12. Meeting online per la settimana mondiale dell'astronomia, ICRANet Isfahan (Iran), 11-12 Maggio 2021

La settimana mondiale dell'astronomia è un evento pubblico annuale, che ha l'obiettivo di informare gli studenti ed il pubblico sull'astronomia e l'astrofisica e di creare un'atmosfera dinamica per discussioni scientifiche pubbliche sull'astronomia tra accademici, scienziati e studenti al fine di poter interagire e scambiare nuove idee in questo campo.
Questo evento è stato organizzato dal Dr. Soroush Shakeri (ICRANet-Isfahan) e dal Dipartimento di fisica dell'IUT nelle giornate dell'11 e 12 Maggio 2021 in formato virtuale. In questo meeting, diversi scienziati dalla Germania e dall'Iran si sono riuniti per discutere diversi tematiche legate all'astronomia. Il meeting è iniziato l'11 Maggio alle h 16:30 (IRST), con un interessante presentazione del Dr. Behnam Javanmardi dell'Università di Bonn (Germania), dal titolo "Cosmological inconsistencies and Hubble Constant", ed è andato avanti con un'accesa discussione tra il Dr. Javad Taghizadeh Firouzjaee (K.N. Toosi University of Technology, Tehran), su "The Mystery of Black Holes" e il recente Premio Nobel per la fisica. Nel secondo giorno di meeting, la Dott.ssa Sedighe Sajadian (Dipartimento di fisica IUT, Isfahan) ha parlato di differenti metodi per scoprire pianeti extrasolari e della possibilità che ci sia vita al si là del nostro sistema solare. Alla fine, il Dr. Mahdi Kord Zangeneh (Shahid Chamran University, Ahvaz) ha presentato un'esaustiva illustrazione della cosmologia e dei recenti traguardi in astrofisica, in cui ha avuto una discussione interattiva con gli studenti circa diverse ricerche attive in questo campo.
Per leggere la notizia sulla newsletter della IUT:
https://iscoweb.iut.ac.ir/sites/iscoweb/files/u758/nl-no.18-_may_2021.pdf

13. Pubblicazioni recenti

Becerra-Vergara, E. A.; Argüelles, C. R.; Krut, A.; Rueda, J. A.; Ruffini, R., Hinting a dark matter nature of Sgr A* via the S-stars, to be published in Monthly Notices of the Royal Astronomical Society Letters.
The motion data of the S-stars around the Galactic center gathered in the last 28 yr imply that Sgr A* hosts a supermassive compact object of about 4×10⁶ M_⊙, a result awarded with the Nobel Prize in Physics 2020. A non-rotating black hole (BH) nature of Sgr A* has been uncritically adopted since the S-star orbits agree with Schwarzschild geometry geodesics. The orbit of S2 has served as a test of General Relativity predictions such as the gravitational redshift and the relativistic precession. The central BH model is, however, challenged by the G2 post-peripassage motion and by the lack of observations on event-horizon-scale distances robustly pointing to its univocal presence. We have recently shown that the S2 and G2 astrometry data are better fitted by geodesics in the spacetime of a self-gravitating dark matter (DM) core - halo distribution of 56 keV-fermions, "darkinos", which also explains the outer halo Galactic rotation curves. This Letter confirms and extends this conclusion using the astrometry data of the 17 best-resolved S-stars, thereby strengthening the alternative nature of Sgr A* as a dense core of darkinos.
ArXiv: https://arxiv.org/abs/2105.06301


J. A. Rueda and R. Ruffini, The Quantum Emission of an Alive Black Hole, Third Award-Winning Essay of the "Gravity Research Foundation 2021 awards for essays on Gravitation", to be published in a special issue of IJMPD in October 2021.
A long march of fifty years of successive theoretical progress and new physics discovered using observations of gamma-ray bursts, has finally led to the formulation of an efficient mechanism able to extract the rotational energy of a Kerr black hole to power these most energetic astrophysical sources and active galactic nuclei. We here present the salient features of this long-sought mechanism, based on gravito-electrodynamics, and which represents an authentic shift of paradigm of black holes as forever "alive" astrophysical objects.
GRF Award Announcement website: https://www.gravityresearchfoundation.org/announcement
ArXiv: https://arxiv.org/abs/2105.07890


