1. GRB 050814 at z = 5.3 and a Mean Redshift of 2.8 for Swift GRBs A&A, in press (astro-ph/0509888) Páll Jakobsson Robert Priddey Darach Watson Priya Natarajan Andrew Levan Jens Hjorth Brian L. Jensen Javier Gorosabel Johan P. U. Fynbo Nial Tanvir Jesper Sollerman Kristian Pedersen X 2.7

2. GRB 050814 t 90 = 65 +40 -20 s (poorly constrained). XRT source @ 138 s. UVOT @ 167 s: V > 20.5 mag. NOT observations of OA @ 14 hours: V > 25.2 mag; R = 23.4 mag; I = 20.6 mag. R – I  2.8 mag  β  11.7 UKIRT detection in the NIR (J and K).

3. Spectral Energy Distribution

4. GRB 050814 (z = 5.3)GRB 050904 (z = 6.3) Tagliaferri et al. (2005)

5. Spectral Energy Distribution

6.  2 (z) for GRB 050814 z = 5.3 ± 0.3 β = 1.0 (fixed) A V  0.9 mag

7. The Redshift Distribution of Swift LGRBs Is it consistent with models were GRBs trace the global star formation? Important to construct a “clean” sample as unbiased as possible. Metallicity dependence?

8. Selection Criteria Small error circles: XRT localization (68). Sufficiently small Galactic extinction: A V < 0.5 mag (46). Quick distribution of XRT error circles for a relatively rapid follow-up: after 1 March 2005 (39). Reject bursts with an unsuitable declination: above +70 º or below –70 º (36). A total of 83 long-duration Swift GRBs

9. The Sample (36 bursts) 050315 050318 050319 050401 050406 050412 050416A 050502B 050505 050525 050603 050714B 050716 050726 050730 050801 050802 050803 050814 050819 050820A 050822 050824 050904 050908 050915A 050922B 050922C 051001 051006 051008 051012 051016A 051016B 051117A 051117B 1.95 1.44 3.24 2.90 < 3.5 0.65 < 8.5 4.27 0.61 2.82 < 8.0 < 5.0 3.97 < 2.0 1.71 5.3 2.61 0.83 6.29 3.34 < 13.0 2.20 0.94 GRB zzz

10. Cumulative Fraction Natarajan et al. (2005)Gorosabel et al. (2004)

11. At least 6% @ z > 5 050315 050318 050319 050401 050406 050412 050416A 050502B 050505 050525 050603 050714B 050716 050726 050730 050801 050802 050803 050814 050819 050820A 050822 050824 050904 050908 050915A 050922B 050922C 051001 051006 051008 051012 051016A 051016B 051117A 051117B 1.95 1.44 3.24 2.90 < 3.5 0.65 < 8.5 4.27 0.61 2.82 < 8.0 < 5.0 3.97 < 2.0 1.71 5.3 2.61 0.83 6.29 3.34 < 13.0 2.20 0.94 GRB zzz