TITLE:   GCN CIRCULAR
NUMBER:  14120
SUBJECT: GRB 121229A: VLT/X-shooter redshift
DATE:    12/12/29 14:38:02 GMT
FROM:    Valerio D'Elia at ASDC  <delia@asdc.asi.it>

J. P. U. Fynbo (DARK/NBI), N. R.  Tanvir (U. Leicester), V. D'Elia
(ASDC, INAF), A. de Ugarte Postigo (IAA-CSIC and DARK/NBI),
D. Malesani (DARK), O. E. Hartoog (Uva, NL), D. Xu (DARK), H. Flores
(Obs. Paris), A. J. Levan (U. Warwick), B. Milvang-Jensen (DARK/NBI)

We observed the field of GRB 121229A (Sonbas et al., GCN 14115; Varela
et al., GCN 14117) with the ESO VLT equipped with the X-shooter
spectrograph. Observations started at 07:00 UT on 2012-12-29 (2 hr
after the BAT trigger), for a total exposure time of ~30 min in each
of the UVB, VIS, and NIR arms, covering the wavelength range
3000-21000A.

The spectrum exhibits two relatively broad troughs (centered at ~ 3800
and 4500 A) which we interpreted as Lyman-beta and -alpha features,
respectively, at z=2.707. We measured the HI column density,
logN(HI)~21.7, from the Lyman-alpha feature. At this redshift there
are tentative indications of other metal absorption features, although
they are weak and we have yet to establish their significance. The
lack of strong resonance metal lines, together with the low X-ray
absorption (Sonbas et al., GCN 14115), suggests a low metallicity. We
also report a tentative evidence for an intervening MgII absorber at
z=1.658

We acknowledge the excellent support of the ESO observing staff, in
particular Maja Vu?kovi?.


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