Jet Radiation Research Articles

The Detection Prospect of the Counter Jet Radiation in the Late Afterglow of GRB 170817A

The central engine of a gamma-ray burst (GRB) is widely believed to launch a pair of oppositely moving jets, i.e., the forward jet moving toward us and the counter jet regressing away. The forward jet generates the radiation typically observed in GRBs, while the counter jet has not been detected yet due to its dimness. GRB 170817A, a short burst associated with a binary neutron star merger event, is a nearby event (z = 0.0097) with an off-axis structured energetic forward jet and hence probably the most suitable target for searching the counter jet radiation. Assuming the same properties for the forward and counter jet components as well as the shock parameters, the fit to the multiwavelength afterglow emission of GRB 170817A suggests a peak time ∼quite a few ×103 day of the counter jet radiation, but the detection prospect of this new component is not promising. Anyhow, if the shock parameters (ϵ e and ϵ B) of the counter jet component are (a few times) higher than that of the forward shock, e.g., the posterior results of the magnetic energy fraction of the forward shock and the counter jet are log10ϵB =−4.23−0.69+1.42 and log10ϵB,cj =−3.65−2.11+3.06 , respectively, as still allowed by the current data, the counter jet afterglow emission will be enhanced and hence may be detected. A few hours of exposure by JWST in the F356W band will stringently test such a scenario.

Ejecta from double-shock loaded tin target by hohlraum radiation and plasma jet

Ejecta from double-shock loaded tin target by hohlraum radiation and plasma jet

Dark Matter searches with photons at the LHC

We unveil blind spot regions in dark matter (DM) direct detection (DMDD), for weakly interacting massive particles with a mass around a few hundred GeV that may reveal interesting photon signals at the LHC. We explore a scenario where the DM primarily originates from the singlet sector within the Z3-symmetric Next-to-Minimal Supersymmetric Standard Model (NMSSM). A novel DMDD spin-independent blind spot condition is revealed for singlino-dominated DM, in cases where the mass parameters of the higgsino and the singlino-dominated lightest supersymmetric particle (LSP) exhibit opposite relative signs (i.e., κ < 0), emphasizing the role of nearby bino and higgsino-like states in tempering the singlino-dominated LSP. Additionally, proximate bino and/or higgsino states can act as co-annihilation partner(s) for singlino-dominated DM, ensuring agreement with the observed relic abundance of DM. Remarkably, in scenarios involving singlino-higgsino co-annihilation, higgsino-like neutralinos can distinctly favor radiative decay modes into the singlino-dominated LSP and a photon, as opposed to decays into leptons/hadrons. In exploring this region of parameter space within the singlino-higgsino compressed scenario, we study the signal associated with at least one relatively soft photon alongside a lepton, accompanied by substantial missing transverse energy (ɆT) and a hard initial state radiation jet at the LHC. In the context of singlino-bino co-annihilation, the bino state, as the next-to-LSP, exhibits significant radiative decay into a soft photon and the LSP, enabling the possible exploration at the LHC through the triggering of this soft photon alongside large ɆT and relatively hard leptons/jets resulting from the decay of heavier higgsino-like states.

The Power of Relativistic Jets: A Comparative Study

We present the results of a comparison between different methods to estimate the power of relativistic jets from active galactic nuclei (AGN). We selected a sample of 32 objects (21 flat-spectrum radio quasars, 7 BL Lacertae objects, 2 misaligned AGN, and 2 changing-look AGN) from the very large baseline array (VLBA) observations at 43 GHz of the Boston University blazar program. We then calculated the total, radiative, and kinetic jet power from both radio and high-energy gamma-ray observations, and compared the values. We found an excellent agreement between the radiative power calculated by using the Blandford and Königl model with 37 or 43 GHz data and the values derived from the high-energy γ-ray luminosity. The agreement is still acceptable if 15 GHz data are used, although with a larger dispersion, but it improves if we use a constant fraction of the γ-ray luminosity. We found a good agreement also for the kinetic power calculated with the Blandford and Königl model with 15 GHz data and the value from the extended radio emission. We also propose some easy-to-use equations to estimate the jet power.

Jet Structure and Burst Environment of GRB 221009A

We conducted a comprehensive investigation of the brightest-of-all-time GRB 221009A, using new insights from very high-energy (VHE) observations from LHAASO and a complete multiwavelength afterglow data set. Through data fitting, we imposed constraints on the jet structure, radiation mechanisms, and burst environment of GRB 221009A. Our findings reveal a structured jet morphology characterized by a core+wing configuration. A smooth transition of energy within the jet takes place between the core and wing, but with a discontinuity in the bulk Lorentz factor. The jet structure differs from both the case of the short GRB 170817A and the results of numerical simulations for long-duration bursts. The VHE emission can be explained by the forward shock synchrotron self-Compton radiation of the core component, but requiring a distinctive transition of the burst environment from uniform to wind-like, suggesting the presence of complex pre-burst mass ejection processes. The low-energy multiwavelength afterglow is mainly governed by the synchrotron radiation from the forward and reverse shocks of the wing component. Our analysis indicates a magnetization factor of 5 for the wing component. Additionally, by comparing the forward shock parameters of the core and wing components, we find a potential correlation between the electron acceleration efficiency and both the Lorentz factor of the shock and the magnetic field equipartition factor. We discuss the significance of our findings, potential interpretations, and remaining issues.

