ICRANet Newsletter

ICRANet Newsletter
February/March 2021

English - French - Italian - Portuguese - Russian

SUMMARY
1. Astronomers get their First Look at the Dynamics of the Base of a Relativistic Jet
2. The Sixteenth Marcel Grossmann virtual Meeting (MG16), July 5-9, 2021
3. Inauguration of ICRANet Mazandaran center, February 28, 2021
4. New Cooperation Protocol ICRA-ICRANet-Alzahra University, February 9, 2021
5. Renewal of 3 ICRANet Cooperation Agreements in Iran
6. New Memorandum of Understanding and Agreement for cooperation in Relativistic Astrophysics ICRA - University of Sciences and Technology of China (USTC), March 16, 2021
7. Cooperation Protocol ICRANet - Ulugh Beg Astronomical Institute of Uzbekistan Academy of Sciences (UBAI), March 26, 2021
8. 43° COSPAR Scientific Assembly meeting (online), January 28-February 4, 2021
9. Prof. Ruffini seminar for Space Science at Drop tower, ZARM Bremen (Germany), March 8, 2021
10. Rencontres de Moriond on Gravitation (poster session), March 9-11, 2021
11. New results on the AXP 4U 01242+61 out of collaboration of ICRANet and ITA
12. Recent publications

1. Astronomers get their First Look at the Dynamics of the Base of a Relativistic Jet

Synopsis of the Astrophysical Journal paper "Observing the Time Evolution of the Multi-Component Nucleus of 3C 84" by Brian Punsly, Hiroshi Nagai, Tuomas Savolainen and Monica Orienti.
Relativistic astrophysical jets are some of the most energetic objects in the Universe. They are driven by compact objects, primarily black holes. The jets from the supermassive black holes can have powers >10⁴⁰ Watts and last for a million years. They are intense pencil beams of energy that terminate in enormous plume or lobe, an order of magnitude larger than the largest galaxies. The bases of the jets, where the jets originate, are too small to be within the reach of modern telescopes. Thus, the Event Horizon Telescope (EHT) that can image the base of the jet in the nearby galaxy, M87. The observations are so difficult, that we are lucky to have one successful observation every few years. Thus, one cannot track the dynamics of the base of the jet over time scales of weeks to a year when all the significant changes occur.
Consequently, a team of astronomers looked to the nearby extragalactic radio source 3C 84 that is much brighter than M87 to glimpse the dynamics of a jet near its source for the first time. They were able to use a high efficiency global network of telescopes, the Very Long Baseline Array, that is operated by National Radio Astronomy Observatory. This telescope can efficiently observe on a regular basis, but with a resolution of only 25% of EHT. The fact that 3C 84 is the brightest extragalactic object in the sky at the observed frequency allows for very high signal to noise and the use of novel high resolution data reduction schemes invented for this purpose. ICRANet astrophysicist, Brian Punsly, patiently waited throughmany years of monthly monitoring until the base of the of the southerly directed jet started to evolve. Over twenty months, the central engine ejected a high energy plasma source to the east not the south - perpendicular to the pencil beam jet! Not only that it moved at only 9% of the speed of light, very slow by relativistic standards. Now that we can see the base of the jets, we can intelligently describe their genesis in the future.


Brian Mathew Punsly from Mathew California University, Los Angeles USA is a member of ICRANet Faculty Staff.
Link to the article: https://arxiv.org/abs/2102.07272

