{
  "bibcode": "1999GCN...289....1D",
  "body": "GRB 970228: Redshift and properties of the host galaxy\n\nS. G. Djorgovski, S. R. Kulkarni, J. S. Bloom (Caltech), and D. A. Frail\n(NRAO) report on behalf of the Caltech-CARA-NRAO GRB Collaboration:\n\nSpectra of the host galaxy of GRB 970228 were obtained in the course of\nseveral runs at the Keck-II 10-m telescope.  A prominent emission line at \n6319 A was observed in at least 3 independent data sets, along with a very \nblue continuum, showing no apparent breaks between about 4000 and 8900 A.  \nWe interpret this emission line as [O II] 3727 at z = 0.695 +- 0.002.\nMoreover, possible emission lines are detected corresponding to [Ne III] \n3869 and [O III] 5007 at the same redshift.  We thus consider this redshift\nto be practically secure.\n\nAssuming a cosmology with H_0 = 65 km/s/Mpc, Omega_0 = 0.2, and Lambda_0 = 0, \nwe derive the luminosity distance of 1.28 e28 cm.  The measured fluence from\nUlysses (cf. Hurley et al. 1997, ApJ, 485, L1) of 4.3 e-6 erg/cm2 then implies \nE(gamma,isotropic) = 5.2 e51 erg.\n\nWe detect continuum flux in the V band of about 0.12 uJy, uncertain by at \nleast 20%.  This is in an excellent agreement with the published ground-based \nand HST photometry, corresponding to V ~ 26 mag.\n\nThe [O II] line has the equivalent width 75 +- 15 A (observed), or 44 +- 9 A \n(restframe), typical for star-forming galaxies at comparable redshifts.  The\nvery blue continuum suggests little restframe extinction in this galaxy.\n\nIn the following estimates, we assume a Galactic extinction correction A(V) = \n0.75 mag.  From the [O II] line flux, we estimate SFR = 0.47 Msun/yr, and from\nthe continuum power at 2800 A (rest), SFR = 0.35 Msun/yr.  Both of these are \nuncertain by at least 30%.  The absolute restframe B band luminosity of the \ngalaxy corresponds to about 0.05 to 0.1 L_* today.  Thus, neither the SFR \nnor the SFR per unit mass are especially high.\n\nThis note can be cited.\n\n[GCN OPERATOR'S NOTE (04 May 99):  This archived copy was corrected\nfor the mistaken citation that BATSE yielded the fluence.  The true\nsource of the fluence for the burst came from Ulysses.]",
  "circularId": 289,
  "createdOn": 925754733000,
  "email": "george@oracle.caltech.edu",
  "subject": "GRB 970228: Redshift and properties of the host galaxy",
  "submitter": "George Djorgovski at Caltech/Palomar  <george@oracle.caltech.edu>",
  "eventId": "GRB 970228"
}