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Bulletin ICRANet
Avril-Mai 2020

1. Statistiques sur le COVID-19
2. Magnetic field and rotation of the newborn neutron star in binary-driven hypernovae inferred from the X-ray afterglow of long gamma-ray bursts
3. Le Gouvernement arménien assigne une bourse doctorale à ICRANet Arménie, 21 Mai, 2020
4. "Gerbertus 2020 - Scientific Rationale", meeting podcast, 7 Mai 2020
5. Webinar COVID, Tucson, USA, 19 Mai 2020
6. Le 4ème Zeldovich meeting devient virtuel
7. Appel à propositions conjointes "BRFFR - ICRANet 2020"
8. Publications récentes
9. Evaluation interne de l’article du Dr Liang Li "Thermal Components in Gamma-Ray Bursts. II. Constraining the Hybrid Jet Model", publié sur ApJ
10. Evaluation interne de l’article co-rédigé par le Prof. Shesheng Xue "Supercritically charged objects and electron-positron pair creation" et publié sur Physical Review D

1. Statistiques sur le COVID-19

1 À partir du 15 Avril 2020, on offre à tous les membres ICRANet, notre rapport quotidien sur le COVID-19. Veuillez cliquer sur ce lien pour à la page web d’ICRANet:
La fonction logistique phénoménologique est utilisée pour modéliser l'évolution de la pandémie de COVID-19 dans différents pays. Le modèle logistique est utilisé principalement en épidémiologie et offre un aperçu des dynamiques de transmission du virus. Les données proviennent de l'Université Johns Hopkins. Cependant, nous observons qu'on a besoin de modèles plus raffinés afin d'évaluer les dynamiques de transmission du COVID-19, qui prennent en compte les mesures spécifiques adoptées dans chaque pays.

2. Magnetic field and rotation of the newborn neutron star in binary-driven hypernovae inferred from the X-ray afterglow of long gamma-ray bursts

ThLe nouveau article redigé par Rueda, J. A., Ruffini R., Karlica M., Moradi R., Wang Y., Magnetic Fields and Afterglows of BdHNe Inferences from GRB 130427A, GRB 160509A, GRB 160625B, GRB 180728A and GRB 190114C, a été publié par The Astrophysical Journal, 893:148 le 20 Avril 2020. À cette occasion, l’ICRA et l’ICRANet ont sorti un communiqué de presse titré "Magnetic field and rotation of the newborn neutron star in binary-driven hypernovae inferred from the X-ray afterglow of long gamma-ray bursts".
Ce communiqué de presse, disponible sur le site web d’ICRANet (, a été circulé par l’American Astronomical Society AAS le 18 Mai 2020 (en Anglais) ainsi que par l’INAF ( le 25 Mai 2020 (en Italien).


Ci-dessous le communiqué de presse ICRA-ICRANet.

