Transcript GRB – The Afterglow

The standard model: Fireball
ep
E~1052 erg
Central
Engine
??
Shells are optically thick. Internal
pressure (due to high energy density)
drives the acceleration and internal
energy is converted into kinetic
energy.
G
r
The standard model: Fireball + Internal shock
Shock
E~1052 erg
Central
Engine
??
G
Shock transfers
energy to the
particles and
magnetic field
Prompt emission is
synchrotron
Most of the internal energy has
been converted into kinetic and
the shell coast with constant G
r
The Internal shock model explains ...
… but open issues:
1) Efficiency
2) Hard spectra
GRB – The Afterglow (light curve)
F(E, t) ~ t
– 1.5
GRB – The Afterglow (spectrum)
Swift confirmed the structure in the afterglow lightcurve
The standard model: Fireball + Internal + External shock
GRB
AFTERGLOW
E~1052 erg
Central
Engine
??
G
Merged shells are
decelerated by the
ISM
r
The standard model: synchrotron emission from external shocks
N()
c < m

The standard modell: Fireball + Internal + External shock
GRB
AFTERGLOW
E~1052 erg
Progenitor &
Central
Engine ??
G
Q: What is the “central engine”?
Merged shells are
decelerated by the
ISM
r
At these distances gamma-ray bursts would have
an energy of 1052 erg to 1054 erg if they emitted
isotropically. That is up to the rest mass of the sun
turned into gamma-rays in 10 seconds!
The standard model: Fireball + Internal + External shock
GRB
AFTERGLOW
E~1052 erg
Central
Engine
??
G
Merged shells are
decelerated by the
ISM
r
Long GRB are in SF regions
where most massive stars
occur
GRB Host Galaxies: types
GRB sono in
galassie
tipicamente
irregolari subluminous.
(Fruchter et al
2005)ha mostrato
che le galassie dei
GRB sono molto
piu’ piccole,
irregolari e
tipicamente la
posizione dei GRB
e’ strettamente
correlata con le
zone di piu’ alta
luminosita’
all’interno delle
stesse galassie
GRB Host Galaxies: types
GRB Host Galaxies
GRB SN connection – The first
SN 1998bw
GRB 980425
Type Ic supernova, d = 36 Mpc
Etot ~ 3 x 1052 erg
GRB E ~ 8 x 1047 erg;
V=3x104 Km/s
T= 23 s
of a massive CO star
(Iwamoto et al 1998; Woosley, Eastman, & Schmidt 1999)
Ia binaria con nana bianca – no H
vecchie
II stella massiccia  Fe56 – si H
giovani
Types Ib and Ic supernovae are caused by the core collapse
of massive stars. A Wolf-Rayet star, with a core of about 10 solar
M
These stars have shed (or been stripped of) their outer
envelope of hydrogen, and, when compared to the spectrum of
Type Ia supernovae, they lack the absorption line of silicon.
Compared to Type Ib, Type Ic supernovae are believed to have
lost more of their initial envelope, including most of their
helium. The two types are usually referred to as stripped
core-collapse supernovae
GRB SN connection – The second
SN 2003dh GRB 030329
GRB E ~ 10
T ~ 60 sec
z=0.1685
52
erg
GRB/SN Connection – a few
GRB 980425 (40 Mpc)
GRB 030329 (z=0.17)
GRB 031203 (z=0.1) GRB 060218 (150 Mpc)
(Galama et al. 1998, Matheson et al. 2003, Malesani et al. 2004, Pian et al. 2006)
GRB/SN are more luminous
SN1998bw
SN2003dh
SN2003lw
SN2006aj
Woosley and Bloom (2006)
Long GRB central engine
qjet = 0.1 rad; Ljet = 1050-1051 erg/s
ms magnetar
Collapsar
Supranova
(NS)
(BH+disk)
(delayed
BH+disk)
B~1015 G
M>Mcrit
Delay ~ year
(clean environ)
“Cold” fireball
“Cold & Hot” fireball
Adv: fallback
Today, there are two principal models being discussed
for GRBs of the “long-soft” variety:
• The collapsar model
MacFadyen and Zhang (2005)
• The millisecond magnetar
Glatzmaier
The Collapsar model: BH + (fed) disk
Collapsar – the jet’s fate
Ejet=3x1050 erg
M*=15Msun
R*=9x1010 cm
tjet ~ 8 s
G ~ 200
The standard model: Fireball + Internal + External shock
GRB
AFTERGLOW
E~1052 erg
Central
Engine
??
