The many mysteries of gamma-ray bursts R. Mochkovitch (IAP-Paris) All starts as a James Bond movie… Moscow: August 5, 1963. Treaty Banning Nuclear Weapon Tests in the Atmosphere, in Outer Space and under Water
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The many mysteries of gamma-ray bursts
R. Mochkovitch (IAP-Paris)
All starts as a James Bond movie…
Moscow: August 5, 1963
Advanced Topics in Astrophysics - Llafranc 4-6 May, 2011
Treaty Banning Nuclear Weapon Tests in the Atmosphere, in Outer Space and under Water
Signed by the Original Parties, the Union of Soviet Socialist Republics, the United Kingdom of Great Britain and Northern Ireland and the United States of America at Moscow: 5 August 1963 The Governments of the United States of America, the United Kingdom of Great Britain and Northern Ireland, and the Union of Soviet Socialist Republics, hereinafter referred to as the "Original Parties,"Proclaiming as their principal aim the speediest possible achievement of an agreement on general and complete disarmament under strict international control in accordance with the objectives of the United Nations which would put an end to the armaments race and eliminate the incentive to the production and testing of all kinds of weapons, including nuclear weapons,Seeking to achieve the discontinuance of all test explosions of nuclear weapons for all time, determined to continue negotiations to this end, and desiring to put an end to the contamination of man's environment by radioactive substances,Have agreed as follows:
1. Each of the Parties to this Treaty undertakes to prohibit, to prevent, and not to carry out any nuclear weapon test explosion, or any other nuclear explosion, at any place under its jurisdiction or control:(a) in the atmosphere; beyond its limits, including outer space; or under water, including territorial waters or high seas; or
How to detect a nuclear explosion in the atmosphere?
→ with gamma rays !
To sign a treatyis fine but one wants to be sure itisrespected …
The « VELA » project(3 pairs of satellites launchedin 1963, 64 and 65)
The first gamma ray burst
A great diversity of light curves
20 – 1000 keV
Simple broken power-law spectra
● Isotropy: both short and long GRBs are uniformlydistributed on the sky
First hint for a cosmological distance scale
Gamma ray error boxes are too large
→ Beppo-SAX : GRB monitor + X-ray cameras
on Feb. 28, 1997
GRB 970508 : z = 0.835
Afterglowsallow to measure the redshift
● directly, fromthe afterglowitself
● undirectly, via the host galaxy (more uncertain)
the first redshift !
the first redshift !
Fe and Mg lines
z = 0.225 (short burst)
Confirmation: GRBs are locatedatcosmological distances !
The afterglow: spectral and temporal evolution
● progressive shift of the emission to lowerenergies :
X→ visible→ radio
● approximative power lawdecay (with accidents: breaks, bumps)
● long bursts
spectroscopic or photometric signature of an underlying supernova
z = 0.17
Supernova bump at late times
Type Ic SN: exploding WR star
But not all SNe Ic give a GRB !
→ Additional ingredients required:
- Very massive ?
- Very metal poor ?
- Very rapidly rotating ?
● short bursts
severalSHBsassociated to elliptical (non star forming) galaxies
z = 0.26
● long delaybetweenobject formation and GRB
● no SN bump→stronglimit on underlyingsupernova
Coalescence of compact objects
● The duration of source activity
1 ms – 1000 s
● More sensitive thanBeppo/HETE
● Earlyfollow-up in X and V → more redshifts ( z = 2.8; zmax = 8.2 !)
a window opens on the earlyafterglowevolution
Surprises in X-rays !
Initial steep decay Extended plateaus Flares
Basic constraints :
● temporal variability : ~1ms→ compact objects
● GRBswithknownz→Egiso = 1048 (shortestbursts)→1054 erg = M c2 !
● the compactnessproblem:→ large Thomson opticaldepth
solution:emissionfromrelativisticallymovingmaterial : G > 100
→Lorentz boost/relativisticbeamingsupress pair creation
● progenitors and rate
long GRBs: RGRB ~ 0.1 - 1 Gpc-3yr-1extremeSNIc
short GRBsRSHB ~ ? coalescence of compact objects
1) The central engine and the production of a relativisticoutflow
2) The origin of the gamma ray emission
3) The production of the afterglow
1) Verydifficult and poorlyunderstood :
● GR, relativistic hydro, superstrongmagneticfields
2) From the thermal/magnetic/kineticenergy of the flow
● a wellstudied scenario: internalshocks
3)The best understood (maybe):
● relativisticshockpropagating in the source environment
The “standard” model
Log R (m)
Collapse of a massive rapidly rotating star (long GRBs)
Coalescence of two compact objects
(NS/BH) (short GRBs)
The central engine
• A black holewith an accretion torus
Mochkovitch, Hernanz, Isern & Martin, 1993
Relativistic jets : a lot of energyinjectedintovery few baryons (E/Mc2 >> 1)
“ baryonic pollution problem ”
• Milli-second proto-magnetar
● The extraction of energy
● not very efficient:
●from the BH: Blandford-Znajek process
● from the disk: magnetized wind
● The acceleration of the flow
Thermal (fireball model)adiabatic expansion of a radiativelydominated plasma: g, e+e- pairs + a few baryons (baryon load: h = E/Mc2 )initiallyconfinedwithin R0 ~ 10 – 100 km
thermal energy→ kineticenergy of the baryons
Radiative phase: Gα R and T α R-1
Matterdominated phase: G→ h(for R ≳ h R0)
No strong thermal component at transparency
→ hint for magnetic acceleration ?
(Daigne & Mochkovitch, 2002)
E = 1053erg
G1 > G2
The prompt gamma-ray emission
Nice results(Daigne & Mochkovitch, 1998)
But: no shock if s > 1 at the location of IS (RIS~ 1015 cm)
and low efficiency < 5%
→ Alternative to internal shocks:
comptonization at the photosphere
One big mystery: why so many different gamma-ray light curves ?
complex, very spiky
with a pause
2470: c !
2064: 1 m/day
Do you know what it is ?
Peu de cabra comú
Goose neck barnacle