The change of paradigm in gamma-ray burst (GRBs) physics and astrophysics introduced by the binary driven hypernova (BdHN) model, proposed and applied by the ICRA-ICRANet-INAF members in collaboration with the University of Ferrara and the University of Côte d'Azur, has gained further observational support from the X-ray emission in long GRBs. These novel results are presented in the new article [1], published on April 20, 2020, in The Astrophysical Journal, co-authored by J. A. Rueda, Remo Ruffini, Mile Karlica, Rahim Moradi, and Yu Wang.
The GRB emission is composed by episodes: from the hard X-ray trigger and the gamma-ray prompt emission, to the high-energy emission in GeV, recently observed also in TeV energies in GRB 190114C, to the X-ray afterglow. The traditional model of GRBs attempts to explain the entire GRB emissions from a single-component progenitor, i.e. from the emission of a relativistic jet originating from a rotating black hole (BH). Differently, the BdHN scenario proposes GRBs originate from a cataclysmic event in the last evolutionary stage of a binary system composed of a carbon-oxygen (CO) star and a neutron star (NS) companion in close orbit. The gravitational collapse of the iron core of the CO star produces a supernova (SN) explosion ejecting the outermost layers of the star, and at the same time, a newborn NS (νNS) at its center. The SN ejecta trigger a hypercritical accretion process onto the NS companion and onto the νNS. Depending on the size of the orbit, the NS may reach, in the case of short orbital periods of the order of minutes, the critical mass for gravitational collapse, hence forming a newborn BH. These systems where a BH is formed are called BdHN of type I. For longer periods, the NS gets more massive but it does not form a BH. These systems are BdHNe II. Three-dimensional simulations of all this process showing the feasibility of its occurrence, from the SN explosion to the formation of the BH, has been recently made possible by the collaboration between ICRANet and the group of Los Alamos National Laboratory (LANL) guided by Prof. C. L. Fryer, see Figure 1 and [2].
The role of the BH for the formation of the high-energy GeV emission has been recently presented in The Astrophysical Journal in [3]. There, the"engine" composed of a Kerr BH, with a magnetic field aligned with the BH rotation axis immersed in a low-density ionised plasma, gives origin, by synchrotron radiation, to the beamed emission in the MeV, GeV, and TeV, currently observed only in some BdHN I, by the Fermi-LAT and MAGIC instruments. In the new publication [1], the ICRA-ICRANet team addresses the interaction of the νNS with the SN due to hypercritical accretion and pulsar-like emission. They show that the fingerprint of the νNS appears in the X-ray afterglow of long GRBs observed by the XRT detector on board the Niels Gehrels Swift observatory. Therefore, the νNS and the BH have well distinct and different roles in the long GRB observed emission.
The emission from the magnetized νNS and the hypercritical accretion of the SN ejecta into it, gives origin to the afterglow observed in all BdHN I and II subclasses. The early (~few hours) X-ray emission during the afterglow phase is explained by the injection of ultra-relativistic electrons from the νNS into the expanding ejecta, producing synchrotron radiation; see Figure 2. The magnetic field inferred from the synchrotron analysis agrees with the expected toroidal/longitudinal magnetic field component of the νNS. Furthermore, from the analysis of the XRT data of these GRBs at times t>104 s, it has been shown that the power-law decaying luminosity is powered by the νNS rotational energy loss by the torque acted upon it by its dipole+quadrupole magnetic. From this, it has been inferred that the νNS possesses a magnetic field of strength ~ 1012-1013 G, and a rotation period of the order of a millisecond; see Figure 3. It is shown in [1], that the inferred millisecond rotation period of the νNS agrees with the conservation of angular momentum in the gravitational collapse of the iron core of the CO star which the νNS came from.
The inferred structure of the magnetic field of the "inner engine"' agrees with a scenario in which, along the rotational axis of the BH, it is rooted in the magnetosphere left by the NS that collapsed into a BH. On the equatorial plane, the field is magnified by magnetic flux conservation.

[1] J. A. Rueda, R. Ruffini, M. Karlica, R. Moradi, and Y. Wang, Astroph. J. 893, 148 (2020), 1905.11339.
[2] L. Becerra, C. L. Ellinger, C. L. Fryer, J. A. Rueda, and R. Ruffini, Astroph. J. 871, 14 (2019), 1803.04356.
[3] R. Ruffini, R. Moradi, J. A. Rueda, L. Becerra, C. L. Bianco, C. Cherubini, S. Filippi, Y. C. Chen, M. Karlica, N. Sahakyan,et al., Astroph. J. 886, 82 (2019).

Figure 1. Taken from [1]. Schematic evolutionary path of a massive binary up to the emission of a BdHN. (a) Binary system composed of two main-sequence stars, say 15 and 12 solar masses, respectively. (b) At a given time, the more massive star undergoes the core-collapse SN and forms a NS (which might have a magnetic field B∼1013 G). (c) The system enters the X-ray binary phase. (d) The core of the remaining evolved star, rich in carbon and oxygen, for short CO star, is left exposed since the hydrogen and helium envelope have been striped by binary interactions and possibly multiple common-envelope phases (not shown in this diagram). The system is, at this stage, a CO-NS binary, which is taken as the initial configuration of the BdHN model [2]. (e) The CO star explodes as SN when the binary period is of the order of few minutes, the SN ejecta of a few solar masses start to expand and a fast rotating, newborn NS, for short νNS, is left in the center. (f) The SN ejecta accrete onto the NS companion, forming a massive NS (BdHN II) or a BH (BdHN I; this example), depending on the initial NS mass and the binary separation. Conservation of magnetic flux and possibly additional MHD processes amplify the magnetic field from the NS value to B∼1014 G around the newborn BH. At this stage the system is a νNS-BH binary surrounded by ionized matter of the expanding ejecta. (g) The accretion, the formation and the activities of the BH contribute to the GRB prompt gamma-ray emission and GeV emission.

