Non-thermal Emission Research Articles

Supercritical colliding wind binaries

Context. Particle-accelerating colliding-wind binaries (PACWBs) are systems that are formed by two massive and hot stars and produce nonthermal radiation. The key elements of these systems are fast winds and the shocks that they create when they collide. Binaries with nonaccreting young pulsars have also been detected as nonthermal emitters, again as a consequence of the wind–wind interaction. Black holes might produce nonthermal radiation by this mechanism if they accrete at super-Eddington rates. In such cases, the disk is expected to launch a radiation-driven wind, and if this wind has an equatorial component, it can collide with the companion star yielding a PACWB. These systems are supercritical colliding wind binaries. Aims. We aim to characterize the particle acceleration and nonthermal radiation produced by the collision of winds in binary systems composed of a superaccreting black hole and an early-type star. Methods. We estimated the terminal velocity of the disk-driven wind by calculating the spatial distribution of the radiation fields and their effect on disk particles. We then found the location of the wind collision region and calculated the timescales of energy gain and losses of relativistic particles undergoing diffusive particle acceleration. With this information, we were able to compute the associated spectral energy distribution of the radiation. We calculated a number of specific models with different parameters to explore this scenario. Results. We find that the interaction of winds can produce nonthermal emission from radio up to tens of GeV, with luminosities in the range of ∼1033–1035 erg s−1, which for the most part are contributed by electron synchrotron and inverse Compton radiation. Conclusions. We conclude that supercritical colliding wind binaries, such as some ultraluminous X-ray sources and some Galactic X-ray binaries, are capable of accelerating cosmic rays and producing nonthermal electromagnetic emission from radio to γ-rays, in addition to the thermal components.

Intermediate-mass black holes: finding of episodic, large-scale, and powerful jet activity in a dwarf galaxy

ABSTRACT Dwarf galaxies are characterized by a very low luminosity and low mass. Because of significant accretion and ejection activity of massive black holes, some dwarf galaxies also host low-luminosity active galactic nuclei (AGNs). In a few dwarf AGNs, very long baseline interferometry (VLBI) observations have found faint non-thermal radio emission. SDSS J090613.77+561015.2 is a dwarf AGN owning an intermediate-mass black hole (IMBH) with a mass of $M_\mathrm{BH} = 3.6^{+5.9}_{-2.3}\times 10^5 \mathrm{ M}_{\odot }$ and showing a rarely seen two-component radio structure in its radio nucleus. To further probe their nature, i.e. the IMBH jet activity, we performed additional deep observations with the European VLBI Network (EVN) at 1.66 and 4.99 GHz. We find the more diffuse emission regions and structure details. These new EVN imaging results allow us to reveal a two-sided jet morphology with a size up to about 150 mas (projected length ∼140 pc) and a radio luminosity of about 3 × 1038 erg s−1. The peak feature has an optically thin radio spectrum and thus more likely represents a relatively young ejecta instead of a jet base. The EVN study on SDSS J090613.77+561015.2 demonstrates the existence of episodic, relatively large-scale, and powerful IMBH jet activity in dwarf AGNs. Moreover, we collected a small sample of VLBI-detected dwarf AGNs and investigated their connections with normal AGNs. We notice that these radio sources in the dwarf AGNs tend to have steep spectra and small linear sizes, and possibly represent ejecta from scaled-down episodic jet activity.

A phase lag between disc and corona in GRMHD simulations of precessing tilted accretion discs

In the course of its evolution, a black hole (BH) accretes gas from a wide range of directions. Given a random accretion event, the typical angular momentum of an accretion disc would be tilted by ∼60∘ relative to the BH spin. Misalignment causes the disc to precess at a rate that increases with BH spin and depends on disc morphology. We present general-relativistic magnetohydrodynamic (GRMHD) simulations spanning a full precession period of highly tilted (60∘), moderately thin (h/r=0.1) accretion discs around a rapidly spinning (a≃0.9) BH. While the disc and jets precess in phase, we find that the disc wind/corona, sandwiched between the two, lags behind by ≳10°. For spectral models of BH accretion, the implication is that hard non-thermal (corona) emission lags behind the softer (disc) emission, thus potentially explaining some properties of the hard energy lags seen in Type-C low frequency quasi-periodic oscillations in X-ray binaries. While strong jets are unaffected by this disc-corona lag, weak jets can stall when encountering the lagging corona at distances r∼100 BH radii. This interaction may quench large-scale jet formation.

