arXiv subjects

Vincent Tatischeff

Publications and source records attributed to Vincent Tatischeff.

At least 19 recordsLinked to original sources

arXiv2026

Gamma-Ray Burst Polarimetry with the COMCUBE-S CubeSat Swarm -- Design and Performance Simulations

COMCUBE-S (COMCUBE-S (Compton Telescope CubeSat Swarm) is a proposed mission aimed at understanding the radiation mechanisms of ultra-relativistic jets from Gamma-Ray Bursts (GRBs). It consists of a swarm of 16U CubeSats carrying a state-of-the-art Compton polarimeter and a bismuth germanium oxide (BGO) spectrometer to perform timing, spectroscopic and polarimetric measurements of the prompt emission from GRBs. The mission is currently in a feasibility study phase (Phase A) with the European Space Agency to prepare an in-orbit demonstration. Here, we present the simulation work used to optimise the design and operational concept of the microsatellite constellation, as well as estimate the mission performance in terms of GRB detection rate and polarimetry. We used the MEGAlib software to simulate the response function of the gamma-ray instruments, together with a detailed model for the background particle and radiation fluxes in low-Earth orbit. We also developed a synthetic GRB population model to best estimate the detection rate. These simulations show that COMCUBE-S will detect about 2 GRBs per day, which is significantly higher than that of all past and current GRB missions. Furthermore, simulated performance for linear polarisation measurements shows that COMCUBE-S will be able to uniquely distinguish between competing models of the GRB prompt emission, thereby shedding new light on some of the most fundamental aspects of GRB physics.

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arXiv2026

$γ$-Ray Lines -- Signatures of Nucleosynthesis, Cosmic Rays, Positron Annihilation, and Fundamental Physics

The nuclear $γ$-ray lines in the MeV range of the electromagnetic spectrum hold a vast variety of astrophysical, particle-physical, and fundamental physical information that is otherwise extreme difficult to access. MeV $γ$-ray line observations provide the most direct evidence for ongoing nucleosynthesis in galaxies by measuring freshly produced radioactive isotopes from massive stars, supernovae, classical novae, or binary neutron star mergers. Their flux ratios can determine the low-energy cosmic-ray spectrum in different objects and of the Milky Way as a whole. Different phases of the interstellar medium are traced by hot nucleosynthesis ejecta, cooling positrons, or cosmic-ray interactions with molecular clouds. Positron annihilation itself can be considered as an astrophysical messenger as their production and destruction in typical space environments is inevitable. Finally, as-of-yet unknown signatures from beyond standard model physics might have their elusive imprints in $γ$-ray lines. This Chapter gives an overview of historical $γ$-ray line measurements, newest results, and open questions that may only be solved by a new generation of MeV telescopes.

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arXiv2025

Transient gamma rays from the 2021 outburst of the recurrent nova RS Ophiuchi: the effect of gamma-ray absorption

In 2021, RS Ophiuchi was the first nova to be detected in the very-high-energy (TeV) gamma-ray domain, directly testifying of efficient acceleration of charged particles up to at least the TeV range at the nova shock. Surprisingly, the TeV gamma-ray signal peaks $\sim 2$ days after the GeV signal and the origin of this delay has still not been clearly understood. We investigate the possibility that this delay is due to the effect of gamma-ray absorption resulted from interactions between gamma rays and optical photons copiously emitted during the outburst. We model particle acceleration at a nova shock to obtain the gamma-ray emission produced in interactions between the accelerated particles and the shocked gas. The effect of gamma-ray absorption is then included in details using the radiative transfer equation. We find that this can naturally account for the delay between the peaks of GeV and TeV gamma-ray lightcurves. This result emphasizes the importance of gamma-ray absorption for interpreting gamma-ray observations of novae in the TeV range which, in turn, demonstrates the necessity of a multi-wavelength view for unraveling the underlying physics of particle acceleration in these systems.

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arXiv2024

Hard X-ray and gamma-ray detectors

Space-based astronomy of hard X-rays and gamma rays covers more than seven orders of magnitude in photon energy, from 10 keV to several hundred GeV. Detecting cosmic photons in this energy range is a challenge, due to the relatively low probability of interaction of high-energy photons with matter and the high background noise generated in space detectors by environmental charged particles and radiation. However, the development of new detection technologies is constantly improving the performance of space-based X- and gamma-ray telescopes. This chapter presents the different detectors used in this field of astronomy, their configuration within space telescopes and some proposals for new instruments.