Figure 2. Taken from [1]. Model evolution of synchrotron spectral luminosity at various times compared with measurements in various spectral bands for GRB 160625B.

Figure 3. Taken from [1]. The brown, deep blue, orange, green and bright blue points correspond to the bolometric (about ∼ 5 times brighter than the soft X-ray observed by Swift-XRT data) light-curves of GRB 160625B, 160509A, 130427A, 190114C and 180728A, respectively. The solid lines are theoretical light-curves obtained from the rotational energy loss of the νNS powering the late afterglow (t ≥ 5 × 103 s, white background), while in the earlier times (3 × 102 ≤ t ≤ 5 × 103 s, blue background), the kinetic energy of the SN ejecta plays also an important role. Because of the necessity of having a significant sample to extract the physical properties of the νNS (magnetic field and rotation rate), the analysis was limited to late part of the afterglow, say at times t ≥ 3 × 102 s, where data are more available. At earlier times, only GRB 130427A and GRB 190114C in this same have available data.

Link to the article in ApJ:

ICRA-ICRANet press release:

INAF press release:

3. Le Gouvernement arménien assigne une bourse doctorale à ICRANet Arménie, 21 Mai, 20202020

Le 21 Mai 2020, le Gouvernement de la République d’Arménie a approuvé les bourses doctorales pour l’année académique 2020-2021. Le centre ICRANet en Arménie a obtenue une bourse doctorale. Une bourse supplémentaire sera approuvé au mois de Juin. L’examen final d’admission aura lieu à la fin du mois de Juin.
Cette nouvelle est disponible (en Arménien) sur le site web du système d’information légal d’Arménie:

4. "Gerbertus 2020 - Scientific Rationale", meeting podcast, 7 Mai 2020

C. Sigismondi, ICRA/Sapienza

Figure 4: Sylvestre II (1854, Turin).

