TITLE: GCN GRB OBSERVATION REPORT NUMBER: 289 SUBJECT: GRB 970228: Redshift and properties of the host galaxy DATE: 99/05/03 18:05:33 GMT FROM: George Djorgovski at Caltech/Palomar GRB 970228: Redshift and properties of the host galaxy S. G. Djorgovski, S. R. Kulkarni, J. S. Bloom (Caltech), and D. A. Frail (NRAO) report on behalf of the Caltech-CARA-NRAO GRB Collaboration: Spectra of the host galaxy of GRB 970228 were obtained in the course of several runs at the Keck-II 10-m telescope. A prominent emission line at 6319 A was observed in at least 3 independent data sets, along with a very blue continuum, showing no apparent breaks between about 4000 and 8900 A. We interpret this emission line as [O II] 3727 at z = 0.695 +- 0.002. Moreover, possible emission lines are detected corresponding to [Ne III] 3869 and [O III] 5007 at the same redshift. We thus consider this redshift to be practically secure. Assuming a cosmology with H_0 = 65 km/s/Mpc, Omega_0 = 0.2, and Lambda_0 = 0, we derive the luminosity distance of 1.28 e28 cm. The measured fluence from Ulysses (cf. Hurley et al. 1997, ApJ, 485, L1) of 4.3 e-6 erg/cm2 then implies E(gamma,isotropic) = 5.2 e51 erg. We detect continuum flux in the V band of about 0.12 uJy, uncertain by at least 20%. This is in an excellent agreement with the published ground-based and HST photometry, corresponding to V ~ 26 mag. The [O II] line has the equivalent width 75 +- 15 A (observed), or 44 +- 9 A (restframe), typical for star-forming galaxies at comparable redshifts. The very blue continuum suggests little restframe extinction in this galaxy. In the following estimates, we assume a Galactic extinction correction A(V) = 0.75 mag. From the [O II] line flux, we estimate SFR = 0.47 Msun/yr, and from the continuum power at 2800 A (rest), SFR = 0.35 Msun/yr. Both of these are uncertain by at least 30%. The absolute restframe B band luminosity of the galaxy corresponds to about 0.05 to 0.1 L_* today. Thus, neither the SFR nor the SFR per unit mass are especially high. This note can be cited. [GCN OPERATOR'S NOTE (04 May 99): This archived copy was corrected for the mistaken citation that BATSE yielded the fluence. The true source of the fluence for the burst came from Ulysses.]