2. The Sixteenth Marcel Grossmann virtual Meeting (MG16), July 5-9, 2021

The Sixteenth Marcel Grossmann Meeting on Recent Developments in Theoretical and Experimental General Relativity, Astrophysics and Relativistic Field Theories (MG16) will take place virtually from Monday July 5 through Friday July 9, 2021.
It is be organized by ICRA (Rome, Italy), ICRANet (Pescara, Italy) and the associated ICRANet centers including Yerevan, Armenia; Minsk, Belarus; Rio de Janeiro, Brazil; USTC, China; Isfahan, Iran; Stanford University and the University of Arizona, USA.
During this five days online conference, a variety of topics will be discussed in the plenary and parallel sessions. Each day of the meeting there will be three program blocks of three hours each: one plenary session and two parallel sessions in revolving order to address the three major continental time zones:
Central European Summer Time:
Block 1: 6:30-9:30
Block 2: 9:30-12:30
Block 3: 16:30-19:30

The first plenary session will start at 9:30 on Monday, the second one will start at 16:30 on Tuesday, the third one at 6:30 on Wednesday and so on. Recordings of plenary session will be available next day on YouTube. Each block will have 10 sessions running in parallel, each session will have 9 talks.
The MG16 website is http://www.icra.it/mg/mg16. All the information about the plenary and parallel session programs, the registration and the abstract submission are available on the Indico platform at the following link: https://indico.icranet.org/event/1/. If you want to join the conference, please register both at our Indico website and at the MG16 conference at your earliest convenience:
Register at Indico website: https://indico.icranet.org/register/
Register at the MG16 meeting: https://indico.icranet.org/event/1/registrations/
Once you register, you will be in our database and you will receive further communications about the MG16 meeting.

The timeline is:
* March 15, 2021: registration opening
* April 15, 2021: abstract submission opening
* May 15, 2021: registration closure
* June 15, 2021: abstract submission closure

The registration fee will be:
* Regular fee: 150 Euros (up to April 1) - postponed to April 15
* Late fee: 250 Euros (after April 15)
* Reduced fee: 50 Euros (applied to students, retired scientists and auditors up to April 1) - postponed to April 15
* Late Reduced fee: 80 Euros (applied to students, retired scientists and auditors after April 15)

For any query, please contact mg16[AT]icranet.org

3. Inauguration of ICRANet Mazandaran center, February 28, 2021

It is or pleasure to announce that on Saturday February 28, 2021, the ICRANet Center at the University of Mazandaran - UMZ (Iran) has been inaugurated. This is the second ICRANet center in Iran. The inauguration ceremony was attended by Dr. Kourosh Nozari, Professor of physics and President of the University of Mazandaran, and by Dr. Behzad Eslampanah, Professor of physics at the University of Mazandaran. During a meeting held at the Office of International and Scientific Cooperation (OISC), President Nozari, a distinguished Iranian physicist, reiterated the importance of ICRANet and described it as an important research center which can play a pivotal role in enhancing physics research in the University of Mazandaran and, indeed, in Iran. He also welcomed any sort of academic collaboration between ICRANet and the UMZ and said that the center is ready to further strengthen the bilateral collaboration with ICRANet.


For the press release (in English) please see the University of Mazandaran official website:
http://en.int.umz.ac.ir/index.aspx?siteid=122&fkeyid=&siteid=122&pageid=13816&newsview=26386.

4. New Cooperation Protocol ICRA-ICRANet-Alzahra University, February 9, 2021

On February 9, 2021 an agreement on scientific cooperation between ICRA, ICRANet and Alzahra University (Iran) was signed by Dr. Mahnaz Molanazari (Chancellor of Alzahra University), Prof. Mohammad Taghi Mirtorabi (Associate Professor, Physics and Chemistry Department of Alzahra University), by Prof. Remo Ruffini (Director of ICRANet) and by Prof. Jorge A. Rueda (ICRANet Faculty Professor). The main joint activities to be developed under the framework of this agreement include: the promotion of theoretical and observational activities within the field of Relativistic Astrophysics; the institutional exchange of faculty members, researchers, post-doctorate fellows and students; the promotion of technological developments; the development of Data Centers for Astrophysical data in all wavebands; the organization of training and teaching courses, seminars, conferences, workshops or short courses, the development of inter-institutional research areas associated to local graduate programs and joint publications. The agreement will be valid for 5 years.
For the text of the agreement (both in English and Persian) please see: http://www.icranet.org/index.php?option=com_content&task=view&id=1360

