ICRANet Newsletter

ICRANet Newsletter
October/November 2020

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SUMMARY
1. Open Universe survey of Swift-XRT GRB fields: Flux-limited sample of HBL blazars
2. Numerical scheme for evaluating the collision integrals for triple interactions in relativistic plasma
3. The Extreme Red Excess in Blazar Ultraviolet Broad Emission Lines
4. Congratulations to Prof. Carlos Arguelles, ICRANet collaborator, awarded the Prize Estímulo in Astronomy by the National Academy of Science of Argentina, October 2020
5. The Renewal of the collaboration agreement ICRANet – ITA, September 2020
6. Renewal of the collaboration agreement ICRANet – Campus Bio-medico University of Rome, October 2020
7. ICRANet-Armenia received additional funding from the Ministry of Education, Science, Culture and Sports of Armenia, October 19, 2020
8. European Researchers’ Night 2020
9. Recent publications

1. Open Universe survey of Swift-XRT GRB fields:
Flux-limited sample of HBL blazars

A new paper co-authored by Paolo Giommi and another 24 co-authors with this title has been published on the 13 of October 2020 in Astronomy and Astrophysics journal.


Open Universe is an initiative under the auspices of the United Nations Office for Outer Space Affairs (UNOOSA) with the objective of making astronomy and space science data more openly available, easily discoverable, free of bureaucratic, administrative or technical barriers, and therefore usable by the widest possible community, from professional researchers to all people interested in space science and astronomy, including students, non-professionals, and amateur scholars of the subject.
In this new paper Giommi et al. present for the first time an X-ray survey that is large and deep enough to allow the selection of a statistically complete flux-limited sample of blazars of this type with radio flux-densities .20 mJy. This work also demonstrates that complex data analysis projects can in principle be carried out by non-experts, one of the main goals of the United Nations Open Universe initiative.
The deepest fields, obtained investing several megaseconds of exposure time of the largest operating X-ray observatories like Chandra and XMM, reach sensitivities well below 10^-15 erg cm^-2 s^-1 but cover very small areas of sky. The Rosat All Sky Survey still the only available all sky survey, is relatively shallow, only reaching a flux limit of a few times 10^-13 erg cm^-2 s^-1 in the 0.5–2.0 keV band. Therefore, as can be seen from Fig. 1, the Open Universe survey of Swift-XRT GRB fields (OUSXG) represented by the dashed green line is currently the largest survey available.

Link to the paper https://doi.org/10.1051/0004-6361/202037921

2. Numerical scheme for evaluating the collision integrals for triple interactions in relativistic plasma

A new paper co-authored by Mikalai Prakapenia, Ivan Siutsou and Gregory Vereshchagin with this title has been published in November issue of the journal Physics of Plasmas.

Fig. 2. Photon emissivity is presented as a function of temperature with fixed energy 0.05 kT/mec2.

Relativistic plasmas are of interest in astrophysics and in laboratory experiments. Kinetics of relativistic plasma has been studied in ICRANet in the last decade with application to thermalization of electron-positron-photon plasma in gamma-ray bursts. In particular, the role of direct and inverse triple processes has been clarified in thermalization process. The new paper [1] co-authored by Mikalai Prakapenia (PhD student of the Belarusian State University and IRAP PhD program), Ivan Siutsou (researcher at the B.I. Stepanov Institute of Physics of the National Academy of Sciences of Belarus) and Gregory Vereshchagin (ICRANet professor) deals with first principles calculation of collision integrals for three particle processes in relativistic plasmas. Existing numerical codes treated these processes approximately, using thermal rates or various approximations such as nonrelativistic/ultrarelativistic or soft/hard photon limits. The new kinetic code developed in ICRANet [2] performs direct numerical integration of matrix elements of Quantum Electrodynamics over the phase space of interacting particles. In 2018 a numerical scheme for binary processes was developed [3]. The code takes into account quantum statistics of particles, so that quantum condensation of photons [4] as well as Pauli blocking in degenerate electron-positron plasma [5] can be studied as well. This year a new scheme was proposed and successfully implemented for calculation of triple interactions.

