What made GRBs 060505 & 060614? Palli Jakobsson Johan Fynbo: jfynbo@astro.ku.dk Palli Jakobsson Centre for Astrophysics Research (University of Hertfordshire)

Light Curves • ↓ GRB 060505 (z = 0.09) GRB 060614 (z = 0.13) Duration ~ 4 s Duration ~ 100 s • ↓ Ofek et al. (2007) Fynbo et al. (2006); Della Valle et al. (2006); Gal-Yam et al. (2006)

GRB 060505 Host Galaxy Z ~ 14% Solar MB ~ -19.6 mag AV < 0.09 mag Spec. SFR ~ 4 M○ yr-1 (L/L*)-1 Little extinction (Balmer decrement) t = 17 days SN 1998bw SN 2002ap Fynbo et al. (2006); Thöne et al. (2007) + poster (P.05); Ofek et al. (2007)

GRB 060614 Host Galaxy MB ~ -15.3 (tiny – much smaller than 060505 host) Spec. SFR ~ 3 M○ yr-1 (L/L*)-1 Little extinction (Balmer decrement) t = 11 days SN 2002ap

Wrong Redshifts (z > 1)? Schaefer & Xiao (2006); Cobb et al. (2006) GRB 060614 has -- strong UV detections: z < 1.1 -- no absorption components in OA spectrum, as expected for low-z, but not for a high-z burst with a foreground galaxy. -- no sign of a host @ z ~ 1 in HST images. . GRB 060505 has -- P < 10-3 of accidentally landing right on top of a small star-forming region within a spiral galaxy.

Is There a Problem (no SN)? Both hosts are actively star-forming. 060505 occurred in a star-forming knot. No SN: predicted as a variant of the original collapsar model, e.g. collapse of a massive star with an explosion energy so small that most of the 56Ni falls back into the BH (e.g. Fryer et al. 2006). 060505 duration of 4 s is near the ~5 s duration which Donaghy et al. (2006) find as the point of roughly equal probability of a given burst lying in either “short”/”long” class.

Lag/Luminosity: Short/Long Divide ?? Vanderspek et al. (2004) Gehrels et al. (2006)

Classification Problem? long GRBs (t > 2 s) ≠ massive star death short GRBs (t < 2 s) ≠ compact object merger Type I & II GRBs (Zhang et al. 2007) (ambiguous + not operational, difficult to use) Type III?? WD/NS merger (King et al. 2007) Keep an open mind!