Canonical GRB Research Articles

Constraining Low-luminosity Gamma-Ray Bursts as Ultra-high-energy Cosmic Ray Sources Using GRB 060218 as a Proxy

Abstract We study the connection between low-luminosity gamma-ray bursts (llGRBs) and ultra-high-energy cosmic rays (UHECRs) using the canonical low-luminosity GRB 060218 as a proxy. We focus on the consequential synchrotron emission from electrons that are coaccelerated in the UHECR acceleration region, comparing this emission to observations. Both the prompt and afterglow phases are considered. For the prompt phase, we assume the coaccelerated electrons are injected with a power-law distribution instantaneously (without additional heating or reacceleration), which results in bright optical-UV emission in tension with observations. For the afterglow phase, we constrain the total kinetic energy of the blast wave by comparing electron thermal synchrotron radiation to available radio data at ∼ 3 days. Considering mildly relativistic outflows with bulk Lorentz factor Γ ≳ 2 (slower transrelativistic outflows are not treated), we find that the limited available energy does not allow for GRB 060218-like afterglows to be the main origin of UHECRs. This analysis independently constrains the prompt phase as a major UHECR source as well, given that the prompt energy budget is comparable to that of the afterglow kinetic energy. More generally, our study demonstrates that synchrotron emission from thermal electrons is a powerful diagnostic of the physics of mildly relativistic shocks.

EVIDENCES FOR A DOUBLE COMPONENT IN THE EMISSION OF GRB 101023

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, with a P-GRB lasting 4s.

Evidence for a proto-black hole and a double astrophysical component in GRB 101023

[Shortened] Context: [...] we point out a striking similarity between GRB 101023 and GRB 090618. We explore the possibility that these sources are members of a new GRB family related to a single core-collapse. We use this understanding of the source in order to infer the unobserved redshift of GRB 101023. [...]. Aims: In precise analogy with GRB 090618 we aim to analyze the 89s of emission of GRB 101023 to see if we are in presence of two different episodes: the first one presenting a characteristic Black-body temperature evolution, evolving in time with a broken power-law, and the second one consistent with a canonical GRB. [...] Results: We confirm that the first episode can be well fit by a Black body plus a power-law model. The temperature changes with time following a broken power law, and the photon index of the power-law component presents a soft to hard evolution. We estimate the radius of this source, increasing with time with a velocity of 1.5x10^4 km/s. The second episode appears to be a canonical GRB. By using the Amati relation and the Atteia relation, we determine the cosmological redshift, z ~ 0.9 +- 0.084 (stat.) +- 0.2 (sys.). [...]. Particularly striking is the scaling law of the soft X-ray component of the afterglow. Conclusions: We identify GRB 090618 and GRB 101023 with a new family of GRBs presenting a double astrophysical component. A first one, related to the proto-black hole, prior to the process of gravitational collapse (episode 1) and a second one which is the canonical GRB (episode 2) emitted during the formation of the black-hole. [...] This analysis indicates progress towards developing a GRB distance indicator based on the understanding of the P-GRB and the prompt radiation as well as the soft X-Ray behavior of the late afterglow.

GRB060614: a “fake” short GRB from a merging binary system

(Shortened) CONTEXT: [...] GRB060614 is the first nearby long duration GRB clearly not associated to a bright Ib/c supernova. Moreover, its duration (T_{90} ~ 100s) makes it hardly classifiable as a short GRB. It presents strong similarities with GRB970228, the prototype of the new class of fake short GRBs that appear to originate from the coalescence of binary neutron stars or white dwarfs spiraled out into the galactic halo. AIMS: Within the GRB scenario based on the model, we test if GRB060614 can be a fake or disguised short GRB. [...] METHODS: We fit GRB060614 light curves in Swift's BAT (15-150keV) and XRT (0.2-10keV) energy bands. Within the fireshell model, light curves are formed by two well defined and different components: the Proper-GRB (P-GRB), emitted at the fireshell transparency, and the extended afterglow, due to the interaction between the leftover accelerated baryonic and leptonic shell and the CBM. RESULTS: We determine the two free parameters describing the GRB source within the fireshell model. [...] A small average CBM density [...] is inferred, typical of galactic halos. The first spikelike emission is identified with the P-GRB and the following prolonged emission with the extended afterglow peak.[...] CONCLUSIONS: The anomalous GRB060614 finds a natural interpretation within our canonical GRB scenario: it is a disguised short GRB. [...] This result points to an old binary system, likely formed by a white dwarf and a neutron star, as the progenitor of GRB060614 and well justify the absence of an associated SN Ib/c. Particularly important for further studies of the final merging process are the temporal structures in the P-GRB down to 0.1s.