5. Renewal of 3 ICRANet Cooperation Agreements in Iran

Renewal of the Cooperation Protocol ICRANet - Isfahan University of Technology (IUT), February 26, 2021


On February 26, 2021 the Cooperation Protocol between ICRANet and Isfahan University of Technology - IUT (Iran) has been renewed. The renewal has been signed by Prof. Sayyed Mahdi Abtahi (President of IUT) and by Prof. Remo Ruffini (Director of ICRANet). This agreement will be valid for further 5 years and the main joint activities to be developed under its framework include: the promotion of theoretical and observational activities within the field of Relativistic Astrophysics; the institutional exchange of faculty members, researchers, post-doctorate fellows and students; the promotion of technological developments; the development of Data Centers for Astrophysical data in all wavebands; the organization of training and teaching courses, seminars, conferences, workshops or short courses, the development of inter-institutional research areas associated to local graduate programs and joint publications.
For the text of the agreement see:
http://www.icranet.org/index.php?option=com_content&task=view&id=1059
For the IUT newsletter on this issue (in English) see:
https://internationalnews.iut.ac.ir/book_treasure.php?mod=viewbook&book_id=31&slc_lang=en&sid=1


Renewal of the Cooperation Protocol ICRANet - Institute for Advanced Studies in Basic Sciences (IASBS), March 1, 2021


On March 1, 2021 the Cooperation Protocol between ICRANet and Institute for Advanced Studies in Basic Sciences - IASBS (Iran) has been renewed. The renewal has been signed by Prof. Babak Karimi (President of IASBS) and by Prof. Remo Ruffini (Director of ICRANet). This agreement will be valid for further 5 years and the main joint activities to be developed under its framework include: the promotion of theoretical and observational activities within the field of Relativistic Astrophysics; the institutional exchange of faculty members, researchers, post-doctorate fellows and students; the promotion of technological developments; the development of Data Centers for Astrophysical data in all wavebands; the organization of training and teaching courses, seminars, conferences, workshops or short courses, the development of inter-institutional research areas associated to local graduate programs and joint publications.
For the text of the agreement see:
http://www.icranet.org/index.php?option=com_content&task=view&id=1058


Renewal of the Agreement ICRANet - Shiraz University, March 5, 2021


On March 5, 2021 the Cooperation Agreement between ICRANet and Shiraz University (Iran) has been renewed. The renewal has been signed by Prof. Dr. Hamid Nadgaran (Chancellor of Shiraz University) and by Prof. Remo Ruffini (Director of ICRANet). This agreement will be valid for further 5 years and the main joint activities to be developed under its framework include: the promotion of theoretical and observational activities within the field of Relativistic Astrophysics; the institutional exchange of faculty members, researchers, post-doctorate fellows and students; the promotion of technological developments; the development of Data Centers for Astrophysical data in all wavebands; the organization of training and teaching courses, seminars, conferences, workshops or short courses, the development of inter-institutional research areas associated to local graduate programs and joint publications.
For the text of the agreement see:
http://www.icranet.org/index.php?option=com_content&task=view&id=1062

6. New Memorandum of Understanding and Agreement for cooperation in Relativistic Astrophysics ICRA - University of Sciences and Technology of China (USTC), March 16, 2021

