Low-Resolution Spectroscopy of Gamma-Ray Burst Optical Afterglows: Biases in the Swift
Sample(ApJ Supplement, 2009, 185, 526-573)
Palli JakobssonCentre for Astrophysics & Cosmology
University of Iceland
Low-Resolution Spectroscopy of Gamma-Ray Burst Optical Afterglows: Biases in the Swift
Sample(ApJ Supplement, 2009, 185, 526-573)
Palli JakobssonCentre for Astrophysics & Cosmology
University of Iceland
The dark burst diagram (βOX)
Jakobsson et al. (2004)
Definition of βOX
Sari et al. (1998)
X-ray
Optical
Definition of βOX
Sari et al. (1998)
X-ray
2.0 < p < 2.5Optical
The dark burst diagram (βOX)
Swift Identification of Dark Gamma-Ray Bursts: Jakobsson et al. (2004)
The dark burst diagram (βOX)
The sample1. 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 GRBs75% have an optical/NIR afterglow
The 3 sub-samples1. GRBs with redshifts measured from OA spectroscopy.
2. GRBs with detected optical/NIR afterglow, but no afterglow-based redshift.
3. GRBs with no detection of the OA.
72
35
39
The dark burst diagram (βOX)[z from OA][OA but no z][no OA]
14%38%>39
%
050904 (z = 6.3)
080913 (z = 6.7)
XRT excess absorption distribution
KS test probability(1 and 2): 2 x 10-3
KS test probability(1 and 3): 7 x 10-7
βOX vs. X-ray excess absorption
dark bursts
Redshift distribution: 146 GRBs
< 18% @ z > 7<z> =
2.2
Grupe et al. (2007)
Cumulative redshift distribution
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