Le congrès annuel en l’honneur de Gerbert d’Aurillac, scientifique, astronome scolaire et Pape, a été inauguré Mardi 7 Mai 2020. Cet évent a été coordonné, comme aussi les 2 précédents en Novembre 2019 et Janvier 2020, par et dans le centre ICRANet de Pescara à niveau international.
Le programme du meeting 2020 est centré sur la Lune, sur comme elle était vue il y a 1000 anné Lune de Gerbert, avec l’idée de réfléchir sur l’histoire de l’astronomie et de l’héritage culturale. Les étudiants du Lycée Galileo Galilei de Pescara, ainsi que ceux du Lycée Galileo Ferraris de Rome, en participant aux programs européen d’autonomisation de la didactique (projets PON), sont en train de travailler sur les principaux sujets du programme.
Entre les motivations qui poussent à étudier Gerbert, je propose une sélection: "Pourquoi Gerbert n’a pas un cratère sur la Lune, même s’il a été le premier à propager un traité sur l’Astrolabe avant l’année 1000?"
Il a enseigné Astronomie dans le Quadrivium de la Cathédrale de Reims en France et était considéré comme une référence scientifique dans plusieurs siècles après sa mort dans le camp du Computus mathématique (ayant aussi été le premier à utiliser les nombres arabes et l’abaque) et de la musique. Il a laissé à la littérature un traité sur la géométrie et un épistolaire de 220 lettres (Patrologia Latina, volume 90): un cas unique de préservation de cette culture médiévale. Hermann de Reichenau, après un demi-siècle, était censé être l’auteur de ce traité de l’astrolabe, mais il a été prouvé que l’auteur original était Gerbert. Hermann a son cratère et Gerbert no...en plus, Gerbert a construit le premier montagne équatorial documenté, décrit dan son épistolaire (à Constantine, 980 AD sur lequel j’ai écrit un livre, La Sfera da Gerberto al Sacrobosco, Athenaeum Regina Apostolorum, Rome 2009).
Gerbert a été respecté dans toute l’Europe comme l’homme le plus important de son temps, quand il a été élu Pape par Otto III en 999, selon les uses de son temps, et il a choisi le nom de Sylvestre II. Une légende médiéval successive (dans Guillaume de Malmesbury et dans Benno d’Osnabruck), l’a transformé dans un magicien, qui construit une tête (Golem) capable de dire «oui» ou «no», grâce à laquelle Gerbert savait qu’il ne serait pas mort avant d’aller à Jérusalem. Le 3 Mai 1003, il est allé célébrer la messe dans l’Eglise catholique de la sainte croix, aujourd’hui appelé S. Croce en Jérusalem et à ce temps-là "Basilica Hierusalem" construite par Helen la mère de Constantine, en y emmenant la terre de Jérusalem après avoir trouvé la relique de la croix. Pendant cette messe, Gerbert tombait malade et compris que la fin approchait, comme prèvu par le Golem. Il est décédé le 12 Mai 1003 et ça c’est la raison pour laquelle nous célébrons ce congres dans la première partie du mois de Mai à partir de 2003, un millénaire après sa mort. Il a été enterré dans la Basilique Saint-Jean-de-Latran.
Le lent processus qui a conduit à la réhabilitation de Gerbert a eu lieu en 1620 avec le polonais dominicain Bzovsky et suite à la publication de son epistolarium et de son manuel dans la Patrologie latine autour du 1700. Dans la deuxième partie du 19° siècle, Nicolay Bubnov publiait, en Russie, ses œuvres mathématiques (1899), aujourd’hui disponibles sur Google books. En 1970, Klaus Jurgen Sachs trouva un manuscrit à Madrid sur le traité musical De Mensura Fistularum du 11° siècle attribué à Gerbert, qui prouvait encore une fois qu’il était le centre réel de la culture contemporaine avant et après l’année 1000. Clyde Brockett en 1995 et Flavio G. Nuvolone (1942-2019) ont étudié la composition "Carme Figuratum" (980) écrite par Gerbert à Otto II, qui inclut les nombres arabes qu’il a d’abord introduit dans l’Europe latine. L’approche à l’étude de Gerbert doit nécessairement être multidisciplinaire. Notre objective est de promouvoir le développement de ces études à travers internet, en utilisant aussi le journal académique Gerbertus, fondé en 2010 auprès de l’Observatoire de Paris avec trois ISSN: journal, CD et online. L’édition du 2020 reconnait l’important contribution aux études sur Gerbert, effectué par le Professeur Flavio Giuseppe Nuvolone (2 Septembre 1942 - 11 Décembre 2019), qui a publié plusieurs livres sur Gerbert et a organisé plusieurs meetings depuis 1983, quand il a commencé collaborer avec Michele Tosi au Journal de Bobbio Archivum Bobiense. Son activité principale était auprès de l’Université de Fribourg comme Professeur de Patrologie, mais ensuite il est devenu un investigateur multidisciplinaire de la figure de Gerbert. Parler avec lui a été un moyen pour entrer en contact direct avec l’esprit et le milieu dans lequel Gerbert agi. La résilience de la vie de Gerbert et sa foi catholique solide, ont été bien investigué par le Prof. Nuvolone.
La mort de George V. Coyne (19 Janvier 1933 - 11 Février 2020), ancien Directeur de la Specola Vaticana, a été, pour la communauté scientifique, la perte d’une personne qui a constamment conduite son existence en synergie entre science et foi, comme Gerbert. Tous les deux seront honorés dans cette occasion.
Les sujets comme la botanique, la philosophie, la didactique, l’optique, la physique solaire ont toujours invité les jeunes à s’approcher aux sciences, comme Gerbert a rendu possible pour la première fois dans son école Cathédrale de Reims, à travers l’enseignement du quadrivium (mathématique, géométrie, astronomie et musique) ainsi que du trivium (grammatique, rhétorique et dialectique), et l’études des écrivains latins profanes et Aristote. La contribution musicale composée par Stefano Carciofalo Parisse est un hommage au grand maitre Gerbert, auteur soit de la musique que du traité musical sur ça en 980, De Mensura Fistularum. Un cratère sur la lune devrait être dédié à Gerbert.
Pour des information en plus sur cet événement, son programme et le matériel téléchargeable:
Le journal académique dédié à Gerbert, à l’histoire de la science médiéval et à la didactique peut être consulté ici:

5. Webinar COVID, Tucson, USA, 19 Mai 2020

Le 19 Mai, le Prof. Ruffini a été invite à participer au webinar sur le COVID, organisé à Tucson (Arizona, USA) par le Prof. Johan Rafelski. Le webinar a été introduit par les salues de bienvenu du Prof. Rafelski, n continuant avec la présentation du Prof. Giorgio Torrieri (en collaboration avec le Prof. Alessio Notari) sur les facteurs de risque de transmission du COVID-19. Ensuite, le Prof. Ruffini, en collaboration avec le Prof. Narek Sahakyan (Directeur du centre ICRANet Arménie), a présenté son discours "Real danger: critical COVID-triggers seen in statistical analysis", le Prof. Berndt Muller a présenté son discours sur les analyses fiables sur le COVID-19 et leurs résultats et, finalement, le Prof. John W. Clark a fait sa présentation.

Figure 5: le Prof. Ruffini participle au webinar sur le COVID webinar, organisé par le Prof. Johan Rafelski à Tucson le 19 Mai 2020.

Cet evenement a été enregistré et peut etre visionné ici:
• site web ICRANet:

• site web de l’Université d’Arizona:
• Zoom playback:

6. Le 4ème Zeldovich meeting devient virtuel

Compte tenu de la pandémie de COVID-19, le 4ème Zeldovich meeting aura lieu virtuellement du 7 à l’11 Septembre 2020, en collaboration entre l’ICRANet et l’Académie Nationale de Sciences de Belarus en tant que organisateurs et hôtes. Tous les participants qui étaient enregistrés restent confirmé.
La participation sera gratuite, la date limite pour les registrations a été prolongée au 31 Juillet 2020 ainsi que la date limite pour soumettre un résumé a été prolongée au 15 Aout 2020. Les proceedings de ce meeting seront publiés dan le journal Astronomy Reports.
Pour majeurs détails:

7. Appel à propositions conjointes "BRFFR - ICRANet 2020"


En Avril 2020, a Belarusian Republican Foundation for Fundamental Research (BRFFR) et ICRANet ont annoncé un appel à propositions pour projets scientifiques conjointes dan le domain de l’Astrophysique Relativiste. Les domaines scientifiques couverts par cet appel sont l’Astrophysique relativiste, la cosmologie et la gravitation. Les candidatures des équipes de recherché internationales, y compris ces des scientifiques bélarussiens, doivent être présentées en utilisant des formulaires de demande convenus par les 2 organisations : les équipes bélarussiennes postulent pour la BRFFR, tandis-que les autres équipes internationales postulent pour ICRANet. La durée des projets est jusqu’à 2 années, et la date limite pour envoyer les candidatures est le 15 Septembre 2020.
Pour informations supplémentaires sur l’appel à propositions et pour télécharger le formulaire de demande:

8. Publications récentes

Rueda, J. A., Ruffini R., Karlica M., Moradi R., Wang Y., Magnetic Fields and Afterglows of BdHNe Inferences from GRB 130427A, GRB 160509A, GRB 160625B, GRB 180728A and GRB 190114C, 893:148 (13pp), 2020 April 20.
GRB 190114C is the first binary-driven hypernova (BdHN) fully observed from initial supernova (SN) appearance to the final emergence of the optical SN signal. It offers an unprecedented testing ground for the BdHN theory, which is here determined and further extended to additional gamma-ray bursts (GRBs). BdHNe comprise two subclasses of long GRBs, with progenitors a binary system composed of a carbon-oxygen star (COcore) and a neutron star (NS) companion. The COcore explodes as an SN, leaving at its center a newborn NS (νNS). The SN ejecta hypercritically accretes on both the νNS and the NS companion. BdHNe I arevery tight binaries, where the accretion leads the companion NS to gravitationally collapse into a black hole (BH). In BdHN II, the accretion rate onto the NS is lower, so there is no BH formation. We observe the same afterglow structure for GRB 190114C and other selected examples of BdHNe I (GRB 130427A, GRB 160509A, GRB 160625B) and for BdHN II (GRB 180728A). In all cases, the afterglows are explained via the synchrotron emission powered by the νNS, and their magnetic field structures and their spin are determined. For BdHNe I, we discuss the properties of the magnetic field embedding the newborn BH, which was inherited from the collapsed NS and amplified during the gravitational collapse process, and surrounded by the SN ejecta.

