Stochastic wake field particle acceleration in Gamma-Ray Bursts

1
Stochastic wake field particle acceleration in
Gamma-Ray Bursts
Barbiellini G., Longo F.(1), Omodei N.(2),
Giulietti D., Tommassini P.(3) , Celotti A.(4),
Tavani M.(5)
(1) University INFN Trieste (2) INFN Pisa
(3) University of Pisa (4) SISSA Trieste (5)
IASF/INAF Rome University of RomeII
Gamma-Ray Burst (GRB) are major explosive
phenomena of our Universe in need of an
explanation. The typical light curves are
characterized by short pulses, which can last
from few milliseconds up to hundred of seconds.
We investigate the possibility that, for specific
conditions, the prompt emission from GRB can be
so powerful and short-pulsed to strongly
influence the surrounding plasma. Recent
laboratory experiments clearly indicate that
powerful laser beam pulses of tens of femtosecond
duration hitting on target plasmas cause
efficient particle acceleration and betatron
radiation up to tens of MeV. We discuss the
possibility that a very intense initial burst of
radiation produced by GRBs satisfies the
intensity and temporal conditions to cause
stochastic wake-field particle acceleration in a
surrounding plasma of moderate density. We
consider a simple but realistic GRB model for
which particle wake-field acceleration can first
be excited by a very strong low-energy precursor,
and then be effective in producing the observed
prompt X- ray and gamma-ray GRB emission. We also
briefly discuss some of the consequences of this
novel GRB emission mechanism.
THE FIREBALL MODEL
GRB AFTERGLOW EMISSION

• GRB PROMPT EMISSION
• Brief intense episode of gamma-ray
• emission in the 10 keV 10 MeV energy
• range with 10-6 erg cm-2 fluence
• Isotropic direction in the sky
• Non thermal spectrum

• Relativistic motion of the emitting region
• Shock mechanism converts the kinetic energy of
  the shells into radiation.

• External Shock
• Synchrotron SSC
• High conversion efficiency
• Not easy to justify the rapid variability

Djorgoski et al. (2000)
Costa et al. (1997)
- Emission in the X-ray to Radio band
lasting for longer periods (hrs to
months) - Confirmation of Cosmological
distance - Jetted nature of emission
Spectral shape
Temporal behaviour

• Internal Shocks
• Source activity
• Synchrotron Emission
• Rapid time Variability
• Low conversion efficiency

Spatial distribution
Kippen et al. (1998)
GRB PROGENITOR
THE COMPTON TAIL PHENOMENUM

• Search for Post Burst emission in prompt GRB
  energy band
• Looking for high energy afterglow (overlapping
  with prompt emission) for constraining
  Internal/External Shock Model
• Sum of Background Subtracted Burst Light Curves
• Tails out to hundreds of seconds decaying as
  temporal power law ? 0.6 ? 0.1
• Common feature for long GRB
• Not related to presence of low energy afterglow
• 3 equally populated classes
• Bright bursts
• Peak counts gt1.5 cm-2 s-1
• Mean Fluence 1.5 ? 10-5 erg cm-2
• Dim bursts
• peak counts lt 0.75 cm-2 s-1
• Mean fluence 1.3 ? 10-6 erg cm-2

Q cts/peak cts

• BRIGHT GRB
• ? DIM GRB

• Long Burst progenitor in Massive rotating
• stars
• Evidence from GRB localized in Star
• Forming regions
• Evidence from SN explosion

Image credits to CXO/NASA

• Connaughton (2002), ApJ 567, 1028

IMPLICATIONS
COMPTON TAIL INTERPRETATION

• Bright bursts (tail at 800 s)
• Peak counts gt1.5 cm-2 s-1
• Mean Fluence 1.5 ? 10-5 erg cm-2
• Q 4.0 ? 0.8 10-4 (5 ?) fit over PL
• ? 1.3
• Dim bursts (tail at 300s)
• peak counts lt 0.75 cm-2 s-1
• Mean fluence 1.3 ? 10-6 erg cm-2
• Q 5.6 ? 1.4 10-3 (4 ?) fit over PL
• ? 2.8

R 1015 cm n 108-109 cm-3 ?R R ? 0.1

• Prompt luminosity
• Compton Reprocessed luminosity
• Q ratio

• Presence of dense material
• in front of GRB
• Which is the effect for
• GRB emission?

Barbiellini et al. (2004) MNRAS 350, L5
APPLICATION TO GRB
PLASMA WAKEFIELD ANALOGY
CONCLUSIONS
Stochastic Factor
(Ta Phuoc et al. 2005)
Scaling Relations
1
3

• Jetted structure of GRB
• Presence of Material around GRB
• Compton tail measurement relevant for
• GRB source mechanism
• Plasma acceleration mechanism
• Plasma Physics and Astrophysics

Power Density
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Laser Pulse tlaser 3 10-14 s Laser Energy 1
Joule Gas Surface 0.01 mm2 Gas Volume Density
1019 cm3 Power Surface Density ?W 3 1018 W
cm-2