Modeling the Multiwavelength Spectral Energy Distributions of the Fermi-4LAC Bright Flat-spectrum Radio Quasars

In this paper, we present a long-term multiwavelength investigation focusing on 12 distinct samples of Fermi-4LAC bright flat-spectrum radio quasars (FSRQs). Detailed variability and spectral analyses of γ-ray, X-ray, and ultraviolet/optical data obtained by the Fermi Large Area Telescope, the Swift X-ray Telescope, and the Swift Ultraviolet and Optical Telescope were performed over a period of about 14 yr, spanning from 2008 October to 2022 October. These analyses provide insights into characterizing the variations within different activity states. To efficiently reproduce the multiwavelength simultaneous/quasi-simultaneous spectral energy distributions (SEDs) of the samples, we propose a novel approach for constraining the model parameters. By analyzing the parameters of the energy spectral curvature (β), the peak frequency (ν pk), the peak luminosity (L pk), the Compton dominance parameter (A C), and the variability timescale (t var) in different activity states, we can estimate the values of the jet radiation region parameters for the samples. Subsequently, we utilize the synchrotron-self-Compton and external Compton processes, employing a logarithmic-parabolic spectral shape to approximate the observed spectra of the sample sources, while considering the induced regime for the physical parameters. The model results show that: (1) by effectively reproducing SEDs in various active states of bright FSRQs, the parameters within the emission region were reasonably constrained; (2) compared to other active states, the emission region of the jet exhibits a reduced radius during the high state, while the magnetic field strength increases during the low state; and (3) for bright FSRQs in a high-activity state, there is an enhancement of the Doppler factor, often exhibiting a tendency toward energy equipartition.

A cooling flow around the low-redshift quasar H1821+643

ABSTRACT H1821+643 is the nearest quasar hosted by a galaxy cluster. The energy output by the quasar, in the form of intense radiation and radio jets, is captured by the surrounding hot atmosphere. Here, we present a new deep Chandra observation of H1821+643 and extract the hot gas properties into the region where Compton cooling by the quasar radiation is expected to dominate. Using detailed simulations to subtract the quasar light, we show that the soft-band surface brightness of the hot atmosphere increases rapidly by a factor of ∼30 within the central $\sim\!{10}\ \rm kpc$. The gas temperature drops precipitously to $\lt 0.4\rm \,\, keV$ and the density increases by over an order of magnitude. The remarkably low metallicity here is likely due to photoionization by the quasar emission. The variations in temperature and density are consistent with hydrostatic compression of the hot atmosphere. The extended soft-band peak cannot be explained by an undersubtraction of the quasar or scattered quasar light and is instead due to thermal interstellar medium. The radiative cooling time of the gas falls to only $12\pm 1\rm \,\, Myr$, below the free fall time, and we resolve the sonic radius. H1821+643 is therefore embedded in a cooling flow with a mass deposition rate of up to $3000\ {\rm M}_{\odot}\,{\rm yr}^{-1}$. Multiwavelength observations probing the star-formation rate and cold gas mass are consistent with a cooling flow. We show that the cooling flow extends to much larger radii than can be explained by Compton cooling. Instead, the active galactic nucleus appears to be underheating the core of this cluster.

Intranight Variability of Ultraviolet Emission from High-z Blazars

Rapid intranight variability of continuum and polarization in blazars is a valuable tool for probing the beaming of a relativistic jet and the associated population of the relativistic particles. Although such intranight variability in the rest-frame optical continuum has been extensively studied, there is a scarcity in the rest-frame ultraviolet (UV), where the variability might be caused by a secondary population of relativistic particles. To address this gap, we recently reported, for the first time, an intranight variability study of a sample of high-z blazars (Chand et al., 2022), with the monitored optical radiation is being their rest-frame UV radiation. Here, we discuss in detail the implications of this investigation, including a proper comparison of high-z blazar samples with fractional optical polarization (popt) lower and greater than 3%. In this context, we also report an intranight variability study of an additional high-z blazar at z = 2.347, namely J161942.38+525613.41, monitored over three sessions, each lasting approximately five hours. Our investigation does not reveal any compelling evidence for a stronger intranight variability of the UV emission in high polarization blazars, in contrast to the blazars monitored in the rest-frame blue-optical. We also discuss this trend in the light of the suggestion that the synchrotron radiation of blazar jets in the UV/X-ray regime may arise from a relativistic particle population different from that radiating up to near-infrared/optical frequencies.