Observational connection of non-thermal X-ray emission from pulsars with their timing properties and thermal emission

ABSTRACTThe origin and radiation mechanisms of high-energy emissions from pulsars have remained mysterious since their discovery. Here we report, based on a sample of 68 pulsars, observational connection of non-thermal X-ray emissions from pulsars with their timing properties and thermal emissions, which may provide some constraints on theoretical modeling. Besides strong correlations with the spin-down power $\dot{E}$ and the magnetic field strength at the light cylinder Blc, the non-thermal X-ray luminosity in 0.5–8 keV, Lp, represented by the power-law component in the spectral model, is found to be strongly correlated with the highest possible electric field strength in the polar gap, Epc, of the pulsar. The spectral power index Γp of that power-law component is also found, for the first time in the literature, to strongly correlate with $\dot{E}$, Blc, and Epc, thanks to the large sample. In addition, we found that Lp can be well described by Lp ∝ T5.96 ± 0.64R2.24 ± 0.18, where T and R are the surface temperature and the emitting-region radius of the surface thermal emission, represented by the blackbody component in the spectral model. Γp, on the other hand, can be well described only when timing variables are included and the relation is $\Gamma _{\rm p}= \log (T^{-5.8\pm 1.93}R^{-2.29\pm 0.85}P^{-1.19\pm 0.88}\dot{P}^{0.94\pm 0.44})$ plus a constant. These relations strongly suggest the existence of connections between surface thermal emission and electron–positron pair production in pulsar magnetospheres.

Gaussian Process Modeling Blazar Multiwavelength Variability: Indirectly Resolving Jet Structure

Blazar jet structure can be indirectly resolved by analyzing the multiwavelength variability. In this work, we analyze the long-term variability of blazars in radio, optical, and X-ray energies with the Gaussian process (GP) method. The multiwavelength variability can be successfully characterized by the damped-random walk model. The nonthermal optical characteristic timescales of 38 blazars are statistically consistent with the γ-ray characteristic timescales of 22 blazars. For three individual sources (3C 273, PKS 1510-089, and BL Lac), the nonthermal optical, X-ray, and γ-ray characteristic timescales are also consistent within the measured 95% errors, but the radio timescale of 3C 273 is too large to be constrained by the decade-long light curve. The synchrotron and inverse-Compton emissions have the same power spectral density, suggesting that the long-term jet variability is irrelevant to the emission mechanism. In the plot of the rest-frame timescale versus black hole mass, the optical-γ-ray timescales of the jet variability occupy almost the same space with the timescales of accretion disk emission from normal quasars, which may imply that the long-term variabilities of the jet and accretion disk are driven by the same physical process. It is suggested that the nonthermal optical-X-ray and γ-ray emissions are produced in the same region, while the radio core, which can be resolved by very long baseline interferometry, locates at a far more distant region from the black hole. Our study suggests a new methodology for comparing thermal and nonthermal emissions, which is achieved by using the standard GP method.