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arXiv2024

Origin of $^{60}$Fe nuclei in cosmic rays: the contribution of local OB associations

The presence of live $^{60}$Fe nuclei (lifetime of 3.8~Myr) in cosmic rays detected by the ACE/CRIS instrument suggests a nearby nucleosynthesis source. $^{60}$Fe is primarily produced in core-collapse supernovae, and we aim to clarify whether the detected $^{60}$Fe nuclei can be associated with a particular local supernova. We consider 25 OB associations and sub-groups located within 1 kpc of the solar system based on recent $Gaia$ census. A model is developed that combines stellar population synthesis within these OB associations, cosmic-ray acceleration within associated superbubbles, and cosmic-ray transport to the solar system. The most critical model parameter impacting $^{60}$Fe cosmic-ray production is the explodability criterion, which determines if a massive star ends its life as a supernova. Our study points to the Sco-Cen OB association as the most probable origin of the observed $^{60}$Fe nuclei, particularly suggesting they were accelerated in the Sco-Cen superbubble by a young supernova aged $\leq500$ kyr with a progenitor mass of approximately $13-20~M_\odot$. A less likely source is the supernova at the origin of the Geminga pulsar 342 kyr ago, if the progenitor originated in the Orion OB1 association. The contribution of local OB associations to the cosmic-ray density of stable $^{56}$Fe is estimated to be around 20\%, with some sensitivity to cosmic ray acceleration efficiency and diffusion coefficient. These findings shed light on the origins of cosmic-ray nuclei, connecting them to nucleosynthesis events within our local cosmic neighborhood.

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arXiv2023

Nova explosions -- The fascinating gamma-ray emitting recurrent nova RS Ophiuchi

Classical and recurrent nova explosions occur on top of white dwarfs accreting H-rich matter from a companion main sequence or red giant star, in a close binary system. In the recent years, since the launch of the Fermi gamma-ray satellite by NASA in 2008, several novae have been detected by Fermi/LAT (LAT: Large Area Telescope) in high-energy (HE) gamma rays, with energies larger than 100 MeV. This emission is known to be related to the acceleration of particles in the internal and/or external shocks occurring early after the thermonuclear nova explosion. However, very-high-energy (VHE) gamma-rays, with energies larger than 100 GeV, produced as a consequence of nova explosions have only been discovered very recently, in the recurrent nova RS Oph, that had an outburst in August 2021. These require the acceleration of protons, and not only of electrons; this was in fact predicted theoretically - based in observations at other wavelengths - in the previous eruption of RS Oph, in 2006, but has not been confirmed observationally until now. We review the origin of the different types of gamma-ray emission in novae and highlight the relevance of the recent VHE gamma-ray emission discoveries for the nova theory, mainly in the field of the mass ejection and the associated particle (electrons and protons) acceleration processes.

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arXiv2022

Orbits and background of gamma-ray space instruments

Gamma-ray telescopes in space are bombarded by large fluxes of charged particles, photons and secondary neutrons. These particles and radiation pose a threat to the nominal operation of satellites and limit the detection sensitivity of gamma-ray instruments. The background noise generated in gamma-ray space detectors by impinging particles is always much higher than the astrophysical signal to be detected. In this chapter, we present the different types of orbits suitable for gamma-ray missions, discussing their advantages and disadvantages, as well as the value of experiments embarked in stratospheric balloons. We then review the physical properties of all the background components in the different orbits and the stratosphere.