On March 16, 2021 ICRA (International Center for Relativistic Astrophysics) has signed both a Memorandum of Understanding and an Agreement for cooperation in Relativistic Astrophysics with the University of Sciences and Technology of China (USTC). Both the documents have been signed by Prof. Yuao Chen (Dean of the School of Physical Sciences) and by Prof. Remo Ruffini (President of ICRA and Director of ICRANet).
The mission of both the Agreement for cooperation in Relativistic Astrophysics and the MoU will be to cooperate in research and education in the field of Relativistic Astrophysics. The ways in which collaboration in these fields may be realized include the exchange and visit of faculty/staff Professors as well as the implementation of joint education and research programs. Both parties agree to collaborate on graduate education in the field of Relativistic Astrophysics and each party can nominate up to five students annually as program candidates: those students should gain the required degree qualification and skill training in USTC first, and then screened out to come to ICRA for joint project R&D with attendance of the relevant lectures, if necessary. Both those joint documents will be valid for 5 years.
For the text of the Agreement for cooperation in Relativistic Astrophysics see: http://www.icranet.org/documents/agreementICRA-USTC.pdf
For the text of the Memorandum of Understanding see: http://www.icranet.org/documents/mouICRA-USTC.pdf

7. Cooperation Protocol ICRANet - Ulugh Beg Astronomical Institute of Uzbekistan Academy of Sciences (UBAI), March 26, 2021

On March 26, 2021 a Cooperation Protocol between ICRANet and the Ulugh Beg Astronomical Institute of Uzbekistan Academy of Sciences (UBAI) was signed. The document has been signed by Prof. Shuhrat Ehgamberdiev (Director of UBAI), by Prof. Bobomurat Ahmedov (UBAI), by Prof. Remo Ruffini (Director of ICRANet) and by Prof. Jorge A. Rueda (ICRANet Faculty Professor). The main joint activities to be developed under the framework of this agreement include: the promotion of theoretical and observational activities within the field of Relativistic Astrophysics; the institutional exchange of faculty members, researchers, post-doctorate fellows and students; the promotion of technological developments; the development of Data Centers for Astrophysical data in all wavebands; the organization of training and teaching courses, seminars, conferences, workshops or short courses, the development of inter-institutional research areas associated to local graduate programs and joint publications. The agreement will be valid for 5 years.
For the text of the agreement see:
http://www.icranet.org/index.php?option=com_content&task=view&id=1362

8. 43° COSPAR Scientific Assembly meeting (online), January 28-February 4, 2021

The 43° COSPAR Scientific Assembly meeting has been held virtually from January 28 to February 4, 2021. On February 3, Prof. Ruffini, Director of ICRANet, gave a lecture titled "On the energy extraction from a Kerr Black Hole by Blackholic quanta in GRBs and AGNs".
Here is the abstract: Almost fifty years after the paper "Introducing the Black Hole" by Ruffini and Wheeler and the Black Hole (BH) mass energy formula by Christodoulou, Ruffini and Hawking, we can finally assert that we have been observing the moment of creation of a BH in the BdHN I in GRB 190114C, GRB 130427A, GRB 160509A and GRB 160625B, with the corresponding rotational energy extraction process. The first appearance of the Supernova, the SN-rise, triggering the BdHN has been identified. The hypercritical accretion on the SN ejecta on the new NS (νNS) created in the SN, is shown to originate the X-ray afterglow observed by the NASA Niels-Gehrels SWIFT satellite (SWIFT). The hypercritical accretion of the SN on the NS binary companion in the BdHN I model leads to the formation of the newly formed BH. The onset of the GeV radiation coinciding with the BH formation has revealed self similar structures in the time resolved spectral analysis of all sources. Consequently, we find evidence for quantized-discrete-emissions in all sources, with energy quanta of 10³⁷ ergs with repetition time of 10^-14 sec. GRBs are the most complex systems ever successfully analyzed in Physics and Astrophysics, and they may well have a role in the appearance of life in the Cosmos. The corresponding analysis for Active Galactic Nuclei (AGN), scaling simply by the Black Hole mass, will be illustrated. These results have been made possible by a long-lasting theoretical activity, a comprehensive unprecedented high quality data analysis, an observational multi-messenger effort by the astronomical, the physical and the space research communities. This observational effort is well epitomized by the original Vela Satellites, the NASA Compton space mission (CGRO), the Italo-Dutch Beppo SAX satellite, the Russian Konus Wind Satellite, the SWIFT satellite, the Italian AGILE satellite, the NASA FERMI mission and most recently the Chinese satellite HXMT. These space missions have been assisted by radio and optical equally outstanding observational facilities from the ground.

