Agnieszka Janiuk

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Agnieszka Janiuk
N. Copernicus Astronomical Center, Warsaw
Gamma Ray Bursts from Collapsing Massive Stars
Collaborations R. Moderski (CAMK), D.
Proga(UNLV), Y. Yuan (ChAS), R. Perna (JILA), T.
Di Matteo (CMU), B. Czerny (CAMK), D. Cline
(UCLA), S. Otwinowski (CERN), C. Matthey (CERN)
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To emit fireball, the engine must be very
energetic. To produce shocks, the engine must be
active and variable for a long time
1014 cm
Gamma rays are believed to come from the internal
shocks, produced in the relativistic (Ggt100)
fireball.
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Digression what makes the jet?

• Jets are ubiquitous in nature AGNs, QSOs, XRBs,
  YSOs, GRBs...
• They are not required by any physical law (such
  as energy conservation).
• The 3 proposed mechanisms of jet acceleration
• Radiation pressure
• Thermal expansion
• Magnetic fields and rotation
• Jet is domineted by
• Poynting flux (small scales)
• Matter (large scales)
• Jets are collimated by
• Accretion disk/coronal walls
• Pressure gradients in the environment
• Surrounding matter-dominated jet
• Poynting-jet is able to collimate itself through
  the toroidal B field

Fragile, 2008 (arXiv0810.0526)
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The model of a central engine for GRB must
answer, which astrophysical process produces the
relativistic fireball that emits gamma-rays.
Important constraints (Piran 2005)

• Timescales and variability dt/T 10-3 10-4
  for 80 of bursts
• Short and long GRB dichotomy
• Short - hard GRBs (T90lt2 s)?
• Long -soft GRBs (T90 gt 2s)?
• Energy (significant fraction of the binding
  energy for compact object)?
• Collimation (1o lt ? lt 20o)?
• Rates (about 3 10-5 per year per galaxy)?

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To emit fireball, the engine must be very
energetic. To produce shocks, the engine must be
active and variable for a long time. The most
popular model invokes the internal shocks in the
jet that produce gamma rays and variability (Sari
Piran 1997). Also, variability can be well
reproduced with a shot-gun model (Heinz
Begelman 1999).
Janiuk, Czerny, Moderski et al. (2006)?
Kinematic jet model theoretical lightcurves of
long GRBs, depending on the observers viewing
angle Tested against observations lightcurves,
PDS spectra Prokopiuk Janiuk, in prep.
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Collapse of massive star favored for long GRBs -
associacion with star forming galaxies (e.g.
Fruchter et al. 2006)? - concurrent SN-like
outbursts (Bloom et al. 1999 Stanek et al.
2003)? - redshift distribution follows the star
formation rate (Coward 2007)?
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Supernovae

• type I rapid lightcurve evolution
• ? - type Ia standard
• - type Ib He lines produced in the massive
  ejecta, by non-thermal excitation by fast
  particles emitted by the (56)Ni -gt (56)Co-gt
  (56)Fe decay.
• - type Ic progenitor must be either an
  extreme WR star, or a binary (Nomoto 1995)?
• - type II progenitor is a massive red giant

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Supernovae observed in associacion with GRBs -
SN1998 bw GRB 980425 - SN 2003 dh GRB 030329 -
SN 2003 lw GRB 031203 - SN 2006 aj XRF
060218 ? All of these are Type Ic All have broad
line spectra -gt ejection velocities 50,000
km/s They account for 20 of the BL SN Ic 2
of all SN Ic
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• Hypernova
• - very high expansion velocity
• - bright luminosity
• - postulated to be an energetic outburst produced
  by a collapsar (Woosley 1993 Paczynski 1998)?
• - very strong explosion energy (gt few x 1051
  ergs)?
• - strong evidence for assymetry (Nomoto et al.
  2005)?
• - massive star models fit well the observed
  hypernovae ( Mazzali et al. 2006)?
• - large uncertainty in modeling due to the
  initial mass function of massive stars (5-40
  core collapse SN form the black hole Fryer
  Kalogera 2001)?

Eta Carinae future candidate for hypernova
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• Hypernovae are rare (about 1000 times less
  frequent than normal SN (Soderberg et al. 2006)
• All hypernovae have been classified as Ib/c SN
  (no H lines, nor He lines in the spectra)
  probably a subset of them

Rates of Supernova vs. Hypernova

• Rate of all core-collapse SN 6x10-3 /yr/galaxy
  ( Fryer et al. 2007)
• Type Ib/c are 15 of all core collapse
• Hypernovae are 5-10 of observed type I b/c
• 1-10 of SN Ib/c can be associated with GRBs
  this coincides with that of hypernovae
• Rate of all core-collapse increases with
  redshift (no specific data for I b/c or
  hypernova)?