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arXiv2022

Cosmic ray production in superbubbles

We compute the production of cosmic rays in the dynamical superbubble produced by a cluster of massive stars. Stellar winds, supernova remnants and turbulence are found to accelerate particles so efficiently that the nonlinear feedback of the particles must be taken into account in order to ensure that the energy balance is not violated. High energy particles do not scatter efficiently on the turbulence and escape quickly after each supernova explosion, which makes both their intensity inside the bubble and injection in the interstellar medium intermittent. On the other hand, the stochastic acceleration of low energy particles hardens the spectra at GeV energies. Because cosmic rays damp the turbulence cascade, this hardening is less pronounced when nonlinearities are taken into account. Nevertheless, spectra with hard components extending up to 1 to 10 GeV and normalised to an energy density of 1 to 100 eV cm$^{-3}$ are found to be typical signatures of cosmic rays produced in superbubbles. Efficient shock reacceleration within compact clusters is further shown to produce hard, slightly concave spectra, while the presence of a magnetised shell is shown to enhance the confinement of cosmic rays in the bubble and therefore the collective plasma effects acting on them. We eventually estimate the overall contribution of superbubbles to the galactic cosmic ray content and show typical gamma-ray spectra expected from hadronic interactions in superbuble shells. In both cases, a qualitative agreement with observations is obtained.

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arXiv2021

Nonlinear particle reacceleration by multiple shocks

When the pressure of particles accelerated at shock waves is no longer negligible compared to the kinetic pressure of the gas, the linear theory of diffusive shock acceleration breaks down. This is expected in particular when the shock sweeps up preexisting cosmic rays, or when multiple shocks reaccelerate successively the same particles. To describe these systems, one has to account for the nonlinear backreaction of the particles on the magnetohydrodynamic flow. Using an up-to-date semi-analytical model of particle reacceleration at nonlinear shocks, we show that the presence of prexisting energetic particles strongly affects the shock profile, in such a way that the reacceleration of non thermal particles or the acceleration of particles from the thermal bath becomes less efficient. We further describe the evolution of the distribution of particles after several shocks and study the properties of the asymptotic solution. We detail the case of identical shocks as well as more realistic scenarios, including the heating of the medium or superbubble environments. When the particles are efficiently confined in the acceleration region, it is generally found that the spectrum converges toward a concave solution after a few tens of shocks, with a spectral index around 3.5 at the highest energy. The postshock cosmic ray pressure reaches an asymptotic value of about 4-5% of the ram pressure of one shock. Most of the shock pressure is transferred to escaping particles.

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arXiv2021

The Origin of Galactic Cosmic Rays as Revealed by their Composition

Galactic cosmic-rays (GCRs) are thought to be accelerated in strong shocks induced by massive star winds and supernova explosions sweeping across the interstellar medium. But the phase of the interstellar medium from which the CRs are extracted has remained elusive until now. Here, we study in detail the GCR source composition deduced from recent measurements by the AMS-02, Voyager 1 and SuperTIGER experiments to obtain information on the composition, ionisation state and dust content of the GCR source reservoirs. We show that the volatile elements of the CR material are mainly accelerated from a plasma of temperature higher than $\sim 2$ MK, which is typical of the hot medium found in galactic superbubbles energised by the activity of massive star winds and supernova explosions. Another GCR component, which is responsible for the overabundance of $^{22}$Ne, most likely arises from acceleration of massive star winds in their termination shocks. From the CR-related $γ$-ray luminosity of the Milky Way, we estimate that the ion acceleration efficiency in both supernova shocks and wind termination shocks is of the order of $10^{-5}$. The GCR source composition also shows evidence for a preferential acceleration of refractory elements contained in interstellar dust. We suggest that the GCR refractories are also produced in superbubbles, from shock acceleration and subsequent sputtering of dust grains continuously incorporated into the hot plasma through thermal evaporation of embedded molecular clouds. Our model explains well the measured abundances of all primary and mostly primary CRs from H to Zr, including the overabundance of $^{22}$Ne.

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arXiv2021

INTEGRAL serendipitous observations of solar and terrestrial X-rays and gamma rays

ESA's INTEGRAL space mission has achieved unique results for solar and terrestrial physics, although spacecraft operations nominally excluded the possibility to point at the Sun or the Earth. The Earth avoidance was, however, exceptionally relaxed for special occultation observations of the Cosmic X-ray Background (CXB), which on some occasions allowed the detection of strong X-ray auroral emission. In addition, the most intense solar flares can be bright enough to be detectable from outside the field of view of the main instruments. This article presents for the first time the auroral observations by INTEGRAL and reviews earlier studies of the most intense solar flares. We end by briefly summarising the studies of the Earth's radiation belts, which can be considered as another topic of serendipitous science with INTEGRAL.

