What made GRBs 060505 & 060614?

Palli JakobssonCentre for Astrophysics Research

(University of Hertfordshire)

Johan Fynbo: jfynbo@astro.ku.dk

Light CurvesGRB 060505 (z = 0.09) GRB 060614 (z = 0.13)

Fynbo et al. (2006); Della Valle et al. (2006); Gal-Yam et al. (2006)

Duration ~ 4 s Duration ~ 100 s

•↓Ofek et al. (2007)

GRB 060505 Host Galaxy

Fynbo et al. (2006); Thöne et al. (2007) + poster (P.05); Ofek et al. (2007)

MB ~ -19.6 mag

Spec. SFR ~ 4 M○ yr-1 (L/L*)-1

Little extinction (Balmer decrement)SN 2002apSN 1998bwt = 17 days

Z ~ 14% Solar

AV < 0.09 mag

GRB 060614 Host Galaxy

t = 11 days SN 2002ap

MB ~ -15.3 (tiny – much smaller than 060505 host)

Spec. SFR ~ 3 M○ yr-1 (L/L*)-1

Little extinction (Balmer decrement)

Wrong Redshifts (z > 1)?

• GRB 060614 has

• GRB 060505 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.

-- P < 10-3 of accidentally landing right on top of a small star-forming region within a spiral galaxy.

Schaefer & Xiao (2006); Cobb et al. (2006)

Is There a Problem (no SN)?

• Both hosts are actively star-forming. 060505 occurred in a star-forming knot.

• 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.

• 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).

Lag/Luminosity: Short/Long Divide

Gehrels et al. (2006)

Vanderspek et al. (2004)??

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!