Download Gamma-ray bursts and hypernovae

Gamma-ray bursts and hypernovae
Konstantin Postnov
Sternberg Astronomical Institute
Moscow
Erice-2004, July 6, 2004
Outlook
• Introduction
• GRB as superstrong cosmic explosions
• Association with supernovae – a critical
view
• Thermal effects in ambient plasma
• Conclusions
BATSE rate ~1 per day
No repetions, full isotropy
`Brief course’ of history of GRBs
• 1967- Discovery by American military Vela satellite
1973 – Declassified for scientific community
End of 1970s – `Konus’ experiments onboard Russian Veneras
(E.P.Mazets et al)
• 1991-2000 – `BATSE’ (CGRO) era. Largest homogeneous
data (a few thousands) on GRBs. Debates on galactic vs
extragalactic origin
• 1997-… Afterglow era. Discovery of afterglows in X-ray
(BeppoSAX, 1997), optical, radio. Triumph of cosmological
model for (long) GRB origin. Multivawelength GRB astronomy
1998 – possible association of GRB980425 with nearby
peculiar type Ic SN1998bw. Start of hypernova era (?)
Observed:
•
•
•
•
•
•
•
+
General properties
Duration: 0.1-1000 s
Fluence:
S~10-7-10-3
erg/cm2
Spectrum: nonthermal,
10keV-100 MeV
Variability: high, 1-10 ms
Rate:
1 per day
Location:
z=0.17-4.5,
(but 980425 z=0.0085),
star-forming galaxies
Associated events: X-ray
(~100%), optical (~70%),
radio (~50%) afterglows
F(t)~t-α α~1-2
Environment signatures:
transient X-ray em./abs.
lines, metal rich material
Derived (for long GRBs
only!):
• Isotropic energy release
Eγ=4πdl2/(1+z) ~1051 -1054
erg (but 980425 ~1048)
• Evidence for jets from
afterglow breaks θj~0.010.1
• Points to ‘standard’ energy
release ΔE~1050-1051erg
equally shared in kinetic
energy and radiation
• Photon energy correlations
vFν~Eiso
• Association with SN Ib/c
GRB spectra:
Two power laws smoothly joined together (Band et al 1993):

f (E) 
 (2   ) E 
 E peak 
 E 
A
 , E  (   ) 
 exp 

100
keV
E
2






peak


 (   ) E peak 
A

(2


)100
keV


(   )

 E peak 
 E 

 exp(    ), E  (   ) 

