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GRBsCENTRAL -ENGINE

& FLARes

WARSAW- 2009

Guido Chincarini &

Raffaella margutti

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From a serenegarden

ToA violent universe

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WE WILL SHOW • GRBs generalities• & Optical follow up at ESO

&in preparation for publication

• Characteristic time of the central engine activity is about 1000 s.

• The energy on flare – residuals activity is about 1051 erg. Rest Frame 2.187 – 14.43 keV.

• We estimate an activity time [ ~ 20 s ] and the time the central engine is active compared to the total time of the afterglow.

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GENERALITIES

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What is a Gamma –Ray Burst ? (1)Hu

bble

Dee

p Fi

eld

EXTRA –galacticevents

GRB060614

Host Galaxy

At cosmologicaldistances (z=6.7)

Local Universe(z<0.1)

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What is a Gamma –Ray Burst ? (2)

EXPLOSIONS linked to the death of starsE1053 erg

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Here we will be dealing with long GRBs . That is the prompt emission lasts generally more than two seconds. The Host Galaxy is a late type with rather high specific star formation rate.

Short GRBs occur in early and late type Galaxies

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What is a Gamma –Ray Burst ? (3)

TRANSIENT NON-PERIODIC events with duration between 0.1-100 s(prompt gamma emission)

-ray emission

VELA

SwiftAGILEINTEGRALFermi….. MAXI

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What is a Gamma –Ray Burst ? (4)

MULTI-WAVELENGTHLONG- LASTING

emission(months, years)

Swift

TRIGGER!!!!

After

glow

REM

Robotic Telescopes

10

Swift – XRT – SERVICE - OPT Follow UP –UNIQUE

PIASI

INAF

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GRB080329B – See eventually Movie - STOP Show – VLC – Open in GRB - Plot

Here the real challenge for the future

Time since BAT trigger in seconds

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Log(Time)

Log

(Flu

x)

t break1 t break2

t-1

t-2

t-3

Prompt

Afterglow

A long GRBexplosion

Black Hole

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Light Curve Morphology -

Time

Flux

old intrumentst - 1

t - 2

t -3t break t break

Many afterglows have a typical pattern

Steep – flat – steep

Prompt EmissionTail

External shock ?Afterglow

WE ADD FLARES

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A is behind the shock front of the amount

d = R/2

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Light Curve Morphology -

Time

Flux

old intrumentst - 1

t - 2

t -3

In the Swift era – Base for the analysis

t break t break

Many afterglows have a typical pattern

Steep – flat – steep

Prompt EmissionTail

Active Engine Old typeAfterglow

ADD FLARES

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1 1

1

2

12

120

2

1

1

exp 0

1 41

( )1

r

r

r dr r r

m m

tt

dt dec riset

dec risr d

tt d r t I t A for tF t tt d r d r t

WidthA e

F tasymetry

t t e t

e

Norris 2005Kocevski, Ryde,Liang 2003

(Norris 1996)(Kobayashi)Et al. 1997

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GRB050724 and Flare activity

To keep the sample very controlled we disregarded in this work the flares observed in SGRBs. However to illustrate a classical example we show the light curve of GRB050724 and a possible empirical interpretation of the early decay and of the late flare. All fits have been applied using the Norris 2005 function.

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GRB060115 We show a possible fitting of the background light curve and the various flares fitted by a norris 2005 function

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GRB051117A

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GRB050904 not used. Late flare activity rather unusual and evolutionary effects may be important. The effect on the mean light curve is shown in any case later on.

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Light curve from GRB050904 flares

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The sample – 36 GRBsMargutti – Bernardini – et al.

• Long GRBs – For instance no GRB050724.• Only GRBs with spectroscopic redshift.• Flares must be detectable by naked eye.• The analysis has been done on the GRB rest

frame.• The standard light curve has been subtracted.• The common energy interval to all flares is

finally from 2.187 to 14.43 keV.

GRB FLARESCONCLUSIONS

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Charecteristic time of the central engine activity is about 1000 s.

The energy on flare activity is about 1051 erg. Full agreement with previous indipendent analysis [COSPAR] – However here proper energy band rest frame

We estimate an activity time [ ~ 20 s ] and the time the central engine is active compared to the total time since the alert of the GRB.

