{
  "bibcode": "1998GCN...139....1D",
  "body": "GRB 980703:  Spectrum of the proposed optical counterpart\n\nS. G. Djorgovski, S. R. Kulkarni (Caltech), R. Goodrich (WMKO), \nD. A. Frail (NRAO), and J. S. Bloom (Caltech), report on behalf \nof the Caltech GRB collaboration:\n\nAnalysis of the spectra of the proposed optical/radio counterpart of \nGRB 980703 (see GCN Circ. 128, 136, 137) gives the following results:\n\nThe strong emission line is definitively identified as [O II] 3727 at\nthe redshift z_em = 0.9660 +- 0.0002.  It has the equivalent width of\n90 +- 2 Angstroms (observed), or 45.7 +- 1 A in the restframe.  This\nis somewhit higher than typical for galaxies at comparable redshifts\nand magnitudes.  After correcting for the as-yet unknown contribution\nof the GRB afterglow to the continuum flux, these numbers will be higher.\nThe observed line flux is 2.7e-16 erg/cm2/s.\n\nThere are several absorption features identified as Fe II (2344, 2374,\n2383, 2587, and 2600 A) and Mg II (2796 and 2803) lines, with the mean\nredshift z_abs = 0.9653 +- 0.0007, superposed on an otherwise featureless\nUV continuum.  This too is typical of actively star-forming galaxies at\nsimilar redshifts.  We also see the 4000-Angstrom break.\n\nThe observed spectrophotometric magnitude at the epoch of these \nobservations (July 7.6 UT) are:  B = 23.3, V = 22.65, and R = 21.9 mag, \nwith the zero-point uncertain by a few tenths of a magnitude, due to the\nunknown slit losses.  The UV continuum blueward of the [O II] line can\nbe described with a power-law F_nu ~ nu**alpha, with alpha = -1.5 +- 0.2,\npossibly indicative of a modest extinction.\n\nAssuming a Friedmann cosmology with H_0 = 65 km/s/Mpc, Omega_0 = 0.2, and\nLambda_0 = 0, the luminosity distance at this redshift is 1.9208e28 cm.\nOur observed [O II] line flux then translates to the restframe line\nluminosity of 1.25e42 erg/s.  Assuming the conversion from Kennicutt\n(1992), the implied star formation rate is about 63 M_sun/yr, even \nwithout any extinction or slit-loss corrections.\n\nWe thus conclude that the host galaxy of GRB 980703 is a compact starburst\nobject.  This gives some support to the models which associate origins of\nGRBs with massive star formation.\n\nFurther observations of the object are in progress.\n\nThis note can be cited.",
  "circularId": 139,
  "createdOn": 899885000000,
  "email": "george@oracle.caltech.edu",
  "subject": "GRB 980703:  Spectrum of the proposed optical counterpart",
  "submitter": "George Djorgovski at Caltech/Palomar  <george@oracle.caltech.edu>",
  "eventId": "GRB 980703"
}