Li, Liang, Thermal Components in Gamma-Ray Bursts. II. Constraining the Hybrid Jet Model, The Astrophysical Journal, Volume 894, Issue 2, id.100.
In explaining the physical origin of the jet composition of gamma-ray bursts (GRBs), a more general picture, i.e., the hybrid jet model (which introduced another magnetization parameter σ0 on the basis of the traditional fireball model), has been well studied in Gao & Zhang. However, it still has not yet been applied to a large GRB sample. Here, we first employ the "top-down" approach of Gao & Zhang to diagnose the photosphere properties at the central engine to see how the hybrid model can account for the observed data as well, through applying a Fermi GRB sample (eight bursts) with the detected photosphere component, as presented in Li (our Paper I). We infer all physical parameters of a hybrid problem with three typical values of the radius of the jet base (r0 = 107, 108, and 109 cm). We find that the dimensionless entropy for all the bursts shows η≫ 1 while the derived (1+σ0) for five bursts (GRB 081224, GRB 110721A, GRB 090719, GRB 100707, and GRB 100724) is larger than unity, indicating that in addition to a hot fireball component, another cold Poynting-flux component may also play an important role. Our analysis also shows that in a few time bins for all r0 in GRB 081224 and GRB 110721A, the magnetization parameter at ∼1015 cm (1+σr15) is greater than unity, which implies that internal-collision-induced magnetic reconnection and turbulence may be the mechanism to power the nonthermal emission, rather than internal shocks. We conclude that the majority of bursts (probably all) can be well explained by the hybrid jet problem.

Vereshchagin, G. V.; Siutsou, I. A., Diffusive photospheres in gamma-ray bursts, Monthly Notices of the Royal Astronomical Society, Volume 494, Issue 1, pp.1463-1469, April 2020.
Photospheric emission may originate from relativistic outflows in two qualitatively different regimes: last scattering of photons inside the outflow at the photospheric radius or radiative diffusion to the boundary of the outflow. In this work, the measurement of temperature and flux of the thermal component in the early afterglows of several gamma-ray bursts along with the total flux in the prompt phase is used to determine initial radii of the outflow as well as its Lorentz factors. Results indicate that in some cases the outflow has relatively low Lorentz factors (Γ< 10), favouring cocoon interpretation, while in other cases Lorentz factors are larger (Γ> 10), indicating diffusive photospheric origin of the thermal component, associated with an ultra relativistic outflow.

Cheng-Jun Xia, She-Sheng Xue, Ren-Xin Xu, and Shan-Gui Zhou, "Supercritically charged objects and electron-positron pair creation", Phys. Rev. D, Vol. 101, Iss. 10 — 15 May 2020.
We investigate the stability and e+e- pair creation of supercritically charged superheavy nuclei, udQM nuggets, strangelets, and strangeon nuggets based on the Thomas-Fermi approximation. The model parameters are fixed by reproducing masses and charge properties of these supercritically charged objects reported in earlier publications. It is found that udQM nuggets, strangelets, and strangeon nuggets may be more stable than 56Fe at the baryon number A≳315,5×104, and 1.2×108, respectively. For those stable against neutron emission, the most massive superheavy element has a baryon number ∼965, while udQM nuggets, strangelets, and strangeon nuggets need to have baryon numbers larger than 39, 433, and 2.7×105. The e+e- pair creation will inevitably start for superheavy nuclei with charge numbers Z≥177, for udQM nuggets with Z≥163, for strangelets with Z≥192, and for strangeon nuggets with Z≥212. A universal relation Q/Re=(me--μe)/α is obtained at a given electron chemical potential -μe, where Q is the total charge and Re the radius of electron cloud. The maximum number of Q without causing e+e- pair creation is then fixed by taking -μe=-me. For supercritically charged objects with -μe<-me, the decay rate for e+e- pair production is estimated based on the Jeffreys-Wentzel-Kramers-Brillouin (JWKB) approximation. It is found that most positrons are emitted at t≲10-15 s, while a long lasting positron emission can be observed for large objects with R≳1000  fm. The emission of positrons and electron-positron annihilation from supercritically charged objects may be partially responsible for the short γ-ray burst during the merger of binary compact stars, the 511 keV continuum emission, as well as the narrow faint emission lines in x-ray spectra from galaxies and galaxy clusters.

