GammaRay Bursts Emission Components During the Earliest Epoch Felix Ryde Stockholm University

1
Gamma-Ray Bursts Emission Components During the
Earliest EpochFelix RydeStockholm University
2
Outline

• Introduction basic observations
• Why relativistic, collimated outflow?
• Models Evidence for and against the collapsar
  model. Fireball Physics. Curvature effect
• Comparison with observations spectra, light
  curves and spectral evolution
• Conclusions and future observations.

3
Introduction

• Gamma-ray bursts (GRBs) were discovered
  accidentally by the Vela Satellites which were
  launched by the USA to monitor compliance with
  the ban on nuclear tests in space.
• - The discovery of GRBs was announced .
  by Klebesadel et al. in 1973.

• The bursts last for a few msec 103 s.
• - The fluence (energy/area) is between
  10-7 - 10-4 erg cm-2.
• - The peak of the spectrum lies between
  10 keV MeV.
• A few observed every day
• - The distribution is isotropic.
• - (1/million years/galaxy)
• - Explosions in the early Universe
  median distance of z1 (0.4 Tuniv)
• Birth cry of a black hole

Note 1 Click on underlined text to jump to see
the details of the particular item.
Note 2 To return back to this slide, click on
the underlined headline of the slide you jumped
to.
4
GRB light-curves
Fishman Meegan, 1995 (Ann. Rev. AA)
Time after Trigger s
Time after Trigger s
Time after Trigger s
The CGRO was launched in 1991 and removed from
orbit on June 4, 2000. It detected a total of
2704 GRBs during the 9 year period. The energy
range for COMTEL was 1-30 Mev EGRET energy range
was 20 Mev to 30 Gev. And the BATSE had
detectors covering energy range of 25-50 kev,
50-100 kev and 100-300 kev.
5
Spectral Evolution Crider et al. 1997, Ryde 1999
GRB spectrum
Fishman Meegan, 1995, Ann. Rev. AA 33, 427
Composite CGRO spectrum 70 keV - 10 MeV
Energy
Preece et al. 2000, Ap. J. Supp., 126, 19
(Photon index)
Line-of-death of OTTS
(Photon index)
6
GRB Duration
BATSE observations
Long bursts with soft spectra
Short bursts with hard spectra
2 s
Note 1 To return back to the original slide,
click on the underlined headline at the top of
the slide.
7
ISOTROPY
Note 1 To return back to the original slide,
click on the underlined headline at the top of
the slide.
8
Observations
Discovery Emission/Aborption
lines Cosmological, no spectral lines gt
Afterglow, hostgalaxies More Afterglows ?????

• Vela 1967-1970
• Solar Maximum Mission 1972
• HEAO-3 1972
• Cos-B 1975
• Granat/Sigma 1989
• Compton GRO 1991
• Beppo SAX 1996
• Hete 2001
• INTEGRAL 2002

9
Compton Gamma-Ray Observatory
BATSE

• Burst and Transient Source Experiment (BATSE)
• Mission period 1991 - 2000
• Number of GRBs detected 2300
• 8 detector modules
• Energy range 10 - 2000 keV
• Energy resolution 20 (10) at 100 keV
• Time resolution 64 ms

10
2
2025 cm
8 modules on each corner of the CGRO Large
Area Detectors (LAD) Spectroscopic Detectors
(SD)
2
127 cm
11
Confirmation of cosmological distance

• The launch of BeppoSAX (Italian-Dutch satellite)
  in 1996 improved the angular localization of
  bursts by a factor of about 20 and enabled search
  for optical counterparts. This lead in early 1997
  to the discovery of fading optical afterglow and
  measurement of redshift, z.
• We now have redshift for about 35 GRBs the
  median z1.
• For isotropic explosion the total energy in
  gamma-rays alone is of order 1054 erg.