2


 100keV 


Slopes α, β and peak energy Epeak vary with
time
Generally, spectrum gets
softer:
...but not always:
…and even gets harder:
GRB 941017 (Gonzalez et al. 2003)
EGRET-TASC detection
Duration: ~150 s
A new, very hard
component appeared:
E2 FE~E1, Epeak>200 MeV
Signals hadronic component
(UHECR) with subsequent
photomeson interactions?
(Dermer & Atoyan,2004)
(Gonzalez et al.’03)
Amati et al. (’02,’03): Eiso-z, Ep-Eiso
correlations
22 events with known z and spectra:
Lg Epeak~0.45 lg Eiso
Are older GRB more energetic?
Explanation of GRB spectra (not fully
satisfactory…)
Standard synchrotron shock model (SSM):
Optically thin synchrotron radiation by energetic
electrons left to radiate without further
acceleration. Electrons are accelerated by the
Fermi mechanism in relativistic shocks created by
the “central engine” (dN/dE~E-p, p~2.2-2.3)
BUT: many individual GRB do not fit this! Additional
acceleration, IC, change in electron energy index p
with time, etc., etc., etc. are invoked
Basic model: ultrarelativistic (Γ>100) jets
associated with hyperstrong (1051 erg)
explosion (a “hypernova”)
Term “hypernova” introduced by B.Paczynski (1998) according
to energy release in an explosive cosmic event
• Nova (thermonuclear explosion on white dwarf surface)
ΔE ~ 10-9Mc2~1045erg
galactic rate ~ 1 per a few year
• Supernova (core collapse of massive star, SNII,Ib,Ibc or
th/n explosion of a WD with MCh~(mPl/mp)3mp~ 1.3 M)
ΔE ~ 10-1Mc2~1053erg (~binding energy of neutron
star, mostly in neutrino)
kinetic energy ~1050erg (~binding energy of
stellar envelope)
galactic rate ~ 1 per a few 10s years
● Hypernova (core collapse associated with black hole
formation? Requires the most extremal conditions
e.g.B~1015G, rapid rotation, etc.)
ΔEγ ~1051-52erg
kinetic energy >1051erg
galactic rate ~ 1 per a few 104-106 years
Evolution of massive stars:
M<25 M neutron star
M>25 M black hole:
Hypernova MNi>0.1 M
Ekin>1 foe
Faint supernova
Nomoto et al.2004
Fireball models for GRBs
• Rees & Meszaros (1992, 1994…) Recent review: Piran 2004
• Thermal energy of explosion is converted to kinetic energy of
thin baryon shell with ultrarelativistic speed (Γ>100) to avoid
compactness problem and explain non-thermal spectra
• GRB is produced by internal (most likely) shocks within the
expanding shell, or by external shock in inhomogeneous ISM.
• Internal shocks  GRB itself, external shock in ISM  Xray, optical, radio emission of the GRB `afterglow”
• Initial interaction of GRB ejecta  Reverse shock
propagating inward and decelerating fireball ejecta. Erases
the memory of the initial conditions. Expansion approaches
self-similarity (Blandford & McKee solution, 1976) ΓBM~r-3/2
(simply from E0~(4π/3)r3n0 mpc2Γ2 )
• Parameters: E0, no (const or 1/r2), Γ0, p, εB, εe
ES
IS
RS
Γ2> Γ1
?
GRB
Afterglow
Optical afterglows (synchrotron emission
from relativistic blast wave in ISM)
990123
021211
Early: reverse shock
in the ejecta
Late: external shock
in ISM
Breaks in ag lc:
decelerated jet
Jet beaming effect in the GRB light curves
Θ~1/Γ(t)~t3/8
θ0
Γ(r)~r-3/2~t-3/8
r
t~r/Γ2
Emitting area: A~r2θ2~r2/Γ2~Γ4 t2/Γ2~t10/8, θ<θ0,t<tj
A~r2θ02~Γ4t2~t1/2,
θ>θ0, t>tj
 A increases slower after t>tj Θ(tj)=θ0
Observed emission~(emitting area)x(specific intensity)
For SSM, I~(B2γe2)’ Γ~(εBΓ2)(εeΓ2)Γ~Γ5~t-15/8
so
F(t<tj) ~ AxI ~ t10/8t-15/8 ~ t-5/8
F(t>tj) ~
t1/2t-15/8 ~ t-11/8
θ0=0.16(n0/E0,iso)1/8(tj/days)3/8
Eγ=E0,iso(θo2/2)
E0,iso=4πdl(z)2S/(1+z)
Evidence for associated SNe
1.
GRB980425 and peculiar type Ib/c SN 1998bw in nearby
galaxy ESO184-g8 (z=0.0085)
1998bw – model light curve
SN2002ap – spectral evolution modeling
2. Bumps in the late (10-30 days) optical
afterglows
Yet another case: GRB 021211
Special cases: GRB 030329 – nearest
(z=0.168), brightest (S~10-4erg/cm2)
Host: a SMC-like star-forming galaxy
SN 2003dh signature in light curve?
Difficult to directly accommodate!
SN2003dh spectral apperance (Matheson
et al 2003)
Zooming in MMT spectra
Also in the VLT spectra:
Detailed light curve
GRB030329: but earliest optical spectra
(BTA 6m telescope, Sokolov et al. 2003)
difficult to explain by shock breakout as pre-SN must be compact!
Light-curve residuals – could supernova do
this?
Optical variability and polarisation
suggests structured environment
Greiner et al.
2003
List of GRB/SN associations
+s
(from Dar 2004)
W49B – a hypernova remnant? (Keohane
et al. 2004)
red: molecular
hydrogen 2.12μ
(Palomar Hale WIRC)
green: 1.64μ FeII
(Palomar Hale WIRC)
blue: Fe Kα
(Chandra). No NS.
HN explosion in
a molecular cloud
a few thousand
yrs ago?
Clues from radio observations
• Radio scintillations
in ISM: Fresnel
radius ~5
µasdirect
measurement of
angular size 
evidence for
relativistic motion
(970508, 030329)
