Examinando por Autor "Guidorzi, C."
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Ítem A blast from the infant universe: the very high- z GRB 210905A(EDP Sciences, 2022-09) Rossi, A.; Frederiks, D.D.; Kann, D.A.; De Pasquale, M.; Pian, E.; Lamb, G.; D'Avanzo, P.; Izzo, L.; Levan, A.J.; Malesani, D.B.; Melandri, A.; Nicuesa Guelbenzu, A.; Schulze, S.; Strausbaugh, R.; Tanvir, N.R.; Amati, L.; Campana, S.; Cucchiara, A.; Ghirlanda, G.; Della Valle, M.; Klose, S.; Salvaterra, R.; Starling, R.L.C.; Stratta, G.; Tsvetkova, A.E.; Vergani, S.D.; D'Aì, A.; Burgarella, D.; Covino, S.; D'Elia, V.; Postigo, A. De Ugarte; Fausey, H.; Fynbo, J.P.U.; Frontera, F.; Guidorzi, C.; Heintz, K.E.; Masetti, N.; Maiorano, E.; Mundell, C.G.; Oates, S.R.; Page, M.J.; Palazzi, E.; Palmerio, J.; Pugliese, G.; Rau, A.; Saccardi, A.; Sbarufatti, B.; Svinkin, D.S.; Tagliaferri, G.; Van Der Horst, A.J.; Watson, D.J.; Ulanov, M.V.; Wiersema, K.; Xu, D.; Zhang, J.We present a detailed follow-up of the very energetic GRB 210905A at a high redshift of z = 6.312 and its luminous X-ray and optical afterglow. Following the detection by Swift and Konus-Wind, we obtained a photometric and spectroscopic follow-up in the optical and near-infrared (NIR), covering both the prompt and afterglow emission from a few minutes up to 20 Ms after burst. With an isotropic gamma-ray energy release of Eiso = 1.27−0.19+0.20 × 1054 erg, GRB 210905A lies in the top ∼7% of gamma-ray bursts (GRBs) in the Konus-Wind catalogue in terms of energy released. Its afterglow is among the most luminous ever observed, and, in particular, it is one of the most luminous in the optical at t ≳ 0.5 d in the rest frame. The afterglow starts with a shallow evolution that can be explained by energy injection, and it is followed by a steeper decay, while the spectral energy distribution is in agreement with slow cooling in a constant-density environment within the standard fireball theory. A jet break at ∼46.2 ± 16.3 d (6.3 ± 2.2 d rest-frame) has been observed in the X-ray light curve; however, it is hidden in the H band due to a constant contribution from the host galaxy and potentially from a foreground intervening galaxy. In particular, the host galaxy is only the fourth GRB host at z > 6 known to date. By assuming a number density n = 1 cm−3 and an efficiency η = 0.2, we derived a half-opening angle of 8.4 ° ±1.0°, which is the highest ever measured for a z ≳ 6 burst, but within the range covered by closer events. The resulting collimation-corrected gamma-ray energy release of ≃1 × 1052 erg is also among the highest ever measured. The moderately large half-opening angle argues against recent claims of an inverse dependence of the half-opening angle on the redshift. The total jet energy is likely too large to be sustained by a standard magnetar, and it suggests that the central engine of this burst was a newly formed black hole. Despite the outstanding energetics and luminosity of both GRB 210905A and its afterglow, we demonstrate that they are consistent within 2σ with those of less distant bursts, indicating that the powering mechanisms and progenitors do not evolve significantly with redshift.Ítem The Peculiar Short-duration GRB 200826A and Its Supernova(Institute of Physics, 2022-06-01) Rossi, A.; Rothberg, B.; Palazzi, E.; Kann, D.A.; D'Avanzo, P.; Amati, L.; Klose, S.; Perego, A.; Pian, E.; Guidorzi, C.; Pozanenko, A.S.; Savaglio, S.; Stratta, G.; Agapito, G.; Covino, S.; Cusano, F.; D'Elia, V.; Pasquale, M. De; Valle, M. Della; Kuhn, O.; Izzo, L.; Loffredo, E.; Masetti, N.; Melandri, A.; Minaev, P.Y.; Guelbenzu, A. Nicuesa; Paris, D.; Paiano, S.; Plantet, C.; Rossi, F.; Salvaterra, R.; Schulze, S.; Veillet, C.; Volnova, A.A.Gamma-ray bursts (GRBs) are classified into long and short events. Long GRBs (LGRBs) are associated with the end states of very massive stars, while short GRBs (SGRBs) are linked to the merger of compact objects. GRB 200826A was a peculiar event, because by definition it was an SGRB, with a rest-frame duration of 1/40.5 s. However, this event was energetic and soft, which is consistent with LGRBs. The relatively low redshift (z = 0.7486) motivated a comprehensive, multiwavelength follow-up campaign to characterize its host, search for a possible associated supernova (SN), and thus understand the origin of this burst. To this aim we obtained a combination of deep near-infrared (NIR) and optical imaging together with spectroscopy. Our analysis reveals an optical and NIR bump in the light curve whose luminosity and evolution are in agreement with several SNe associated to LGRBs. Analysis of the prompt GRB shows that this event follows the E p,i-E iso relation found for LGRBs. The host galaxy is a low-mass star-forming galaxy, typical of LGRBs, but with one of the highest star formation rates, especially with respect to its mass ( logM∗/M⊙=8.6, SFR ∼4.0 M ⊙ yr-1). We conclude that GRB 200826A is a typical collapsar event in the low tail of the duration distribution of LGRBs. These findings support theoretical predictions that events produced by collapsars can be as short as 0.5 s in the host frame and further confirm that duration alone is not an efficient discriminator for the progenitor class of a GRB. © 2022. The Author(s). Published by the American Astronomical Society.