Thermal and Nonthermal Emission from a Peculiar Long-duration GRB 211211A

Long-duration GRB 211211A that lacks a supernova emission even down to very stringent limits at such a low redshift z = 0.076 and is associated with kilonova emission, suggests that its physical origin is from a binary compact star merger. By reanalyzing its data observed with the Gamma-Ray Burst Monitor on board the Fermi mission, we find that both time-integrated and time-resolved spectra can be fitted well by using a 2SBPL plus blackbody (2SBPL+BB) model in the prompt emission. The bulk Lorentz factors (Γph) of the outflow can be inferred by invoking the observed thermal emission at the photosphere radius within a pure fireball model, and we find out that the temporal evolution of Γph seems to be tracking with the light curve. The derived values of Γph are also consistent with the Γph–L γ,iso/E γ,iso correlations that had been found in other bursts. Moreover, we also calculate the magnetization factor σ 0 in the central engine and σ ph at the photosphere radius within the framework of a hybrid jet model, and find that the values of both 1 + σ 0 and 1 + σ ph are larger than 1 for different time slices. It suggests that at least the Poynting-flux component is indeed existent in the outflow. If this is the case, one possible physical interpretation of thermal and nonthermal emissions in GRB 211211A is from the contributions of both annihilation and the Blandford–Znajek mechanisms in the relativistic jet when a stellar mass black hole resides in the central engine.

Identifying the energy release site in a solar microflare with a jet

Context. One of the main science questions of the Solar Orbiter and Parker Solar Probe missions deals with understanding how electrons in the lower solar corona are accelerated and how they subsequently access interplanetary space. Aims. We aim to investigate the electron acceleration and energy release sites as well as the manner in which accelerated electrons access the interplanetary space in the case of the SOL2021-02-18T18:05 event, a GOES A8 class microflare associated with a coronal jet. Methods. This study takes advantage of three different vantage points, Solar Orbiter, STEREO-A, and Earth, with observations drawn from eight different instruments, ranging from radio to X-ray. Multi-wavelength timing analysis combined with UV/EUV imagery and X-ray spectroscopy by Solar Orbiter/STIX (Spectrometer/Telescope for Imaging X-rays) is used to investigate the origin of the observed emission during different flare phases. Results. The event under investigation satisfies the classical picture of the onset time of the acceleration of electrons coinciding with the jet and the radio type III bursts. This microflare features prominent hard X-ray (HXR) nonthermal emission down to at least 10 keV and a spectrum that is much harder than usual for a microflare with γ = 2.9 ± 0.3. From Earth’s vantage point, the microflare is seen near the limb, revealing the coronal energy release site above the flare loop in EUV, which, from STIX spectroscopic analysis, turns out to be hot (i.e., at roughly the same temperature of the flare). Moreover, this region is moving toward higher altitudes over time (∼30 km s−1). During the flare, the same region spatially coincides with the origin of the coronal jet. Three-dimensional (3D) stereoscopic reconstructions of the propagating jet highlight that the ejected plasma moves along a curved trajectory. Conclusions. Within the framework of the interchange reconnection model, we conclude that the energy release site observed above-the-loop corresponds to the electron acceleration site, corroborating that interchange reconnection is a viable candidate for particle acceleration in the low corona on field lines open to interplanetary space.

Magnetic Fields, Star Formation Rates, and Gas Densities at Sub-kiloparsec Scales in a Pilot Sample of Nearby Galaxies

We have estimated the magnetic field strengths of a sample of seven galaxies using their nonthermal synchrotron radio emission at meter wavelengths, and assuming energy equipartition between magnetic fields and cosmic-ray particles. We tested for deviation of magnetic fields from energy equipartition with cosmic-ray particles, and found that deviations of ∼25% are typical for the sample galaxies. Spatially resolved star formation rates (SFRs) were estimated for the seven galaxies along with five galaxies studied previously. For the combined sample of 12 galaxies, the equipartition magnetic fields (B eq) are correlated with the SFR surface densities (ΣSFR) at sub-kiloparsec scales with B eq ∝ , consistent with model predictions. We estimated gas densities (ρ gas) for a subsample of seven galaxies using archival observations of the CO rotational transitions and the atomic hydrogen (H i) 21 cm line and studied the spatially resolved correlation between the magnetic fields and ρ gas. Magnetic fields and gas densities are found to be correlated at sub-kiloparsec scale as B eq ∝ . This is broadly consistent with models, which typically predict B ∝ .

