GRB 060927 at very high redshift

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GRB 060927 at very high redshift

Detection of GRB 060927 at z = 5.47

ApJ submitted (arXiv:0706.1257)

Alma Ruiz Velasco

Johan P. U. Fynbo

Daniele Malesani

Dong Xu

Dark Cosmology Centre

Dansk Fysisk Selskab, 19 Juni 2007

Heather Swan

University of Michigan

Eleonora Troja

Rhaana Starling

University of Leicester

+ 50 co­authors


● Observations

● Light Curve

Outline

● Spectroscopy and Redshift

GRBs as probes of the Dark Ages?


Light Curve


2.6 days

I = 24.85

VLT Afterglow

15.5 days

I > 25.8


Spectrum


Spectrum of GRB 050904

Totani, et al 2006


Fitting the Red Damping Wing

HI Column density log(N HI ) = 22.5


The visible

Universe

*

GRB060927

J. R. Gott et al, 2005


The Swift Sample

• 83 Swift GRBs with low Galactic

extintion and promptly determined

XRT position

• 46 with spectroscopic redshift

measurements

• 22 with redshift upper limits

(afterglow colors, lyman break, host)

• 18 with no redshift constraints


Redshift Distribution

*The arrows indicate upper limits


How many GRBs at high z?

GRBs with unknown z or upper limit

of z > 6: ) 20 candidates

GRBs with T 90

> 14 s ) 16

• and low column density in X­ray

spectra: ) 6

• and ¯ ox

< 0.5 ) 1?


Fraction of Swift GRBs at z > 6

• conservative upper limit of ≈ 19%

• upper limit of ≈8%

(six + GRB 050904 => 7/83)

• lower limit ≈1% (GRB 050904)


Conclusions

GRB 060927 is the second most distant

burst spectroscopically confirmed

• The use of the Lyα damping wing seen

in the afterglow of the GRBs as a

diagnostic of reionization could be

unsuitable

at least, 1% of the GRBs detected by

Swift have z > 6

GRBs afterglows from z > 6 can be

easily detected with small telescopes


Thank You

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