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a complete sample of long bright Swift GRBs: correlation studies. Paolo D’Avanzo INAF-Osservatorio Astronomico di Brera. S. Campana (OAB) S. Covino (OAB) D. Fugazza (OAB) G. Ghirlanda (OAB). G. Ghisellini (OAB) A. Melandri (OAB) L. Nava (APC) R. Salvaterra (IASF-MI).

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a complete sample of long bright swift grbs correlation studies
a complete sample of long bright Swift GRBs: correlation studies

Paolo D’Avanzo

INAF-Osservatorio Astronomico di Brera

S. Campana (OAB) S. Covino (OAB)

D. Fugazza (OAB)

G. Ghirlanda (OAB)

G. Ghisellini (OAB)

A. Melandri (OAB)

L. Nava (APC)

R. Salvaterra (IASF-MI)

B. Sbarufatti (OAB) G. Tagliaferri (OAB)

S.D. Vergani (OAB)

towards a complete sample
towards a complete sample

Swift/BAT [180/540]

  • most of the GRBs lack of measured redshift due to:
  • observing conditions from ground
  • bad weather
  • high galactic extinction
  • late observations
  • ...
  • intrinsic biases
  • redshift desert
  • dark bursts
  • ...

Salvaterra et al. 2012, ApJ

towards a complete sample1
towards a complete sample

Swift/BAT [180/540]

  • Jakobsson et al. (2004) provides some criteria to select GRBs with favorable observing condition from ground:
  • XRT position with 12h
  • low Galactic extinction: AV<0.5
  • declination: -70°<δ<+70°
  • distant from Sun: θ>55°

Daniele Malesani

talk

Jakobsson [132/248]

Salvaterra et al. 2012, ApJ

towards a complete sample2
towards a complete sample

Swift/BAT [180/540]

Jakobsson [132/248]

Swift/BAT6 [55/58]

BAT6: Jakobsson criteria + bright in the BAT band

6 times worst sensitivity with respect to BAT

Salvaterra et al. 2012, ApJ

bat 6 redshift distribution
BAT6 redshift distribution

mean (median) z = 2.23 (2.14)

Daniele Malesani talk

Hjorth et al. 2012

in spite of the severe cut in photon flux the mean (median) redshift is 1.82 (1.62) and the distribution extend at least up to z=5.47

Salvaterra et al. 2012, ApJ

complete sample overview
complete sample: overview
  • highlights of some results obtained so far from our complete sample:
  • GRB luminosity function (Salvaterra et al. 2012, ApJ, 749, 68 )
      • need of evolution?
  • prompt emission spectral correlations (Nava et al., 2012, MNRAS, 421, 1256)
      • complete vs incomplete samples
      • redshift evolution?
  • correlations of γand X-rays rest frame properties (D’Avanzo et al., 2012, MNRAS, in press)
      • relative contribution of prompt and afterglow
      • radiative efficiency
  • distribution of the X-ray absorptions (Campana et al. 2012, MNRAS, 421, 1697)
      • complete vs incomplete samples
  • dark bursts (Melandri et al. 2012, MNRAS, 421, 1265)
      • redshift and luminosity distributions
      • nature
complete sample overview1
complete sample: overview
  • highlights of some results obtained so far from our complete sample:
  • GRB luminosity function (Salvaterra et al. 2012, ApJ, 749, 68 )
      • need of evolution?
  • prompt emission spectral correlations (Nava et al., 2012, MNRAS, 421, 1256)
      • complete vs incomplete samples
      • redshift evolution?
  • correlations of γand X-rays rest frame properties (D’Avanzo et al., 2012, MNRAS, in press)
      • relative contribution of prompt and afterglow
      • radiative efficiency
  • distribution of the X-ray absorptions (Campana et al. 2012, MNRAS, 421, 1697)
      • complete vs incomplete samples
  • dark bursts (Melandri et al. 2012, MNRAS, 421, 1265)
      • redshift and luminosity distributions
      • nature

Andrea Melandri

talk on Friday

no evolution model
no evolution model

no evolution model provides a poor fit of the data (KS~5x10-5)

Salvaterra et al. 2012, ApJ

luminosity evolution model
luminosity evolution model

Salvaterra et al. 2012, ApJ

density evolution model
density evolution model

Salvaterra et al. 2012, ApJ

density evolution model1
density evolution model

Salvaterra et al. 2012, ApJ

e iso normalized light curve
“Eiso-normalized” light curve

D’Avanzo et al. 2012, MNRAS in press

e iso normalized light curve1

the 2-10 keV X-ray luminosity correlates linearly with Eiso

“Eiso-normalized” light curve

trf=5 min

trf=1 h

LX

trf=11 h

trf=24 h

Eiso

D’Avanzo et al. 2012, MNRAS in press

slide20

5 min

strong correlations

with scatters

increasing and

significances

decreasing with time

1 h

1. LX∝Eiso1.0

σ=0.25 ÷ 0.48

2. LX ∝ Liso0.9

σ=0.34 ÷ 0.47

3. LX ∝ Ep1.6

σ=0.35 ÷ 0.43

LX

11 h

24 h

hint for an additional

component (afterglow)

rising up at late times

Eiso

Liso

Ep

D’Avanzo et al. 2012, MNRAS in press

prompt and afterglow contribution
prompt and afterglow contribution

steep decay

plateau/shallow decay

normal decay

D’Avanzo et al. 2012, MNRAS in press

prompt and afterglow contribution1
prompt and afterglow contribution

steep decay

plateau/shallow decay

normal decay

  • At trf = 5 min the X-ray luminosity strongly correlates with Eiso and Liso -> LX is still dominated by the prompt emission and ~2/3 of the X-ray light curves are in the plateau/shallow decay phase.
  • - The plateau/shallow decay phase is likely dominated by the central engine activity (Zhang et al. 2006)
  • At later times (trf > 1 hr) almost all events show the normal decay (X-ray luminosity afterglow dominated).

D’Avanzo et al. 2012, MNRAS in press

grb radiative efficiency
GRB radiative efficiency

EK,iso

νX > νC

(Panaitescu & Kumar 2002)

LX,24h

p~2.3

εe= 0.1

εB= 0.01

<Eiso/EK,iso>= 0.06 (σ=0.14)

6% of average radiative efficiency

(Freedman & Waxmann 2001; Berger et al. 2003;

Granot et al. 2006; Zhang et al. 2007; Berger 2007; Nakar 2007)

D’Avanzo et al. 2012, MNRAS in press

conclusions
conclusions
  • This complete sample (90%) of bright long Swift GRBs allows for the first time to study the GRB population in an unbiased way
  • GRB luminosity function
      • strong evolution (luminosity and/or density) is required
      • GRBs (assuming no lum. evo.) peak at higher z with respect to stars
      • observed z-distribution does not allow to distinguish among evo. models
  • prompt emission spectral correlations
      • Amati & Yonetoku correlations are confirmed with 1 outlier (~2%)
      • no redshift evolution of the slope is found
  • correlations of γand X-rays rest frame properties
      • strong correlations withσincreasing and significances decreasing with time
      • plateau/shallow decay powered by central engine
      • similar radiative efficiency for GRB (average of 6% of the total EK)
  • 5 papers published + 2 in preparation

more to come...

someone stole stefano s badge
Someone stole Stefano’s badge…

…without the badge he cannot attend the social dinner

we heard some rumors1
we heard some rumors…

…it seems that one of these guys might be the responsible

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