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• The collapsar
• Woosley (1993) SN Type Ib 'failed' because of a
  fast rotation of the Wolf-Rayet star
• Paczynski (1998) some GRBs must be linked to the
  cataclysmic deaths of massive stars -gt hypernovae
• MacFadyen Woosley (1999) and follow up works
  hydrodynamical computations of the relativistic
  jet propagation through the stellar envelope

MacFadyen Woosley (1999)?

• Two reasosns for SN to fail (Fryer 1999)
• Large ram pressure at the top of the convective
  zone
• Large binding energy for the most massive stars

GRB progenitors the most massive stars, that
fail to produce an explosion under the standard
core-collapse supernova
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The collapsar engine of a GRB

• Must form a black hole in the center of the star
• Must produce sufficient angular momentum to form
  a disk around black hole
• Must eject the hydrogen envelope, so that the
  jet can punch out of the star

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Progenitors of the I b/c Supernovae single or
binary stars?

• Most massive stars (Mass gt 20 solar masses
  Hirshi et al. 2004)?
• Wolf-Rayet stars have lost the H envelope due to
  strong winds
• Single stars only fast rotating stars above
  solar metallicity produce strong shocks and eject
  lots of nickel (Heger at al. 2003)?
• Fast rotating stars can mix their envelopes,
  burning effectively H into He (Yoon Langer
  2005)?
• Binary stars mass transfer can eject matter and
  lead to He star formation.
• Possibly, gt75 of all massive stars are in close
  binaries (Kobulnicky et al. 2006)?

SN 2008D
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Single stars only fast rotating stars above
solar metallicity produce strong shocks and eject
lots of nickel (Heger at al. 2003)?
This GRB rate must be lower by a
factor Indicating the fraction of stars that
retain large angular momentum
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Metallicity measurements

• Wind mass loss sensitive to metallicity
• At lower metallicities, weaker winds allow more
  massive cores gt GRBs probably will not occur
  above solar metallicity
• Metallicity measurements
• Absorption lines in the GRB afterglows
• Emission lines of HII regions in the GRB host
  galaxy
• Interstellar extinction in the host galaxy
• Morphology of the host galaxy, e.g. Compared to
  SMC/LMC

Nebula NGC 2359
There is no consistent picture direct
measurements argue for higher Z, while indirect
measurements indicate lower Z.
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Progenitors of Hypernovae

• Most of the currently discussed progenitors do
  not distinguish between fallback and direct
  collapse black holes
• GRBs probably will not occur at solar
  metallicity, if we need a direct collapse to
  black hole. At lower metallicities, weaker winds
  allow more massive cores.
• Below 0.4 ZSun, the stars cannot loose the He
  envelope (Heger 2003).
• Star is either born rotating rapidly, or is spun
  up by interaction (tidal forces, merger). In
  binaries, the companion is used to strip off the
  hydrogen envelope without the angular momentum
  loss.
• Single stars can also loose the H envelope
  because of mixing and burning to He (Yoon
  Langer 2002). But if the He envelope is also
  lost, these models are ruled out.

WR124
Constraints are more restrictive for single-star
models, but without better understanding of
winds we cannot say more (Fryer et al. 2007).
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How long is a long GRB?
(Janiuk, Proga, Moderski. 2008a, 2008b)
Chemical composition and density distribution in
the pre-SN star (Woosley Weaver 1995)
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How the pre-collapse star rotates?

• The distribution of specific angular momentum in
  the pre-SN star unknown.
• Stellar evolution models
• Neglect centrifugal forces
• Do not accurately treat the angular momentum
  transport through magnetic fields
• Sensitive to the loss of ang. momentum through
  wind
• Some assumptions we have made
• Polar angle dependence (differential rotation)?
• Radius dependence (rigid rotation, with a
  possible cut-off on lspec)?
• Constant ratio of centrifugal to gravitational
  forces

lspec l0 (1-cos ?)? lspec l0 (r/rin)sin2?
(Janiuk et al. 2008a, 2008b)
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Conditions for torus existence
The rotation must prevent the envelope material
from the radial infall onto BH.
Specific angular momentum
lspec gt lcrit 2GMBH/c (2-A2(1-A)1/2)1/2

• BUT
• Black hole mass is growing fast (accretion rate
  of 0.01-1 Msun/s)
• Spin can be changing
• gt the GRB is emitted only until lgtlcrit is
  satisfied.