9. Evaluaton interne de l’article du Dr Liang Li "Thermal Components in Gamma-Ray Bursts. II. Constraining the Hybrid Jet Model" publié sur ApJ

Since the early days, the standard model for Gamma-Ray Bursts (GRBs) attempted to explain all the different phases of the GRB event (precursor, prompt emission, afterglow, high-energy GeV emission, ecc.) as originating from a single ultrarelativistically expanding jet. Also within ICRANet it was initially followed a similar approach. However, after twenty years of observations, and thanks to the much better observational data provided by the new satellites, it became increasingly difficult to deal with the unveiling richness of the GRB phenomenon within this simple traditional approach. Therefore, ICRANet scientists started to follow a completely alternative approach in which all the different phases of the GRB event come from different physical processes occurring in the progenitor binary system, without involving necessarily ultrarelativistic dynamics. It is therefore important at this stage to have papers analyzing GRB observations within the two different approaches, the traditional and the alternative one, to present the corresponding possible strengths and weaknesses.
The paper by Liang Li "Thermal Components in Gamma-Ray Bursts. II. Constraining the Hybrid Jet Model" published in The Astrophysical Journal Supplement Series, 242:16, 2019, uses the traditional approach and follows the previous work on identification of thermal emission in GRBs and its interpretation as the photospheric emission in the fireball model. This work follows the idea introduced in the paper by Zhang et al. [Nature Astronomy, 2 (2018) 69], who interpreted emission in GRB 160625B as transition from unmagnetized to magnetized fireball. This work was extended by Liang Li in the paper published previously in The Astrophysical Journal Supplement Series, 242:16, 2019. The physical model behind this picture is developed by Gao and Zhang [ApJ, 801 (2015) 103]. There, in addition to the dimensionless entropy eta they introduce a magnetization parameter sigma. It was shown in the paper by Meszaros and Rees, ApJ 733:40 2011 that strongly magnetized outflows accelerate slowly, compared to unmagnetized ones. This is the main difference, causing the dependence of the observed photospheric emission on the degree of magnetization. Gao and Zhang provide analytic formula which connect the observed parameters such as luminosity, flux and temperature to the physical parameters of the underlying outflow, namely the Lorentz factor, photospheric radius, nozzle radius and magnetization parameter. The nonthermal component is not explained, it is assumed that a fraction of the jet luminosity is transformed into nonthermal radiation with a given spectrum. The top-down approach, introduced in this work based on the work of Pe'er, et al., ApJL, 664, 1, 2007, and used also by Liang Li, allows to infer physical parameters of the outflow directly from the observed quantities.

The paper mentions two major shortcomings of the analysis:
1. The underlying theoretical model is based on the key assumption that both the GRB prompt emission and the x-ray afterglow originate from an ultrarelativistic jet with a Lorentz Gamma factor 10^2--10^3. Such a jetted emission was introduced since the very early days of GRB modelling to reduce the GRB energy budget, and was justified with the purported presence of "achromatic jet breaks" in the x-ray afterglow light curves. However, after 20 years of observations, no real achromatic jet break has been observed in any x-ray afterglow light curve [see e.g. Pisani et al., ApJ, 833 (2016) 159]. Only some chromatic jet breaks have actually been observed, whose explanation is currently the subject of active research but which cannot be connected to an ultrarelativistic jet dynamics. Moreover, in Ruffini et al. [ApJ, 852 (2018) 53] it has been shown, in a model independent way, that in the early phases of the x-ray afterglow light curves there are clear signatures of the presence of a thermal emitter which expands with a Lorentz Gamma factor less than 4, and no evidence of an ultrarelativistic expansion. The key assumption of the presence of an ultrarelatvistic jet is therefore not supported by the X-ray afterglow data.
2. More than half of the analysed GRBs have no measured cosmological redshift. Therefore, for these sources it is not possible to define the precise cosmological rest frame. In Ruffini et al. [ApJ, 852 (2018) 53] it was shown that many of the common features of the GRB light curves become evident only when the data are analysed in the cosmological rest frame of each source but are hidden when data are seen in the observer frame.

