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

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


• 
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.
 12
Iodine
Sodium
 detectors
(NaI:





 =>
Much
beWer
photo‐peak
efficiency
and
effecHve
area
 8
keV
to
1
MeV)
 above
1
MeV
:
 
BATSE
maximal
energy
~10
MeV.
 
GBM


maximal
energy
~40
MeV.
 =>
Spectroscopy
of
hard
bursts
possible
with
GBM.
 2
Germanate
Bismuth
detectors
























 • 
GBM
has
:
 (BGO:
200
keV
to
40
MeV)
  
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
 on
TGFs)
and
SGRs
(see
Chryssa
Koveliotou
and
Ersin
 Gogus
talks)
 2/10
 Sylvain
Guiriec
–
Fermi
Symposium
2009


• 
About
68
short
GRBs
detected
with
GBM
 since
since
July,
2008.
 • 
Short
GRBs
correspond
to
~20%
of
the
 total
GRBs
detected
with
GBM
 Sample
criteria
for
this
analysis
 • 
T 50 
<
1s
 • 
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.
 3/10
 Sylvain
Guiriec
–
Fermi
Symposium
2009


Standard
model
before
the
Fermi
Era
 • 
Various
model
tested
:
  
Power‐law
with
exponenHal
decay
 (comptonized)
  
Band
funcHon
  
Comptonized+PL
  
Band+PL
 AddiHonal
component
onen
present
in
Fermi’s
GRB
spectra
 • 
Fit
performed
with
the
analysis
package
Rmfit
 • 
Choice
of
the
best
model
:
staHsHcal
improvement
of
the
 Castor
Cstat
value
between
models
according
to
the
addiHonal
 degree
of
freedom
 4/10
 Sylvain
Guiriec
–
Fermi
Symposium
2009


Band
(Cstat:
699/607
dof)
 Comptonized
+
PL
(Cstat:
689/606
dof)
 NaI
 Count
spectrum
 BGO
 υF υ 
spectrum
 The
addiHonal
component
dominates
the
standard
Band
funcHon
at
both
low
and
high
Energy
 5/10
 Sylvain
Guiriec
–
Fermi
Symposium
2009


Name
 Model
 Parameters
of
the
Band
func7on
 PL
 Castor
 Cstat
/
dof
 E peak 
(keV) 
 α
 β
 index
 GRB
090227B
 Compt
 706/608
 + 90 + 0.02 -0.52 2227 − 0.02 − 85 + 97 + 0.02 + 0.27 Band
 699/607
 2116 -0.50 -3.35 − 0.02 − 0.39 − 95 Compt+PL
 + 96 + 0.05 + 0.06 689/606
 1995 -0.36 -1.37 − 0.05 − 91 − 0.06 Band+PL
 686/605
 + 205 + 0.05 + 0.58 + 0.05 1947 -0.36 -3.44 -1.51 − 0.13 − 0.80 − 98 − 0.04 GRB
090228
 Compt
 813/729
 + 52 + 0.03 862 -0.59 − 0.03 − 47 Band
 813/728
 + 50 + 0.03 + 0.64 860 -0.59 -3.77 − 0.03 − 0.64 − 49 + 0.11 Compt+PL
 + 47 + 0.09 795/727
 722 -0.23 -1.63 − 42 − 0.10 − 0.15 Band+PL
 + 0.10 + 1.14 795/726
 + 45 + 0.03 723 -0.24 -4.74 -1.64 − 41 − 0.10 −∞ − 0.02 GRB
090510
 Compt
 + 0.02 922/851
 + 255 4797 -0.77 − 237 − 0.02 Band
 911/850
 + 0.02 + 0.20 + 290 4383 -0.75 -2.80 − 278 − 0.02 − 0.28 Compt+PL
 + 265 + 0.08 + 0.04 897/849
 3731 -0.51 -1.35 − 246 − 0.07 − 0.04 Band+PL
 897/848
 + 284 + 0.08 + 0.75 + 0.04 3695 -0.51 -3.65 -1.38 − 265 − 0.08 −∞ − 0.03 (GBM+LAT)
 Band+PL
 + 0.06 + 0.14 + 0.03 + 280 3936 -0.58 -2.83 -1.62 − 260 − 0.05 − 0.20 − 0.03 • 
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
E peak 
values
than
for
long
GRBs
 (=>
quesHon
during
Ehud
talk
:
short
vs
long
GRBs
with
GBM)
 • 
Steep
β
values
 (which
confirm
the
comment
from
Guido
to
Nicola
in
the
previous
talk)
 6/10
 • 
GBM
only
results
and
GBM+LAT
fits
are
consistent
for
GRB
090510
 Sylvain
Guiriec
–
Fermi
Symposium
2009


The
existence
of
addiHonal
components
in
these
3
GRBs
is
 consistent
with
LAT
data
 See
Poster
Valerie
Connaughton
P3‐171
(Wed‐Thur)
 7/10
 Sylvain
Guiriec
–
Fermi
Symposium
2009


GRB
090227B
 GRB
090228
 • 
Similar
to
what
we
observed
in
long
GRBs
 GRB
090510
 but
contracted
in
Hme
and
shined
to
higher
 10000
 energy
(Ford
et
al.).
 • 
E peak 
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.
 8/10
 Sylvain
Guiriec
–
Fermi
Symposium
2009


α
<
‐3/2
:
 e ‐ 
synchrotron
 α
<
‐2/3
:
 • 
α
nearly
systemaHcally
violates
the
 emission
valid
 e ‐ 
synchrotron
 synchrotron
line
of
death
of
‐2/3.
 for
fast
cooling
 emission
valid
 for
slow
cooling
 • 
E peak 
evolves
over
an
incredible
 broad
range
of
energy
 9
 9/10
 Sylvain
Guiriec
–
Fermi
Symposium
2009


Time-integrated spectra • Time-integrated spectra are best fit with Band+Power law model => Additional component : electron SSC or hadronic emission • The additional power law dominates the standard Band spectrum at low and high energy => low energy extension of the PL challenges all the models 
 • The hardest short GRBs have Epeak values well above those of the hardest long GRBs. Fine time-resolved spectroscopy • Short GRBs have similar light curves than long GRBs but contracted in time and shifted towards higher energy, and appear to have steeper β . E peak tracks the light curves and spreads over a broad energy range 
 • => 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)
 • α in the time resolved spectroscopy violates the synchrotron limits ( Frederic Daigne talk: possible answer with IC ?) 10/10
 Sylvain
Guiriec
–
Fermi
Symposium
2009


Band
(Cstat:
699/607
dof)
 Comptonized
+
PL
(Cstat:
689/606
dof)
 NaI
 Count
spectrum
 BGO
 υF υ 
spectrum
 The
addiHonal
component
dominates
the
standard
Band
funcHon
at
both
low
and
high
Energy
 12/10
 Sylvain
Guiriec
–
Fermi
Symposium
2009


Band
(Cstat:
813/728
dof)
 Comptonized
+
PL
(Cstat:
795/727
dof)
 NaI
 Count
spectrum
 BGO
 υF υ 
spectrum
 The
addiHonal
component
dominates
the
standard
Band
funcHon
at
both
low
and
high
Energy
 13/10
 Sylvain
Guiriec
–
Fermi
Symposium
2009


Band
(Cstat:
911/850
dof)
 Comptonized
+
PL
(Cstat:
897/849
dof)
 NaI
 Count
spectrum
 BGO
 υF υ 
spectrum
 The
addiHonal
component
dominates
the
standard
Band
funcHon
at
both
low
and
high
Energy
 14/10
 Sylvain
Guiriec
–
Fermi
Symposium
2009