An alternative interpretation of GRB 970228 data and nature

Following the recent theoretical interpretation of GRB 090618 and GRB 101023, we here interpret GRB 970828 in terms of a double episode emission: the first episode, observed in the first 40 s of the emission, is interpreted as the proto-black-hole emission; the second episode, observed after t 0 +50 s, as a canonical gamma ray burst. The transition between the two episodes marks the black hole formation. The characteristics of the real GRB, in the second episode, are an energy of E e + e − tot = 1.60 × 10 53 erg, a baryon load of B = 7 × 10 −3 and a bulk Lorentz factor at transparency of Γ = 142.5. The clear analogy with GRB 090618 would require also in GRB 970828 the presence of a possible supernova. We also infer that the GRB exploded in an environment with a large average particle density n ≈ 10 3 part/cm 3 and dense clouds characterized by typical dimensions of (4 − 8) × 10 14 cm and δn/n ∝ 10. Such an environment is in line with the observed large column density absorption, which might have darkened both the supernova emission and the GRB optical afterglow.

1999

. Gamma-ray bursts (GRBs) are thought to result from the interaction of an extremely relativistic outflow interacting with a small amount of material surrounding the site of the explosion. Multi-wavelength observations covering the γ-ray to radio wavebands allow investigations of this 'fireball' model. On 23 January 1999 optical emission was detected while the γ-ray burst was still underway. Here we report the results of γ-ray, optical/infra-red, sub-mm, mm and radio observations of this burst and its afterglow, which indicate that the prompt and afterglow emissions from GRB 990123 are associated with three distinct regions in the fireball. The afterglow one day after the burst has a much lower peak frequency than those of previous bursts; this explains the short-lived nature of the radio emission, which is not expected to reappear. We suggest that such differences reflect variations in the magnetic-field strengths in the afterglow emitting regions.

Arxiv preprint astro-ph/ …, 1998

We present the results of the monitoring of the GRB 970111 field that started 19 hours after the event. This observation represents the fastest ground-based follow-up performed for GRB 970111 in all wavelengths. As soon as the detection of the possible GRB 970111 X-ray afterglow was reported by Feroci et al. (1998) we reanalyzed the optical data collected for the GRB 970111 field. Although we detect small magnitude variability in some objects, no convincing optical counterpart is found inside the WFC error box. Any change in brightness 19 hours after the GRB is less than 0.2 mag for objects with B < 21 and R < 20.8. The bluest object found in the field is coincident with 1SAX J1528.8+1937. Spectroscopic observations revealed that this object is a Seyfert-1 galaxy with redshift z = 0.657, which we propose as the optical counterpart of the X-ray source. Further observations allowed to perform multicolour photometry for objects in the GRB 970111 error box. The colourcolour diagrams do not show any object with unusual colours. We applied a photometric classification method to the objects inside the GRB error box, that can distinguish stars from galaxies and estimate redshifts. We were able to estimate photometric

Science

Fourth Huntsville gamma-ray burst symposium, 1998

We examine what we regard as key observational results on GRB 970228 and GRB 970508 and show that the accumulated evidence strongly suggests that γ-ray bursts (GRBs) are cosmological fireballs. We further show that the observations suggest that GRBs are not associated with the nuclear activity of active galactic nuclei, and that late-type galaxies are more prolific producers of GRBs. We suggest that GRBs can be used to trace the cosmic history of the star-formation rate. Finally, we show that the GRB locations with respect to the star-forming regions in their host galaxies and the total burst energies can be used to distinguish between different theoretical models for GRBs.

The Astrophysical Journal, 1997

We present the discovery observations for the optical counterpart of the γ-ray burster GRB 970508 and discuss its light curve in the context of the fireball model. We analyze the HST data for this object, and conclude that any underlying galaxy must be fainter than R = 25.5. We also present a detailed analysis of the HST images of GRB 970228 claimed to show a proper motion of the optical counterpart and conclude that, within the uncertainties, there is no proper motion. We examine several aspects of the neutron-star merger model for γ-ray bursts. In particular, we use this model to predict the redshift distribution of γ-ray bursters, and adopting a recent determination of the cosmic star-formation history, we show that the predicted distribution of log N − log P relation is consistent with that observed for GRBs.

Science, 1999

Arxiv preprint arXiv: …, 2007

The luminosity and the spectral distribution of the afterglow of GRB 031203 have been presented within our theoretical framework , which envisages the GRB structure as composed by a proper-GRB, emitted at the transparency of an electron-positron plasma with suitable baryon loading, and an afterglow comprising the "prompt emission" as due to external shocks. In addition to the GRB emission, there appears to be a prolonged soft X-Ray emission lasting for 10 6 -10 7 seconds followed by an exponential decay. This additional source has been called by us URCA-3. It is urgent to establish if this component is related to the GRB or to the Supernova (SN). In this second case, there are two possibilities: either the interaction of the SN ejecta with the interstellar medium or, possibly, the cooling of a young neutron star formed in the SN 2003lw process. The analogies and the differences between this triptych GRB 031203 / SN 2003lw / URCA-3 and the corresponding ones GRB 980425 / SN 1998bw / URCA-1 and GRB 030329 / SN 2003dh / URCA-2, as well as GRB 060218 / SN 2006aj are discussed.

International Journal of Modern Physics: Conference Series, 2013

In this work we present the results of the analysis of GRB 101023 in the fireshell scenario. We infered its redshift from the Amati Relation, obtaining z=0.9. Its light curve is very similar to the already studied GRB 090618, in the sense that it presents a double emission. We called each part Episode 1 and Episode 2. We performed a time-resolved spectral analysis with RMFIT using different spectral models, and fitted the light curve with a numerical code integrating the fireshell equations of motion. We used Fermi GBM data to build the light curve, in particular the second NaI detector, in the range (8.5-1000 keV). We considered different hypotheses about which part of the light curve could be the GRB and analyzed all of them. We noticed a great variation of the temperature with time in the first episode and almost no variation of the progenitor radius. The first emission does not match the requirements for a GRB, while the second part perfectly agrees with being a canonical GRB, w...

GRB 090618 offered an unprecedented opportunity to have coordinated data, by the best of the X and Gamma Ray observatories, of the nearest (z = 0.54) energetic source (10 54 erg). Using the Fermi-GBM observations of this GRB, we have analyzed this source to explore the possibility of having components yet to be observed in other sources. We show that it is not possible to interpret GRB 090618 within the framework of the traditional single component GRB model. We argue that the observation of the first episode of duration of around 50s could not be a part of a canonical GRB, while the residual emission could be modeled easily with the models existing in literature. In this work we have considered the case of the fireshell scenario.