As smaller analogs of Active Galactic Nuclei (AGN), X-ray Binaries (XRBs) are also capable of launching jets that accelerate particles to high energies. In this work, we reexamine XRB jets as potential sources of high-energy cosmic rays (CRs) and explore whether they could provide a significant second Galactic component to the CR spectrum. In the most intriguing scenario, XRB-CRs could dominate the observed spectrum above the so-called "knee" feature at $\sim 3 \times 10^{15}$ eV, offering an explanation for several key issues in this transition zone from Galactic to extragalactic CRs. We discuss how such a scenario could be probed in the near future via multi-messenger observations of XRB jets, as well as diffuse Galactic neutrino flux measurements.
Cosmic ray interactions that produce high-energy neutrinos also inevitably generate high-energy gamma rays, which finally contribute to the diffuse high-energy gamma-ray background after they escape the sources. It was recently found that, the high flux of neutrinos at $\sim30$ TeV detected by IceCube lead to a cumulative gamma-ray flux exceeding the Fermi isotropic gamma-ray background at 10-100 GeV, implying that the neutrinos are produced by hidden sources of cosmic rays, where GeV-TeV gamma-rays are not transparent. Here we suggest that relativistic jets in tidal disruption events (TDEs) o…
Observations of the spectacular, blazar-like tidal disruption event (TDE) candidates Swift J1644+57 and J2058+05 show that the conditions required for accelerating protons to 10^{20} eV appear to be realized in the outer jet, and possibly in the inner jet as well. Direct and indirect estimates of the rate of jetted-TDEs, and of the energy they inject, are compatible with the observed flux of ultra-high energy cosmic rays (UHECRs) and the abundance of presently contributing sources. Thus TDE-jets can be a major source of UHECRs, even compabile with a pure proton composition.
Active Galactic Nuclei (AGN) and their relativistic jets are believed to be potential sites of ultra-high-energy (UHE) cosmic ray acceleration. This paper reviews basic observational findings as well as requirements on source energetics, and then discusses the relevance of different acceleration sites and mechanisms, such as black hole gap, shock in back-flows or jet shear acceleration. When put in context, the result suggests that Fermi-type particle acceleration at trans-relativistic shocks and/or in shearing, relativistic flows offers the most promising framework for UHECR production in AGN…
In stark contrast to their laboratory and terrestrial counterparts, the cosmic jets appear to be very stable. We propose that the reason behind this remarkable property is the loss of causal connectivity across these jets, caused by their rapid expansion in response to fast decline of external pressure with the distance from the "jet engine". In atmospheres with power-law pressure distribution, the total loss of causal connectivity occurs, when the power index k>2 - the steepness which is expected to be quite common for many astrophysical environments. This conclusion does not seem to depend o…
We propose a novel model to produce ultrahigh-energy cosmic-rays (UHECRs) in gamma-ray burst jets. After the prompt gamma-ray emission, hydrodynamical turbulence is excited in the GRB jets at or before the afterglow phase. The mildly relativistic turbulence stochastically accelerates protons. The acceleration rate is much slower than the usual first-order shock acceleration rate, but in this case it can be energy-independent. The resultant UHECR spectrum is so hard that the bulk energy is concentrated in the highest energy range, resulting in a moderate requirement for the typical cosmic ray l…
Supernova remnants are believed to be the main sites where Galactic cosmic rays originate. This scenario, however, fails to explain some of the features observed in the cosmic-ray spectrum. Microquasars have been proposed as additional candidates, because their non-thermal emission indicates the existence of efficient particle acceleration mechanisms in their jets. A promising scenario envisages the production of relativistic neutrons in the jets, that decay outside the system injecting relativistic protons to the surroundings. The first investigations of this scenario suggest that microquasar…
