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Thanks to the observations by Fermi-GBM and Konus-Wind satellites we have identified GRB 090227B as the first example of genuine short GRBs: short bursts with the same inner engine of the long GRBs but endowed with a severely low value of the Baryon load, B\lesssim 5\times 10^{-5}. The emission from GRB 090227B mainly consists in a first spike lasting 96 ms with a significant thermal emission and an observed temperature kT=517 keV , which we identify with the P-GRB, followed by a softer emission shrinked on the first one, whose separation from the first one is of the order of 10^{-3} – 10^{-2} s. This second emission is identified with the extended afterglow. We estimate from our theoretical model the cosmological redshift z=1.61 and, consequently, we derive the total energy E^{tot}_{e^+e^-}=2.83 \times 10^{53} ergs, the Baryon load B=4.13\times 10^{-5}, the Lorentz factor at transparency \Gamma=14365, and the intrinsic duration \Delta t \sim 0.35 s. We also determine the average density of the CircumBurst Medium (CBM),n_{CBM}=1.9\times10^{-5} particles/cm^3. There is no evidence of beaming in the system. In view of the recent developed theory of the neutron stars configuration, we estimate the masses of the stars, m_1=m_2=1.34 M_{sun}, their radii, R_1=R_2=12.24 km, and the thickness of their crusts, \sim 0.47 km, consistent with the above values of the Baryon load, of the energetics as well as of the low interstellar medium and of the intrinsic time scale of the signal.

Session

Accepted

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Time

Talk

Title

Abstract

The bright short-hard GRB 090510, observed by AGILE and Fermi-GBM and LAT, is the first short burst with the GeV emission. Optical observations located the host galaxy of GRB 090510 at the redshift of z=0.903 and it was identified as a late type elliptical or early-type spiral galaxy. On the ground of the theoretical results of GRB 090227B and of the similarity between their spectra, we interpret GRB 090510 as a member of the class of genuine short GRBs. Without addressing the nature of the small precursor, in the main episode we identify the first 128 ms as the P-GRB with an observed temperature kT=645 keV, and the following system of spike-like structures as the extended afterglow. Using the isotropic energy E^{tot}_{e^+e^-}=1.08\times 10^{53} ergs, we derive the Baryon load B=5.03\times 10^{-5}, the Lorentz factor at transparency \Gamma=11938, and the average density of the CircumBurst Medium (CBM),n-{CBM}=1.26\times 10^{-5} particles/cm^3, consistent with the observations. The main outcome of this analysis is the fact that the GeV emission has to be taken into account in the transparency emission in order to get the agreement between the observed energy and temperature of the P-GRB and the theoretical ones from the theory. We are currently analyzing different possible interpretations on this new results.

Session

Accepted

Order

Time

Talk

Title

Abstract

Thanks to the observations by Fermi-GBM and Konus-Wind satellites we have identified GRB 090227B as the first example of genuine short GRBs: short bursts with the same inner engine of the long GRBs but endowed with a severely low value of the Baryon load, B\lesssim5\times10^{-5}. The emission from GRB 090227B mainly consists in a first spike lasting 96 ms with a significant thermal emission and an observed temperature kT=517 keV , which we identify with the P-GRB, followed by a softer emission shrunk on the first one, whose separation from the first one is of the order of 10^{-3}-–10^{-2} s. This second emission is identified with the extended afterglow. We estimate from our theoretical model the cosmological redshift z=1.61 and, consequently, we derive the total energy Edya=2.83\times10^{53} ergs, the Baryon load B=4.13\times10^{-5}, the Lorentz factor at transparency \Gamma=1.44\times10^4, and the intrinsic duration \Delta t\sim0.35 s. We also determine the average density of the CircumBurst Medium (CBM),n_{CBM}=1.9\times10^{-5} particles/cm^3. There is no evidence of beaming in the system. In view of the recent developed theory of the neutron stars configuration, we estimate the masses of the stars, m_1=m_2=1.34M_{sun}, their radii, R_1=R_2=12.24 km, and the thickness of their crusts, \sim0.47 km, consistent with the above values of the Baryon load, of the energetics as well as of the low interstellar medium and of the intrinsic time scale of the signal.

Session

Accepted

Order

Time

Talk

Title

Abstract

The bright short GRB 090510, observed by AGILE and Fermi-GBM and LAT, is the first short burst with the GeV emission. Optical observations located the host galaxy of GRB 090510 at the redshift of z=0.903 and it was identified as a late type elliptical or early-type spiral galaxy. On the ground of the theoretical results of GRB 090227B and of the similarity between their spectra, we interpret GRB 090510 as a member of the class of genuine short GRBs. Without addressing the nature of the small precursor, in the main episode we identify the first 128 ms as the P-GRB with an observed temperature kT=645 keV, and the following system of spike-like structures as the extended afterglow. Using the isotropic energy E_{dya}=1.08\times10^{53} ergs, we derive the Baryon load B=5.03\times10^{-5}, the Lorentz factor at transparency \Gamma=1.19\times10^4, and the average density of the CircumBurst Medium (CBM),n_CBM=1.26\times10^{-5} particles/cm^3, consistent with the observations. The main outcome of this analysis is the fact that the GeV emission has to be taken into account in the transparency emission in order to get the agreement between the observed energy and temperature of the P-GRB and the theoretical ones from the theory. We are currently analyzing different possible interpretations on this new results.

Session

Accepted

Order

Time

Talk

Title

Abstract

According to the recent theoretical interpretation of GRB 090618, GRB 101023 and GRB 970828, bursts originating from binary systems composed of Massive Star + Neutron Star (MS+NS) present a double episode emission. The first episode, called Proto Black-Hole (PBH), is related to the supernova explosion of the MS; the second episode, is the emission of a GRB, originated from the accretion onto the NS from the companion, leading to the formation of a BH. In some of such systems the initial conditions could not trigger the emission of a GRB and, consequently, we could observe a single episode, the PBH emission. GRB 970925 is the first example of this new class of sources. Due to the lack of X-rays data, its redshift is unknown. Within our analysis, we compare and contrast the PBH of GRB 970925 with the other sources above mentioned and we give an estimate of the cosmological redshift and of the main quantities of such a PBH. In particular, we show the similarities with another possible single PBH episode examined by Guiriec et al. (2011), GRB 100724B.

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