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ICRANet Newsletter



ICRANet Newsletter
Aprile-Maggio 2020



SOMMARIO
1. Statistiche sul 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. Il Governo armeno assegna una fellowship per dottorato di ricerca ad ICRANet Armenia, 21 Maggio 2020
4. "Gerbertus 2020 - Scientific Rationale", podcast meeting, 7 Maggio 2020
5. COVID webinar, Tucson USA, 19 Maggio 2020
6. Il 4° Zeldovich meeting diventa virtuale
7. Bando congiunto "BRFFR - ICRANet" 2020
8. Pubblicazioni recenti
9. Valutazione interna sul paper del Dr Liang Li "Thermal Components in Gamma-Ray Bursts. II. Constraining the Hybrid Jet Model" pubblicato in ApJ
10. Valutazione interna sul paper pubblicato come coautore dal Prof. Shesheng Xue "Supercritically charged objects and electron-positron pair creation" su Physical Review D



1. Statistiche sul COVID-19

1 A partire dal 15 Aprile 2020, l'ICRANet metterà a disposizione di tutti i suoi membri, i propri report quotidiani sul COVID-19. Si veda il nostro sito web: http://www.icranet.org/covid19-statistics.
La funzione logistica fenomenologica è utilizzata per modellare l'evoluzione dell'epidemia di COVID-19 in diversi paesi. Il modello logistico è utilizzato principalmente in epidemiologia e fornisce spunti sulle dinamiche di trasmissione del virus. I dati sono forniti dall'Università John Hopkins. Tuttavia osserviamo che, per valutare le dinamiche di trasmissione del COVID-19, c'è bisogno di modelli maggiormente rifiniti, che prendono in considerazione le misure specifiche adottate in ogni paese.



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

Il nuovo articolo, i cui coautori sono 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, é stato pubblicato su The Astrophysical Journal, 893:148 il 20 Aprile 2020. Per questa occasione, l'ICRA e l'ICRANet hanno redatto una press release dal titolo "Magnetic field and rotation of the newborn neutron star in binary-driven hypernovae inferred from the X-ray afterglow of long gamma-ray bursts".
Questa press release, consultabile sul sito ICRANet (http://www.icranet.org/communication/18052020/eng.pdf), è stata ritrasmessa e fatta circolare sia dall'American Astronomical Society AAS il 18 Maggio 2020 (in inglese) che dall'INAF (http://www.inaf.it/it/notizie-inaf/campo-magnetico-e-rotazione-della-stella-di-neutroni-neonata-nelle-ipernove-binary-driven-derivato-dall2019afterglow-x-dei-lampi-di-raggi-gamma-lunghi) il 25 Maggio 2020 (in italiano).

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Di seguito, la press release ICRA-ICRANet (in inglese).

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).


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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.

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

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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 all'articolo su ApJ:
https://doi.org/10.3847/1538-4357/ab80b9

Press release ICRA-ICRANet:
http://www.icranet.org/communication/18052020/eng.pdf

Press release INAF: http://www.inaf.it/it/notizie-inaf/campo-magnetico-e-rotazione-della-stella-di-neutroni-neonata-nelle-ipernove-binary-driven-derivato-dall2019afterglow-x-dei-lampi-di-raggi-gamma-lunghi#null



3. Il Governo armeno assegna una fellowship per dottorato di ricerca ad ICRANet Armenia, 21 Maggio 2020

Il 21 Maggio 2020, il Governo della Repubblica di Armenia, ha assegnato le fellowships per i dottorati di ricerca per l'anno accademico 2020-2021. Il centro ICRANet Armenia ha ottenuto una fellowship per il dottorato di ricerca. Un'ulteriore posizione sarà assegnata al centro nel mese di Giugno. L'esame finale per l'ammissione si terrà a fine Giugno.
La notizia ufficiale è consultabile (in armeno) sul sito del sistema informatico legale armeno: http://www.arlis.am/DocumentView.aspx?DocID=142700



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

C. Sigismondi, ICRA/Sapienza

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Figura 4: Silvestro II (1854, Torino).