The results were confronted with known analytic expressions obtained assuming thermal equilibrium. As an example, in Figure 1 photon emissivity is presented as a function of temperature with fixed energy 0.05 kT/m_ec² is presented (from top to bottom) for double Compton scattering, relativistic bremsstrahlung, three-photon annihilation, and radiative pair production. Overall, excellent agreement with known expressions was found.
This work was supported within the joint BRFFR-ICRANet-2018 funding programme under Grant No. F19ICR-001.
Mikalai Prakapenia defended his PhD thesis under the supervision of Prof. Vereshchagin on 27 of November 2020 in the National Academy of Sciences of Belarus.
The ICRANet seminar with discussion of recent results obtained in this work will be organized on the 10 of December 2020 by ICRANet via the Gotomeeting platform. The link to follow this meeting on the ICRANet Youtube channel event will be sent separately.

Links to the paper:
Journal: https://aip.scitation.org/doi/10.1063/5.0022931
Arxiv: https://arxiv.org/abs/2010.14348

References:
[1] M. A. Prakapenia, I. A. Siutsou and G. V. Vereshchagin, Numerical scheme for evaluating the collision integrals for triple interactions in relativistic plasma, Phys. Plasmas 27, 113302 (2020) pp. 1-10.
[2] G.V. Vereshchagin and A.G. Aksenov, Relativistic Kinetic Theory With Applications in Astrophysics and Cosmology, Cambridge University Press, 2017.
[3] M. A. Prakapenia, I. A. Siutsou, and G. V. Vereshchagin, Numerical scheme for treatment of Uehling–Uhlenbeck equation for two-particle interactions in relativistic plasma, Journal of Computational Physics, Volume 373 (2018), pp. 533–544.
[4] M. A. Prakapenia and G. V. Vereshchagin, Bose-Einstein condensation in relativistic plasma, EPL 128 (2019) 50002.
[5] M. A. Prakapenia and G. V. Vereshchagin, Pauli blocking effects in thermalization of relativistic plasma, Phys. Lett. A, Vol. 384 (2020) 126679.

3. The Extreme Red Excess in Blazar Ultraviolet Broad Emission Lines

The new article coauthored by Brian Punsly, Paola Marziani, Marco Berton and Preeti Kharb “The Extreme Red Excess in Blazar Ultraviolet Broad Emission Lines”, has been published in The Astrophysical Journal, Volume 903, Number 44 on October 30, 2020.


We present a study of quasars with very redward asymmetric (RA) ultraviolet (UV) broad emission lines (BELs). An excess of redshifted emission has been previously shown to occur in the BELs of radio-loud quasars and is most extreme in certain blazars. Paradoxically, blazars are objects that are characterized by a highly relativistic blueshifted outflow toward Earth. We show that the red emitting gas, see Fig. 3, resides in a very broad component (VBC) that is typical of Population B quasars that are defined by a wide Hβ BEL profile. Empirically, we find that RA BEL blazars have both low Eddington rates (≤ 1%) and an inordinately large (order unity) ratio of long-term time-averaged jet power to accretion luminosity. The latter circumstance has been previously shown to be associated with a depressed extreme UV ionizing continuum. Both properties conspire to produce a low flux of ionizing photons, two orders of magnitude less than typical Population B quasars. We use CLOUDY models to demonstrate that a weak ionizing flux is required for gas near the central black hole to be optimally ionized to radiate BELs with high efficiency (most quasars overionize nearby gas, resulting in low radiative efficiency). The large gravitational redshift and transverse Doppler shift result in a VBC that is redshifted by ~2000–5000 km s^-1 with a correspondingly large line width. The RA BELs result from an enhanced efficiency (relative to typical Population B quasars) to produce a luminous, redshifted VBC near the central black hole.

The article is available here: https://doi.org/10.3847/1538-4357/abb950
ArXiv e-print: https://arxiv.org/abs/2009.05082

4. Congratulations to Prof. Carlos Arguelles, ICRANet collaborator, awarded the Prize Estímulo in Astronomy by the National Academy of Science of Argentina, October 2020

It is our pleasure to announce that on October 5, 2020, Prof. Carlos Arguelles, ICRANet collaborator, was awarded the Prize Estimulo in Astronomy “Dr. Jorge Sahade” by the National Academy of Science of Argentina. Prof. Arguelles is a researchers at CONICET La Plata and at the Department of Astronomical Sciences and Geophysics of the Universidad Nacional de La Plata (FCAG, UNLP) in Buenos Aires, Argentina. The prize has been officially assigned virtually on November 2020. He received this prize for his studies on the Dark Matter and for a recent work presenting an alternative mathematical model which questioned the existence of a Black Hole at the centre of the Milky Way. Time ago, Prof. Arguelles has also been awarded by the Gravity Research Foundation (GRF) with a prize which has previously been assigned, starting from 1949, to eminent scientists such as, for example, Stephen Hawking.

