grb spectral-energy correlations: perspectives and issues g. ghirlanda + g. ghisellini, l. nava, z....
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GRB Spectral-Energy correlations: perspectives and
issues
G. Ghirlanda + G. Ghisellini, L. Nava, Z. Bosnjak, C. Firmani, I. Cabrera, F. Tavecchio & A. Celotti
Why?
1) tools for understanding GRB physics
2) tools to standardize GRB energetics cosmology
G. Ghirlanda – 2008 Nanjing Gamma Ray Burst Conference
Epeak Eiso0.57
2red=7.2 (60 dof)
s=0.2
Epeak Eg1.05
2red=0.89 (23 dof)
s=0.08
Liso Ep1.62 T45
-0.49
2red=0.7 (16 dof)
s=0.06
Liso t - 1.05
2red=9.6 (34 dof) 2
red=100 (46 dof)
Liso V 3.0
Amati et al. 2002
Ghirlanda et al. 2004
Firmani et al. 2005
Norris et al. 2000
Reichart et al. 2000Ramirez-Ruiz & Fenimore 2000
Liso0.57 Epeak 1.85
Yonetoku et al. 2004
Spectral-energy correlations: true physics or selection effects?
(I) GRBs with z
(II) + GRBs without z
(III) Still not convinced ?
(V) news
Q.
Physical interpretation(e.g. Rees & Meszaros 2006, Thomson, Meszaros & Rees 2006)
Study selection effects
(IV) Thermal component?
Epeak – Eiso
9 SAX (GRBM+WFC)
5 CGRO (Batse)
15 Hete-II (Fr.+WXC)
20 Konus et al.
27(/41) Swift (BAT)
35 before Nov. 200441 since Nov. 2004
03.047.0 isopeak EE
76 GRBs with z and Epeak
Amati et al. 2002, 2006, Nava et al. 2006, Ghirlanda et al. 2008 … etc
Evolution with redshift?
Slope of the 76 GRBs
NO
GRBs with F>Flim
Ep [Emin, Emax]
REST FRAME
OBSERVER FRAME
No segregation in z in the obs. frame
obs frame Ep-fluence correlation : (Lloyd, Petrosian & Mallozzi 2000; Lamb et al. 2005; Sakamoto et al. 2005)
Instrumentalselection
effcts
obsObs Frame Epeak - F
High fluence – intemediate/low Epeak
low fluence – intemediate/high Epeak
Selection
effects
Trigger threshold: which flux to trigger?(Band 2003,
2006)
Spectral threshold: which fluence to measure Epeak?
)(minmin EA
ENF
eff
obspeak
Assume GRB spectrum
Background
Detector response
a=1 b=2.3 Epeak Fbol
the error on Epeak(fit) < 100% in 97.7% of cases Fit with single powerlaw is excluded at 2σ
Trigger threshold: which flux to trigger?(Band 2003,
2006)
Spectral threshold: which fluence to measure Epeak?
Gh
irla
nd
a e
t al.
2008
BATSE could not detect this burst
BATSE could detected this burst
BATSE certainly detected this burstand measured Epeak
CONCLUSIONS (I)
76 GRBs (updated to Oct. 2007) with z and spectrum
1) No evolution of the Epeak-Eiso correlation with redshift.
2) A correlation is found in the observer frame
05.039.0 bolobspeak FE
3.1) no z segregation
3.2) Instrumental selection effect: a) trigger threshold not biasing b) spectral analysis threshold yes on Swift no on Batse/Sax
HOW is populated the Ep-Fluence plane?
Q: are there intermediate/low fluence bursts (i.e. between those with z and the spectral analisys curves)??
Nava et al. 2008 submitted
HOW is populated the Ep-Fluence plane? Add GRBs without redshift
From the literature
Sakamoto et al. 2005Butler et al. 2007 (freq)Kaneko et al. 2005GCNs (Golenetski et al. …)
Build a complete spectral sample of BATSE bursts down to ~2x10-6 erg/cm2
Extend the Bright Batse GRB sample (Kaneko et al. 2005) to lower fluences
Bright BATSE
Peak energy distribution
Fainter BATSE
Ep = 160 keV
BATSE bursts
Nava e
t al.
20
08
su
bm
itte
dOutliers of the Epeak – Eiso correlation
6% of BATSE bursts are outliers
Isotropic luminosity Isotropic energy
The Ep-Liso “Yonetoku” correlation The Ep-Eiso “Amati” correlation
Nava e
t al.
20
08
su
bm
itte
dThe Ep-Flux plane and the outliers of the Ep-Liso correlation
CONCLUSIONS (II)
Ep-Fluence or Ep-Peak flux show strong correlations
Add bursts without redshifts (+ a complete BATSE sample)
The 20?? Ep-Eiso correlation will have a different slope & larger scatter but maybe not for the Ep-Liso correlation
6% of outliers of the Ep-Eiso
0.3% of outliers of the Ep-Liso
Strong Ep-Fluence correlation
Strong Ep-Peak flux correlation
Still not convinced ? Are the spectral-energy correlations revealing a
physical process or simply due to selection effects?
Liang, Dai & Wu 2004 noted that an Ep-Liso correlation holds WITHIN single bursts!
Still not convinced ? Are the spectral-energy correlations revealing a
physical process or simply due to selection effects?
We have studied the time resolved spectra of BATSE GRBs with measured redshifts
Bosnjak et al. 2008 (to be subm.)
Ep-Liso “Y
onetoku”Ep-Liso is equivalent to Ep(t)-Liso(t)
Ep-Liso correlation found with time integrated spectra holds also within a burst!!
Physical o
rigin fo
r
this
!
Interpretation of the <Epeak> Eg,iso0.5
“Geometrical” models: Eichler & lenvinson 2005a,b; Toma et al. 2005
“Radiative” models: Rees & Meszaros 2005; Tompson 2006; Thompson, Meszaros & Rees 2006
If the spectrum of GRBs is dominated by a thermal balck body component then the luminosity is naturally LINKED to the peak energy.
Evidence of Black Body in GRBs:
Ghirlanda, Celotti, Ghisellini 2003 980326, 970111, 911118, 910807, 910927 [Spectrum is thermal black body in the inital phase (~2 sec), later a non-thermal component dominates.]
Bosnjak, Celotti, Ghirlanda 2005 990413
Ryde 2005, 2006 Fit with Black body + Powerlaw
(4) Interpretation – Thermal BB
Band model fits
Black Body + powerlaw fits
Thermal components in GRB spectra
Thermal interpretation of the Amati relation
Time resolved spectra (BB+PL)
Time integrated spectrum = sum of time resolved
5 GRBs detected by BATSE and with WFC data the BB+PL fit to the BATSE data is inconsistent with the X-ray (WFC) data. A single Band model is the best fit.
Ghirlanda et al. 2007
Last slide … more News: the Ep-Eg corrlation
Ghirlanda et al. 2007
Pre swift-era bursts Swift era bursts (up to March 2007)Swift era bursts of the last yearJet Breaks from the
Optical