Plasma heating and particle acceleration in collisionless shocks through astrophysical observations

Supernova remnants (SNRs), the products of stellar explosions, are powerful astrophysical laboratories, which allow us to study the physics of collisionless shocks, thanks to their bright electromagnetic emission. Blast wave shocks generated by supernovae (SNe) provide us with an observational window to study extreme conditions, characterized by high Mach (and Alfvénic Mach) numbers, together with powerful nonthermal processes. In collisionless shocks, temperature equilibration between different species may not be reached at the shock front. In this framework, different particle species may be heated at different temperatures (depending on their mass) in the post-shock medium of SNRs. SNRs are also characterized by broadband nonthermal emission stemming from the shock front as a result of nonthermal populations of leptons and hadrons. These particles, known as cosmic rays, are accelerated up to ultrarelativistic energies via diffusive shock acceleration. If SNRs lose a significant fraction of their ram energy to accelerate cosmic rays, the shock dynamics should be altered with respect to the adiabatic case. This shock modification should result in an increase in the total shock compression ratio with respect to the Rankine–Hugoniot value of 4. Here, I show that the combination of x-ray high resolution spectroscopy (to measure ion temperatures) and moderate resolution spectroscopy (for a detailed diagnostic of the post-shock density) can be exploited to study both the heating mechanism and the particle acceleration in collisionless shocks. I report on new results on the temperatures measured for different ion species in the remnant of the SN observed in 1987 in the Large Magellanic Cloud (SN 1987A). I also discuss evidence of shock modification recently obtained in the remnant of SN 1006 a. D., where the shock compression ratio increases significantly as the angle between the shock velocity and the ambient magnetic field is reduced.

Modeling Hadronic Gamma-Ray Emissions from Solar Flares and Prospects for Detecting Nonthermal Signatures from Protostars

We investigate gamma-ray emission in the impulsive phase of solar flares and the detectability of nonthermal signatures from protostellar flares. Energetic solar flares emit high-energy gamma rays of GeV energies, but their production mechanism and emission site are still unknown. Young stellar objects, including protostars, also exhibit luminous X-ray flares, but the triggering mechanism of the flaring activity is still unclear owing to the strong obscuration. Nonthermal signatures in millimeter/submillimeter and gamma-ray bands are useful to probe protostellar flares owing to their strong penetration power. We develop a nonthermal emission model of the impulsive phase of solar flares, where cosmic-ray protons accelerated at the termination shock produce high-energy gamma rays via hadronuclear interaction with the evaporation plasma. This model can reproduce gamma-ray data in the impulsive phase of a solar flare. We apply our model to protostellar flares and show that the Cherenkov Telescope Array will be able to detect gamma rays of TeV energies if particle acceleration in protostellar flares is efficient. Nonthermal electrons accelerated together with protons can emit strong millimeter and submillimeter signals via synchrotron radiation, whose power is consistent with the energetic millimeter/submillimeter transients observed from young stars. Future gamma-ray and millimeter/submillimeter observations from protostars, coordinated with a hard X-ray observation, will unravel the nonthermal particle production and triggering mechanism of protostellar flares.

GRB 080503: A Very Early Blue Kilonova and an Adjacent Nonthermal Radiation Component

The temporal behavior of the very dim optical afterglow of GRB 080503 is at odds with the regular forward shock afterglow model and a sole kilonova component responsible for optical emission has been speculated in some literature. Here we analyze the optical afterglow data available in archive and construct time-resolved spectra. The significant detection by Keck I in G/R bands at t ∼ 3 days, which has not been reported before, as well as the simultaneous Gemini-North r-band measurement, are in favor of a power-law spectrum that is well consistent with the optical to X-ray spectrum measured at t ∼ 4.5 days. However, for t ≤ 2 days, the spectrum is thermal-like and a straightforward interpretation is a kilonova emission from a neutron star merger, making it, possibly, the first detection of a very early kilonova signal at t ∼ 0.05 day. A nonthermal nature of optical emission at late times (t ∼ 2 days), anyhow, cannot be ruled out because of the large uncertainty of the g-band data. We also propose to classify the neutron star merger induced optical transients, according to the temporal behaviors of the kilonova and the nonthermal afterglow emission, into four types. GRB 080503 would then represent the first observation of a subgroup of neutron star merger driven optical transients (i.e., type IV) consisting of an early blue kilonova and an adjacent nonthermal afterglow radiation.

