Gamma Ray Bursts: open Gamma Ray Bursts: open issues issues Brief history Brief history Power Power Short history of the paradigm: Short history of the paradigm: internal vs external shocks internal vs external shocks Afterglows: external shocks Afterglows: external shocks The spectral-energy relations The spectral-energy relations GRBs for cosmology GRBs for cosmology Gabriele Ghisellini – Osservatorio Gabriele Ghisellini – Osservatorio di Brera di Brera
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Gamma Ray Bursts: open issues Brief history Power Short history of the paradigm: internal vs external shocks Afterglows: external shocks The.
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Gamma Ray Bursts: open Gamma Ray Bursts: open issuesissues
Brief historyBrief historyPowerPowerShort history of the paradigm: Short history of the paradigm:
internal vs external shocksinternal vs external shocksAfterglows: external shocksAfterglows: external shocksThe spectral-energy relationsThe spectral-energy relationsGRBs for cosmologyGRBs for cosmology
Gabriele Ghisellini – Osservatorio di Gabriele Ghisellini – Osservatorio di Brera Brera
Gamma-Ray Bursts: The story Gamma-Ray Bursts: The story beginsbegins
Treates banning nuclear tests between USA and USSR in early 60s
19921992 Pure fireball made by Pure fireball made by e+e- . Focussing by e+e- . Focussing by gravitationgravitation
19921992 Dirty fireball polluted by baryons. Re-conversion of Dirty fireball polluted by baryons. Re-conversion of bulk kinetic into radiation through shocks with external bulk kinetic into radiation through shocks with external mediummedium
19941994 Internal shocks due to shells moving with different Internal shocks due to shells moving with different
Why internal shocks?Why internal shocks?
Spikes have Spikes have same same durationduration
A process A process that that repeats repeats itselfitself
Peak energy – Isotropic energy Peak energy – Isotropic energy CorrelationCorrelation
EEp
eak
peak(1
+z
(1+
z))
Nava e
t al.
2006;
Gh
irla
nd
a e
t al.
2007
Nava e
t al.
2006;
Gh
irla
nd
a e
t al.
2007
“Am
ati”
(62)
“Ghi
rlan
da”
(25)
1- cos 1- cos jetjet
Gh
irla
nd
a,
Gh
isellin
i, L
azzati
& F
irm
an
i 2004
Gh
irla
nd
a,
Gh
isellin
i, L
azzati
& F
irm
an
i 2004
Lu
min
osit
y
Lu
min
osit
y
dis
tan
ce
dis
tan
ce
redshiftredshiftGRBs can b
e use
d as c
osmolo
gical
GRBs can b
e use
d as c
osmolo
gical
RULERS !
RULERS !
Supernovae
GRBsGRBs
Problems:Problems: 1: Efficiency 1: Efficiency
Efficiency=Radiated/total energyEfficiency=Radiated/total energyOnly the RELATIVE kinetic energy can be used!Only the RELATIVE kinetic energy can be used!
Shells of Shells of equal equal massesmasses
Shells of Shells of equal equal energiesenergies
final final ~ (~ (1122))1/21/2
Dyn
am
ical effi
cie
ncy
(%)
5%
Pir
o a
str
o-p
h/0
001436
Pir
o a
str
o-p
h/0
001436
A lot of kinetic energy should remain to power the A lot of kinetic energy should remain to power the afterglowafterglow
X-ray and optical behave X-ray and optical behave differentlydifferently
X-rays: X-rays: steep-flat-steep-flat-
steepsteep
TA
Is this “real” afte
rglow? i.e. e
xternal
Is this “real” afte
rglow? i.e. e
xternal
shock?
shock?
Early (normal) prompt: Early (normal) prompt: >>1/j
Late prompt: Late prompt: >1/j
Late prompt: Late prompt: =1/j
Late prompt: Late prompt: <1/j
”real” after-glow
Ghisellini et al. Ghisellini et al. 20072007
Long lasting engine??Long lasting engine??
• RRss/c ~ 10/c ~ 10-4-4 s (for a 10 solar mass s (for a 10 solar mass
BH)BH)• Even 10 s are 10Even 10 s are 1055 dynamical times dynamical times• Two-phase accretion? Two-phase accretion?
ConclusionsConclusions
““Paradigm”: internal+external shocks, Paradigm”: internal+external shocks, synchrotron for both: synchrotron for both: it helps, but it it helps, but it is limitingis limiting
Efficiency is an issueEfficiency is an issue
Progenitors for long: done. For short: Progenitors for long: done. For short: not yetnot yet
Central engine? How long does it live?Central engine? How long does it live?
GRBs as probes of the far universe GRBs as probes of the far universe (continue…)(continue…)
There can be a Black Body … butThere can be a Black Body … but
Time resolved Time resolved spectraspectra
Time integrated Time integrated spectrumspectrum
The same The same occurs for ALL occurs for ALL GRBs detected GRBs detected by BATSE and by BATSE and with WFCwith WFCG
hir
lan
da e
t al.
G
hir
lan
da e
t al.
2007b
2007b
MemoryMemory
Epeak
=509 keV
Epeak
=503 keV Epeak
= 416 keV
Time [sec]
cts/sec
Epeak
= 390 keV
EF(E)
EF(E)
EF(E)
GRB spectrum evolves with time within GRB spectrum evolves with time within single burstssingle bursts
Ghirlanda PhD Ghirlanda PhD thesisthesis
phot
/cm
^2 s
ec
Hard to Soft Hard to Soft evolutionevolution
Epe
ak
Epeak
, t), t)
Decrease Decrease independent of the independent of the rise and decay of rise and decay of the fluxthe flux
Epeak
time
Tracking Tracking evolutionevolution
Photon Photon fluxflux
Correlated with
EEpeakpeak(t)(t), , (t) (t) ,,(t)(t)
By construction, internal shocks By construction, internal shocks should all be equal.should all be equal.
Then, why does the spectrum Then, why does the spectrum evolve?evolve?
SpectraSpectraSpectra
Fis
hm
an
& M
eeg
an
1995
Fis
hm
an
& M
eeg
an
1995
EEpeakpeak
Prompt Prompt radiation: radiation:
Synchrotron?Synchrotron?
Energy spectrum of a cooling electronEnergy spectrum of a cooling electron