GRB 970228 and a class of GRBs with an initial spikelike emission

(Shortened) The Swift and HETE-2 discovery of an afterglow associated possibly with short GRBs opened the new problematic of their nature and classification. This has been further enhanced by the GRB060614 observation and by a re-analysis of the BATSE catalog leading to the identification of a new GRB class with "an occasional softer extended emission lasting tenths of seconds after an initial spikelike emission". We plan: a) to fit this new class of "hybrid" sources within our "canonical GRB" scenario, where all GRBs are generated by a "common engine" (i.e. the gravitational collapse to a black hole); b) to propose GRB970228 as the prototype of the such a class. We analyze BeppoSAX data on GRB970228 in the 40-700 keV and 2-26 keV energy bands within the "fireshell" model. We find that GRB970228 is a "canonical GRB", like e.g. GRB050315, with the main peculiarity of a particularly low CircumBurst Medium (CBM) average density n_{cbm}~10^{-3} #/cm^3. We also simulate the light curve corresponding to a rescaled CBM density profile with n_{cbm}=1 #/cm^3. From such a comparison it follows that the total time-integrated luminosity is a faithful indicator of the GRB nature, contrary to the peak luminosity which is merely a function of the CBM density. We call attention on discriminating the short GRBs between the "genuine" and the "fake" ones. The "genuine" ones are intrinsically short, with baryon loading B \la 10^{-5}, as stated in our original classification. The "fake" ones, characterized by an initial spikelike emission followed by an extended emission lasting tenths of seconds, have a baryon loading 10^{-4} \la B \leq 10^{-2}. They are observed as such only due to an underdense CBM consistent with a galactic halo environment which deflates the afterglow intensity.

GRB 060218 and GRBs associated with supernovae Ib/c

We plan to fit the complete gamma- and X-ray light curves of the long duration GRB060218, including the prompt emission, in order to clarify the nature of the progenitors and the astrophysical scenario of the class of GRBs associated to SNe Ib/c. The initial total energy of the electron-positron plasma E_{e^\pm}^{tot}=2.32\times 10^{50} erg has a particularly low value similarly to the other GRBs associated with SNe. For the first time we observe a baryon loading B=10^{-2} which coincides with the upper limit for the dynamical stability of the fireshell. The effective CircumBurst Medium (CBM) density shows a radial dependence n_{cbm} \propto r^{-\alpha} with 1.0<\alpha<1.7 and monotonically decreases from 1 to 10^{-6} particles/cm^3. Such a behavior is interpreted as due to a fragmentation in the fireshell. Analogies with the fragmented density and filling factor characterizing Novae are outlined. The fit presented is particularly significant in view of the complete data set available for GRB060218 and of the fact that it fulfills the Amati relation. We fit GRB060218, usually considered as an X-Ray Flash (XRF), as a "canonical GRB" within our theoretical model. The smallest possible black hole, formed by the gravitational collapse of a neutron star in a binary system, is consistent with the especially low energetics of the class of GRBs associated with SNe Ib/c. We give the first evidence for a fragmentation in the fireshell. Such a fragmentation is crucial in explaining both the unusually large T_{90} and the consequently inferred abnormal low value of the CBM effective density.