As of May 2002, redshift for 27 GRBs were known,
with a mean z of 1.27 median z 0.99. This
information is from Djorgavskis lecture at the
Harvard GRB meeting in May 2002.
12
GRB 970228
In 1997 Beppo-SAX discovered the X-ray
counterparts afterglow
arc-min accuracy positions
GRB 990705
This enabled follow-up observations of the
afterglow by optical telescopes and
identifications of the host galaxies
Cosmological distance!
13
GRB 990123
990123 reached 9th magnitude for a few moments!
First optical GRB afterglow detected
simultaneously
14
Physical Model
15
GRB Explosions are Highly Relativistic
In this case we should not see any gs above
MeV and see thermal emission
You do see that
In most cases you do not see that
Relativistic outflow solves this problem
1. 2. Photon energy in source frame smaller by a
factor of G
(G100-1000)
High energy density in any case leads to
relativistic flow Paczynski 1986, ApJ 308,
L43 Goodman 1986, ApJ 308, L47
Note This is an animation slide. You need to
click on the mouse several times to display all
the texts.
16
Reference Frames and relativisitc time
transformations
Variability time and source size
Second photon emitted at t
Shell and photon emitted at t0
vtR
Observer frame
G
photon
c t
Comoving frame
Lab frame
Shell moving at
17
Spherical or Conical?
If , no observable distinction
1. As a result of relativistic beaming effect
observer can see only a limited portion of
the ejecta
Observer
2. Since the opening angle does not change,
the dynamical evolution is the same.
18
Note This is an animation slide. You need to
click on the mouse several times to display all
the texts.
19
As a blast wave (external shock) sweeps a larger
volume of ISM, it is decelerated. The Lorentz
factor finally becomes lower than
Spherical adiabatic expansion
The blast wave begins to expand side ways and it
is decelerated exponentially.
We can determine the opening angle from the break
time of the afterglow light curve.
20
GRBs as constant energy reservoirs.
Frail et al.

• Collimation brings down the total energy required
  for the explosion
• 
  ...conspiracy? Testable.

21
Models for GRBs that can produce low-baryonic
load, relativistic outflows
Collapsar model
Merger of n-n or n- BH
(Woosley 93 Paczynski 98)
(Narayan, Paczynski Piran, 92 )
Short Bursts (lt 2s)
1. Occurrence 2. Energy availability Collimation
brings down the total energy required.
Long Bursts (gt 2s)
22
Hypernova
23
Jet piercing through the body of the progenitor
star approx 7s introducing instabilities,
Kelvin-Helmholtz
Pstar gt Pjet gt collimation 3 deg.
51
Low and high density and G. Cocoon
lt10 erg
24
5.
SN-explosion
4.
3.
2.
1.
Neutrinos GW
25
Evidence in Support of the Collapsar Model
1. Bursts are found at a median distance of 3
kpc from the center of their host galaxies.

3. X-ray emission lines GRB 991216 , 011211?
Note that
is OK for the collapsar model
Note 1 Click on underlined text to jump to see
the details of the particular item.
Note 2 To return back to this slide, click on
the underlined headline of the slide you jumped
to.
26
The Supernova Connection
GRB011121
Afterglow faded like supernova
Data showed presence of gas like a stellar wind
Indicates some sort of supernova and not a NS/NS
merger
GRB offset from center of host galaxy
Bloom, Kulkarni Djorgovski, March 2002, AJ
(using 21 GRBs)
27
2.Plateau in Optical Light-curve
Galama et al., ApJ, 2000, 536, 185
GRB 980326 also had a plateau, Bloom et al.,
Nature, 1999 GRB 011121 Bloom et al.,
astro-ph/0203391
Note Click on the underlined headline (at the
top) to return back to the slide.
28
Evidence Against Collapsar model
1. Nearly constant energy in relativistic outflow.
2. Very low density in 1 case the highest
density one find is 30 cm-3 which is
perhaps too low for giant clouds.
4. It is unlikely to get short duration bursts in
this model.
In one case (GRB 011121) the radio data seems
to require r-2 density profile (Price et al.
2003).

