2 nd FermiSymposiumWashingtonDCTuesday,November3 rd ,2009 - - PowerPoint PPT Presentation

SLIDE 1

2nd
Fermi
Symposium
–
Washington
DC
‐
Tuesday,
November
3rd,
2009


SLIDE 2

2/10


• GBM
has
an
effecHve
area
1/36
of
its
famous
predecessor
BATSE


=>
GBM
required
bright
events
BUT


• Even
if
smaller,
GBM/BGO
detectors
are
much
thicker


with
higher
z.
 =>
Much
beWer
photo‐peak
efficiency
and
effecHve
area
 above
1
MeV
:
 
BATSE
maximal
energy
~10
MeV.
 
GBM


maximal
energy
~40
MeV.
 =>
Spectroscopy
of
hard
bursts
possible
with
GBM.


• GBM
has
:


 
much
more
available
on‐board
memory.
  
a
much
higher
telemetry
downlink
budget.
  
a
beWer
data
design
for
Time
Tag
Events
(TTE).
 
=>
Data
available
with
a
Hme
resoluHon
down
to
2
μs,
 128
spectral
channels
from
8
keV
to
40
MeV
and
from
 ‐30
to
300
s.
 
=>
Ideal
for
the
study
of
short
events
like
short
GRBs,
 TGFs
(see
Michael
Briggs
talk
and
Jerry
Fishman
poster


• n
TGFs)
and
SGRs
(see
Chryssa
Koveliotou
and
Ersin


Gogus
talks)


12
Iodine
Sodium
 detectors
(NaI:





 8
keV
to
1
MeV)
 2
Germanate
Bismuth
detectors
























 (BGO:
200
keV
to
40
MeV)


Sylvain
Guiriec
–
Fermi
Symposium
2009


SLIDE 3

3/10


• About
68
short
GRBs
detected
with
GBM


since
since
July,
2008.


• Short
GRBs
correspond
to
~20%
of
the


total
GRBs
detected
with
GBM


• T50
<
1s


Sample
criteria
for
this
analysis


• Fluence
>
2e‐6
erg/cm2
=>
bright
enough
for
Hme‐resolved
spectroscopy
with
GBM


=>
This
selecHon
results
in
3
brightest
and
hardest
short
GRBs
 detected
with
GBM
so
far:


• GRB
090227B

• GRB
090228

• GRB
090510


In
all
the
following,
spectral
analysis
performed
from
8
keV
to
40
MeV.


Sylvain
Guiriec
–
Fermi
Symposium
2009


SLIDE 4

4/10


• Fit
performed
with
the
analysis
package
Rmfit

• Various
model
tested
:

• Choice
of
the
best
model
:
staHsHcal
improvement
of
the


Castor
Cstat
value
between
models
according
to
the
addiHonal
 degree
of
freedom
  
Power‐law
with
exponenHal
decay
 (comptonized)
  
Band
funcHon
  
Comptonized+PL
  
Band+PL


Standard
model
before
the
Fermi
Era
 AddiHonal
component
onen
present
in
Fermi’s
GRB
spectra


Sylvain
Guiriec
–
Fermi
Symposium
2009


SLIDE 5

5/10


Band
(Cstat:
699/607
dof)
 Comptonized
+
PL
(Cstat:
689/606
dof)
 Count
spectrum
 υFυ
spectrum


The
addiHonal
component
dominates
the
standard
Band
funcHon
at
both
low
and
high
Energy
 NaI
 BGO


Sylvain
Guiriec
–
Fermi
Symposium
2009


SLIDE 6

6/10
 Name
 Model
 Parameters
of
the
Band
func7on
 PL
 Castor
 Cstat
/
dof
 Epeak
(keV)
 α
 β
 index
 GRB
090227B
 Compt
 706/608
 Band
 699/607
 Compt+PL
 689/606
 Band+PL
 686/605
 GRB
090228
 Compt
 813/729
 Band
 813/728
 Compt+PL
 795/727
 Band+PL
 795/726
 GRB
090510
 Compt
 922/851
 Band
 911/850
 Compt+PL
 897/849
 Band+PL
 897/848


(GBM+LAT)
 Band+PL


• Comp
+
PL
is
systemaHcally
prefered
=>
Existence
of
an
addiHonal
component
in
these
3
GRBs

• Value
of
the
index
of
the
addiHonal
PL
similar
in
all
these
bursts

• Higher
Epeak
values
than
for
long
GRBs
(=>
quesHon
during
Ehud
talk
:
short
vs
long
GRBs
with
GBM)