Il congresso annuale in onore di Gerberto d'Aurillac, scienziato, astronomo e Papa, è stato inaugurato giovedì 7 Maggio 2020. Questo evento è stato coordinato a livello internazionale dal centro ICRANet di Pescara, come nel caso dei 2 meeting precedenti che si sono tenuti a Novembre 2019 e Gennaio 2020.
Il programma di questo meeting è centrato sulla luna: la luna di Gerberto è stata osservata 1000 anni fa, con l'idea di riflettere su una grande parte della storia dell'astronomia e sulla sua eredità culturale. Gli studenti del Liceo scientifico Galileo Galilei di Pescara, così come quelli dell'Istituto tecnico Galileo Ferraris di Roma, partecipando a progetti europei di sviluppo didattico (progetti PON), stanno lavorando sui principali temi affrontati durante questo meeting.
Tra le motivazioni che spingono a studiare Gerberto, ne propongo una:'Come mai Gerberto non ha un cratere sulla luna, pur essendo stato il primo a divulgare un Trattato sull'astrolabio prima dell'anno 1000"?
Gerberto ha insegnato Astronomia nel Quadrivio della Cattedrale di Reims in Francia ed è stato considerato un punto di riferimento scientifico per molti secoli dopo la sua morte, soprattutto nel calcolo matematico (essendo anche stato il primo ad utilizzare i numeri arabi e l'abaco) e nella musica. Ha lasciato alla letteratura un trattato in geometria e 220 lettere epistolari (Patrologia Latina volume 90): un caso unico di preservazione di questa cultura medievale. Mezzo secolo dopo, Ermanno di Reichenau è ritenuto l'autore del Trattato sull'astrolabio, ma è stato dimostrato che l'autore originale era Gerberto. Ermanno ha il suo cratere sulla luna e Gerberto no…inoltre, Gerberto ha costruito il primo monte equatoriale documentato, descritto nel suo epistolario (a Costantino, 980 AC sul quale ho scritto un libro, La Sfera da Gerberto al Sacrobosco, Athenaeum Regina Apostolorum, Roma 2009).
Gerberto è stato rispettato in tutta Europa come l'uomo più conosciuto del suo tempo, quando è stato eletto Papa da Otto III nel 999, secondo gli usi dell'epoca, scegliendo il nome di Silvestro II. Una successiva leggenda medioevale (in Guglielmo da Malmesbury e in Benno di Osnabruck), lo ha trasformato in un mago che ha costruito una testa (Golem) capace di dire "si"o "no", grazie alla quale Gerberto ha scoperto che non sarebbe morto fino a quando non fosse andato a Gerusalemme. Il 3 Maggio 1003 andò a celebrare messa nella chiesa romana di Santa Croce, oggi chiamata S. Croce a Gerusalemme e a quel tempo chiamata Basilica Hierusalem (costruita dalla madre di Costantino, Elena), portando li la terra di Gerusalemme, dopo aver trovato la reliquia della Croce. Durante questa messa, Gerberto si ammalò e capì che la sua fine stava arrivando, come aveva predetto il Golem. E' morto il 12 Maggio 1003 e questa è la ragione per cui il congresso in suo onore si tiene, a partire dal 2003, nella prima parte del mese di Maggio. E' stato seppellito nella Basilica di San Giovanni in Laterano.
Il lento processo di riabilitazione di Gerberto avvenne nel 1620 grazie al polacco dominicano Bzovsky e in seguito alla pubblicazione del suo epistolario e del suo libro nella Patrologia Latina intorno al 1700 (ora su wikipedia, nella sezione Latino). Nella seconda parte del 19° secolo, Nicolay Bubnov pubblicò, in Russia, il suo lavoro matematico (1899), ora disponibile su google books. Nel 1970, Klaus Jurgen Sachs trovò a Madrid un manoscritto sul trattato musicale De Mensura Fistularum, risalente all'11° secolo e attribuibile a Gerberto, che prova ulteriormente che lui fu il vero centro della cultura contemporanea prima e dopo il 1000. Clyde Brockett nel 1995 e Flavio G. Nuvolone (1942-2019) hanno studiato approfonditamente la composizione 'Carme Figuratum' (980) scritta da Gerberto a Otto II, che includeva i numeri arabi che lui stesso aveva introdotto per la prima volta nell'Europa latina. L'approccio allo studio di Gerberto è necessariamente inter-multi disciplinare e le sorprese non sono ancora finite. Il nostro compito è quello di mantenere questi studi e di promuovere il loro sviluppo attraverso il web, usando anche il giornale accademico Gerberto, fondato nel 2010 nell'Osservatorio di Parigi con 3 ISSN: paper, CD e online. L'edizione del 2020 riconosce l'immenso contributo dato nello studio di Gerberto dal Professor Flavio Giuseppe Nuvolone (2 Settembre 1942 - 11 Dicembre 2019), che ha pubblicato diversi libri su Gerberto e ha tenuto diversi meetings dal 1983, quando ha iniziato a collaborare con Michele Tosi al giornale di Bobbio Archivum Bobiense. La sua principale attività si è tenuta presso l'Università di Friburgo come titolare della cattedra di Patrologia, ma è diventato uno studioso multidisciplinare nel cercare di inquadrare la figura di Gerberto. Parlare con lui è stato un modo per entrare in contatto diretto con lo spirito e l'ambiente in cui Gerberto ha operato. La resilienza della vita di Gerberto e la sua solida fede cattolica, sono state reinterpretate dal Professor Nuvolone con grande discrezione e profondità.
La perdita di George V. Coyne (19 Gennaio 1933- 11 Febbraio 2020), ex Direttore della Specola Vaticana, è, per la comunità scientifica, la perdita di una persona che ha condotto con naturalezza una vita in sinergia con scienza e fede, così come fece Gerberto. Entrambi sono stati ricordati in questa occasione.
Temi come la botanica, la filosofia, la didattica, l'ottica, la fisica solare hanno sempre attirato i giovani studenti facendoli approcciare allo studio delle scienze, come Gerberto in primis rese possibile nella sua Cathedral School a Reims, insegnando nel quadrivium (matematica, geometria, astronomia e musica) insieme al classico trivium (grammatica, retorica, dialettica), che lui ha interpretato come lo studio anche di scrittori latini profane come Aristotle. Il contributo musicale preparato da Stefano Carciofalo Parisse è un omaggio al grande maestro Gerberto, autore sia della musica che del trattato teorico su essa del 980, De Mensura Fistularum. Un cratere sulla luna dovrebbe essere dedicato a Gerberto, almeno, e sul lato verso la terra.
Per maggiori informazioni su questo evento, sul programma e sul materiale scaricabile: http://www.icranet.org/index.php?option=com_content&task=view&id=1317
Il giornale accademico dedicato a Gerberto, alla storia della scienza medievale e alla didattica, è disponibile al seguente link: http://www.icra.it/gerbertus