This is the fourth in a series of companion papers showing that, when an efficient dynamo can be maintained by accretion disks around supermassive black holes in Active Galactic Nuclei (AGNs), it will lead to the formation of a powerful, magnetically-collimated helix that could explain both the observed jet/radiolobe structures on very large scales and ultimately the enormous power inferred from the observed ultra high energy cosmic rays (UHECRs) with energies > 10^19 eV. Many timescales are involved in this process. Our hyper-resistive magnetohydrodynamic (MHD) model provides a bridge between…
The origin of Galactic cosmic rays remains a matter of debate, but supernova remnants are commonly considered to be the main place where high-energy cosmic rays are accelerated. Nevertheless, current models predict cosmic-ray spectra that do not match observations and the efficiency of the acceleration mechanism is still undetermined. On the other hand, the contribution of other kinds of sources to the Galactic cosmic-ray population is still unclear, and merits investigation. In this work we explore a novel mechanism through which microquasars might produce cosmic rays. In this scenario, micro…
We recently proposed that structured (spine-sheath) jets associated to BL Lac objects offer a suitable environment for the production of the extragalactic high-energy ($E>100$ TeV) neutrino recently revealed by IceCube. Our previous analysis was limited to low-power BL Lac objects. We extend our preliminary study to the entire BL Lac population. We assume that the power of cosmic rays as well as the radiative luminosity of the sheath depend linearly on the the jet power. In turn, we assume that the latter is well traced by the $γ$-ray luminosity. We exploit the BL Lac $γ$-ray luminosity functi…
Espresso is a novel acceleration model for Ultra-High-Energy Cosmic Rays (UHECRs), where lower-energy CRs produced in supernova remnants experience a one-shot reacceleration in the relativistic jets of powerful Active Galactic Nuclei (AGNs) to reach energies up to $10^{20}$ eV. To test the espresso framework, we follow UHECR acceleration bottom-up from injection to the highest energies by propagating 100,000 particles in realistic 3D magneto-hydrodynamic (MHD) simulations of ultra-relativistic jets. We find that simulations agree well with analytical expectations in terms of trajectories of in…
In the espresso scenario, ultra-high-energy (UHE) cosmic rays (CRs) are produced via a one-shot reacceleration of galactic-like CRs in the relativistic jets of active galactic nuclei, independently of the scattering rate dictated by magnetic fluctuations. In Mbarek & Caprioli (2019), we traced test-particle CRs in high-resolution magnetohyrodynamic (MHD) jet simulations and found that the associated spectral slope, chemical composition, and anisotropy are consistent with UHECR phenomenology. In this work, we extend such an analysis by including sub-grid pitch-angle scattering to model small-sc…
IceCube has detected a cumulative flux of PeV neutrinos, which origin is unknown. Blazars, active galactic nuclei with relativistic jets pointing to us, are long and widely expected to be one of the strong candidates of high energy neutrino sources. The neutrino production depends strongly on the cosmic ray power of blazar jets, which is largely unknown. The recent null results in stacking searches of neutrinos for several blazar samples by IceCube put upper limits on the neutrino fluxes from these blazars. Here we compute the cosmic ray power and PeV neutrino flux of Fermi-LAT blazars, and fi…
Compact binary mergers, with neutron stars or neutron star and black-hole components, are thought to produce various electromagnetic counterparts: short gamma-ray bursts (GRBs) from ultra-relativistic jets followed by broadband afterglow; semi-isotropic kilonova from radioactive decay of r-process elements; and late time radio flares; etc. If the jets from such mergers follow a similar power-law distribution of Lorentz factors as other astrophysical jets then the population of merger jets will be dominated by low-Γ values. The prompt gamma-rays associated with short GRBs would be suppressed fo…
Despite all the already existing observational data, current models still cannot explain completely the excessive energy output and the time variability of GRB. One of the reasons for this is the lack of a good model of the central engine of GRB. A major problem in the proposed models with a black hole (BH) in the center is that they don't explain the observed evidences of late time activity of the central engine. In this paper we are starting the search for a possible model of that central engine as a rotating compact body of still unknown nature. The formation of jets in the new model lies e…
