1. Is the Amati relation due to selection effects? Lara Nava In collaboration with G. Ghirlanda, G.Ghisellini, C. Firmani Egypt, March 30-April 4, 2009 NeutronStars & GammaRayBursts INAF - Osservatorio Astronomico di Brera, Italy Universita’ degli Studi dell’Insubria, Como, Italy

2. Amati and Yonetoku relations E iso [erg] L peak,iso [erg/s] scatter = 0.22scatter = 0.26

3. No instr. selection effects Possible instr. selection effects Observational planes Amati Yonetoku E peak,obs – Fluence E peak,obs – Peak Flux No instr. selection effects Possible instr. selection effects Fluence [erg] Peak Flux [erg/cm 2 s] E peak,obs [keV]

4. Instrumental Selection Effects TRIGGER THRESHOLD SPECTRAL ANALYSIS THRESHOLD Minimum Energy Peak Flux: P lim (E peak,obs ) Peak flux E peak Allowed region Minimum Fluence: F lim (E peak,obs ) E peak Fluence

5. HETE: Sakamoto et al. 2005 Swift/BAT: Butler et al. 2007 (freq) BATSE: Kaneko et al. 2006 Konus/Wind: Golenetskii et al. (GCNs) Amati relation in the observational plane All GRBs with redshift All GRBs with published E peak and Fluence

6. Build a complete spectral sample of BATSE bursts down to ~ 10 -6 erg/cm 2 Extend the Bright BATSE GRB sample (Kaneko et al. 2006) to lower fluences Density contours Nava et al., 2008, MNRAS

7. E peak,obs distribution of BATSE bursts bright faint Lower fluences correspond to lower E peak Considering the whole sample we found: ‹Ep› = 160 keV

8. Yonetoku relation in the observational plane HETE: Sakamoto et al. 2005 Swift/BAT: Butler et al. 2007 (freq) BATSE: Kaneko et al. 2006 Konus/Wind: Golenetskii et al. (GCNs) E peak,obs [keV]

9. Bosnjak et al. 2009 (submitted) E peak -L iso Ep-Liso correlation found with time integrated spectra holds also within a burst!!

10. FERMI (preliminary results from GCN) Fluence [erg] Peak Flux [erg/cm 2 s]

11. Summary Correlation in the observer frame Determined by selection effects Without z same region that with z Short bursts AMATIYONETOKU YES NO (larger) YES The Yonetoku correlation is more fundamental and requires more attention and theoretical efforts to explain its physical origin NO Within a single burst See talk tomorrow by Ghirlanda

13. E peak -Fluence or E peak -Peak Flux show strong correlations Add bursts without redshifts (+ a complete BATSE sample) In the future E peak -E iso correlation will have a different slope & larger scatter but maybe not for the E peak -L iso correlation 6% of outliers of the E peak -E iso 0.3% of outliers of the E peak -L iso Strong E peak -Fluence correlation Strong E peak -Peak Flux correlation Summary

14. What about short bursts? Short bursts populate the same region of long bursts in the E peak,obs -Peak Flux plane. They can be consistent with the E peak -L iso correlation Short bursts have similar Epeak but lower fluences in respect to Long bursts. They cannot be consistent with the E peak -E iso correlation

15. E peak -E iso correlation: 6% of BATSE bursts are outliers Summary: The existence of a correlation in the plane E peak,obs -Fluence is not determined by instrumental biases However, they affect the slope and the dispersion of the E peak -E iso correlation Swift/BAT bursts are strongly biased by the spectral and trigger threshold and by the very small energy range → flat correlation in the observational plane → flat correlation in the rest frame plane E peak -E iso E peak -L iso

16. No redshift evolution Rest frame plane Observational plane

17. E peak -E iso correlation: 6% of BATSE bursts are outliers

18. Build a complete spectral sample of BATSE bursts down to ~ 10 -6 erg/cm 2 Extend the Bright Batse GRB sample (Kaneko et al. 2005) to lower fluences Red points: bright BATSE bursts from Kaneko et al. 2006 Green points: 100 lower fluence bursts representatives of around 1000 bursts (our analysis)