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The black hole grows due to accretion
The time evolution of the collapsar gt iterative
procedure 1. BH mass iron core mass 2. Envelope
schells accrete 3. Check for conditions given by
the changing BH mass and spin
Various possible accretion scenarios
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GRB requires large accretion rate and spinning BH
Schwarzschild and Kerr BH case Janiuk Proga,
2008, ApJ, 675, 519 Janiuk, Moderski Proga,
2008, ApJ, in press
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Hyperaccretion neutrino-cooled disk

• - Cooling mechanisms neutrino emission,
• advection, Helium photodisintegration,
• radiation
• - Neutrinos can be absorbed and scattered
• - Equation of state should treat the species
• under the condition of reactions equilibrium
• and supplemented by the charge neyutrality
• condition

Electron-positron capture and beta-decay p e-
? n ?e n e ? p ?e n ? p e-
?e Thermal emission e e- ? ?i ?i n n ?
n n ?i ?i ? ??e ?e
-
-
-
-
-
-
?
p
e-
n
(Popham, Woosley Fryer 1999 Di Matteo, Perna
Narayan 2002 Kohri Mineshige 2002 Janiuk et
al. 2004 Kohri, Narayan Piran 2005 Janiuk et
al. 2007 Chen Beloborodov 2007)?
e
a
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• The disk accreting at rates gt 0.1 MSun s-1 is so
  hot and dense (T1010-1011 K, ?1010-1012 g cm-3)
  that the plasma is totally opaque to photons, and
  neutrinos can also be trapped
• Energy from the disk can be extracted by neutrino
  annihilation
• Alternatively, energy can be extracted by the
  magnetic field and spinning black hole (the
  Blandford-Znajek mechanism)

Chen Beloborodov (2007)?
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Efficiency of neutrinos depends on initial
accretion rate, and decreases in time
Janiuk et al. (2004)?
Chen Beloborodov (2007)?
Neutrino annihilation inefficient when accretion
rate lt 0.01 Msun/s. This will slightly depend on
viscosity and black hole spin.
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We end up with three kinds of jets from the
collapsar
0-1.5 s
0-430 s
0-130 s
Precursor jet, powered by v-v large m, small A
-
First jet, powered by both v-v and BH
rotation large m, large A
-
Second jet, powered by BH rotation small m,
large A
.
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Precursors found in 20 of BATSE sample
Lazzati (2005)
GRB 0803319B
Brightest optical counterpart mv 5.3
Empirical model of a 2-component jet fitted with
two opening angles (Racusin et al. 2008)?
Image from Pi of the sky, http//grb.fuw.edu.pl
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• Instabilities in the accreting torus possible
  mechanism of causing a long time gap between the
  precursor and the burst, or the short-term
  variability seen in the prompt phase (Wang
  Meszaros 2007).
• Precursor phase in the prompt emission seen in
  some GRBs, might be produced by the jet breaking
  through envelope (Paczynski 1998 Ramirez-Ruiz et
  al. 2002)
• Recent hydro Simulations by Morsony, Lazzati
  Begelman (2007) found three distinct phases
  during the jet propagation precurosr jet,
  shocked phase and unshocked phase.

• Density, pressure and gamma_inf at time 30 s.
• Cocoon high ?, high P, low G
• Precursor high G, off-axis
• Shocked jet low ?, high P, high ?
• Unshocked jet low ?, low P, high G

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Instabilities in the accretion disk - May be
related to the late-time activity of the GRB
(such as X-ray flares e.g. Perna et al. 2006)?
- proposed as the sources of gravitational waves,
that may probe the angular momentum of the
collapsing star (Fryer et al. 2002)? - Black
hole spin can be coupled to the disk, enhancing
the strength of the instability, then possibly
detectable by LIGO (van Putten 2005)?
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Thermal instability the local density and
pressure drops, while the temperature
increases. Our solution is based on the detailed
treatment of the EOS, coupling the
beta-equilibrium and the neutrino trapping
effects, as well as including the information of
the chemical composition in the process of Helium
photodisintegration.
Janiuk et al. (2007)?
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Summary
GRB long durations may provide constraints for
the rotation law in the pre-SN star. The minimum
accretion rate limit for the neutrino-powered
jets, in the Schwarzschild black hole models,
results in GRB durations up to 40-100 s. The
minimum accretion rate and BH spin limit, for
jets powered by both neutrinos and black hole
spin, results in GRB durations up to 50-130
s. The above values will be smaller if the H/He
envelope was already stripped In the Kerr black
hole models, we find the solutions corresponding
to three kinds of jets precursor jet, early jet
and late jet, powered by different mechanisms.
Possibly, the opening angle of these jets is
changing, which would have some observational
consequences. The instabilities in the accreting
torus play important role for the observed
emission
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Constraints on the GRB progenitor from
observations and SN models

• Type Ic SN gt progenitor must loose the H and
  most of He envelope
• Occur in the brightest parts of galaxies gt come
  from the most massive stars
• Occur in metallicities from 0.01 to 1 gt single
  star models strongly constrained
• Single star models may require mixing to burn H
  into He effectively
• Binary star models fit better to the
  observational constraints

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Thank you