Limits on the non-thermal emission of the WR–WR system Apep

Colliding-wind binaries (CWBs) constitute an emerging class of γ-ray sources powered by strong, dense winds in massive stellar systems. The most powerful of them are those binaries hosting a Wolf-Rayet (WR) star. Following the recent discovery of Apep – the closest known Galactic WR–WR binary – we discuss the non-detection of its putative high-energy emission by the Fermi Large Area Telescope (Fermi-LAT) in this Letter. The limits reported in the GeV regime can be used to set a lower limit on the magnetic field pressure density within the shocked wind-collision region (WCR), and to exclude Apep as a bright γ-ray emitting binary. Given that this WR–WR system is the most luminous CWB identified until now at radio wavelengths, this result proves unambiguously that non-thermal synchrotron emission is not a suitable identifier for the subset of γ-ray emitters in this class of particle accelerators. Rather, Apep could be an interesting case of study for magnetic field amplification in shocked stellar winds.

The sculpting of rectangular and jet-like morphologies in supernova remnants by anisotropic equatorially confined progenitor stellar winds

ABSTRACT Thermonuclear and core-collapse supernova remnants (SNRs) are the nebular leftovers of defunct stars. Their morphology and emission properties provide insights into the evolutionary history of the progenitor star. But while some SNRs are spherical, as expected from a point-like explosion expanding into a roughly uniform medium, many others exhibit complex non-spherical morphologies that are often not easily explained. In this work, we use 3D magnetohydrodynamic simulations to show that rectangular and jet-like morphologies can be explained by supernovae (SNe), either type Ia or type II, expanding within anisotropic, bipolar stellar wind bubbles driven by the progenitor star. The stellar wind has an anisotropic density distribution, which channels the SN ejecta differently depending on the anisotropy characteristics. We compute synthetic thermal (X-ray) and non-thermal (synchrotron) emission maps from our numerical simulations to compare with observations. We find rectangular morphologies are generated when the stellar wind has a high-mass loss rate and forms a dense, narrow disc at the equatorial region. Instead, a jet-like or ear-like morphology is obtained when the stellar wind develops a wide, dense disc. Stellar winds with low mass-loss rates do not strongly influence the SNR morphology. Finally, our synthetic synchrotron and X-ray maps for the high mass-loss rate case qualitatively agree with the observations of the SNRs G332.5-5.6 and G290.1-0.8.

A powerful (and likely young) radio-loud quasar at z = 5.3

We present the discovery of PSO J191.05696+86.43172 (hereafter PSO J191+86), a new powerful radio-loud quasar (QSO) in the early Universe (z = 5.32). We discovered it by cross-matching the NRAO VLA Sky Survey (NVSS) radio catalog at 1.4 GHz with the first data release of the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS PS1) in the optical. With a NVSS flux density of 74.2 mJy, PSO J191+86 is one of the brightest radio QSO discovered at z ∼ 5. The intensity of its radio emission is also confirmed by the very high value of radio loudness (R > 300). The observed radio spectrum of PSO J191+86 shows a possible turnover around ∼1 GHz (i.e., ∼6 GHz in the rest frame), making it a gigahertz-peaked spectrum (GPS) source. However, variability could affect the real shape of the radio spectrum, because the data in hand were taken ∼25 years apart. By assuming a peak in the observed radio spectrum between 1 and 2 GHz (i.e., ∼6 and 13 GHz in the rest-frame) we find a linear size of the source of ∼10–30 pc and a corresponding kinetic age of 150–460 yr. This would make PSO J191+86 a newly born radio source. However, the large X-ray luminosity (5.3×1045 erg s−1), the flat X-ray photon index (ΓX = 1.32), and the optical–X-ray spectral index (αox̃ = 1.329) are typical of blazars. This could indicate that the nonthermal emission of PSO J191+86 is Doppler boosted. Further radio observations (both on arcsec and parsec scales) are necessary to better investigate the nature of this powerful radio QSO.

