Santorini, 1 September 2005
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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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E pian inaf trieste astronomical observatory

Santorini, 1 September 2005

Multiwavelength Spectral Properties of

Gamma-Ray Bursts

E. Pian - INAF, Trieste Astronomical Observatory


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


E pian inaf trieste astronomical observatory

Spectral evolution of prompt event

2-26 keV

40-700 keV

Frontera et al. 2000


E pian inaf trieste astronomical observatory

More on spectral evolution


E pian inaf trieste astronomical observatory

When does the afterglow start?

I(E,t) 

S(t1,t2) = fluence

R(t1,t2)  S(t1,t2) / S(t2,) =

= K(1,2)[ ]


E pian inaf trieste astronomical observatory

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


E pian inaf trieste astronomical observatory

GRB920723

Burenin et al. 1999

Tkachenko et al. 2000

See also GRB980923, Giblin et al. 1999


E pian inaf trieste astronomical observatory

radio

GRB990510

Harrison et al. 1999; Wijers et al. 1999

optical

Pol. flux


E pian inaf trieste astronomical observatory

WFC

last peak

 = 1

NFI

GRB990510

 = 2

Pian et al 2001


E pian inaf trieste astronomical observatory

WFC

NFI

GRB990510


E pian inaf trieste astronomical observatory

Synthetic spectra

From external

Shock model

Ec

Em

Sari et al. 1998


E pian inaf trieste astronomical observatory

Time behavior

of peak energy


E pian inaf trieste astronomical observatory

GRB990123

WFC

MECS

2-10 keV

15-28 keV

PDS

Maiorano et al. 2004

Corsi et al. 2004


E pian inaf trieste astronomical observatory

GRB990123 (z = 1.6)

Fruchter et al. 1999


E pian inaf trieste astronomical observatory

GRB041219a: Optical flash from internal shocks

RAPTOR

Internal shock

ROTSE-I

Reverse shock

Akerlof et al. 1999; Vestrand et al. 2005


E pian inaf trieste astronomical observatory

Optical Flashes

Guidorzi et al. 2005


E pian inaf trieste astronomical observatory

GRB050502a

z = 3.793

Liverpool 2m telescope

+ Robonet consortium

Forward shock in ISM

In variable density

Environment

Guidorzi et al. 2005


E pian inaf trieste astronomical observatory

X-ray Flashes


E pian inaf trieste astronomical observatory

XRF030723

Fynbo et al. 2004

Soderberg et al. 2004

Tominaga et al. 2004


E pian inaf trieste astronomical observatory

  • 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


E pian inaf trieste astronomical observatory

XRF020427

BSAX

WFC

WFC

MECS

CXO

GRBM

z ≾ 1

  • > 200

    Epeak < 5.5 keV

Amati et al. 2004


E pian inaf trieste astronomical observatory

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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