[AAVSO-HEN] GRB 090902B: Gemini-N absorption redshift

[grb at aavso.org]

The following is a GCN Circular circulated via the AAVSO network.
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TITLE:   GCN CIRCULAR
NUMBER:  9873
SUBJECT: GRB 090902B: Gemini-N absorption redshift
DATE:    09/09/03 08:23:17 GMT
FROM:    Antonino Cucchiara at PSU  <cucchiara at astro.psu.edu>

A. Cucchiara, D. B. Fox (PSU), N. Tanvir (U. Leicester),
E. Berger (Harvard U.) report on behalf of a large collaboration.

"On 2009 September 3.27 UT we observed the Fermi/LAT GRB 090902B
(Bissaldi et al., GCN 9866, de Palma 9867) with the Gemini-N
telescope equipped with the GMOS spectrograph.

A single object has been found at the position of the Swift/XRT
afterglow (Kennea et al. GCN 9868, Perley et al., GCN 9870) in
our acquisition image.

A pair of 900 sec exposures spectra were obtained with a wavelength
coverage of 4500-7500A under good conditions.
The spectrum reveals a series of metal absorption features,
MgII[2796,2803], MgI[2853],MnII[2606], FeII[2600], MnII[2594],
FeII[2586], FeII[2260], SiII[1808], SiII*[1816].

All these features are consistent with a redshift of z = 1.822,
which, therefore, we conclude is the redshift of GRB 090902B.


We thank the Gemini-N staff for performing this observation,
in particular Ricardo Schiavon."