Particle acceleration by magnetic reconnection is now recognized as an important process in magnetically dominated regions of galactic and extragalactic black hole sources. This process helps to solve current puzzles specially related to the origin of the very high energy flare emission in these sources. In this review, we discuss this acceleration mechanism and show recent analytical studies and multidimensional numerical SRMHD and GRMHD (special and general relativistic magnetohydrodynamical) simulations with the injection of test particles, which help us to understand this process both in r…
Consider a dynamic general relativistic spacetime in which the proper infinitesimal interval along one spatial coordinate direction decreases monotonically with time, while the corresponding intervals increase along other spatial directions. In a system undergoing such complete anisotropic collapse/expansion, we look for the formation of a cosmic double-jet configuration: free test particles in the ambient medium, relative to the collapsing system, gain energy from the gravitational field and asymptotically line up parallel and antiparallel to the direction of collapse such that their Lorentz …
In Mbarek & Caprioli (2019), we laid the groundwork for studying the espresso paradigm Caprioli (2015), a reacceleration mechanism to boost galactic CRs to UHECR levels. Our bottom-up approach uses realistic 3D MHD simulations of relativistic AGN jets and accounts for all of the crucial ingredients of a universal acceleration theory: injection, acceleration, and escape in realistic environments. Our results are consistent with the main features of UHECR spectra, i.e., power-law slopes, chemical composition, and anisotropy. In Mbarek & Caprioli (2021), we refine our model by including sub-grid …
The IceCube collaboration has reported neutrinos with energies between ~30 TeV and a few PeV that are significantly enhanced over the cosmic-ray induced atmospheric background. Viable high-energy neutrino sources must contain very high-energy and ultra-high energy cosmic rays while efficiently making PeV neutrinos. Gamma-ray Bursts (GRBs) and blazars have been considered as candidate cosmic-ray accelerators. GRBs, including low-luminosity GRBs, can be efficient PeV neutrino emitters for low bulk Lorentz factor outflows, although the photopion production efficiency needs to be tuned to simultan…
By proposing a pure leptonic radiation model, we study the potential gamma-ray emissions from jets of the low-mass X-ray binaries. In this model, the relativistic electrons that are accelerated in the jets are responsible for radiative outputs. Nevertheless, dynamics of jets are dominated by the magnetic and proton-matter kinetic energies. The model involves all kinds of related radiative processes and considers the evolution of relativistic electrons along the jet by numerically solving the kinetic equation. Numerical results show that the spectral energy distributions can extend up to TeV ba…
The black hole MAXI J1820+070 was discovered during its 2018 outburst and was extensively monitored across the electromagnetic spectrum. Following the detection of relativistic radio jets, we obtained four Chandra X-ray observations taken between 2018 November and 2019 May, along with radio observations conducted with the VLA and MeerKAT arrays. We report the discovery of X-ray sources associated with the radio jets moving at relativistic velocities with a possible deceleration at late times. The broadband spectra of the jets are consistent with synchrotron radiation from particles accelerated…
In the last 10 years multi-wavelength fast variability studies of low mass X-ray binaries have shown a dramatic development. A key discovery was the detection of O-IR sub-second fluctuations in two black-hole transients, lagging the X-rays by $\approx$0.1 s. This demonstrated how the fluctuations observed in the inflow could be transferred to the jet, allowing therefore also to study in a completely new way the physical processes which take place at the base of the jet. In this paper we review the latest developments of the study of jets with this new approach, focusing on the results obtained…
We present results of the first ever three-dimensional (3D) magnetohydrodynamic (MHD) simulations of the accretion-ejection structure. We investigate the 3D evolution of jets launched symmetrically from single stars but also jets from warped disks in binary systems. We have applied various model setups and tested them by simulating a stable and bipolar symmetric 3D structure from a single star-disk-jet system. Our reference simulation maintains a good axial symmetry and also a bipolar symmetry for more than 600 rotations of the inner disk confirming the quality of our model setup. We have then…
