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 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 sample Swift /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: A V <0.5 declination: -70°< δ <+70° distant from Sun: θ >55° Daniele Malesani talk

Salvaterra et al. 2012, ApJ towards a complete sample Swift /BAT [180/540] Jakobsson [132/248] BAT6 : Jakobsson criteria + bright in the BAT band 6 times worst sensitivity with respect to BAT Swift /BAT 6 [55/58]

Salvaterra et al. 2012, ApJ BAT 6 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 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 γ and 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 γ and 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

GRB luminosity function

introduction basic assumptions GRBs follow the star formation (Li 2008; Hopkins & Beacom 2006) form of the GRB LF cut-off: power-law + exponential cut-off at low luminosities double power-law we explore different evolution models no evolution GRB luminosity evolution GRB rate density evolution

jointly fit the BATSE logN-logP and the z-distribution of the complete sample Salvaterra et al. 2012, ApJ grb luminosity function BATSE

no evolution model provides a poor fit of the data (KS~5x10 -5 ) Salvaterra et al. 2012, ApJ no evolution model

Salvaterra et al. 2012, ApJ luminosity evolution model

Salvaterra et al. 2012, ApJ density evolution model

Salvaterra et al. 2012, ApJ density evolution model

Salvaterra et al. 2012, ApJ comparison with a deeper sample Median predicted redshift =2.05± % at z>5 consistent with observations (Greiner et al. 2011; Perley et al. 2009) luminosity and density evolution predict similar observed redshift distributions

Salvaterra et al. 2012, ApJ GRB intrinsic z-distribution assumes no luminosity evolution GRB intrinsic distribution peaks at higher redshift with respect to stars, requiring: - higher z for the first break z 1 =1 → z 1 =2.5 or - harder second power-law a 2 =0.055 → a 2 =2.4 Li 2008

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 “E iso -normalized” light curve

the 2-10 keV X-ray luminosity correlates linearly with Eiso D’Avanzo et al. 2012, MNRAS in press “E iso -normalized” light curve Eiso LXLX t rf =5 min t rf =1 h t rf =11 h t rf =24 h

D’Avanzo et al. 2012, MNRAS in press 1. L X ∝ Eiso 1.0 σ =0.25 ÷ L X ∝ Liso 0.9 σ =0.34 ÷ L X ∝ Ep 1.6 σ =0.35 ÷ 0.43 strong correlations with scatters increasing and significances decreasing with time Eiso Liso Ep LXLX 5 min 1 h 11 h 24 h hint for an additional component (afterglow) rising up at late times

D’Avanzo et al. 2012, MNRAS in press prompt and afterglow contribution steep decay plateau/shallow decay normal decay

D’Avanzo et al. 2012, MNRAS in press prompt and afterglow contribution steep decay plateau/shallow decay normal decay -At t rf = 5 min the X-ray luminosity strongly correlates with E iso and L iso -> L X 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 (t rf > 1 hr) almost all events show the normal decay (X-ray luminosity afterglow dominated).

grb is outliers for the “too high” Ep D’Avanzo et al. 2012, MNRAS, in press the “outlier”

D’Avanzo et al. 2012, MNRAS in press GRB radiative efficiency E K,iso (Panaitescu & Kumar 2002) ν X > ν C p ~2.3 ε e = 0.1 ε B = 0.01 = 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) L X,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 γ and X-rays rest frame properties strong correlations with σ increasing and significances decreasing with time plateau/shallow decay powered by central engine similar radiative efficiency for GRB (average of 6% of the total E K ) 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…

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

HEHE