G
Merged shells are
decelerated by the
ISM
r
Progenitors
(current paradigm)
Still controversial
e.g. both early
and late type
galaxies
Short
(t < 2 s)
Supported by:
-Hosts
-Position within hosts
Long
-Direct association with SNIbc
(t > 2 s)
Short Gamma-Ray burst cannot be produced in SN
Their location is not only in star formation regions 
Figure 7. Snapshots of simulation of two neutron stars merger
(each neutron star has 1.4M8 and ≈ 30 km diameter). Initially,
they are less than 10 km apart, and moving at around v = 0.2c.
The simulation began with a pair of magnetized neutron stars
orbiting just 11 miles apart. Each star 1.5 times the mass of the
sun into a sphere just 17 miles across and generated a magnetic
field about a trillion times stronger than the sun's.
In 15 milliseconds, the two neutron stars crashed, merged and
transformed into a rapidly spinning black hole weighing 2.9 suns.
The edge of the black hole, known as its event horizon, spanned
less than six miles. A swirling chaos of superdense matter with
temperatures exceeding 18 billion degrees Fahrenheit surrounded
the newborn blackhole. The merger amplified the strength of the
combined magnetic field, but it also scrambled it into disarray.
Over the next 11 milliseconds, gas swirling close to the speed of
light continued to amplify the magnetic field, which ultimately
became a thousand times stronger than the neutron stars'
original fields. At the same time, the field became more
organized and gradually formed a pair of outwardly directed
funnels along the black hole's rotational axis.
From simulations:
Merger time:
Inspiral phase: 106 yrs
Final 100 km less than 1 second
Crash: 15 millisecond
spinning black hole
magnetic field amplification
magnetic tower
11 millisecond: jets
 Ifwith
G the
not
 Formation
of
a
GRB
could
begin
either
Fireball Model
merger
two compact
objects
the collapse

The offireball
expands
andor with uniform,
faster shells
of
a
massive
star
collects ISM
collide with
slower
54 ergsones,

As
a
result,
an
energy
as
high
as
E~10
can
 It starts to be decelarated and
and
internal
6 cm)
be
released
in
a
compact
volume
of
space
(~10
an external shock forms
shocks form
A
of e+/epairs, photons
and baryons is

Thefireball
inital
evolution
is
 Part
of
formed and
energy in
inverted:
bulkexpands
kineticconverting
energy is thermal
the kinetic
bulk kinetic
baryons
converted
into energy
internal carried
energy by the
energy
is
originally
present
in the explosion site (Mb)
across
the shock
front
converted in
internal
The
When accelerated
the thermalelectrons
motion becomes
sub
prompt
relativistic,
the bulk Lorentz
factor saturates
radiate
via synchrotron
emission
emissionto G
2
=E/M
c
~ 1016 cm
b
 afterglow emission
~ 1013 cm
The fireball model
How to derive clues on the
nature of the progenitor?
n < 1 cm-3 and uniform medium
d
E.g. afterglow phase:
emission processes,
circum-burst
medium (density and
structure)
I will
consider the
link with the
GW domain
~ 1013 cm
~ 1016 cm
GW emission from GRB progenitors
Long GRB: no in-spiral phase, only
merger and ring-down
Short GRB: we expect the GW
signal to be emitted in 3 phases: inspiral, merger and ring-down
Long GRBs: the progenitor
Collapsar model (e.g. Woosley 1998):
 “GRB as the birth cry of a BH”: when the collapse of the iron core of a
rotating massive progenitor proceeds directly to a BH formation, the
stellar mantle falls into the newly formed BH and angular momentum
slows the collapse along the equator, ultimately forming an accretion disk
that, within a few seconds, launches particle jets along the rotation axis
powering a GRB”
 “The jets pass through the outer shells of the star and, combined with
the vigorous winds of newly forged radioactive metals blowing off the disk
inside, give rise to the supernova event”
 Collisions among shells of the jet moving at different velocities, far
from the explosion and moving close to light speed, create the GRB, which
can only be seen if the jet points toward us
Short GRBs: the progenitor
General picture:
Merger events of NS+NS or BH+NS systems widely favored:
 Seems unlikely that typical energies of short GRBs set free during the
dynamical merging; the following accretion phase in a postmerger system
consisting of a central BH and a surrounding torus is much more promising
 BH-torus system geometry: relatively baryon-poor regions along the
rotational axis  thermal energy release preferentially above the BH poles
via e.g.  anti- annihilation  can lead to collimated, highly relativistic jets
of baryonic matter if thermal energy deposition rate per unit solid angle
sufficiently large.