Energy to power the flares noy yet known. Accretion, spinning down pf msgnetar, …….. TBD ….

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Back up

WARSAW 2009 26Figure from Kumar & Mahon 2008

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Syn. cooling & curvatureKumar&Panaitescu

DermerSari et al.

This equation is quite robust. It is valid for both the forward and reverse shock and it is independent of whether the reverse shock is relativistic or Newtonian.

Fennimore et al. Width = k E-0.42

If we assume the main factor is the curvature effect we have the following [The Observer way, however see later more formal derivation by Lazzati & Perna:

1

11

21

12

2

2

12;2

2 1

0.29

peak

peak

peak peak peak

peak

f

f

f f f

f

f t with

ftt f

tf

HPFW t t t

HPFWt

2

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+

tej+tej tej

22 2

2

2 2 2 2 2

2

2

1

ej ej ejFlare t t t

flare flare ej

ej ejflare

ejflare ej

ejflare ej

ej

flare flare

R R R

c t c t t c

t tt

tt t

tt t t

ttt t

12

12

12

2 1 4 2 2

2 1 0.25

2 1 1

FWHM

Peak

FWHM

Peak

FWHM Peak

Peak ej

tt

tt

t tt t

External

Lazy

tej tflare

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1 2 p w r d

50 80 63 163 .49 42 121

250 80 141 227 .35 74 153

450 80 190 259 .31 90 170

650 80 228 281 .28 101 181

850 80 261 300 .27 110 190

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GRB060526

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<>= 0.29 ± 0.53

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Slope 1.79

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Note I have the same type of graph withTAU increasing with WIDTH

slope 0.78 ± 0.014

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<> = 0.36 ± 0.2

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( ) dec rise

dec rise

asymetry

Norris 2005

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...

da bd dt tNorm

br br

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Corr

elati

on

Mea

n w

idth

En

ergy

. To

thi

s th

e BA

T da

ta

for

Flar

es

in

com

mon

ar

e be

ing

adde

d.

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Log versus Log

GRB060512T90 = 8.4 s – z =0.44

See GCNs

GRB070124short

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THESE ARE SOME OF THE HYPOTHESIS & PROBLEMS

SEE A FEW EXAMPLES

•Do we need to subtract the background underlying curve always?•If yes we should know where it is coming from – BAT observations. Is the precursor having any role?•Is it always the last flare for the early XRT slope or a combination of spikes or something else.•Decay slope and cooling – How to approach it best.

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GRB 060111A

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Do we need the underlying power law light

Curve?

GRB 060111A - S

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GRB060714 – See also Krimm et al., 2007, ApJ 665 - 554

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Light Curve Morphology -

Time

Flux

old intrumentst - 1

t - 2

t -3

In the Swift era – Base for the analysis

t break t break

Many afterglows have a typical pattern

Steep – flat – steep

Prompt EmissionTail

Active Engine Old typeAfterglow

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Mechanism producing the jets?• The observed flares have similarities to the variability

observed during the prompt emission. They must be related to the activity of the central engine at time at which the flares are observed.

• Conversion of internal energy into bulk motion with hydrodynamic collimation.

• Energy deposition from neutrinos.• Energy released from rapidly spinning newly born

magnetar and magnetic collimation and acceleration.

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# GRBs Analyzed– April 15- 2008

247 - GRBs

83 with z

7 - No spectra

Not early observ

66 OK

15 no steep decay

7 single power law

44 steep decay or flare

26 with flare

11 No steep decay

15 steep

8 1 spectrum

5 many spectra const

2 spectral evolution

18 no flares

10 only 1 spectrum

4 More than 1 same

4 spectral evolution

164 no z

10 One PL

41 Flares

75 no FlaresVarious Fits

31 low stat orlate Obs

7 No lc

IN 4 bands and TOT

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Flares [UPDATE 080530]

47 GRBs

67 Flares

29 Redshift No z

33 - 69 C0733 – 77 F07

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NORRIS 2005

• CH 1 25 – 50 keV• CH 2 50 – 100• CH 3 100 – 300• CH > 300

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GRB050502B - Three components