In dynamic spacetimes in which asymmetric gravitational collapse/expansion is taking place, the timelike geodesic equation appears to exhibit an interesting property: Relative to the collapsing configuration, free test particles undergo gravitational "acceleration" and form a double-jet configuration parallel to the axis of collapse. We illustrate this aspect of peculiar motion in simple spatially homogeneous cosmological models such as the Kasner spacetime. To estimate the effect of spatial inhomogeneities on cosmic jets, timelike geodesics in the Ricci-flat double-Kasner spacetime are studie…
We argue that some scenarios for the enigmatic supernova (SN) iPTF14hls and its progenitor require a strong binary interaction. We examine scenarios that attribute the extra power of iPTF14hls to a magnetar, to a late fallback on to the neutron star (NS) that launches jets, to an interaction of the ejecta with a circumstellar matter (CSM), or to a common envelope jets SN (CEJSN). For each of these four scenarios, we study the crucial process that supplies the extra energy and conclude that a binary companion to the progenitor must be present. For the magnetar scenario and late jets we claim th…
Accreting black holes are known to power relativistic jets, both in stellar-mass binary systems and at the centres of galaxies. The power carried away by the jets, and hence the feedback they provide to their surroundings, depends strongly on their composition. Jets containing a baryonic component should carry significantly more energy than electron-positron jets. While energetic considerations and circular polarisation measurements have provided conflicting circumstantial evidence for the presence or absence of baryons, the only system in which baryons have been unequivocally detected in the …
We simulate the influence of the energy that the merger process of two neutron stars (NSs) releases inside a red supergiant (RSG) star on the RSG envelope inner to the merger location. In the triple star common envelope evolution (CEE) that we consider a tight binary system of two NSs spirals-in inside an RSG envelope and because of mass accretion and dynamical friction the two NS merge. We deposit merger-explosion energies of 3e50 and 1e51 erg at distances of 25Ro and 50Ro from the center of the RSG, and with the three-dimensional hydrodynamical code FLASH we follow the evolution of the RSG e…
We discuss time-dependent gravitational fields that "accelerate" free test particles to the speed of light resulting in cosmic double-jet configurations. It turns out that complete gravitational collapse along a spatial axis together with corresponding expansion along the other two axes leads to the accelerated motion of free test particles up and down parallel to the collapse axis such that a double-jet pattern is asymptotically formed with respect to the collapsed configuration.
In this work, at first we present a model of studying astrophysical flows of binary systems and microquasars based on the laws of relativistic magnetohydrodynamics. Then, by solving the time independent transfer equation, we estimate the primary and secondary particle distributions within the hadronic astrophysical jets as well as the emissivities of high energy neutrinos and $γ$-rays. One of our main goals is, by taking into consideration the various energy-losses of particles into the hadronic jets, to determine through the transport equation the respective particle distributions focusing on…
In the following paper we present an internal shocks model, iShocks, for simulating a variety of relativistic jet scenarios; these scenarios can range from a single ejection event to an almost continuous jet, and are highly user configurable. Although the primary focus in the following paper is black hole X-ray binary jets, the model is scale and source independent and could be used for supermassive black holes in active galactic nuclei or other flows such as jets from neutron stars. Discrete packets of plasma (or `shells') are used to simulate the jet volume. A two-shell collision gives rise …
An introduction is given to a meeting on the role of massive and stellar black holes in powering non-thermal activity in a rich variety of cosmic sources. Relevant properties of magnetized, spinning black holes are summarized and their observational expression, within galactic nuclei, in terms of radio loudness and Fanaroff-Riley class, is briefly described. The dependence of the accretion mode on the rate and manner of the mass supply beyond the black hole sphere of influence is also discussed. It is argued that hydromagnetic outflows from accretion disks are generally expected over as many a…