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arXiv2021

Gamma-ray Astrophysics in the MeV Range: the ASTROGAM Concept and Beyond

The energy range between about 100 keV and 1 GeV is of interest for a vast class of astrophysical topics. In particular, (1) it is the missing ingredient for understanding extreme processes in the multi-messenger era; (2) it allows localizing cosmic-ray interactions with background material and radiation in the Universe, and spotting the reprocessing of these particles; (3) last but not least, gamma-ray emission lines trace the formation of elements in the Galaxy and beyond. In addition, studying the still largely unexplored MeV domain of astronomy would provide for a rich observatory science, including the study of compact objects, solar- and Earth-science, as well as fundamental physics. The technological development of silicon microstrip detectors makes it possible now to detect MeV photons in space with high efficiency and low background. During the last decade, a concept of detector ("ASTROGAM") has been proposed to fulfil these goals, based on a silicon hodoscope, a 3D position-sensitive calorimeter, and an anticoincidence detector. In this paper we stress the importance of a medium size (M-class) space mission, dubbed "ASTROMEV", to fulfil these objectives.

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arXiv2020

Time-dependent high-energy gamma-ray signal from accelerated particles in core-collapse supernovae: the case of SN 1993J

Some core-collapse supernovae are likely to be efficient cosmic-ray accelerators up to the PeV range, and therefore, to potentially play an important role in the overall Galactic cosmic-ray population. The TeV gamma-ray domain can be used to study particle acceleration in the multi-TeV and PeV range. This motivates the study of the detectability of such supernovae by current and future gamma-ray facilities. The gamma-ray emission of core-collapse supernovae strongly depends on the level of the two-photon annihilation process: high-energy gamma-ray photons emitted at the expanding shock wave following the supernova explosion can interact with soft photons from the supernova photosphere through the pair production channel, thereby strongly suppressing the flux of gamma rays leaving the system. In the case of SN 1993J, whose photospheric and shock-related parameters are well measured, we calculate the temporal evolution of the expected gamma-ray attenuation by accounting for the temporal and geometrical effects. We find the attenuation to be of about $10$ orders of magnitude in the first few days after the SN explosion. The probability of detection of a supernova similar to SN 1993J with the Cherenkov Telescope Array is highest if observations are performed either earlier than 1 day, or later than 10 days after the explosion, when the gamma-ray attenuation decreases to about $2$ orders of magnitude.

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arXiv2020

Particle acceleration at colliding shock waves

We model the diffusive shock acceleration of particles in a system of two colliding shock waves and present a method to solve the time-dependent problem analytically in the test-particle approximation and high energy limit. In particular, we show that in this limit the problem can be analysed with the help of a self-similar solution. While a number of recent works predict hard ($E^{-1}$) spectra for the accelerated particles in the stationary limit, or the appearance of spectral breaks, we found instead that the spectrum of accelerated particles in a time-dependent collision follows quite closely the canonical $E^{-2}$ prediction of diffusive shock acceleration at a single shock, except at the highest energy, where a hardening appears, originating a bumpy feature just before the exponential cutoff. We also investigated the effect of the reacceleration of pre-existing cosmic rays by a system of two shocks, and found that under certain conditions spectral features can appear in the cutoff region. Finally, the mathematical methods presented here are very general and could be easily applied to a variety of astrophysical situations, including for instance standing shocks in accretion flows, diverging shocks, backward collisions of a slow shock by a faster shock, and wind-wind or shock-wind collisions.

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arXiv2020

Development of an advanced Compton telescope for MeV-range gamma-ray astronomy

An advanced Compton telescope appears to be the best instrument concept for the next generation gamma-ray space observatory in the MeV range. A first prototype of advanced Compton telescope is being developed to match the constraints of a nano satellite mission, with the scientific objective of measuring gamma-ray burst prompt emission polarization. Our instrumental developments for this project are focusing on the position-sensitive calorimeter module, made of a monolithic inorganic CeBr$_3$ scintillator read by a pixelated photodetector. 3D position reconstruction is obtained by deep-learning algorithms that have been optimized down to an uncertainty of 2 mm for each spatial direction.