Investigating the radiative properties of LHAASO J1908 + 0621

ABSTRACT LHAASO J1908+0621 has recently been detected as a source emitting γ-rays with energies above 100 TeV, and multiband observations show that a break around 1 TeV appears in the γ-ray spectrum. We have reanalysed the GeV γ-ray properties of the 100-TeV source using 14 years of data recorded by the Fermi Large Area Telescope (Fermi-LAT). The spectrum in the energy range range 30–500 GeV has an index of 1.50 ± 0.26, which is much smaller than that detected in TeV γ-rays. Additionally, the radiation properties of this source are investigated based on a one-zone time-dependent model. In the model, LHAASO J1908+0621 is associated with a pulsar wind nebula (PWN) powered by the pulsar PSR J1907 + 0602. High-energy particles composed of electrons and positrons are injected into the nebula. Multiband non-thermal emission is produced via synchrotron radiation and inverse Compton scattering (ICS). Taking the effect of radiative energy losses and adiabatic cooling into account, the spectral energy distribution from a model with a broken power law for the distribution of the injected particles can explain the fluxes detected in the γ-ray bands. The results support the idea that LHAASO J1908 + 0621 originates from the PWN powered by PSR J1907 + 0602, and γ-rays with energy above 100 TeV are produced by electrons/positrons in the nebula via ICS.

Suzaku and Chandra study of diffuse X-ray emission from the massive star-forming region RCW 38

Abstract In some massive star-forming regions, diffuse X-ray emission has been observed. It can be classified as thermal emission from sub- or several-keV plasmas, non-thermal emission represented by the power law, or a mixture of them. We have studied the nearby (∼1.7 kpc) young massive star-forming region RCW 38. In a previous study, non-thermal diffuse X-ray emission of 1.25 × 1.75 pc (∼2${_{.}^{\prime}}$5 × 3${_{.}^{\prime}}$5) was reported from Chandra observation. We observed the same region for 72 ks with Suzaku which has a low background and is highly sensitive to spatially extended emission. To detect and consider point source contributions, we also used Chandra data. We divided the area according to the radius from the cluster center. In the inner region (r < 2${_{.}^{\prime}}$0), the existence of the non-thermal component (power law, Γ = 1.7 ± 0.4) was suggested although a two-temperature thermal model (kT = 0.90 ± 0.07 and $6.2^{+7.7}_{-2.3}\:$keV) could not be rejected. In the outer region (r = 2${_{.}^{\prime}}$0–5${_{.}^{\prime}}$5), a two-temperature (kT = 0.95 ± 0.10 and 4.8 ± 0.6 keV) thermal plasma model was favorable. In this paper, the origin of the diffuse X-ray emission is discussed in the context of non-thermal/thermal emission and energetics.

Detection of the Extended γ-Ray Emission from the High Galactic Latitude Calvera’s SNR Candidate

We report the extended GeV γ-ray emission that is spatially associated with the high Galactic latitude supernova remnant (SNR) candidate—Calvera’s SNR with the Pass 8 data recorded by the Fermi Large Area Telescope. The γ-ray spectrum of Calvera’s SNR between 100 MeV and 1 TeV shows an evident (∼3.4σ) spectral curvature at several tens of GeV. The multiwavelength data can be fitted with either a leptonic model or a hadronic one. However, the leptonic model exhibits inconsistency between the flat radio spectrum and the hard GeV γ-ray spectrum of Calvera’s SNR. For the hadronic model, the spectral index of protons should be harder than 1.6 and the total energy of protons is fitted to be more than one order of magnitude higher than the explosion energy of a typical supernova, which also challenges the hadronic model. The evident spectral curvature and the absence of nonthermal X-ray emission from Calvera’s SNR makes it to be an interesting source bridging young-aged SNRs with bright nonthermal X-ray emission and old-aged SNRs interacting with molecular clouds.