Using radio and X-ray data of two powerful radiogalaxies we attempt to find out the role that radio jets (in terms of composition and power) as well as intracluster magnetic fields play in the formation, propagation and acceleration of cosmic rays. For this study we have selected the powerful radio galaxies Hercules A and 3C\,310 because of the presence of ring-like features in their kpc-scale radio emission instead of the usual hotspots. These two FR1.5 lie at the center of galaxy cooling flow clusters in a dense environment. We observed the unique jets of Hercules both in kpc- (multifrequenc…
The origin of ultrahigh-energy cosmic rays (UHECRs) is a half-century old enigma (Linsley 1963). The mystery has been deepened by an intriguing coincidence: over ten orders of magnitude in energy, the energy generation rates of UHECRs, PeV neutrinos, and isotropic sub-TeV gamma rays are comparable, which hints at a grand-unified picture (Murase and Waxman 2016). Here we report that powerful black hole jets in aggregates of galaxies can supply the common origin of all of these phenomena. Once accelerated by a jet, low-energy cosmic rays confined in the radio lobe are adiabatically cooled; highe…
Jet feedback from active galactic nuclei (AGN) is one of the most promising mechanisms for suppressing cooling flows in cool-core clusters. However, the composition of AGN jets and bubbles remains uncertain; they could be thermally dominated, or dominated by cosmic-ray proton (CRp), cosmic-ray electron (CRe), or magnetic energy. In this work, we investigate the evolution and feedback effects of CRp and CRe dominated jets by conducting 3D magnetohydrodynamic simulations of AGN jet-inflated bubbles in the intracluster medium using the FLASH code. We present the evolution of their energies, dynam…
We revisit the suggestion that dual jets can be produced during the inspiral and merger of supermassive black holes when these are immersed in a force-free plasma threaded by a uniform magnetic field. By performing independent calculations and by computing the electromagnetic emission in a way which is consistent with estimates using the Poynting flux, we show that a dual-jet structure is present but energetically subdominant with respect to a non-collimated and predominantly quadrupolar emission, which is similar to the one computed when the binary is in electrovacuum. While our findings set …
The origin of the diffuse extragalactic gamma-ray background, which was measured with the large area telescope (LAT) aboard the Fermi satellite at energy below 820 GeV, and of the diffuse cosmic background of neutrinos, which was observed at much higher energies with the IceCube detector deep under the south pole ice, are among the current unsolved major cosmic puzzles. Here we show that their properties indicate a common origin: the decay of mesons produced in collisions of cosmic rays accelerated in relativistic jets with matter in/near source. Moreover, their properties are those expected i…
We perform Monte Carlo simulations of transrelativistic shear acceleration dedicated to a jet-cocoon system of active galactic nuclei. A certain fraction of galactic cosmic rays in a halo is entrained, and sufficiently high-energy particles can be injected to the reacceleration process and further accelerated up to 100 EeV. We show that the shear reacceleration mechanism leads to a hard spectrum of escaping cosmic rays, $dL_E/dE\propto E^{-1}-E^0$, distinct from a conventional $E^{-2}$ spectrum. The supersolar abundance of ultrahigh-energy nuclei is achieved due to injections at TeV-PeV energi…
It has been proposed that Ultra-High-Energy Cosmic Rays (UHECRs) up to $10^{20}$eV could be produced in the relativistic jets of powerful Active Galactic Nuclei (AGNs) via a one-shot reacceleration of lower-energy CRs produced in supernova remnants (the $\textit{espresso}$ mechanism). We test this theory by propagating particles in realistic 3D magneto-hydrodynamic simulations of ultra-relativistic jets and find that about $10\%$ of the CRs entering the jet are boosted by at least a factor of $\simΓ^2$ in energy, where $Γ$ is the jet's effective Lorentz factor, in agreement with the analytical…
A Tale of Two Jets: Double Relativistic Outflows from Close Binary GRB Progenitors
Institute for Frontier in Astronomy and Astrophysics, Beijing Normal University（北京师范大学前沿天文与天体物理研究院）；School of Physics and Astronomy, Beijing Normal University（北京师范大学物理与天文学院）