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arXiv2019

Cosmic Rays and Interstellar Medium with Gamma-Ray Observations at MeV Energies

Latest precise cosmic-ray (CR) measurements and present gamma-ray observations have started challenging our understanding of CR transport and interaction in the Galaxy. Moreover, because the density of CRs is similar to the density of the magnetic field, gas, and starlight in the interstellar medium (ISM), CRs are expected to affect the ISM dynamics, including the physical and chemical processes that determine transport and star formation. In this context, observations of gamma-ray emission at MeV energies produced by the low-energy CRs are very important and urgent. A telescope covering the energy range between ~0.1 MeV and a few GeV with a sensitivity more than an order of magnitude better than previous instruments would allow for the first time to study in detail the low-energy CRs, providing information on their sources, their spectra throughout the Galaxy, their abundances, transport properties, and their role on the evolution of the Galaxy and star formation. Here we discuss the scientific prospects for studies of CRs, ISM (gas, interstellar photons, and magnetic fields) and associated gamma-ray emissions with such an instrument.

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arXiv2018

Core collapse supernovae as Cosmic Ray sources

Core collapse supernovae (CCSNe) produce fast shocks which pervade the dense circum-stellar medium (CSM) of the stellar progenitor. Cosmic rays (CRs) if accelerated at these shocks can induce the growth of electromagnetic fluctuations in the foreshock medium. In this study, using a self-similar description of the shock evolution, we calculate the growth timescales of CR-driven instabilities. We select a sample of nearby core collapse radio supernova of type II and Ib/Ic. From radio data we infer the parameters which enter in the calculation of the instability growth times. We find that extended IIb SNe shocks can trigger fast intra day instabilities, strong magnetic field amplification and CR acceleration. In particular, the non-resonant streaming instability can contribute to about 50\% of the magnetic field intensity deduced from radio data. This results in the acceleration of CRs in the range 1-10 PeV within a few days after the shock breakout. In order to produce strong magnetic field amplification and CR acceleration a fast shocks pervading a dense CSM is necessary. In that aspect IIn supernovæ~are also good candidates. But a detailed modeling of the blast wave dynamics coupled with particle acceleration is mandatory for this class of object before providing any firm conclusions. Finally, we find that the trans-relativistic object SN 2009bb even if it produces more modest magnetic field amplification can accelerate CRs up to 2-3 PeV within 20 days after the outburst.

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arXiv2018

Gamma-Ray Observations of Nova Sgr 2015 No. 2 with INTEGRAL

INTEGRAL observed the nova V5668 Sgr around the time of its optical maximum on March 21, 2015. Studies at UV wavelengths showed spectral lines of freshly produced Be-7. This could be measurable also in gamma-rays at 478 keV from the decay to Li-7. Novae are also expected to synthesise Na-22 which decays to Ne-22, emitting a 1275 keV photon. About one week before the optical maximum, a strong gamma-ray flash on time-scales of hours is expected from short-lived radioactive nuclei, such as N-13 and F-18. These beta-plus-unstable nuclei should yield emission up to 511 keV, but which has never been observed. The spectrometer SPI aboard INTEGRAL pointed towards V5668 by chance. We use these observations to search for possible gamma-ray emission of decaying Be-7, and to directly measure the synthesised mass during explosive burning. We also aim to constrain possible burst-like emission days to weeks before the optical maximum using the SPI anticoincidence shield (ACS). We extract spectral and temporal information to determine the fluxes of gamma-ray lines at 478 keV, 511 keV, and 1275 keV. A measured flux value directly converts into abundances produced by the nova. The SPI-ACS rates are analysed for burst-like emission using a nova model light-curve. For the obtained nova flash candidate events, we discuss possible origins. No significant excess for the expected gamma-ray lines is found. Our upper limits on the synthesised Be-7 and Na-22 mass depend on the uncertainties of the distance to the nova: The Be-7 mass is constrained to less than $4.8\times10^{-9}\,(d/kpc)^2$, and Na-22 to less than $2.4\times10^{-8}\,(d/kpc)^2$ solar masses. For the Be-7 mass estimate from UV studies, the distance to V5668 Sgr must be larger than 1.2 kpc. During three weeks before the optical maximum, we find 23 burst-like events in the ACS rate, of which six could possibly be associated with V5668 Sgr.

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