Link to Prof. Ruffini presentation on YouTube: https://youtu.be/vT-msfF4E7s

9. Prof. Ruffini seminar for Space Science at Drop tower, ZARM Bremen (Germany), March 8, 2021

On March 8, 2021, Prof. Ruffini, Director of ICRANet, has been invited by Prof. Claus Laemmerzahl to give an online seminar at the ZARM Centrum in Bremen (Germany). This seminar has been inserted in the series of the "Space Science at the Drop Tower seminars" regularly held in the month of march in Bremen. Prof. Ruffini presented a talk titled "Discovery of energy extraction from a Kerr Black Hole by discrete "Blackholic" quanta in GRBs and AGNs".
Here is the abstract: Almost fifty years after the paper "Introducing the Black Hole" by Ruffini and Wheeler and the Black Hole (BH) mass energy formula by Christodoulou, Ruffini and Hawking, we can finally assert that we have been observing the moment of creation of a BH in the BdHN I in GRB 190114C, GRB 130427A, GRB 160509A and GRB 160625B, with the corresponding rotational energy extraction process. The first appearance of the Supernova, the SN-rise, triggering the BdHN has been identified. The hypercritical accretion on the SN ejecta on the new NS (νNS) created in the SN, is shown to originate the X-ray afterglow observed by the NASA Niels-Gehrels SWIFT satellite (SWIFT). The hypercritical accretion of the SN on the NS binary companion in the BdHN I model leads to the formation of the newly formed BH. The onset of the GeV radiation coinciding with the BH formation has revealed self similar structures in the time resolved spectral analysis of all sources. Consequently, we find evidence for quantized-discrete-emissions in all sources, with energy quanta of 10³⁷ ergs with repetition time of 10^-14 sec. GRBs are the most complex systems ever successfully analyzed in Physics and Astrophysics, and they may well have a role in the appearance of life in the Cosmos. The corresponding analysis for Active Galactic Nuclei (AGN), scaling simply by the Black Hole mass, will be illustrated. These results have been made possible by a long-lasting theoretical activity, a comprehensive unprecedented high quality data analysis, an observational multi-messenger effort by the astronomical, the physical and the space research communities. This observational effort is well epitomized by the original Vela Satellites, the NASA Compton space mission (CGRO), the Italo-Dutch Beppo SAX satellite, the Russian Konus Wind Satellite, the SWIFT satellite, the Italian AGILE satellite, the NASA FERMI mission and most recently the Chinese satellite HXMT. These space missions have been assisted by radio and optical equally outstanding observational facilities from the ground.