5. COVID webinar, Tucson USA, 19 Maggio 2020


Il 19 Maggio, il Prof. Ruffini è stato invitato a partecipare al COVID webinar, organizzato a Tucson (Arizona, USA) dal Prof. Johan Rafelski. Il webinar è stato aperto dal discorso del Prof. Rafelski, seguito dalla presentazione del Prof. Giorgio Torrieri (in collaborazione con il Prof. Alessio Notari) sui fattori di rischio per la trasmissione del COVID-19. Il Prof. Ruffini, in collaborazione con il Prof. Narek Sahakyan (Direttore del centreo ICRANet Armenia), ha poi presentato il suo talk "Real danger: critical COVID-triggers seen in statistical analysis", il Prof. Berndt Muller ha presentato il suo talk sulle analisi affidabili del COVID-19 e sui loro risultati e infine il Prof. John W. Clark ha presentato il suo contributo.

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Figura 5: il Prof. Ruffini partecipa al COVID webinar, organizzato dal Prof. Johan Rafelski a Tucson il 19 Maggio 2020.


Questo evento è stato registrato, e può essere visto ai seguenti link:
• sito web ICRANet:
http://www.icranet.org/index.php?option=com_content&task=view&id=1321

• sito web Università dell'Arizona:
https://arizona.hosted.panopto.com/Panopto/Pages/Viewer.aspx?tid=26f8fd43-c2a2-43ac-802d-abc0015fee02
• Zoom playback:
https://arizona.zoom.us/rec/share/yuJxcqv-rD9Oc5Hv9ESFS598HJriT6a8gCYarvsNmEhEopGz7QhSImdAteDITbBw



6. Il 4° Zeldovich meeting diventa virtuale


Data la pandemia di COVID-19, il 4° Zeldovich meeting si terrà virtualmente dal 7 all'11 Settembre 2020, in collaborazione con l'ICRANet e con l'Accademia nazionale delle scienze di Bielorussia in qualità di organizzatori e ospiti.
La partecipazione sarà gratuita, la scadenza per la registrazione è stata estesa fino al 31 Luglio 2020 mentre quella per la sottomissione degli abstract è stata spostata al 15 Agosto 2020. I proceedings del meeting saranno pubblicati in Astronomy Reports journal.
Per maggiori informazioni: http://www.icranet.org/zeldovich4



7. Bando congiunto "BRFFR - ICRANet" 2020


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Ad Aprile 2020, la Belarusian Republican Foundation for Fundamental Research (BRFFR) e l'ICRANet hanno annunciato la pubblicazione di un bando congiunto per progetti di ricerca di base comune, in astrofisica relativistica. Le aree scientifiche interessate dal bando sono l'astrofisica relativistica, la cosmologia e la gravitazione. Le applications congiunte da team di ricerca internazionali, inclusi gli scienziati bielorussi, devono essere presentate simultaneamente, utilizzando l'application form concordata da entrambe le organizzazioni: gli scienziati bielorussi applicano per il BRFFR, quelli internazionali per ICRANet. La durata del progetto è di circa 2 anni, e la scadenza per la presentazione delle domande è il 15 Settembre 2020.
Per maggiori informazioni sul bando e per scaricare l'application form:
http://www.icranet.org/index.php?option=com_content&task=view&id=1311



8. Pubblicazioni recenti

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.
Link: https://doi.org/10.3847/1538-4357/ab80b9


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.
Link: https://iopscience.iop.org/article/10.3847/1538-4357/ab8014


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.
Link: https://doi.org/10.1093/mnras/staa868


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.
Link: https://doi.org/10.1103/PhysRevD.101.103031



9. Valutazione interna sul paper del Dr Liang Li "Thermal Components in Gamma-Ray Bursts. II. Constraining the Hybrid Jet Model" pubblicato in 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].

Link to the paper: https://iopscience.iop.org/article/10.3847/1538-4357/ab8014



10. Valutazione interna sul paper pubblicato come coautore dal Prof. Shesheng Xue "Supercritically charged objects and electron-positron pair creation" su 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.

9


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).

Link to the paper: https://doi.org/10.1103/PhysRevD.101.103031
 
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