TITLE: GCN CIRCULAR NUMBER: 2485 SUBJECT: GRB 021203: A Normal GRB viewed far off axis? DATE: 03/12/11 14:13:33 GMT FROM: Arnon Dar at Technion-Israel Inst. of Tech In the "standard" fireball model, ordinary GRBs, XRFs and low-inferred-luminosity GRBs, such as GRB 980425 are intrinsically different. The low-luminosity GRB 031203 (GCN 2460, 2482) has thus been interpreted as a case that "may bridge GRB 980425 ... and cosmological GRBs" (GCN 2483). In the cannonball model, XRFs and GRBs such as 980425 and 031203 (GCN 2460) are ordinary GRBs, also viewed off-axis but from angles a few times larger than those of ordinary GRBs (astro-ph/0308248). GRB 031203 offers sensitive observational tests of this CB-model unification of XRFs and ALL long-duration GRBs: In the CB-model --and in reality-- both for long GRBs and XRFs, the product of the peak energy Ep (E at max E^2 dn/dE) and the full width at half maximum (FWHM) of the photon flux in a single pulse is approximately 200 keV s, independent of redshift. From the reported 30 s total duration of the single-pulse GRB 031203 (GCN 2460) and from the fairly universal "FRED" temporal shape of GRB pulses, we estimate the FWHM to be ~ 10 s. Consequently, we predict Ep ~ 20 keV. Moreover, from the mean FWHM = 0.92 s of long-duration GRB pulses, from their mean redshift z ~ 1, and from the estimated z ~ 0.105 (GCN 2482) of GRB 031203, we conclude that the value of the Doppler factor of its single pulse was approximately 20 times smaller than the mean value for long GRBs. In the CB model this implies (astro-ph/0308248, astro-ph/0309294) a viewing angle approximately 4 times larger than the average for the bulk of the GRB sample. The predicted equivalent isotropic energy of GRB 031203 should then be ~ 2.5E49 erg. For a Hubble constant of 70 km/[s Mpc], and a FWHM of ~ 10 s, this energy is indeed consistent with that estimated from the reported peak energy flux of 1.3E-7 erg/[cm^2 s] in the 20-200 keV interval (GCN 2460). Due to a large Galactic extinction (E(B-V)=0.971; GCN 2463) in the direction of GRB 031203, a standard-candle supernova akin to SN1998bw placed at the GRB position will reach (around December 20) a peak brightness R ~ 22 in the R band, if the extinction in the host galaxy is negligible. The radio afterglow may first decline for a couple of days (GCN 2483) and then rebrighten, before declining again like t^{-1.33} at later times; further steepening to the universal ~ t^{-2.1} as each specific radio frequency crosses the CB-model's "injection bend" (astro-ph/0204474). - Arnon Dar, Shlomo Dado and Alvaro De Rujula