Link to Prof. Ruffini presentation on YouTube: https://youtu.be/ekYHvNbhv_g

10. Rencontres de Moriond on Gravitation (poster session), March 9-11, 2021

The meeting "Rencontres de Moriond on Gravitation" has been held virtually from March 9 to 11, 2021 through poster presentations from the participants. On Wednesday March 10, Prof. Ruffini, Director of ICRANet, presented a poster titled "Morphology of the X-ray afterglows and of the jetted GeV emission in long GRBs", while Prof. Simonetta Filippi, ICRANet collaborator presented a poster titled "Inferences of GRB 190114C for the Crab pulsar and the supernova remnant".
Here is the abstract of Prof. Ruffini poster: We recall evidence that all short and long gamma-ray bursts (GRBs) have binary progenitors and give new detailed examples. We focus on the binary progenitors of long GRBs, the binary-driven hypernovae (BdHNe), that consist of a carbon-oxygen core (CO core) and a binary neutron star (NS) companion. For binary periods of the order of 5 min, the energetic subclass BdHN I originates when the CO core collapses. They are characterized by: 1) an outstanding energetic supernova (the "SN-rise"); 2) a newborn black hole (BH) originating from the SN hypercritical accretion onto the NS companion. Only in some cases, the newborn BH via the "inner engine"' mechanism, is observed to lead to GeV emission characterized by an isotropic power-law luminosity L_GeV = A_GeV*t^(-α). 3) The new NS (νNS), created at the SN center, accretes matter from the SN ejecta originating the X-ray afterglow with L_X = A_X*t^(-&α;), always present in all BdHN I. We analyze 378 BdHN I and, among them, select four prototypes: GRB 130427A, GRB 160509A, GRB 180720B and GRB 190114C using a time-resolved spectral analysis and derive 1) the spectra, the luminosities and the duration of the SN-rise; 2) the amplitude A_X, the power-law index α_X=1.48±0.32 of their X-ray afterglows, 3) the time-evolution of the νNS spin, and 4) A_GeV and α_GeV=1.19±0.04. From the latter, we infer for the first time the mass and spin of the BH powering long GRBs. We also deduce that there is a special morphology which explains why the GeV emission is present only in some BdHN I, and it is confirmded by dedicated three-dimensional smoothed-particle-hydrodynamics simulations of BdHN I. We conclude that the GeV radiation is observed only when emitted within a cone of half-opening angle of nealry 60 degrees from the normal to the orbital plane. The mass and spin of the Kerr BHs are obtained based upon the GRB "inner engine" originating the GeV emission by extracting the BH rotational energy. We obtain initial BH masses 2.3<M/M_Sun<8.9 and spins 0.27<a/M<0.87, and from their time evolution, we verify, for the first time, the validity of the BH mass-energy formula. Here is the abstract of Prof. Filippi poster: The understanding of binary-driven hypernovae of type I (BdHNe I) has identified the central role of the explosion of the supernova ("SN-rise") as well as of the role of the hypercritical accretion of the SN ejecta onto the binary companion neutron star (NS) and onto the newborn NS (νNS) in determining the GRB dynamics. We model the νNS through the equilibrium sequence of Maclaurin spheroids. By requiring that the νNS period extrapolated on 1000 yr coincides with the one of PSR B0531 + 21 (the Crab pulsar), we determine the initial spin of the νNS to be 0.9 ms, and follow the subsequent rotational and gravitational evolution of the eccentricity. The observed changes in the braking index are proposed to be correlated to pulsar glitches, whose intensities are predicted to be strongly correlated with the pulsar spin. We propose that the progenitor of the Crab nebula and of the Crab pulsar is a GRB very similar to GRB 190114C.

11. New results on the AXP 4U 01242+61 out of collaboration of ICRANet and ITA

Sarah Villanova Borges, a student of Prof. Manuel Malheiro graduated in 2017 at ITA, and a received a master degree under Dr. Claudia Rodrigues at INPE in 2018 published an important article on the AXP 4U 01242+61 explaining all the light curve (in particular the hard x-ray spectrum) of this source using a Hot and massive White Dwarf model in the "The Astrophysical Journal" last year. This work, the modeling and calculations and, the article writing was all done by Sarah, who participated previously in the MGXV meeting with the oral talk on earlier results on this topic.
Now Sarah is accepted for a PhD program in the Department of Physics and Astronomy at the University of Wisconsin Milwaukee with a scholarship.
These results are presented at the AAS channel on YouTube: https://www.youtube.com/watch?v=JPqG7-ifE_k&t=1s
The link to the ApJ article: https://iopscience.iop.org/article/10.3847/1538-4357/ab8add