In the conclusions of the paper it is recalled that the alternative theoretical approach to GRBs developed within ICRANet, the Induced Gravitational Collapse scenario [see e.g. Ruffini et al., ApJ, 832 (2016) 136, and references therein], does not present these shortcomings and may well account for the observations. Within this theoretical model long GRBs originate in binary systems composed by an FeCO core and a companion neutron star, named "Binary Driven Hypernovae" (BdHNe). At the basis of the phenomenon there is not a single ultrarelativistic jet, but each phase of the GRB emission (prompt gamma-ray emission, early X-ray afterglow emission, late x-ray afterglow emission, GeV emission, etc.) comes from a different physical process occurring in the progenitor binary system. The entire photospheric emission is currently being reconsidered within this new approach, overcoming the above shortcomings 1 and 2. In the meantime, we can already say that this new approach gives an answer about the late X-ray afterglow emission: it is due to the newly born neutron star which remains after the explosion of the FeCO core, and no ultrarelativistic dynamics is involved in this process [see e.g. Ruffini et al., ApJ, 869 (2016) 101; Rueda et al., ApJ, 893 (2020) 148].

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10. Evaluation interne de l’article co-rédigé par le Prof. Shesheng Xue "Supercritically charged objects and electron-positron pair creation" et publié sur Physical Review D

In astrophysical systems, there can possibly exist the strong coupling between nucleons and quark matters of large charge number Z and atomic number A, such as udQM nuggets, strangelets, and strangeon nuggets. In order to further understand electron-positron production in such strong coupling matter in connection with the observed phenomena, the authors of this paper study supercritically charged matter by applying the Thomas-Fermi model of chemical potential equilibrium for highly degenerate electrons and the Schwinger model of vacuum polarisation for electron-positron pair production. This research, as shown by the references below, has been well developed for years in ICRANet to understand the physical relevance of electron-positron pair production and annihilation for the astrophysical phenomena of Gamma-Ray Bursts, the 511 keV continuum emission and the narrow ~ 4 keV faint emission lines from galaxies and galaxy clusters.


To understand how the Coulomb energy raised in such a strong coupling matter is balanced, Authors from China use their expertise on the empirical model of Fermi type describing such a strong coupling matter. They make both analytical and numerical analyses of chemical potentials to examine the stability of strong coupling matter against pair production and to obtain the critical values of large charge number Z and atomic number A, as well as the size of strong coupling matter, see Figure. Instead, in the case of Coulomb energy being released, they make numerical calculations by using the pair-production rate in an electron degenerate system, developed within ICRANet, to approximately obtain the time scale and rate of electron-positron pair production as functions of charge number Z and atomic number A, and to give an insight into their relevance for the observations.
This work has been completed by remote collaborations via internet between: Professors Cheng-Jun Xia of Zhejiang University Ningbo Institute of Technology, Ren-Xin Xu of Peking University and Shan-Gui Zhou of Institute of Theoretical Physics, and ICRANet faculty member She-Sheng Xue. Chinese colleagues Xia, Xu and Zhou are experts on the nuclear physics and astro-nuclear physics, in particular the properties of nuclear and quark matter that composes compact stars in our Universe. They are very active in the field and have published many articles in international high impact scientific journals worldwide.

• R. Ruffini, G. Vereshchagin, and S.-S. Xue, Phys. Rep. 487, 1 (2010).
• H. Kleinert, R. Ruffini, and S.-S. Xue, Phys. Rev. D 78, 025011 (2008).
• W.-B. Han, R. Ruffini, and S.-S. Xue, Phys. Lett. B 691, 99 (2010).
• R. Ruffini and S.-S. Xue, Phys. Lett. B 696, 416 (2011).
• M. Rotondo, R. Ruffini, and S.-S. Xue, "Neutral nuclear core vs super charged one," in The Eleventh Marcel Grossmann Meeting (2008) pp. 1352-1355.
• J. Rueda, R. Ruffini, Y. Wang, Y. Aimuratov, U. B. de Almeida, C. Bianco, Y. Chen, R. Lobato, C. Maia, D. Primorac, R. Moradi, and J. Rodriguez, J. Cosmol. Astropart. P. 2018, 006 (2018).

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