29
Summary
1 erg 10-7J
constant
collimated
3. Baryonic mass content of the jet 2x10-7
6x10-6 Mo
Mo1030 kg
4. Low density of surrounding medium 10-3 30
cm-3
5. No firm evidence for r-2 structure (except in
one case)
6. Possible association with star formation i.e.
support for the collapsar model.
Energy in Relativistic Ejecta, Jet Opening Angle
and ISM Density

• Synchrotron model explains the afterglow and
  maybe the prompt emission

30

Internal-External Shock Model for GRBs
Internal collisions Internal Shocks
External Shocks
ISM

GRB
Afterglow
3
31
The Fireball Evolution
Internal-External Model
(10 Mo BH)
Initial Fireball
Saturation Radius t10 s
Internal energy has been transformed into kinetic
energy.
The Primary Engine Stops t?
Dimensionless entropy
Transparency Radius
The shell becomes optically thin photosphere
32
The Fireball Evolution contd
Internal Shocks
G fluctuations within the outflow gives internal
shocks (hierarchical coalescence)
Short Timescale Variability
External Shocks
Shell is sweeping up mass Ekin -gt Eheat
Substantial deceleration when EheatE
33
Spectral Components in the observed spectrum -
Theory

• Synchrotron emission from the shocks

Shock accelerated electron distribution
Synchrotron Emission Spectrum
b1
N(g)
In
log
a1
-(p-1)/2
-p
1/3
-(p1)
Ep
gmin gmax g
nmin nmax n
log
Shock acceleration 1st and 2nd order Fermi
Escape of particles Cooling time acceleration
time (dynamical time)
34
GRB spectrum
Fishman Meegan, 1995, Ann. Rev. AA 33, 427
Preece et al. 2000, Ap. J. Supp., 126, 19
(Photon index)
(p1)/2
-2/3
(Photon index)
35
2. Thermal Photopheric Emission (Black Body)
Lorentz contraction and Light travel effects
t1 gt
36
2. Thermal Black Body Emission (contd)
Thermal baryonic photosphere
shocks
Relativistic wind
tau1
Observer
Approximately the same for all shells
Daigne Mochkovitch (2002) predict that the
thermal emission could be rather bright in the
gamma-rays.
37
Observed spectrum (theory)
Thermal Photophere, T
Photospheric Comptonization, PHC
. 2
L/Mc
Shock Synchrotron, S
Why has one not seen these components clearly
already in the observations?
Shock pair-dominated Comptonization, C
38
Angular SpreadingCurvature Model
Ryde Petrosian 2002, ApJ 578, 290
Visible surface
1/G
impulse response
Angular spreading, due to the light travel time,
will smear out both the spectra and the light
curves of GRBs in the observer frame.
39
Reference Frames and relativisitc time
transformations
Variability time and source size
Comoving frame
vtR
Observer frame
G
c t
Lab frame
However, due to time
dilation, e.g. for the cooling time.
40
Time scales seen in the observer frame
Cooling time scale of the plasma due to
synchrotron and inverse Compton
emission Angular spreading time scale due to
light- travel effects from the curved shock
front Dynamical time scale for the shock
crossing
41
Theoretical Light Curves
Convolution light curve seen in
the observer frame
Intrinsic light curve
Angular spreading
42
Theoretical Spectra
Comoving light curve is an exponential decay
h
F Ep
Observed HIC
Spectra and their evolution from a burst with
similar curvature and crossing times scales
The intrinsic spectra are integrated along the
large crosses. Note that eventhough the
intrinsic spectra do not vary in shape the
observed will soften with time
Curvature HIC
43
More Spectral Evolution
In these examples the intrinsit HIC is a power
law
Observed HIC
with h1.0 while R varies.
The instantaneous, observed spectrum is not the
intrinsic, emitted spectrum. A variety of HIC
shapes can be produced depending on R
44
More HICs
Ep Constant
(F vs. Ep)
R increases
Intrinsic h1.0
R increases
Power-laws (intrinsic and curvature driven HIC)
Intrinsic h0.5
S-shapes
Reaches asymptotically h2.0
(Curvature)
45
Curvature Model Predicts

