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Santorini, 1 September 2005. Multiwavelength Spectral Properties of Gamma-Ray Bursts. E. Pian - INAF, Trieste Astronomical Observatory. Outline. Spectral evolution of prompt event. Transition between multiwavelength prompt event and afterglow.

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Santorini, 1 September 2005

Multiwavelength Spectral Properties of

Gamma-Ray Bursts

E. Pian - INAF, Trieste Astronomical Observatory


Outline

Spectral evolution of prompt event

Transition between multiwavelength prompt

event and afterglow

Diagnostic of circumburst medium from

spectroscopy of the optical flash

X-ray Flashes


Spectral evolution of prompt event

2-26 keV

40-700 keV

Frontera et al. 2000



When does the afterglow start?

I(E,t) 

S(t1,t2) = fluence

R(t1,t2)  S(t1,t2) / S(t2,) =

= K(1,2)[ ]


Transition between

Prompt event and

Afterglow in the

2-10 keV range

Solid curve:

Best fit (K>1)

Dashed curve:

Expected curve

Assuming no

Spectral softening

Between GRB and

afterglow


GRB920723

Burenin et al. 1999

Tkachenko et al. 2000

See also GRB980923, Giblin et al. 1999


radio

GRB990510

Harrison et al. 1999; Wijers et al. 1999

optical

Pol. flux


WFC

last peak

 = 1

NFI

GRB990510

 = 2

Pian et al 2001


WFC

NFI

GRB990510


Synthetic spectra

From external

Shock model

Ec

Em

Sari et al. 1998


Time behavior

of peak energy


GRB990123

WFC

MECS

2-10 keV

15-28 keV

PDS

Maiorano et al. 2004

Corsi et al. 2004


GRB990123 (z = 1.6)

Fruchter et al. 1999


GRB041219a: Optical flash from internal shocks

RAPTOR

Internal shock

ROTSE-I

Reverse shock

Akerlof et al. 1999; Vestrand et al. 2005


Optical Flashes

Guidorzi et al. 2005


GRB050502a

z = 3.793

Liverpool 2m telescope

+ Robonet consortium

Forward shock in ISM

In variable density

Environment

Guidorzi et al. 2005



XRF030723

Fynbo et al. 2004

Soderberg et al. 2004

Tominaga et al. 2004


  • X-Ray Flashes:

  • High z  unlikely

  • large viewing angle

  • low bulk Lorentz factor (dirty fireball)

  • high bulk Lorentz factor

  • low contrast in bulk Lorentz factor


XRF020427

BSAX

WFC

WFC

MECS

CXO

GRBM

z ≾ 1

  • > 200

    Epeak < 5.5 keV

Amati et al. 2004


Summary

Hard-to-soft evolution of prompt gamma-ray event. Peak

Energy decreases while external shock develops

Afterglow starts at ~50% of GRB duration. Transition is

Seen in gamma- and X-ray spectra. Timing of afterglow

May different from GRB

Optical flashes: diagnostic of early emission processes

(GRB990123; GRB041219a) and circumburst medium

(GRB050502a)

XRF: intrinsic difference vs viewing angle. At least some

XRFs may be GRBs with a narrow distribution of Lorentz

factors (XRF020427), and with low contrast in the colliding

shells


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