Examinando por Autor "Maiorano, E."

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    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.
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    A comparison between short GRB afterglows and kilonova AT2017gfo: Shedding light on kilonovae properties
    (Oxford University Press, 2020-04) Rossi, A.; Stratta, G.; Maiorano, E.; Spighi, D.; Masetti, N.; Palazzi, E.; Gardini, A.; Melandri, A.; Nicastro, L.; Pian, E.; Branchesi, M.; Dadina, M.; Testa, V.; Brocato, E.; Benetti, S.; Ciolfi, R.; Covino, S.; D'Elia, V.; Grado, A.; Izzo, L.; Perego, A.; Piranomonte, S.; Salvaterra, R.; Selsing, J.; Tomasella, L.; Yang, S.; Vergani, D.; Amati, L.; Stephen, J.B.
    Multimessenger astronomy received a great boost following the discovery of kilonova (KN) AT2017gfo, the optical counterpart of the gravitational wave source GW170817 associated with the short gamma-ray burst GRB 170817A. AT2017gfo was the first KN that could be extensively monitored in time using both photometry and spectroscopy. Previously, only few candidates have been observed against the glare of short GRB afterglows. In this work, we aim to search the fingerprints of AT2017gfo-like KN emissions in the optical/NIR light curves of 39 short GRBs with known redshift. For the first time, our results allow us to study separately the range of luminosity of the blue and red components of AT2017gfo-like kilonovae in short GRBs. In particular, the red component is similar in luminosity to AT2017gfo, while the blue KN can be more than 10 times brighter. Finally, we exclude a KN as luminous as AT2017gfo in GRBs 050509B and 061201. © 2020 The Author(s).
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    Spectroscopic identification of r-process nucleosynthesis in a double neutron-star merger
    (Nature Publishing Group, 2017-11) Pian, E.; D'Avanzo, P.; Benetti, S.; Branchesi, M.; Brocato, Campana S.; Cappellaro, E.; Covino, S.; D'Elia, V.; Fynbo, J.P.U.; Getman, F.; Ghirlanda, G.; Ghisellini, G.; Grado, A.; Greco, G.; Hjorth, J.; Kouveliotou, C.; Levan, A.; Limatola, L.; Malesani, D.; Mazzali, P.A.; Melandri, A.; Møller, P.; Nicastro, L.; Palazzi, E.; Piranomonte, S.; Rossi, A.; Salafia, O.S.; Selsing, J.; Stratta, G.; Tanaka, M.; Tanvir, N.R.; Tomasella, L.; Watson, D.; Yang, S.; Amati, L.; Antonelli, L.A.; Ascenzi, S.; Bernardini, M.G.; Boër, M.; Bufano, F.; Bulgarelli, A.; Capaccioli, M.; Casella, P.; Castro-Tirado, A.J.; Chassande-Mottin, E.; Ciolfi, R.; Copperwheat, C.M.; Dadina, M.; De Cesare, G.; Di Paola, A.; Fan, Y.Z.; Gendre, B.; Giuffrida, G.; Giunta, A.; Hunt, L.K.; Israel, G.L.; Jin, Z.-P.; Kasliwal, M.M.; Klose, S.; Lisi, M.; Longo, F.; Maiorano, E.; Mapelli, M.; Masetti, N.; Nava, L.; Patricelli, B.; Perley, D.; Pescalli, A.; Piran, T.; Possenti, A.; Pulone, L.; Razzano, M.; Salvaterra, R.; Schipani, P.; Spera, M.; Stamerra, A.; Stella, L.; Tagliaferri, G.; Testa, V.; Troja, E.; Turatto, M.; Vergani, S.D.; Vergani, D.
    The merger of two neutron stars is predicted to give rise to three major detectable phenomena: a short burst of γ-rays, a gravitational-wave signal, and a transient optical-near-infrared source powered by the synthesis of large amounts of very heavy elements via rapid neutron capture (the r-process)1-3. Such transients, named 'macronovae' or 'kilonovae'4-7, are believed to be centres of production of rare elements such as gold and platinum8. The most compelling evidence so far for a kilonova was a very faint near-infrared rebrightening in the afterglow of a short γ-ray burst9,10 at redshift z = 0.356, although findings indicating bluer events have been reported11. Here we report the spectral identification and describe the physical properties of a bright kilonova associated with the gravitational-wave source12 GW170817 and γ-ray burst13,14 GRB 170817A associated with a galaxy at a distance of 40 megaparsecs from Earth. Using a series of spectra from ground-based observatories covering the wavelength range from the ultraviolet to the near-infrared, we find that the kilonova is characterized by rapidly expanding ejecta with spectral features similar to those predicted by current models15,16. The ejecta is optically thick early on, with a velocity of about 0.2 times light speed, and reaches a radius of about 50 astronomical units in only 1.5 days. As the ejecta expands, broad absorption-like lines appear on the spectral continuum, indicating atomic species produced by nucleosynthesis that occurs in the post-merger fast-moving dynamical ejecta and in two slower (0.05 times light speed) wind regions. Comparison with spectral models suggests that the merger ejected 0.03 to 0.05 solar masses of material, including high-opacity lanthanides. © 2017 Macmillan Publishers Limited, part of Springer Nature.