• Vapp ~4c
Frail et al. 1997
Radio observations of GRB030329 (Taylor et al 2004)
1. Directly reveal apparent superluminal
expansion v~3-5c, in accord with
relativistic blast wave model for GRB
afterglows
2. Inconsistent with cannonball model
prediction for plasmoid superluminal motion
(Dado et al 2004) (NB: general problem for
CB model is absence of rapid radio
diffractive scintillations in GRB030329,
though the expected anglular size of
plasmoids ~0.01 µas << Fresnel (5 µas )
scale)
But: radio luminosities of GRB and SN1b/c
are strongly different (Berger et al.2003)
SN/GRB rates
SNIbc in spiral galaxies: 0.2/100yrs/1010L(B)
Local univesre:
~ 108L(B) Mpc-3
SNIbc rate ~ 2 104Gpc-3
GRB rate:
~250 Gpc-3 (factor 3-10 uncert.
due to collimation)
Only a few percent of SNIbc can be
associated with GRBs (unlike CB model).
Additional conditions (e.g. binarity etc.) must
be imposed on the progenitors
‘Standard energy’ issue
Postnov, Prokhorov and Lipunov 1999, 2001 (idea):
1.Standard explosions ΔE ~ 5x1051 ergs
2.Structured jets
Frail et al. 2001 – standard energy from jetcorrected afterglow observations.
Berger et al. 2003 – structured jets from radio
calorimetry of GRB 030329, 980425
Jet-corrected energy release (Frail et al)
Beaming-correction factor for the rate/energy ~30-200
Radio calorimetry – structured jet
(Berger et al. 2003)
Current models: “universal jet” vs “uniform
jet”
Recent discoveries : Light echo on dust for
GRB 031203 (loc. INTEGRAL, X-ray rich)
GRB031203 – SN 2003lw appears
HETE2: GRB-X-ray rich-XRF (Lamb et
al. 2003)
Apparently continuous
transition
GRB=>X-ray rich=>XRF
X-ray flashes: XRF 020903 localization
XRF 020903 host galaxy spectrum
Z=0.251
Star-forming galaxy
Thermal effects in ambient plasma
(Kosenko, Blinnikov, Sorokina, PK, Lundqvist
2001, 2002)
Bisnovatyj-Kogan & Timokhin 1997
First consideration of environmental effects
Fading X-ray emission lines in 011211
Reves et al – XMM observations
of fading (~10 ks) emission lines
Kosenko et al 2002 –
thermal cooling of plasma
clouds heated by GRB
N~106 1-3AU-sized
clds ne~1011 cm-3
within
0.1 pc are needed
Structured environment from X-ray and
optical variability
Jakobsson et al.2004,
Δt~1 hr in optical and
X-ray afterglows
0.5-10 keV
3-5 AU structures!
Mini-SN effects (Blinnikov & Postnov 1997)
on clouds
1.Optical thickness increases
with plasma cooling  appearance
of effective photosphere
2. Clouds cool down producing
“bumps” in afterglow lc
Statistical analysis of GRB distribution inside
host galaxies (Dasha Kosenko’s talk on Wed.
July 7)
Bloom et al
2000, 2001
Tsvetkov et al
2001
Kosenko et al
2004
Basic idea: to
compare GRB
distribution
with other
astronomical
objects (SNe,
XRB…)
Problem: GRB error boxes are (still) ~a few arcsecarcmin  no straightforward comparison can be made
Quantile-diagrams
(surface density)
DM: NFW,
rs= 15 kpc (right)
rs= 4 kpc (left)
Quantile diagrams for error-weighted GRB positions
Error-weighted GRB
distribution vs NFW
and Burkert DM profiles
rs= 15 kpc
rs=4 kpc
Dark matter:
NFW profile (cuspy) ρ(r) ~ 1/(r/rs)(1+(r/rs))2
Burkert
(w/o cusp) ρ(r) ~ 1/(1+r)(1+r2)
Central engine
•
1.
2.
3.
4.
5.
•
1.
2.
3.
Requirements:
Energy ~ 1051 erg (thermal or Poynting-dominated)
Collimation θ0~1-20 degrees
Long & short GRBs (two different engines?)
Rate 0.1-1% of SN rate
Variability δt~1 ms  compact object; GRB duration
T~10-100 s  prolong activity
Models:
Collapsar: ~10 M black hole + 0.1 M accretion disk
formed in a hypernova explosion
Poynting-dominated energy release by rapidly rotating
strongly magnetized newborn neutron star (Usov 1992)
Binary neutron star merging (for short GRBs)
Conclusions (statements)
• GRBs are (rare) violent cosmic explosions in remote
galaxies; some of them are associated with
extremely strong (Ekin> 1051 erg) peculiar SNe
(hypernovae)
• GRB power (1044erg/yr/Mpc3) is comparable with
UHECR power
• GRB explosions produce ultrarelativistic jets and
drive strong shocks in the ambient medium
• Environmental effects are important in shaping
GRB afterglows
• We understand better GRB afterglows than GRB!
Conclusion (Issues to be solved)
• Are all GRB (including short/hard) and XRF really
universal (jets? energies? Off-axis jets?)
• Do GRB really associate with core-collapse
supernovae and (rotating) black hole formation?
• Which is the mechanism for gamma-ray emission
(relativistic shocks? If yes, internal vs external
shocks?)
• Hot (fireball) or cold (Poynting-dominated) jets?
• Association with dark matter? (Are there elliptical
hosts?)
• Close expectations: SWIFT mission (sep ’04) –X-op
afterglows, rapid alerts, good statistics (~100/yr)
• More remote future: GLAST mission (06), highenergy neutrinos(?), gravitational waves(?)…