For the news (in Spanish):
https://laplata.conicet.gov.ar/la-academia-nacional-de-ciencias-exactas-fisicas-y-naturales-distingue-a-un-investigador-del-conicet-la-plata/

5. Renewal of the collaboration agreement ICRANet – ITA, September 2020

On November 2020 ICRANet has received the official confirmation that the agreement between ICRANet and ITA was renewed. The renewal was signed on September 22, 2020 by Prof. Dr. Anderson Ribeiro Correia (Rector of ITA) and by Prof. Remo Ruffini (Director of ICRANet), and will be valid for 3 years starting from April 2020. 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 joint collaboration of faculty members, researchers, post-doctorate fellows and students; the organization of training and teaching courses, seminars, conferences, workshops or short courses, and the joint work on scientific publications.

For the text of the agreement:
http://www.icranet.org/index.php?option=com_content&task=view&id=844.

6. Renewal of the collaboration agreement ICRANet – Campus Bio-medico University of Rome, October 2020

On October 2020, the agreement between ICRANet and the Campus Bio-medico University of Rome has been renewed. This agreement will be valid for 2 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 joint collaboration of faculty members, researchers, post-doctorate fellows and students; the organization of training and teaching courses, seminars, conferences, workshops or short courses, and the joint work on scientific publications.

For the text of the agreement:
http://www.icranet.org/index.php?option=com_content&task=view&id=1219.

7. ICRANet-Armenia received additional funding from the Ministry of Education, Science, Culture and Sports of Armenia, October 19, 2020

On October 19, 2020, the Ministry of Education, Science, Culture and Sports of the Republic of Armenia announced the results of the grant application. We are happy to announce that the ICRANet-Armenia center has been included among the 11 scientific groups that would receive a grant of about 100.000 € for three years (so, around 33.000 € per year). The grant will be used to strengthen the scientific groups, e.g., update the infrastructure, host the international collaborators, etc.

8. European Researchers’ Night 2020

This year, due to the spreading on the Covid-19 pandemic, the European Researchers Night was held virtually on November 27, 2020. On that occasion, Prof. Costantino Sigismondi, ICRANet collaborator and chair of the event, organized a virtual meeting as well as a podcast meeting in order to create a nice occasion for discussion among students and researchers. This event attracted a lot of students and professors, as every year, and offered them a unique opportunity to take part in science activities aiming to showcase both the fascination of research as a career and its significant societal impact.
The virtual meeting started at 4:30 PM on Friday November 27, with the opening remarks made by Prof. Sigismondi and went on with presentations on the “refraction at the sunrise and sunset from the Adriatic Sea to the Tyrrhenian Sea”, on “The Sun in the sign of the Sagittarius and in the Scorpio constellation” and on “Betelgeuse, the dimming supergiant”. Then was the turn of Prof. Gregory Vereshchagin, ICRANet Faculty Professor, which gave a lecture on the Nobel Prize for Physics in 2020. This theoretical section was also integrated with the podcast materials prepared by Prof. Sigismondi as well as by Prof. Paolo Ochner (University of Padova), available on the webpage of the meeting: http://www.icranet.org/index.php?option=com_content&task=view&id=1346.
Following these discussions, 4 students from Liceo Scientifico Galileo Galilei of Pescara and from the IIS Federio Caffé of Rome, have been officially awarded the prize Mersenne, sponsored by the IAU C3 Commission for History and Astronomy of the International Union for Astronomy.
For the 2019 edition of the Prize, Roberta Chiacchiaretta (Liceo Scientifico Galileo Galilei of Pescara) and Gabriele Becagli (IIS Federio Caffé of Rome) have been awarded.
For the 2020 edition of the Prize, Francesco Di Iacovo (IIS Federio Caffé of Rome) and Christian Genghini (IIS Federio Caffé of Rome) have been awarded.
The program of the event and all the relevant podcast materials, can be found at the following link: http://www.icranet.org/index.php?option=com_content&task=view&id=1346.