The Fundamental Plane of GRBs

Gamma-ray bursts (GRBs) exhibit powerful radiation and relativistic jets similar to blazars. However, the central engine of GRBs remains unknown. In this paper, we use the fundamental plane to analyze a sample of GRBs with measured mass. We extend, over ∼12 orders of magnitude, the correlation analysis and fundamental plane with a sample of X-ray binaries, active galactic nuclei (AGNs) including blazars, and brightest cluster galaxies. The fundamental plane of our de-beamed sample, with a measured mass ( = (0.60 ± 0.03)+(0.78 ± 0.02)+7.23 ± 0.95), closely aligns with the findings of previous work on AGNs. This finding suggests that GRBs adhere to the fundamental plane of AGNs and supports the theory proposed in previous work that the central engine of GRBs may be black holes. This observation provides a plausible explanation for the striking similarities between GRBs and AGNs.

Lighting up the LHC with Dark Matter

We show that simultaneously explaining dark matter and the observed value of the muon’s magnetic dipole moment may lead to yet unexplored photon signals at the LHC. We consider the Minimal Supersymmetric Standard Model with electroweakino masses in the few-to-several hundred GeV range, and opposite sign of the Bino mass parameter with respect to both the Higgsino and Wino mass parameters. In such region of parameter space, the spin-independent elastic scattering cross section of a Bino-like dark matter candidate in direct detection experiment is suppressed by cancellations between different amplitudes, and the observed dark matter relic density can be realized via Bino-Wino co-annihilation. Moreover, the observed value of the muon’s magnetic dipole moment can be explained by Bino and Wino loop contributions. Interestingly, “radiative” decays of Wino-like neutralinos into the lightest neutralino and a photon are enhanced, whereas decays into leptons are suppressed. While these decay patterns weaken the reach of multi-lepton searches at the LHC, the radiative decay opens a new window for probing dark matter at the LHC through the exploration of parameter space regions beyond those currently accessible. To complement the current electroweakino searches, we propose searching for a single (soft) photon plus missing transverse energy, accompanied by a hard initial state radiation jet.

An investigation of shock cell-related noise in an installed, full-scale tactical jet engine using acoustical holography

Shock cells in imperfectly expanded supersonic jet flows have been found to contribute to the noise radiated by these jets. Acoustic phenomena such as screech and broadband shock-associated noise have been linked to the shock cell structure in jets. Acoustical holography has been used to study various jet noise source and radiation characteristics. Holography-based reconstructions near the acoustic source in an installed, full-scale tactical jet engine have yielded features indicative of the known shock cell structure in the jet. This paper presents these results and investigates the characteristics of these features, including their distribution and relative amplitudes.

FAST Discovery of a Fast Neutral Hydrogen Outflow

In this letter, we report the discovery of a fast neutral hydrogen outflow in SDSS J145239.38+062738.0, a merging radio galaxy containing an optical type I active galactic nucleus (AGN). This discovery was made through observations conducted by the Five-hundred-meter Aperture Spherical radio Telescope (FAST) using redshifted 21 cm absorption. The outflow exhibits a blueshifted velocity likely up to ∼−1000 km s−1 with respect to the systemic velocity of the host galaxy with an absorption strength of ∼−0.6 mJy beam−1 corresponding to an optical depth of 0.002 at v = −500 km s−1. The mass outflow rate ranges between 2.8 × 10−2 and 3.6 M ⊙ yr−1, implying an energy outflow rate ranging between 4.2 × 1039 and 9.7 × 1040 erg s−1, assuming 100 K < T s < 1000 K. Plausible drivers of the outflow include the starbursts, AGN radiation, and radio jet, the last of which is considered the most likely culprit according to the kinematics. By analyzing the properties of the outflow, AGN, and jet, we find that if the H i outflow is driven by the AGN radiation, the AGN radiation does not seem powerful enough to provide negative feedback, whereas the radio jet shows the potential to provide negative feedback. Our observations contribute another example of a fast outflow detected in neutral hydrogen and demonstrate the capability of FAST in detecting such outflows.

On the gauge-invariance of SCET beyond leading power

We point out that the gauge-invariance of the subleading Lagrangian of soft-collinear effective theory is realised in an intricate way through momentum-conservation violating contributions. Although these terms are disregarded in diagrammatic calculations, the gauge invariance of any physical transition amplitude is preserved due to the soft equations of motion. When not working with gauge-invariant building blocks, individual manifestly gauge-invariant constituent terms in the Lagrangian may give rise to gauge-dependent matrix elements starting at mathcal{O} (λ2). Implications for a gauge-invariant definition of radiative jet functions are discussed.

