Gamma-ray Burst Progenitors Ross Church Department of Astronomy and - - PowerPoint PPT Presentation

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Gamma-ray Burst Progenitors Ross Church Department of Astronomy and - - PowerPoint PPT Presentation

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Gamma-ray Burst Progenitors Ross Church Department of Astronomy and Theoretical Physics, Lund With Melvyn B. Davies (Lund), Andrew Levan (Warwick), Chunglee Kim (West Virginia) Wednesday, February 8, 2012 Binary Stars as Long Gamma-ray

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SLIDE 1

Gamma-ray Burst Progenitors

Ross Church Department of Astronomy and Theoretical Physics, Lund With Melvyn B. Davies (Lund), Andrew Levan (Warwick), Chunglee Kim (West Virginia)

Wednesday, February 8, 2012

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SLIDE 2

Binary Stars as Long Gamma-ray Burst Progenitors

Ross Church Department of Astronomy and Theoretical Physics, Lund With Melvyn B. Davies (Lund), Andrew Levan (Warwick), Chunglee Kim (West Virginia)

Wednesday, February 8, 2012

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Two classes based on duration: long and short

Gamma-ray Bursts

Flashes of gamma-rays from immensely energetic extra- Galactic explosions Afterglow fades and reddens through X-ray, optical & IR to radio Detected from space (Swift, Fermi) Follow-up via ground & space based photometry and spectroscopy

Wednesday, February 8, 2012

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SLIDE 4

Two classes based on duration: long and short

Gamma-ray Bursts

Flashes of gamma-rays from immensely energetic extra- Galactic explosions Afterglow fades and reddens through X-ray, optical & IR to radio Detected from space (Swift, Fermi) Follow-up via ground & space based photometry and spectroscopy

Wednesday, February 8, 2012

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SLIDE 5

Long Gamma-ray Bursts - Observations

Longer-lasting emission, softer spectrum, higher fluence Many bursts show co-incident Type Ib/Ic supernova Found in star-forming regions out to very high redshift

  • Type Ibc supernovae show neither H nor Si lines
  • Thought to be the outcome of core collapse of

massive stars (>40ish solar masses)

  • Winds during the stars’ lifetimes remove the

hydrogen envelopes (and He in the case of Ic) See Hjorth & Bloom, arXiv 1104.2274 for a recent review

Wednesday, February 8, 2012

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SLIDE 6

Long Gamma-ray Bursts - Model

Core collapse of rapidly-rotating massive star Some material falls back into a disc around a newly-formed black hole Rotation leads to high specific angular momentum Accretion of the disc produces relativistic jets at the poles

Woosley (1993) ApJ 405 273

Gamma-ray burst observed if the jet points towards us

Wednesday, February 8, 2012

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SLIDE 7

Problem

Strong winds carry off angular momentum ⇒ spins star down

Wednesday, February 8, 2012

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Problem

Strong winds carry off angular momentum ⇒ spins star down Can a binary companion prevent spin-down?

Potential solution

Wednesday, February 8, 2012

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Close binaries

X

In a close binary, one star will raise tidal motions on the surface

  • f the other.

Orbital angular frequency Ω Spin angular frequency ω

Wednesday, February 8, 2012

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SLIDE 10

Close binaries

X

In a close binary, one star will raise tidal motions on the surface

  • f the other.

Orbital angular frequency Ω Spin angular frequency ω If ω < Ω

Wednesday, February 8, 2012

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SLIDE 11

X

Close binaries

X

In a close binary, one star will raise tidal motions on the surface

  • f the other.

Orbital angular frequency Ω Spin angular frequency ω If ω < Ω

Wednesday, February 8, 2012

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SLIDE 12

Tidal torque transfers angular momentum and can spin the star up

X

Close binaries

X

In a close binary, one star will raise tidal motions on the surface

  • f the other.

Orbital angular frequency Ω Spin angular frequency ω If ω < Ω

Wednesday, February 8, 2012

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SLIDE 13

Tide-powered spin-up

To form an accretion disc after supernova, we require that the material at the edge of the core of mass Mc have specific angular momentum

j < jlso =

√ 6GMc c

Levan, Davies & King (2006), MNRAS 372 1351

Wednesday, February 8, 2012

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SLIDE 14

Tide-powered spin-up

To form an accretion disc after supernova, we require that the material at the edge of the core of mass Mc have specific angular momentum

j < jlso =

√ 6GMc c

Assume that the orbit is tidally locked at its closest point, so

Ω =

√ 6GMc R2

c c

Rc 0.2 R

Levan, Davies & King (2006), MNRAS 372 1351

Wednesday, February 8, 2012

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SLIDE 15

Tide-powered spin-up

To form an accretion disc after supernova, we require that the material at the edge of the core of mass Mc have specific angular momentum

j < jlso =

√ 6GMc c

Assume that the orbit is tidally locked at its closest point, so

Ω =

√ 6GMc R2

c c

Rc 0.2 R Taking a typical iron core radius for 25-50 solar mass stars

acrit = 7.36 R

  • Mc

1.7 M −2/3 Mtot 20 M 1/3

Levan, Davies & King (2006), MNRAS 372 1351

Wednesday, February 8, 2012

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Critical separation for tide-powered spin-up is

acrit = 7.36 R

  • Mc

1.7 M −2/3 Mtot 20 M 1/3

Tide-powered spin-up

The binary must both be close and rather massive ⇒ A black-hole companion after binary interaction has brought the two stars close together Perform binary population synthesis to see whether we expect to form such binaries.