Moradi, R.; Rueda, J. A.; Ruffini, R.; Wang, Y., The newborn black hole in GRB 191014C proves that it is alive, to be published in A&A on May 27, 2021.
A multi-decade theoretical effort has been devoted to finding an efficient mechanism to use the rotational and electrodynamical extractable energy of a Kerr-Newman black hole (BH), to power the most energetic astrophysical sources such as gamma-ray bursts (GRBs) and active galactic nuclei (AGN). We show an efficient general relativistic electrodynamical process which occurs in the "inner engine" of a binary driven hypernova (BdHN). The inner engine is composed of a rotating Kerr BH of mass M and dimensionless spin parameter α, a magnetic field of strength B₀ aligned and parallel to the rotation axis, and a very low-density ionized plasma. Here, we show that the gravitomagnetic interaction between the BH and the magnetic field induces an electric field that accelerates electrons and protons from the environment to ultrarelativistic energies emitting synchrotron radiation. We show that in GRB 190114C the BH of mass M=4.4 M_⊙, α=0.4, and B₀≈4×10¹⁰ G can lead to a high-energy (≳GeV) luminosity of 10⁵¹ erg s⁻¹. The inner engine parameters are determined by requiring 1) that the BH extractable energy explains the GeV and ultrahigh-energy emission energetics, 2) that the emitted photons are not subjected to magnetic-pair production, and 3) that the synchrotron radiation timescale agrees with the observed high-energy timescale. We find for GRB 190114C a clear jetted emission of GeV energies with a semi-aperture angle of approximately 60° with respect to the BH rotation axis.
A&A forthcoming article: https://doi.org/10.1051/0004-6361/201937135
ArXiv: https://arxiv.org/abs/1911.07552


Sahakyan, N., Modeling the broadband emission of 3C 454.3, published in Monthly Notices of the Royal Astronomical Society on April 22, 2021.
The results of a long-term multiwavelength study of the powerful flat spectrum radio quasar 3C 454.3 using Fermi-LAT and Swift XRT/UVOT data are reported. In the γ-ray band, Fermi-LAT observations show several major flares when the source flux was >10⁻⁵ photon cm⁻² s⁻¹; the peak γ-ray flux above 141.6 MeV, (9.22±1.96) × 10⁻⁵ photon cm⁻² s⁻¹ observed on MJD 55519.33, corresponds to 2.15×10⁵⁰ erg s⁻¹ isotropic γ-ray luminosity. The analysis of Swift XRT and UVOT data revealed a flux increase, although with smaller amplitudes, also in the X-ray and optical/UV bands. The X-ray emission of 3C 454.3 is with a hard spectral index of Γ_X = 1.16 -1.75, and the flux in the flaring states increased up to (1.80±0.18) × 10⁻¹⁰erg cm⁻² s⁻¹. Through combining the analysed data, it was possible to assemble 362 high-quality and quasi-simultaneous spectral energy distributions of 3C 454.3 in 2008 -2018, which all were modelled within a one-zone leptonic scenario assuming the emission region is within the broad-line region, involving synchrotron, synchrotron self-Compton, and external Compton mechanisms. Such an extensive modelling is the key for constraining the underlying emission mechanisms in the 3C 454.3 jet and allows to derive the physical parameters of the jet and investigate their evolution in time. The modelling suggests that during the flares, along with the variation of emitting electron parameters, the Doppler boosting factor increased substantially, implying that the emission in these periods has most likely originated in a faster moving region.
DOI: https://doi.org/10.1093/mnras/stab1135