• Can reproduce the basic features of the
  observations, pulse shape and spectral evolution
• HIC Curvature Driven HIC gt power law with h2
• Hard in the beginning and the spectra soften with
  time
• S-shaped HICs for tang tdyn

The angular spreading depends on the
distance Therefore it will affect the thermal
component of the spectrum to a less degree
46
What do the Observations Say? 1. Spectral
Evolution of the gamma-rays
Light Curve
Spectra
47
GRB Cube Spectral and Temporal Evolution of a
Pulse
Ryde 1999, ASP Conf. Proc., vol. 190, p 103
FRED fast rise exponential decay
Smoothly broken power law - Band function
Ep evolution
Intensity contours
48
Hardness-Intensity Correlation
HIC

Pulse 1
Pulse 1
Pulse 2
Pulse 2
39 pulses observed by BATSE that have a power
law HIC (Borgonovo Ryde 2001 ApJ 548, 770)
Curvature Driven HIC
Borgonovo Ryde, 2001 ApJ 548, 770
49
Two GRB pulses that are described by a pure
curvature-driven spectral-evolution
Energy flux vs. Peak energy (HIC)
Decay phase of the pulse
50
Four pulses that not are described by a pure
curvature-driven spectral-evolution
Best fit power law

• 2
• (curvature)

h 2
h 2
h 2
Intrinsic HIC?
51
HIC power law index distribution
52
Deconvolved light curves and spectra

• We can now deconvlove the light curve to find the
  intrinsic spectral behaviour

53
Spectral fits to the time evolution
McQuinn, Ryde, Petrosian 2003
Synchrotron model cannot fit the spectra but the
in combination with the curvature effect the
fits are good! These bursts are dominated by
optically thin synchtrotron emission from
shocks in the relativistic outflow at 10 cm from
the progenitor.
15
54
Intrinsic Light Curve
Comoving Electron pulse (comoving emitted flux)
Observed flux
1625
3067
Convolved electron pulse
Ep Evolution
McQuinn, Ryde, Petrosian, 2003
55
Black Body Fits
McQuinn, Ryde, Petrosian 2003
56
Photosperic Black-Body Evolution
Ryde, McQuinn, Petrosian (2003)
57
Summary of test on dataand concluding remarks

• We find cases which are consistent with optically
  thin synchtroton shock emission. They have
  spectral evolution and are softer due to
  curvature.
• The curvature has masked the intrinsic behaviour
  which can now be revealed
• The comoving pulses are found to be anti-FREDs
• We also find har spectra which are consient with
  the thermal photosphere

58
GRB spectrum
Fishman Meegan, 1995, Ann. Rev. AA 33, 427
Thermal emission from the baryonic
photosphere Curvature effect
Preece et al. 2000, Ap. J. Supp., 126, 19
(Photon index)
Optically thin shock emission Curvature effect
Line-of-death of OTTS
(Photon index)
BB
59
Future Missions

• Swift will be launched in May 2004 and will
  greatly increase the afterglow data base. It will
  fill the gap in the early afterglow data. Its
  three instruments will work together to observe
  GRBs and afterglows in the gamma-ray, X-ray and
  optical wavebands.
• Upgraded ROTSE LOTIS are being deployed.
• GLAST (2007), will provide information about
  emission at GeV and the higher energies. GRBs is
  a key scientific objective of GLAST
• PoGO (200?), will measure X-ray polarization.
  First as a baloon experiment.
• AGILE (200?), will also provide information about
  emission at GeV and higher energies.