Wednesday, February 8, 2012

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M2,pre 7 − 8 M

MBH 5 − 15 M

Population at time of supernova

5 10 20 Companion mass M1/M 3 4 5 6 Pre-supernova separation a/R 5 10 20 Companion mass M1/M 3 4 5 Supernova mass loss ∆M2/M 3 4 5 Supernova mass loss ∆M2/M 5 10 20 Companion mass M1/M 3 4 5 6 Pre-supernova separation a/R

a/R M1/M ∆M2/M ∆M2/M

3 4 5 4 3 5 10 20 3 4 Relevant binaries occupy a well- defined phase space:

a 3 − 5 R

Distribution reflects realistic initial conditions

Wednesday, February 8, 2012

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SLIDE 18

Recap

A binary companion can spin some stars up sufficiently to make a gamma-ray burst. Such binaries should exist but will be rare. Long gamma-ray bursts occur during type Ib/c supernovae of massive, rapidly rotating stars. To spin the star fast enough the companion must be a black hole of roughly ten solar masses.

Wednesday, February 8, 2012

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SLIDE 19

Wednesday, February 8, 2012

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Black-hole formation by accretion

Some black holes are thought to form by fallback (accretion

  • nto a newly-formed massive neutron star).

Figure from MacFadyen, et al. (2001)

Wednesday, February 8, 2012

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Black-hole formation by accretion

Some black holes are thought to form by fallback (accretion

  • nto a newly-formed massive neutron star).

Material from the stellar core is ejected radially to distances up to 1012 cm (107 km)

Figure from MacFadyen, et al. (2001)

Wednesday, February 8, 2012

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Black-hole formation by accretion

Some black holes are thought to form by fallback (accretion

  • nto a newly-formed massive neutron star).

Material from the stellar core is ejected radially to distances up to 1012 cm (107 km) The reverse shock stalls it It falls back and is accreted onto the black hole

Figure from MacFadyen, et al. (2001)

Wednesday, February 8, 2012

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Black-hole formation by accretion

Some black holes are thought to form by fallback (accretion

  • nto a newly-formed massive neutron star).

How does a binary companion affect the fallback? Material from the stellar core is ejected radially to distances up to 1012 cm (107 km) The reverse shock stalls it It falls back and is accreted onto the black hole

Figure from MacFadyen, et al. (2001)

Wednesday, February 8, 2012

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Modelling the effect of the companion

Eject particles radially, with velocities distributed to re-produce the fallback history from hydrodynamical simulations. Treat the particles as “dust” and follow their trajectories in a binary system. Deflected material will form a disc in the orbital plane; follow its accretion onto the newly-formed black hole.

Wednesday, February 8, 2012

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Example trajectories

  • 3
  • 2
  • 1

1 2 x/106 km

  • 2
  • 1

1 2 y/106 km

  • 0.5

0.5 z/106 km z/106 km

Location of supernova Orbit of newly-formed black hole Particle trajectories

Wednesday, February 8, 2012

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SLIDE 26
  • 3
  • 2
  • 1

1 2 3 x/106 km

  • 3
  • 2
  • 1

1 2 3 y/106 km r0 = 1601 km, a = 3.359 R, vrot = 6145 km M1 = 15.61 M, M2 = 5.694 M, ∆ M2 = 2.709 M

The view from above

Newly-formed black hole Material falling back into disc around new black hole (as in single star case) Some gas sufficiently deflected to form a disc around the companion black hole Long fall-back time material lands outside either star’s Roche Lobe

3

  • rot

M1 = 15.61 M, M2 = 5.694 M, , a = 3.359 R, v M = 5 694

Wednesday, February 8, 2012

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First accretion curve

100 1000 10000 t/s 0.01 0.1 1 10 100 1000 10000 Accretion rate (scaled units)

Wednesday, February 8, 2012

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First accretion curve

100 1000 10000 t/s 0.01 0.1 1 10 100 1000 10000 Accretion rate (scaled units)

Early times the same as single star case

Wednesday, February 8, 2012

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First accretion curve

100 1000 10000 t/s 0.01 0.1 1 10 100 1000 10000 Accretion rate (scaled units)

Early times the same as single star case Sharp cut-off from Roche Lobe truncation

Wednesday, February 8, 2012

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SLIDE 30

First accretion curve

100 1000 10000 t/s 0.01 0.1 1 10 100 1000 10000 Accretion rate (scaled units)

Early times the same as single star case Sharp cut-off from Roche Lobe truncation Possible flaring activity?

Wednesday, February 8, 2012

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SLIDE 31

First accretion curve

100 1000 10000 t/s 0.01 0.1 1 10 100 1000 10000 Accretion rate (scaled units)

Early times the same as single star case Sharp cut-off from Roche Lobe truncation Possible flaring activity? Next steps: model M1 disc, look at other binaries

Wednesday, February 8, 2012

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Summary

A black hole binary companion can spin stars up sufficiently to make a gamma-ray burst. This interference can produce sharp light curve breaks & flaring activity. Long gamma-ray bursts occur during type Ib/c supernovae of massive, rapidly rotating stars. Such a binary companion will affect the material that falls back on to the black hole.

Wednesday, February 8, 2012