Preliminary results on SiO maser emission from the AGB binary system: R Aqr.

AbstractBinary/multiple stellar systems are as abundant as single stars. They are very interesting cosmic laboratories as they are related to many astrophysical phenomena. In the case of AGB (and post-AGB) stars, binaries are the most likely explanation for the shaping of non spherical PNe, a long standing problem in stellar evolution. While many binaries are known in the PNe phase, there are few examples in the previous AGB phase. Hydrodynamical models of the binary interaction are available, but well known parameters for orbits are non-existent. We observed the AGB binary system R Aqr at 7 mm using the Global VLBI array in wide-band continuum and SiO masers. The strong SiO masers were used to self-calibrate the observations and pinpoint the location of the AGB component. We used the continuum to try to directly detect the WD companion or its close environments (non-thermal emission from accretion disks/jets). We present our preliminary results for R Aqr on the relative positions of the J=1−0 SiO masers (v=1) with respect to the white dwarf position. This opens a new way to determine orbits in binaries at the AGB phase and better study their role in late stellar evolution and PNe shaping.

The effect of outflows on CMB bounds from Primordial Black Hole accretion

Should Primordial Black Holes (PBHs) exist in nature, they would inevitably accrete baryonic matter in their vicinity. In turn, the consequent emission of high-energy radiation could affect the thermal history of the universe to an extent that can be probed with a number of cosmological observables such as the Cosmic Microwave Background (CMB) anisotropies. However, our understanding of the accretion and radiation emission processes in the context of PBHs is still in its infancy, and very large theoretical uncertainties affect the resulting constraints on the PBH abundance. Building on state-of-the-art literature, in this work we take a step towards the development of a more realistic picture of PBH accretion by accounting for the contribution of outflows. Specifically, we derive CMB-driven constraints on the PBH abundance for various accretion geometries, ionization models and mass distributions in absence and in presence of mechanical feedback and non-thermal emissions due to the outflows. As a result, we show that the presence of such outflows introduces an additional layer of uncertainty that needs to be taken into account when quoting cosmological constraints on the PBH abundance, with important consequences in particular in the LIGO-Virgo-KAGRA observational window.

Modeling Gamma-Ray Burst Afterglow Observations with an Off-axis Jet Emission

Abstract Gamma-ray bursts (GRBs) are fascinating extragalactic objects. They represent a fantastic opportunity to investigate unique properties not exhibited in other sources. Multiwavelength afterglow observations from some short- and long-duration GRBs reveal an atypical long-lasting emission that evolves differently from the canonical afterglow light curves favoring the off-axis emission. We present an analytical synchrotron afterglow scenario and the hydrodynamical evolution of an off-axis top-hat jet decelerated in a stratified surrounding environment. The analytical synchrotron afterglow model is shown during the coasting, deceleration (off- and on-axis emission), and post–jet break decay phases, and the hydrodynamical evolution is computed by numerical simulations showing the time evolution of the Doppler factor, the half-opening angle, the bulk Lorentz factor, and the deceleration radius. We show that numerical simulations are in good agreement with those derived with our analytical approach. We apply the current synchrotron model and successfully describe the delayed nonthermal emission observed in a sample of long and short GRBs with evidence of off-axis emission. Furthermore, we provide constraints on the possible afterglow emission by requiring the multiwavelength upper limits derived for the closest Swift-detected GRBs and promising gravitational-wave events.