9. Recent publications

P. Giommi, Y. L. Chang, S. Turriziani, T. Glauch, C. Leto, F. Verrecchia, P. Padovani, A. V. Penacchioni, F. Arneodo, U. Barres de Almeida, C. H. Brandt, M. Capalbi, O. Civitarese, V. D’Elia, A. Di Giovanni, M. De Angelis, J. Del Rio Vera, S. Di Pippo, R. Middei, M. Perri, A. M. T. Pollock, S. Puccetti, N. Ricard, R. Ruffini and N. Sahakyan, Open Universe survey of Swift-XRT GRB fields: Flux-limited sample of HBL blazars, published in A&A 642, A141 (2020).
Aims. The sample of serendipitous sources detected in all Swift-XRT images pointing at gamma ray bursts (GRBs) constitutes the largest existing medium-deep survey of the X-ray sky. To build such dataset we analysed all Swift X-ray images centred on GRBs and observed over a period of 15 years using automatic tools that do not require any expertise in X-ray astronomy. Besides presenting a new large X-ray survey and a complete sample of blazars, this work aims to be a step in the direction of achieving the ultimate goal of the Open Universe Initiative, which is to enable non-expert people to benefit fully from space science data, possibly extending the potential for scientific discovery, which is currently confined within a small number of highly specialised teams, to a much larger population.
Methods. We used the Swift_deepsky Docker container encapsulated pipeline to build the largest existing flux-limited and unbiased sample of serendipitous X-ray sources. Swift_deepsky runs on any laptop or desktop computer with a modern operating system. The tool automatically downloads the data and the calibration files from the archives, runs the official Swift analysis software, and produces a number of results including images, the list of detected sources, X-ray fluxes, spectral energy distribution data, and spectral slope estimations.
Results. We used our source list to build the LogN-LogS of extra-galactic sources, which perfectly matches that estimated by other satellites. Combining our survey with multi-frequency data, we selected a complete radio-flux-density-limited sample of high energy peaked blazars (HBL). The LogN-LogS built with this data set confirms that previous samples are incomplete below ∼20 mJy.
The article is available here: https://doi.org/10.1051/0004-6361/202037921


M. A. Prakapenia, I. A. Siutsou and G. V. Vereshchagin, Numerical scheme for evaluating the collision integrals for triple interactions in relativistic plasma, published in Physics of Plasmas 27, 113302 (2020).
Binary interactions in relativistic plasma, such as Coulomb and Compton scattering as well as pair creation and annihilation are well known and studied in detail. Triple interactions, namely, relativistic bremsstrahlung, double Compton scattering, radiative pair production, and triple pair production and their inverse processes, are usually considered as emission processes in astrophysical problems, as well as in laboratory plasmas. Their role in plasma kinetics is fundamental [A. G. Aksenov et al., Phys. Rev. Lett. 99, 125003 (2007)]. We present a new conservative scheme for computation of the Uehling–Uhlenbeck collision integral for all triple interactions in relativistic plasma based on direct integration of exact QED matrix elements. Reaction rates for thermal distributions are compared, where possible, with the corresponding analytic expressions, showing good agreement. Our results are relevant for quantitative description of relativistic plasmas out of equilibrium, both under astrophysical and laboratory conditions.
The article is available here: https://aip.scitation.org/doi/10.1063/5.0022931


Sahakyan, N., Israyelyan, D. & Harutyunyan, G., A Multiwavelength Study of Distant Blazar PKS 0537-286, published in Astrophysics (2020).
We report the results of broadband observations of distant blazar PKS 0537-286 (z = 3.1) using data spanning more than ten years from the Fermi Large Area Telescope together with Swift UVOT/XRT archival data taken between 2005 and 2017. In the γ -ray band, the peak flux above 100 MeV, F_γ = (6 23 ± 0 56) ∙ 10^-7 photon cm^-2 s^-1 observed on MJD 57874 within one week, corresponds to L_γ = 2 46 ∙ 10⁴⁹ erg s^-1 isotropic γ -ray luminosity. The Swift XRT data analyses show that the X-ray emission is characterized by a significantly hard photon index, Γ_X-ray ≤ 1.3 , and an X-ray flux of 4 ∙ 10^-12 erg cm^-2 s^-1, which is almost constant over twelve years. The spectral energy distribution is modeled within one-zone leptonic models assuming the emission region is within the broad-line region. The observed X-ray and γ -ray data are modeled as inverse Compton scattering of (i) only synchrotron photons and (ii) synchrotron and external photons on the electron population that produces the radioto-optical emission. The modeling shows that the nonthermal electrons in the jet of PKS 0537-286 have a hard power-law index (<1.9) and that the jet should be particle dominated with a luminosity within 10⁴⁵-10⁴⁶ erg s^-1.
The article is available here: https://doi.org/10.1007/s10511-020-09650-3


