1. Centre for Astrophysics & Cosmology
Low-Resolution Spectroscopy of Gamma-Ray Burst Optical Afterglows: Biases in the Swift Sample
(ApJ Supplement, 2009, 185, )
Palli Jakobsson
Centre for Astrophysics & Cosmology
University of Iceland

3. Centre for Astrophysics & Cosmology
Low-Resolution Spectroscopy of Gamma-Ray Burst Optical Afterglows: Biases in the Swift Sample
(ApJ Supplement, 2009, 185, )
Right, so
Palli Jakobsson
Centre for Astrophysics & Cosmology
University of Iceland

4. The dark burst diagram (βOX)
Jakobsson et al. (2004)

5. Definition of βOX
Optical
X-ray
Sari et al. (1998)

6. Definition of βOX
2.0 < p < 2.5
Optical
X-ray
Sari et al. (1998)

7. The dark burst diagram (βOX)
Swift Identification of Dark Gamma-Ray Bursts: Jakobsson et al. (2004)

8. The dark burst diagram (βOX)

9. The sample March 2005 – September 2008: 146 GRBs
1. A Swift-detected GRB with t90 > 2 s.
2. XRT afterglow position distributed within 12 hours.
3. Small foreground Galactic extinction: AV < 0.5 mag.
4. Favorable declination: -70° < δ < 70°.
5. Sun-to-field distance larger than 55°.
March 2005 – September 2008: 146 GRBs
75% have an optical/NIR afterglow

10. The 3 sub-samples
1. GRBs with redshifts measured from OA spectroscopy. 72
GRBs with detected optical/NIR afterglow, but no
afterglow-based redshift. 35
3. GRBs with no detection of the OA. 39

11. The dark burst diagram (βOX)
[z from OA]
14%
[OA but no z]
38%
[no OA]
>39%
(z = 6.7)
(z = 6.3)

12. XRT excess absorption distribution
KS test probability
(1 and 2): 2 x 10-3
KS test probability
(1 and 3): 7 x 10-7

13. βOX vs. X-ray excess absorption
dark
bursts

14. Redshift distribution: 146 GRBs
Grupe et al. (2007)
< z > 7
<z> = 2.2

15. Cumulative redshift distribution

16. Final slide: with the Miss Universe pageant soon coming up
I think this is an interesting statistically significant result!
Thanks! I’d be happy to answer at least 1 question....