−85 +90

2227

−95 +97

2116

−91 +96

1995

−98 +205

1947

−47 +52

862

−49 +50

860

−42 +47

722

−41 +45

723

−237 +255

4797

−278 +290

4383

−246 +265

3731

−265 +284

3695

−0.02 +0.02

• 0.52

−0.02 +0.02

• 0.50

−0.05 +0.05

• 0.36

−0.13 +0.05

• 0.36

−0.03 +0.03

• 0.59

−0.03 +0.03

• 0.59

−0.10 +0.11

• 0.23

−0.10 +0.10

• 0.24

−0.02 +0.02

• 0.77

−0.02 +0.02

• 0.75

−0.07 +0.08

• 0.51

−0.08 +0.08

• 0.51

−0.39 +0.27

• 3.35

−0.80 +0.58

• 3.44

−0.64 +0.64

• 3.77

−∞ +1.14

• 4.74

−0.28 +0.20

• 2.80

−∞ +0.75

• 3.65

−0.06 +0.06

• 1.37

−0.04 +0.05

• 1.51

−0.15 +0.09

• 1.63

−0.02 +0.03

• 1.64

−0.04 +0.04

• 1.35

−0.03 +0.04

• 1.38

−260 +280

3936

−0.05 +0.06

• 0.58

−0.20 +0.14

• 2.83

−0.03 +0.03

• 1.62
• Steep
β
values
(which
confirm
the
comment
from
Guido
to
Nicola
in
the
previous
talk)


Sylvain
Guiriec
–
Fermi
Symposium
2009


• GBM
only
results
and
GBM+LAT
fits
are
consistent
for
GRB
090510


SLIDE 7

7/10


The
existence
of
addiHonal
components
in
these
3
GRBs
is
 consistent
with
LAT
data
 See
Poster
Valerie
Connaughton
P3‐171
(Wed‐Thur)


Sylvain
Guiriec
–
Fermi
Symposium
2009


SLIDE 8

8/10


• Similar
to
what
we
observed
in
long
GRBs


but
contracted
in
Hme
and
shined
to
higher
 energy
(Ford
et
al.).


• Epeak
tracks
the
light
curves
like
for
the
long


burst.


• The
hardest
part
is
not
always
at
the


beginning.


• The
most
intense
peaks
are
not
always
the


hardest.
 GRB
090227B
 GRB
090228
 GRB
090510


Sylvain
Guiriec
–
Fermi
Symposium
2009


10000


SLIDE 9

9


• Epeak
evolves
over
an
incredible


broad
range
of
energy


• α
nearly
systemaHcally
violates
the


synchrotron
line
of
death
of
‐2/3.


α
<
‐2/3
:
 e‐
synchrotron
 emission
valid
 for
slow
cooling
 α
<
‐3/2
:
 e‐
synchrotron
 emission
valid
 for
fast
cooling


9/10


Sylvain
Guiriec
–
Fermi
Symposium
2009


SLIDE 10

• The hardest short GRBs have Epeak values well above those of the hardest

long GRBs.

• Time-integrated spectra are best fit with Band+Power law model
• Short GRBs have similar light curves than long GRBs but contracted in time

and shifted towards higher energy, and appear to have steeper β. => Additional component : electron SSC or hadronic emission

• Epeak tracks the light curves and spreads over a broad energy range

• α in the time resolved spectroscopy violates the synchrotron limits ( Frederic

Daigne talk: possible answer with IC ?)

• The additional power law dominates the standard Band spectrum at low and

high energy => low energy extension of the PL challenges all the models
 => consistent with the electron synchrotron models in the internal shocks context (AcceleraHon
and
cooling
of
the
electrons
leading
to
a
 hardening
with
the
peak
rise
then
a
sonening
of
the
burst
during
the
pulse
decay)
 Time-integrated spectra Fine time-resolved spectroscopy 10/10


Sylvain
Guiriec
–
Fermi
Symposium
2009


SLIDE 11

SLIDE 12

12/10


Band
(Cstat:
699/607
dof)
 Comptonized
+
PL
(Cstat:
689/606
dof)
 Count
spectrum
 υFυ
spectrum


The
addiHonal
component
dominates
the
standard
Band
funcHon
at
both
low
and
high
Energy
 NaI
 BGO


Sylvain
Guiriec
–
Fermi
Symposium
2009


SLIDE 13

13/10


Band
(Cstat:
813/728
dof)
 Comptonized
+
PL
(Cstat:
795/727
dof)
 Count
spectrum
 υFυ
spectrum


The
addiHonal
component
dominates
the
standard
Band
funcHon
at
both
low
and
high
Energy
 NaI
 BGO


Sylvain
Guiriec
–
Fermi
Symposium
2009


SLIDE 14

14/10


Band
(Cstat:
911/850
dof)
 Comptonized
+
PL
(Cstat:
897/849
dof)
 Count
spectrum
 υFυ
spectrum


The
addiHonal
component
dominates
the
standard
Band
funcHon
at
both
low
and
high
Energy
 NaI
 BGO


Sylvain
Guiriec
–
Fermi
Symposium
2009