MAGIC collaboration, Study of the GeV to TeV morphology of the γ-Cygni SNR (G78.2+2.1) with MAGIC and Fermi-LAT, accepted for publication in A&A in October 2020.
Context. Diffusive shock acceleration (DSA) is the most promising mechanism to accelerate Galactic cosmic rays (CRs) in the shocks of supernova remnants (SNRs). The turbulence upstream is supposedly generated by the CRs, but this process is not well understood. The dominant mechanism may depend on the evolutionary state of the shock and can be studied via the CRs escaping upstream into the interstellar medium (ISM). Aims. Previous observations of the γ-Cygni SNR showed a difference in morphology between GeV and TeV energies. Since this SNR has the right age and is at the evolutionary stage for a significant fraction of CRs to escape, we aim to understand γ-ray emission in the vicinity of the γ-Cygni SNR. Methods. We observed the region of the γ-Cygni SNR with the MAGIC Imaging Atmospheric Cherenkov telescopes between May 2015 and September 2017 recording 87 h of good-quality data. Additionally we analysed Fermi-LAT data to study the energy dependence of the morphology as well as the energy spectrum in the GeV to TeV range. The energy spectra and morphology were compared against theoretical predictions, which include a detailed derivation of the CR escape process and their γ-ray generation. Results. The MAGIC and Fermi-LAT data allowed us to identify three emission regions, which can be associated with the SNR and dominate at different energies. Our hadronic emission model accounts well for the morphology and energy spectrum of all source components. It constrains the time-dependence of the maximum energy of the CRs at the shock, the time-dependence of the level of turbulence, and the diffusion coefficient immediately outside the SNR shock. While in agreement with the standard picture of DSA, the time-dependence of the maximum energy was found to be steeper than predicted and the level of turbulence was found to change over the lifetime of the SNR.
The article is available here: https://arxiv.org/abs/2010.15854


MAGIC collaboration, Detection of the Geminga pulsar with MAGIC hints at a power-law tail emission beyond 15 GeV, published in A&A 643, L14 (2020).
We report the detection of pulsed gamma-ray emission from the Geminga pulsar (PSR J0633+1746) between 15 GeV and 75 GeV. This is the first time a middle-aged pulsar has been detected up to these energies. Observations were carried out with the MAGIC telescopes between 2017 and 2019 using the low-energy threshold Sum-Trigger-II system. After quality selection cuts, ∼80 h of observational data were used for this analysis. To compare with the emission at lower energies below the sensitivity range of MAGIC, 11 years of Fermi-LAT data above 100 MeV were also analysed. From the two pulses per rotation seen by Fermi-LAT, only the second one, P2, is detected in the MAGIC energy range, with a significance of 6.3σ. The spectrum measured by MAGIC is well-represented by a simple power law of spectral index Γ = 5.62 ± 0.54, which smoothly extends the Fermi-LAT spectrum. A joint fit to MAGIC and Fermi-LAT data rules out the existence of a sub-exponential cut-off in the combined energy range at the 3.6σ significance level. The power-law tail emission detected by MAGIC is interpreted as the transition from curvature radiation to Inverse Compton Scattering of particles accelerated in the northern outer gap.
The article is available here: https://doi.org/10.1051/0004-6361/202039131


Soroush Shakeri, Fazlollah Hajkarim, She-Sheng Xue, Shedding New Light on Sterile Neutrinos from XENON1T Experiment, accepted for publication in JHEP in November 2020.
The XENON1T collaboration recently reported the excess of events from recoil electrons, possibly giving an insight into new area beyond the Standard Model (SM) of particle physics. We try to explain this excess by considering effective interactions between the sterile neutrinos and the SM particles. In this paper, we present an effective model based on one-particle-irreducible interaction vertices at low energies that are induced from the SM gauge symmetric four-fermion operators at high energies. The effective interaction strength is constrained by the SM precision measurements, astrophysical and cosmological observations. We introduce a novel effective electromagnetic interaction between sterile neutrinos and SM neutrinos, which can successfully explain the XENON1T event rate through inelastic scattering of the sterile neutrino dark matter from Xenon electrons. We find that sterile neutrinos with masses around 90 keV and specific effective coupling can fit well with the XENON1T data where the best fit points preserving DM constraints and possibly describe the anomalies in other experiments.
The article is available here: https://arxiv.org/abs/2008.05029