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GRBsCENTRAL -ENGINE
& FLARes
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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
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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
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