Constraining the progenitors of long and short GRBs through the study of their environments

Transcription

1 Constraining the progenitors of long and short GRBs through the study of their environments Paolo D Avanzo INAF Osservatorio Astronomico di Brera

2 GRBs are short flashes of gamma rays How much short? Two flavors of GRBs BATSE ('90s) Long Short Dura)on (s) Kouveliotou et al. 1993

3 Another angle Hardness ratio: HR = countrate(hard) countrate(soft) Paradigm: Long/soft Short/hard

4 The third hint Hard band Soft band The hard band leads the soft one Time lag Short GRBs seem to have zero lags Luminosity Time lag

5 Short vs. long GRBs: properties of the prompt emission E peak Amati 2010

6 Short vs. long GRBs: properties of the afterglow emission Short GRBs afterglows are fainter: - less dense environment? - less energetic? Kann et al. 2010

7 GRBs are cosmological and occur in galaxies

8 GRB host galaxies Colors: Blue Hot Young stars Red Cold Old stars

9 Long GRB hosts Emission line spectra Nebular emission lines excited by hot, young stars Blue Hot Young stars

10 The GRB/Supernovae connection Blue Hot Young stars Galama et al. 1998; Stanek et al. 2003; Hjorth et al. 2003; Mazzali et al. 2003; Della Valle et al. 2003; Malesani et al. 2004; Soderber et al Pian et al. 2006; Campana et al Della Valle et al. 2006

11 Short GRB hosts Red Cold Old stars Blue Hot Young stars

12 Short GRB hosts Red Cold Old stars Blue Hot Young stars Berger 2009

13 Short GRB hosts Red Cold Old stars Blue Hot Young stars 1 st summary: Short GRB seem to be less energetic, at lower z and occur in different environments with respect to long GRBs Berger 2009

14 The progenitors of short GRBs Most popular model: Coalescence (merging) of a compact object binary system While orbiting, the two objects emit gravitational waves losing energy: MERGING Such systems are observed in our Galaxy: PSR J

15 The progenitors of short GRBs Most popular model: Coalescence (merging) of a compact object binary system While orbiting, the two objects emit gravitational waves losing energy: MERGING - critical parameter: merging time t m Time between the formation of the system and its coalescence t m a 4 (a: system separation) -> 10 Myr < t m < 10 Gyr - merging can occur in old and young stellar populations - kick velocities: Compact objects are the remnants of core-collapse SNe, that can give a kick The system can escape from the HG-> OFFSET! (1 100 kpc)/low density CBM

16 The progenitors of short GRBs Most popular model: Coalescence (merging) of a compact object binary system While orbiting, the two objects emit gravitational waves losing energy: MERGING Another possibility: dynamical formation of a double compact object system (e.g. in globular clusters) OFFSET/low density CBM

17 Short/hard GRBs no spectral lag in all type of galaxies (or no host galaxy at all) older stellar population no associated SN merger progenitor model Long/soft GRBs spectral lag in SF galaxies younger stellar population many with associated SN collapsar progenitor model

18 Short GRBs: Offsets (I) Salvaterra et al. 2010

19 Short GRBs: host search GRB (D Avanzo et al. 2009) - G1: bright, HG candidate, large offset - BUT G1 is NOT the HG & HG - HG (no offset) R = 25.6 G1 z=0.71 GRB (Piranomonte et al. 2008) - G2: bright, near HG candidate, large offset G2 z= BUT G2 is NOT the HG - HG (no offset) R = 27.3 So, host galaxy identification needs some caution

20 Short GRBs: Offsets (II) no host? GRB (Stratta et al. 2007) -no host galaxy at the optical afterglow position down to R ~ galaxy z~0.09 G2 z=0.11 GRB (Perley et al. 2009) HST > 28.5 mag Berger 2010

21 Short GRBs: Offsets (III) Fong et al. 2010

22 Short GRBs: Extended Emission Is the extended emission a signature of a common progenitor or enivronment? (Troja et al. 2008; D Avanzo et al. 2009; Norris et al. 2010) Perley et al Initial hard spike, followed by a softer tail T90 can be > 2s

23 Short GRBs: Extended Emission Perley et al. 2009

24 Short GRBs: Extended Emission GRB low density CBM Caito et al. 2009

25 GRB T 90 = 1.25 s z = 2.61 (Levesque et al. 2009) t-t 0 = 0.4 d t-t 0 = 16.5 d Telescopio Nazionale Galileo Antonelli et al st spectrum of a SGRB optical afterglow

26 GRB t-t 0 = 35.7 d Antonelli et al Thoene et al. 2011

27 GRB : a SGRB? Antonelli et al. 2009

28 The X-ray absorbing column densities of GRBs Campana et al (sample of 85 LGRBs; < z < 8.1):

29 The X-ray absorbing column densities of GRBs Campana et al (sample of 85 LGRBs; < z < 8.1): Kopac et al. in prep. (sample of 8 SGRBs; < z < 0.923): KS test on the two samples

30 The X-ray absorbing column densities of GRBs Campana et al (sample of 85 LGRBs; < z < 8.1): Kopac et al. in prep. (sample of 8 SGRBs; < z < 0.923): KS test on the two samples

31 The X-ray absorbing column densities of GRBs Campana et al (sample of 85 LGRBs; < z < 8.1): Kopac et al. in prep. (sample of 8 SGRBs; < z < 0.923): KS test on the two samples

32 The X-ray absorbing column densities of GRBs 47 SGRBs promptly observed by Swift-XRT (up to Jan 2011): - 22 with bright X-ray AG - 25 with faint X-ray AG (or no AG at all) Different environments (progenitors)? Campana et al (sample of 85 LGRBs; < z < 8.1): Kopac et al. in prep. (sample of 8 SGRBs; < z < 0.923): KS test on the two samples

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