 -rays produced in internal shocks when blobs of ultra-relativistic matter
in the jet collide with each other. When the jet hits the ISM, the afterglow is
produced
GRB: progenitor models and time duration
Both progenitor types result in the formation of a few solar mass BH,
surrounded by a torus whose accretion can provide a sudden release
of energy, sufficient to power a burst. But different natural timescales
imply different burst durations:
 LONG: death of massive stars  free-fall time of the material
falling on the disk form outside,
tff ≈ 30s(M/10M⊙) −1/2 (R/1010cm)3/2
 SHORT: coalescing compact objects  duration set by the viscous
timescale of the gas accreting onto the newly-formed BH (short due
to the small scale of the system)
Short GRBs progenitor – Compact object merger
Short GRB hosts
cD Elliptical
SFR<0.2 Ms/yr
Gerhels et al. 2005
SF gal with
offset
Elliptical
SFR<0.02 Ms/yr
790613
(old!)
050813
Gal-Yam et al. 2005
Gladders et al. 2005
Short vs Long HOST
properties
(Berger et al. 2008)
Short are in more
luminous and less star
forming galaxies
Redshift
73 Long
29 Swift
15 Sax
17 Hete
N(<z)
… 12
other
Still few Short GRBs with measured redshifts to
infer their N(z), … N(L), …
040924
050813
051221
050724
050509B
050709
Short GRB
050925
Ghirlanda et al. 2006
Swift 5/7 with redshift
Short GRBs: distance scale
Direct (spectroscopic) redshift
measures of ~ 5(swift)+2(Hete)
short bursts
Z~0.11.0
Statistical analysis of BATSE
GRB sample with local galaxies or
clusters
if Short GRBs are at
z<0.1
Z<0.1
… BUT …
GRB 080913 @ z=6.7
T(rest) ~1 s
Belczynski et al. 2006
Eiso~10^48
erg
Short bursts are spectrally
and temporally similar to the
first 2 sec of long bursts!
long
Log Epeak
long
short
Nakar & Piran 2005
a
Ghir,Ghis,Cel 2004
short
…only a (mis)classification case?
Short GRB with
extended emission
Norris et al. 2008,
Gerhels et al. 2007
Log(νFν)
Typical spectrum
Long
Single e- spectrum
Short
Log(ν)
F  
N()  
Ghir06
4/3
-2/3
tcool ~ 10-7 ee (G/100)
2
MeV
3
s
Log(νFν)
-ray: synchrotron emission?
Cooling
Log(ν)
νFν  ν1/2
N(ν)  ν-3/2
Ghir06
A lot of kinetic energy should remain to power the afterglow
Piro astro-ph/0001436
Prompt
SAX X-ray
afterglow
light curve
Eafterglow < Eprompt
Pre-Swift Afterglow
Piro astro-ph/0001436
Prompt
SAX X-ray
afterglow
light curve
Typical Afterglow
Prompt
X-ray Afterglow
Swift public archive
Typical Afterglow
Prompt
X-ray Afterglow
Swift public archive
NEW: Steep-Flat-Steep
Prompt
X-ray Afterglow
Flat
Swift public archive
NEW: Steep-Flat-Steep
Prompt
X-ray Afterglow
Flat
Swift public archive
NEW: X-ray flares
Prompt
X-ray Afterglow
Swift public archive
NEW: X-ray flares
Prompt
X-ray Afterglow
Swift public archive
GRB – The Afterglow
“Typical” afterglow (most
in Opt ; some in X)
Steep-flat-steep (most
X ; some in Opt)
Flux
+ flares
prompt
102
103
104
105
Time
GRB – The Afterglow
Flares
Central engine restart
Flux
prompt
102
103
104
105
Time
X-ray and optical behave differently
GRBs & Cosmology
GRB080916 (z=6.7)
Probes of:
“first light” & PopIII
chemical evolution
large scale structures
cover the epoch of reionization
Lamb 2002
SFR
Figure 11. Light from a GRB and its afterglows travels on its way to the Earth through
circumburst medium, host galaxy medium and intervening absorbers. All of these may
imprint their signature in the spectrum. From left to right: clouds of gas in the early
universe collapsed to form the first (Pop III) massive stars, which probably produced the
first GRBs. GRBs may have preceded the formation of the first galaxies and active galactic
nuclei/quasars, which are powered by supermassive black holes and formed even later. Thus,
GRBs may probe the properties and environment of the first stars and galaxies in the
Universe, as well as properties of the intervening absorbers
Very high z GRBs
?
