kasen 2013)

• Pair-instability explosions (Woosley 2007, Kasen+2011)

• Circumsteller interaction (Blinnikov & Sorokina, Chevalier & Irwin, …)

The Structure and Signals of Neutron Stars 5

Energy from fallback accretion

• Bound material falls back after explosion, forms disk, drives outflow into ejecta, deposits energy

• Jet or wind model: > 1051 ergs / Msun

A. Tchekhovskoy

The Structure and Signals of Neutron Stars 6

Fallback accretion rate• Measure from simulated explosions• Flat at early times, asymptotically t-5/3

Wong+2013Dexter & Kasen (2013)

The Structure and Signals of Neutron Stars 7

Accretion powered supernovae• Fallback accretion could power a wide range

of eventsDexter & Kasen (2013)

The Structure and Signals of Neutron Stars 8

Evidence for a central engine?• Central engine models explain light curve shapes,

high velocities > 104 km / s• Type I: no narrow lines, need massive H-free CSM

Inserra+2013 Chatzapoulos+2012

The Structure and Signals of Neutron Stars 9

Signatures of central engines

• Central engine emission should shine through• Hard X-rays, γ-rays in nebular phase (Kotera+2013)

• Photo-ionization: UV/X-ray flash (Metzger+2014)

Kotera+2013 Metzger+2014

The Structure and Signals of Neutron Stars 10

Signatures of central engines

• Track thermalization:- Free-free (IR), lines

(optical), bound-free (UV/soft X-ray), Compton scattering (high energy)

• Sharp drops in optical light curve from ionization

Kotera+2013

Time

The Structure and Signals of Neutron Stars 11

Optical/UV colors

• Loss of thermalization potentially observable in late time colors

Inserra+2013

The Structure and Signals of Neutron Stars 12

Summary

• Central engine models promising for explaining some super-luminous supernovae– Magnetar spindown or fallback accretion

• Signatures of central engine in optical/UV and high energy emission

• Possible information about stellar collapse and/or compact object birth

The Structure and Signals of Neutron Stars 13

Open Issues• Fallback rate• As in magnetar model:

– Energy deposition in ejecta

• As in collapsar GRBs:– Disk formation– Outflow properties– Interaction of outgoing,

infalling material

The Structure and Signals of Neutron Stars 14

Powering supernova light curves• Thermal

• Radioactive (56Ni) Branch & Tammann (1992)

Kasen & Woosley (2009)Efficiency

The Structure and Signals of Neutron Stars 15

Circumstellar Interaction

• Interaction of ejecta with material at large radius resets internal energy

• Large if Rsh >> R0

Woosley+07

Efficiency

The Structure and Signals of Neutron Stars 16

Magnetar Spindown Power

Kasen & Bildsten (2010)

The Structure and Signals of Neutron Stars 17

Hard X-rays, gamma rays

• For low field strengths, can be significant high energy emission at late times

Kotera+2013

The Structure and Signals of Neutron Stars 18

Soft X-ray flash?• Pulsar could ionize ejecta near peak,

allowing X-rays to escape

Metzger+2014