12. Recent publications

Behzad Eslam Panah, Can the power Maxwell nonlinear electrodynamics theory remove the singularity of electric field of point-like charges at their locations?, accepted for publication in Europhysics Letters (EPL).
YES! We introduce a variable power Maxwell nonlinear electrodynamics theory which can remove the singularity of electric field of point-like charges at their locations. One of the main problems of Maxwell's electromagnetic field theory is related to the existence of singularity for electric field of point-like charges at their locations. In other words, the electric field of a point-like charge diverges at the charge location which leads to an infinite self-energy. In order to remove this singularity a few nonlinear electrodynamics (NED) theories have been introduced. Born-Infeld (BI) NED theory is one of the most famous of them. However the power Maxwell (PM) NED cannot remove this singularity. In this paper, we show that the PM NED theory can remove this singularity, when the power of PM NED is less than s<1/2.
Link ArXiv: https://arxiv.org/abs/2103.08343


Bing Zhang, Yu Wang and Liang Li, Dissecting the Energy Budget of a Gamma-Ray Burst Fireball, published in ApJL on March 1, 2021, Volume 909, number L3.
The jet composition and radiative efficiency of gamma-ray bursts (GRBs) are poorly constrained from the data. If the jet composition is matter-dominated (i.e., a fireball), the GRB prompt emission spectra would include a dominant thermal component originating from the fireball photosphere and a nonthermal component presumably originating from internal shocks whose radii are greater than the photosphere radius. We propose a method to directly dissect the GRB fireball energy budget into three components and measure their values by combining the prompt emission and early afterglow data. The measured parameters include the initial dimensionless specific enthalpy density (η), bulk Lorentz factors at the photosphere radius (Γ_ph) and before fireball deceleration (Γ₀), the amount of mass loading (M), and the GRB radiative efficiency (ηγ). All the parameters can be derived from the data for a GRB with a dominant thermal spectral component, a deceleration bump feature in the early afterglow lightcurve, and a measured redshift. The results only weakly depend on the density n of the interstellar medium when the composition γ parameter (typically unity) is specified.
DOI: https://doi.org/10.3847/2041-8213/abe6ab


Liang Li and Bing Zhang, Testing the High-latitude Curvature Effect of Gamma-Ray Bursts with Fermi Data: Evidence of Bulk Acceleration in Prompt Emission, published in ApJS on March 23, 2021, Volume 253, number 43.
When a gamma-ray burst (GRB) emitter stops emission abruptly, the observer receives rapidly fading emission from high latitudes with respect to the line of sight, known as the "curvature effect". Identifying such emission from GRB prompt-emission lightcurves would constrain the radius of prompt emission from the central engine and the composition of GRB jets. We perform a dedicated search of high-latitude emission (HLE) through spectral and temporal analyses of a sample of single-pulse bursts detected by the Gamma-ray Burst Monitor on board the Fermi satellite. We identify HLE from a subsample of bursts and constrain the emission radius to be RGRB ~ (10¹⁵–10¹⁶) cm from the central engine. Some bursts have the HLE decay faster than predicted by a constant Lorentz factor jet, suggesting that the emission region is undergoing acceleration during prompt emission. This supports the Poynting-flux-dominated jet composition for these bursts. The conclusion is consistent with previous results drawn from spectral-lag modeling of prompt emission and HLE analysis of X-ray flares. Scrivi un messaggio
DOI: https://doi.org/10.3847/1538-4365/abded1