Active Galactic Nuclei (AGNs) and their relativistic jets belong to the most promising class of ultra-high-energy cosmic ray (UHECR) accelerators. This compact review summarises basic experimental findings by recent instruments, and discusses possible interpretations and astrophysical constraints on source energetics. Particular attention is given to potential sites and mechanisms of UHECR acceleration in AGNs, including gap-type particle acceleration close to the black hole, as well as first-order Fermi acceleration at trans-relativistic shocks and stochastic shear particle acceleration in la…
High energy cosmic neutrino fluxes can be produced inside relativistic jets under the envelopes of collapsing stars. In the energy range E ~ (0.3 - 1e5) GeV, flavor conversion of these neutrinos is modified by various matter effects inside the star and the Earth. We present a comprehensive (both analytic and numerical) description of the flavor conversion of these neutrinos which includes: (i) oscillations inside jets, (ii) flavor-to-mass state transitions in an envelope, (iii) loss of coherence on the way to observer, and (iv) oscillations of the mass states inside the Earth. We show that con…
The gamma-ray emission detected from several microquasars can be produced by relativistic electrons emitting through inverse Compton scattering. In particular, the GeV emission detected from Cygnus X-3, and its orbital phase dependence, strongly suggest that the emitting electrons are accelerated in a relativistic jet, and that the optical companion provides the dominant target. Here, we study the effects related to particle transport in the framework of the relativistic jet scenario. We find that even in the most compact binary systems, with parameters similar to Cygnus X-3, particle transpor…
In this work, we simulate $γ$-rays created in the hadronic jets of the compact object in binary stellar systems known as microquasars. We utilize as main computational tool the $3$-D relativistic magneto-hydro-dynamical code PLUTO combined with in house derived codes. Our simulated experiments refer to the SS433 X-ray binary, a stellar system in which hadronic jets have been observed. We examine two new model configurations that employ hadron-based emission mechanisms. The simulations aim to explore the dependence of the $γ$-ray emissions on the dynamical as well as the radiative properties of…
We derive the most up-to-date Swift-Burst Alert Telescope (BAT) blazar luminosity function in the 14-195 keV range, making use of a clean sample of 118 blazars detected in the BAT 105-month survey catalog, with newly obtained redshifts from the BAT AGN Spectroscopic Survey (BASS). We determine the best-fit X-ray luminosity function for the whole blazar population, as well as for Flat Spectrum Radio Quasars (FSRQs) alone. The main results are: (1) at any redshift, BAT detects the most luminous blazars, above any possible break in their luminosity distribution, which means we cannot differentiat…
The diffuse background of very high energy extra-terrestrial neutrinos recently discovered with IceCube is compatible with that expected from cosmic ray interactions in the Galactic interstellar medium plus that expected from hadronic interactions near source and in the intergalactic medium of the cosmic rays which have been accelerated by the jets that produce gamma ray bursts (GRBs).
We calculate the expected effects on the spectral energy distributions and light curves in X-ray binary jets from eclipses by the donor stars. Jets will be eclipsed for all inclination angles, with just the height along the jet where the eclipse takes place being set by the orbital parameters. Typically, eclipses will lead to 5-10\% reductions in the jet emission over a range of a factor of few in wavelength with a periodic modulation. In ideal systems with high inclination angles, relatively even mass ratios, and modest jet speeds, the eclipses may be deeper. We discuss how eclipses can be us…
Unlike mergers of two compact objects containing a neutron star (NS), binary black hole (BBH) mergers are not accompanied by the production of tidally disrupted material, and hence lack the most direct source of accretion to power a jet and generate electromagnetic (EM) radiation. However, following a tentative detection by the Fermi GBM of a $γ$-ray counterpart to GW150914, several alternative ideas were proposed for driving a jet and producing EM radiation. {\em If} such jets were in fact produced, they would however lack the bright cocoon emission that makes jets from binary NSs bright also…