Pop III
Analysis of the Red Damping Wing to
Constrain the Reionization
●
two possibilities for the origin of the damping
wing:
1) A damped Lya system (DLA) associated with the host
galaxy
●
●
DLAs often found in GRB afterglows
GRB 030323 at z=3.372
log NHI (cm-2) ~ 21-22
(Vreeswijk et al. 2004)
2) IGM neutral hydrogen (damping wing of GP trough)
●
If detected, it would give a crucial information on xHI
23 April 2009: a Gamma Ray burst at z=8.1 – 8.3
Tanvir et al.(ESO VLT) + Salvaterra et al. (TNG La Palma)
Epoca della rionizzazione: z = 10.8 fino a z = 6
Bright quasars rari oltre z=7
Oggetti + lontani confermati spettroscopicamente:
Galassia z = 6.96
QSS z = 6.43
z=8.26 = 625 million yrs dopo il Big Bang (4.6% eta’ universo)
Duration 10.3 s (1.1 s nel sistema di rif. del burst) troppo corto?
ma forse gamma + lungo
1) Stelle massicce gia’ presenti
2) Condizioni a epoca rionizzazione
GRBs: distance and energetics
If GRBs are isotropic sources …
GRB – Spectral Properties
GRB Peak Energy
F()
Where most of power
comes out
Eiso =
4  dL(z)2
1+z
F(E,z,…) dE
E
Peak energy – Isotropic energy Correlation
9+2 BeppoSAX GRBs
Amati et al. 2002
Rest
Frame
Eiso
+ 21 GRBs (Batse, Hete-II, Integral)
Eiso
…but is the energy really so huge?
Isotropic
Earth
Beamed
Earth
If the energy were beamed to 0.1% (q~5deg) of the sky,
then the total energy could be 1000 times less
Jet effect
Jet half
opening angle
G >> 1/
Log(F)
G ~ 1/
Jet
break
Log(t)
It is a property of matter moving close to the speed
of light that it emits its radiation in a small angle along its
direction of motion. The angle is inversely proportional to the
Lorentz factor
1
G
,
E.g., G 100 v  0.99995 c
2
2
1 v / c
q 1 / G
G  10
v  0.995 c
This offers a way of measuring the beaming angle. As the
beam runs into interstellar matter it slows down.
Measurements give
an opening angle of
about 5 degrees.
Afterglow light curve presents a chromatic break
Evidence that the GRB outflow
is collimated within a jet with a
certain opening angle
+ 21 GRBs (Batse, Hete-II, Integral)
?
1-cos(q)
Energy budget with beaming
Frail et al.(2001),
Peak energy vs. True energy
Ghirlanda, Ghisellini, Lazzati 2004
cr21.27
Similar to Supernovae Ia
Perlmutter 1998
“Stretching”:
the faster
the brighter
JGRG 17 – G.Gh.
Luminosity
distance
Luminosity distance
Luminosity distance
51 erg
E=1051
erg
E=10
The correlation reduces the scatter
of GRBs in the Hubble Diagram
Stretch-lum (SNIa)
redshift
Ep-Eg correlation (GRB)
redshift
JGRG 17 – G.Gh.
Ep-E
Results
Ghirlanda et al. 2004, Nava et al. 2005
2005, Ghirlanda et al. 2007
17 GRBs (970828 to 041006 – Batse, SAX, Hete-II) + 16 GRBs
(050318 to
061121 – Swift)
1.05
EEp EE
1.03
p

cc2red
dof)
2 =0.89
=1.13(23
(16
dof)
red
17 GRB
25 GRB
JGRG 17 – G.Gh.
15