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)

Salvaterra et al. 2012, ApJ

towards a complete sampleSwift/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 ...


towards a complete sampleSwift/BAT [180/540]

Jakobsson [132/248]

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 Malesanitalk


towards a complete sampleSwift/BAT [180/540]

Jakobsson [132/248]

BAT6: Jakobsson criteria + bright in the BAT band

6 times worst sensitivity with respect to BAT

Swift/BAT6 [55/58]


BAT6 redshift distribution

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

Daniele Malesani talk Hjorth et al.

2012

mean (median) z = 2.23 (2.14)

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: 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 Andr

ea M

elan

dri

talk

on

Frid

ay

GRB luminosity function

jointly fit the BATSE logN-logP and the z-distribution of the complete sample


grb luminosity function

BATSE

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


no evolution model


luminosity evolution model


density evolution model

prompt spectral correlations

correlations are confirmed but 1 outlier is found (~2% see Nava et al. 2008)

Nava et al. 2012, MNRAS

Amati & Yonetoku correlations

no evolution of the slope of the correlations is found

Nava et al. 2012, MNRAS

evolution in redshift?

correlations of rest-frame gamma- and X-ray

properties

D’Avanzo et al. 2012, MNRAS in press

“Eiso-normalized” light curve

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


“Eiso-normalized” light curve

Eiso

LX

trf=5 min

trf=1 h

trf=11 h

trf=24 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

strong correlationswith scatters

increasing and significances

decreasing with time

Eiso Liso Ep

LX

5 min

1 h

11 h

24 hhint for an additional component (afterglow)

rising up at late times


prompt and afterglow contribution

steep decay

plateau/shallow decay

normal decay


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).


GRB radiative efficiencyEK,iso

(Panaitescu & Kumar 2002)

νX > νC

p~2.3εe= 0.1εB= 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)

LX,24h

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...

“the missing badge mistery”

Someone stole Stefano’s badge…

…without the badge he

cannot attend the social

dinner

we heard some rumors…

we heard some rumors…

…it seems that one of these

guys might be the responsible

a complete sample of long bright Swift GRBs: correlation studies

Documents

Transcript of a complete sample of long bright Swift GRBs: correlation studies