Diapositiva 1

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INAF - Osservatorio Astronomico di Brera,
Italy Universita degli Studi dellInsubria,
Como, Italy
Is the Amati relation due to selection effects?
Lara Nava In collaboration with G. Ghirlanda,
G.Ghisellini, C. Firmani
Egypt, March 30-April 4, 2009 NeutronStars
GammaRayBursts
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Amati and Yonetoku relations
Eiso erg
Lpeak,iso erg/s
scatter 0.22
scatter 0.26
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Observational planes Amati
Yonetoku Epeak,obs Fluence
Epeak,obs Peak Flux
Epeak,obs keV
Fluence erg
Peak Flux erg/cm2 s
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Instrumental Selection Effects
Epeak
TRIGGER THRESHOLD
Allowed region
Minimum Energy Peak Flux Plim (Epeak,obs)
Peak flux
SPECTRAL ANALYSIS THRESHOLD
Epeak
Minimum Fluence Flim (Epeak,obs)
Fluence
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Amati relation in the observational plane
All GRBs with published Epeak and Fluence
All GRBs with redshift
HETE Sakamoto et al. 2005 Swift/BAT Butler
et al. 2007 (freq) BATSE Kaneko et al. 2006
Konus/Wind Golenetskii et al. (GCNs)
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Extend the Bright BATSE GRB sample (Kaneko et
al. 2006) to lower fluences
Build a complete spectral sample of BATSE bursts
down to 10-6 erg/cm2
Nava et al., 2008, MNRAS
Density contours
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Epeak,obs distribution of BATSE bursts
Lower fluences correspond to lower Epeak
bright
Considering the whole sample we found Ep
160 keV
faint
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Yonetoku relation in the observational plane
Epeak,obs keV
HETE Sakamoto et al. 2005 Swift/BAT Butler
et al. 2007 (freq) BATSE Kaneko et al. 2006
Konus/Wind Golenetskii et al. (GCNs)
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Epeak-Liso
Bosnjak et al. 2009 (submitted)
Ep-Liso correlation found with time integrated
spectra holds also within a burst!!
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FERMI(preliminary results from GCN)
Fluence erg
Peak Flux erg/cm2 s
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Summary
AMATI
YONETOKU
Correlation in the observer frame
YES
YES
Determined by selection effects
NO
NO
Without z same region that with z
NO (larger)
YES
Within a single burst
YES
NO
Short bursts
See talk tomorrow by Ghirlanda
The Yonetoku correlation is more fundamental and
requires more attention and theoretical efforts
to explain its physical origin
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(No Transcript)
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Summary
Epeak-Fluence or Epeak-Peak Flux show strong
correlations Add bursts without redshifts ( a
complete BATSE sample)
Strong Epeak-Fluence correlation Strong
Epeak-Peak Flux correlation
In the future Epeak-Eiso correlation will have a
different slope larger scatter but maybe not
for the Epeak-Liso correlation
6 of outliers of the Epeak-Eiso 0.3 of
outliers of the Epeak-Liso
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What about short bursts?
Short bursts populate the same region of long
bursts in the Epeak,obs-Peak Flux plane. They can
be consistent with the Epeak-Liso
correlation Short bursts have similar Epeak but
lower fluences in respect to Long bursts. They
cannot be consistent with the Epeak-Eiso
correlation
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Summary The existence of a correlation in the
plane Epeak,obs-Fluence is not determined by
instrumental biases However, they affect the
slope and the dispersion of the Epeak-Eiso
correlation Swift/BAT bursts are strongly biased
by the spectral and trigger threshold and by the
very small energy range ? flat correlation in the
observational plane ? flat correlation in the
rest frame plane
Epeak-Eiso correlation 6 of BATSE bursts are
outliers
Epeak-Eiso Epeak-Liso
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Rest frame plane
No redshift evolution
Observational plane
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Epeak-Eiso correlation 6 of BATSE bursts are
outliers
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Extend the Bright Batse GRB sample (Kaneko et
al. 2005) to lower fluences
Red points bright BATSE bursts from Kaneko et
al. 2006
Green points 100 lower fluence bursts
representatives of around 1000 bursts (our
analysis)
Build a complete spectral sample of BATSE bursts
down to 10-6 erg/cm2