Liang Li, Felix Ryde, Asaf Pe’er, Hoi-Fung Yu, and Zeynep Acuner, Bayesian Time-Resolved Spectroscopy of Multi-Pulsed GRBs: Variations of Emission Properties amongst Pulses, in press on ApJS 2021.
Gamma-ray bursts (GRBs) are highly variable and exhibit strong spectral evolution. In particular, the emission properties vary from pulse to pulse in multi-pulsed bursts. Here, we present a time-resolved Bayesian spectral analysis of a compilation of GRB pulses observed by the Fermi Gamma-ray Burst Monitor (GBM). The pulses are selected to have at least four time-bins with a high statistical significance, which ensures that the spectral fits are well determined and that spectral correlations can be established. The sample consists of 39 bursts, 117 pulses, and 1228 spectra. We confirm the general trend that pulses become softer over time, with mainly the low-energy power-law index α becoming smaller. A few exceptions from this trend exist with the hardest pulse occurring at late times. The first pulse in a burst is clearly different from the later pulses: 3/4 of them violate the synchrotron line-of-death (Preece 1998), while around half of them significantly prefer photospheric emission. These fractions decrease for subsequent pulses. We also find that in 2/3 of the pulses the spectral parameters (α and peak energy) track the light-curve variations. This is a larger fraction compared to what is found in previous samples. In conclusion, emission compatible with the GRB photosphere is typically found close to the trigger time, while the chance of detecting synchrotron emission is greatest at late times. This allows for coexistence of emission mechanisms at late times.
Link: https://arxiv.org/abs/2012.03038


MAGIC collaboration, MAGIC Observations of the Nearby Short Gamma-Ray Burst GRB 160821B, published on February 16, 2021 on ApJ, Volume 908, number 1.
The coincident detection of GW170817 in gravitational waves and electromagnetic radiation spanning the radio to MeV gamma-ray bands provided the first direct evidence that short gamma-ray bursts (GRBs) can originate from binary neutron star (BNS) mergers. On the other hand, the properties of short GRBs in high-energy gamma-rays are still poorly constrained, with only ∼20 events detected in the GeV band, and none in the TeV band. GRB 160821B is one of the nearest short GRBs known at z = 0.162. Recent analyses of the multiwavelength observational data of its afterglow emission revealed an optical-infrared kilonova component, characteristic of heavy-element nucleosynthesis in a BNS merger. Aiming to better clarify the nature of short GRBs, this burst was automatically followed up with the MAGIC telescopes, starting from 24 s after the burst trigger. Evidence of a gamma-ray signal is found above ∼0.5 TeV at a significance of ∼ 3σ during observations that lasted until 4 hr after the burst. Assuming that the observed excess events correspond to gamma-ray emission from GRB 160821B, in conjunction with data at other wavelengths, we investigate its origin in the framework of GRB afterglow models. The simplest interpretation with one-zone models of synchrotron-self-Compton emission from the external forward shock has difficulty accounting for the putative TeV flux. Alternative scenarios are discussed where the TeV emission can be relatively enhanced. The role of future GeV-TeV observations of short GRBs in advancing our understanding of BNS mergers and related topics is briefly addressed.
DOI: https://doi.org/10.3847/1538-4357/abd249


Alessandro Loppini, Alessandro Barone, Alessio Gizzi, Christian Cherubini, Flavio H. Fenton, and Simonetta Filippi, Thermal effects on cardiac alternans onset and development: A spatiotemporal correlation analysis, accepted for publication in Physical Review E on March 9, 2021.
Alternans of cardiac action potential duration represent critical precursors for the development of life-threatening arrhythmias and sudden cardiac death. The system’s thermal state affects these electrical disorders requiring additional theoretical and experimental effort to improve a patient-specific clinical understanding. In such a scenario, we generalize a recent work from {Loppini et al. 100 :020201 (2019)} by performing an extended spatiotemporal correlation study. We consider high-resolution optical mapping recordings of canine ventricular wedges’ electrical activity at different temperatures and pacing frequencies. We aim to recommend the extracted characteristic length as a potential predictive index of cardiac alternans onset and evolution within a wide range of system states. In particular, we show that a reduction of temperature results in a drop of the characteristic length, confirming the impact of thermal instabilities on cardiac dynamics. Moreover, we theoretically investigate the use of such an index to identify and predict different alternans regimes. Finally, we propose a novel constitutive phenomenological law linking conduction velocity, characteristic length, and temperature in view of future numerical investigations.
Link:
https://journals.aps.org/pre/accepted/db078R10MbeEb01f012d1f947e5adcb79433e8120