TITLE:   GCN CIRCULAR
NUMBER:  29552
SUBJECT: GRB 210222B: Redshift from FORS2/VLT
DATE:    21/02/23 08:49:55 GMT
FROM:    Antonio de Ugarte Postigo at IAA-CSIC  <deugarte@iaa.es>

J. F. Agui Fernandez (HETH/IAA-CSIC), A. de Ugarte Postigo (HETH/IAA-CSIC, DARK/NBI), L. Izzo (DARK/NBI), D. Xu (NAOC), D.A. Kann (HETH/IAA-CSIC), D.B. Malesani (DTU Space), J.P.U. Fynbo (DAWN/NBI), K. Wiersema (Warwick U.) report:

We observed the afterglow of GRB 210222B (Gropp et al. GCN 29545; Hu et al. GCN 29546; Strausbaugh et al. GCN 29547; Mong et al. GCN 29548 and GCN 29550; Perley GCN 29549; Zhu et al. GCN 29551) with FORS2, mounted at the Unit Telescope 1 of the Very Large Telescope, at Paranal Observatory, Chile. The observation started at 3:00 UT (4.376 hr after the burst) and consisted of 2x700 s exposures using grism 300V and 2x700 s exposures using grism 300I, which together cover the full range between 3300 and 10100 AA.

In the acquisition image, the afterglow is well detected at V = 19.6 +/- 0.1 mag (Vega).

The spectrum shows continuum over the full range with strong absorption features that we identify as due to Lyman alpha, SII, SiII, SiII*, OI, CII, SiIV, CIV, FeII, AlII and MgII at a common redshift of 2.198, which we identify as the redshift of the GRB. This is consistent with the moderately high redshift already reported by Perley (GCN 29549) based on the photometric decline in the u-band.

We acknowledge excellent support from the ESO staff, in particular Jose Velasquez, Chiara Mazzucchelli, and Jonathan Smoker.