MAGIC collaboration, H.E.S.S. and MAGIC observations of a sudden cessation of a very-high-energy γ-ray flare in PKS 1510‒089 in May 2016, Astronomy & Astrophysics, Volume 648, id.A23, 22 pp.
The flat spectrum radio quasar (FSRQ) PKS 1510−089 is known for its complex multiwavelength behaviour and it is one of only a few FSRQs detected in very-high-energy (VHE, E > 100 GeV) γ rays. The VHE γ-ray observations with H.E.S.S. and MAGIC in late May and early June 2016 resulted in the detection of an unprecedented flare, which revealed, for the first time, VHE γ-ray intranight variability for this source. While a common variability timescale of 1.5 h has been found, there is a significant deviation near the end of the flare, with a timescale of ∼20 min marking the cessation of the event. The peak flux is nearly two orders of magnitude above the low-level emission. For the first time, a curvature was detected in the VHE γ-ray spectrum of PKS 1510 -089, which can be fully explained by the absorption on the part of the extragalactic background light. Optical R-band observations with ATOM revealed a counterpart of the γ-ray flare, even though the detailed flux evolution differs from the VHE γ-ray light curve. Interestingly, a steep flux decrease was observed at the same time as the cessation of the VHE γ-ray flare. In the high-energy (HE, E >  100 MeV) γ-ray band, only a moderate flux increase was observed with Fermi-LAT, while the HE γ-ray spectrum significantly hardens up to a photon index of 1.6. A search for broad-line region (BLR) absorption features in the γ-ray spectrum indicates that the emission region is located outside of the BLR. Radio very-long-baseline interferometry observations reveal a fast-moving knot interacting with a standing jet feature around the time of the flare. As the standing feature is located ∼50 pc from the black hole, the emission region of the flare may have been located at a significant distance from the black hole. If this is indeed a true correlation, the VHE γ rays must have been produced far down in the jet, where turbulent plasma crosses a standing shock.
DOI: https://doi.org/10.1051/0004-6361/202038949


MAGIC collaboration, Broadband Multi-wavelength Properties of M87 during the 2017 Event Horizon Telescope Campaign, The Astrophysical Journal Letters, Volume 911, Issue 1, id.L11, 43 pp.
In 2017, the Event Horizon Telescope (EHT) Collaboration succeeded in capturing the first direct image of the center of the M87 galaxy. The asymmetric ring morphology and size are consistent with theoretical expectations for a weakly accreting supermassive black hole of mass ~6.5 × 10⁹ M_⊙. The EHTC also partnered with several international facilities in space and on the ground, to arrange an extensive, quasi-simultaneous multi-wavelength campaign. This Letter presents the results and analysis of this campaign, as well as the multi-wavelength data as a legacy data repository. We captured M87 in a historically low state, and the core flux dominates over HST-1 at high energies, making it possible to combine core flux constraints with the more spatially precise very long baseline interferometry data. We present the most complete simultaneous multi-wavelength spectrum of the active nucleus to date, and discuss the complexity and caveats of combining data from different spatial scales into one broadband spectrum. We apply two heuristic, isotropic leptonic single-zone models to provide insight into the basic source properties, but conclude that a structured jet is necessary to explain M87's spectrum. We can exclude that the simultaneous γ-ray emission is produced via inverse Compton emission in the same region producing the EHT mm-band emission, and further conclude that the γ-rays can only be produced in the inner jets (inward of HST-1) if there are strongly particle-dominated regions. Direct synchrotron emission from accelerated protons and secondaries cannot yet be excluded.
DOI: https://doi.org/10.3847/2041-8213/abef71


Li-Yang Gao, Ze-Wei Zhao, She-Sheng Xue, Xin Zhang, Relieving the H0 tension with a new interacting dark energy model, accepted for publication in JCAP.
We investigate an extended cosmological model motivated by the asymptotic safety of gravitational field theory, in which the matter and radiation densities and the cosmological constant receive a correction parametrized by the parameters δG and δΛ, leading to that both the evolutions of the matter and radiation densities and the cosmological constant slightly deviate from the standard forms. Here we explain this model as a scenario of vacuum energy interacting with matter and radiation. We consider two cases of the model: {(i) ΛCDM with one additional free parameter δG, with δG and δΛ related by a low-redshift limit relation and (ii) e ΛCDM with two additional free parameters δG and δΛ that are independent of each other.} We use two data combinations, CMB+BAO+SN (CBS) and CMB+BAO+SN+H₀ (CBSH), to constrain the models. We find that, in the case of using the CBS data, neither Λ˜CDM nor eΛCDM can effectively alleviate the H0 tension. However, it is found that using the CBSH data the H₀ tension can be greatly relieved by the models. In particular, in the case of eΛCDM, the H₀ tension can be resolved to 0.71σ. We conclude that as an interacting dark energy model, Λ˜CDM is much better than Λ(t)CDM in the sense of both relieving the H₀ tension and fitting to the current observational data.
ArXiv: https://arxiv.org/abs/2101.10714