General Physical Properties of Fermi Blazars

We study the general physical properties of Fermi blazars using the Fermi fourth source catalog data (4FGL-DR2). The quasi-simultaneous multiwavelength data of Fermi blazars are fitted by using the one-zone leptonic model to obtain some physical parameters, such as jet power, magnetic field, and Doppler factor. We study the distributions of the derived physical parameters as a function of black hole mass and accretion disk luminosity. The main results are as follows. (1) For a standard thin accretion disk, the jet kinetic power of most flat-spectrum radio quasars can be explained by the Blandford–Payne (BP) mechanism. However, the jet kinetic power of most BL Lacertae objects (BL Lacs) cannot be explained by either the Blandford–Znajek mechanism or the BP mechanism. The BL Lacs may have advection-dominated accretion flows surrounding their massive black holes. (2) After excluding the redshift, there is a moderately strong correlation between the jet kinetic power and jet radiation power and the accretion disk luminosity for Fermi blazars. These results confirm a close connection between jet and accretion. The jet kinetic power is slightly larger than the accretion disk luminosity for Fermi blazars. (3) There is a significant correlation between jet kinetic power and gamma-ray luminosity and radio luminosity for Fermi blazars, which suggests that gamma-ray luminosity and radio luminosity can be used to indicate the jet kinetic power.

Asymmetry engendered by symmetric kink–antikink scattering in a degenerate two-field model

In this paper, we analyze the scattering process in a two-field model in [Formula: see text] dimensions, with the special property to have several topological solutions: (i) one with higher rest mass, characterized by a nested defect (lump inside a kink) and (ii) four others having lower rest mass, degenerated, and characterized by a kink inside kink. We investigate kink–antikink symmetric scattering, where the kink and antikink have higher rest mass and the same initial velocity modulus [Formula: see text]. The output of scattering presents a wide range of behaviors, such as annihilation of the kink–antikink pair, the emission of radiation jets, the generation of oscillating pulses and the change of the topological sector. We show that the changing of the topological sector is favored, and only two of the four sectors are possible as outcomes. Moreover, despite the degeneracy in energy, the distribution of the final states is asymmetric in the phase space, being an effect of the presence of vibrational states.

General Physical Properties of Gamma-Ray-emitting Radio Galaxies

We study the radio galaxies with known redshifts detected by the Fermi satellite after 10 yr of data (4FGL-DR2). We use a one-zone leptonic model to fit the quasi-simultaneous multiwavelength data of these radio galaxies and study the distributions of the derived physical parameters as a function of black hole mass and accretion disk luminosity. The main results are as follows. (1) We find that the jet kinetic power of most radio galaxies can be explained by the hybrid jet model based on ADAFs surrounding Kerr black holes. (2) After excluding the redshift, there is a significant correlation between the radiation jet power and the accretion disk luminosity, while the jet kinetic power is weakly correlated with the accretion disk luminosity. (3) We also find a significant correlation between inverse Compton luminosity and synchrotron luminosity. The slope of the correlation for radio galaxies is consistent with the synchrotron self-Compton (SSC) process. The result may suggest that the high-energy components of radio galaxies are dominated by the SSC process.

Combined Surface Heating by Laser Beam and Subsonic Nitrogen Plasma Jet

The paper describes new combined heating capability of the IPMech RAS inductively coupled plasma facility VGU-4. A 200 W ytterbium laser was added to the facility as a source of radiative heating. The cylindrical specimen made of the Buran orbital vehicle’s heat-shielding tile material with a black low catalytic coating was exposed to subsonic pure nitrogen plasma jet and laser radiation. The specimen surface temperature reached 1325 ∘C during combined radiative and convective heating. The maximum heat flux obtained in the combined mode for a laser incident power of 47 W and a VGU-4 HF-generator anode power of 22 kW was 32.1 W/cm2. The convective heat flux from the nitrogen plasma jet at the same anode power was 12.6 W/cm2. Adding a laser to an existing inductively coupled plasma facility gives the future opportunity to better simulate entry into the atmospheres of Mars, Venus, the outer planets and their moons.

Multiwavelength study of the luminous GRB 210619B observed with Fermi and ASIM

ABSTRACT We report on detailed multiwavelength observations and analysis of the very bright and long GRB 210619B, detected by the Atmosphere-Space Interactions Monitor installed on the International Space Station and the Gamma-ray Burst Monitor (GBM) on-board the Fermi mission. Our main goal is to understand the radiation mechanisms and jet composition of GRB 210619B. With a measured redshift of z = 1.937, we find that GRB 210619B falls within the 10 most luminous bursts observed by Fermi so far. The energy-resolved prompt emission light curve of GRB 210619B exhibits an extremely bright hard emission pulse followed by softer/longer emission pulses. The low-energy photon index (αpt) values obtained using the time-resolved spectral analysis of the burst suggest a transition between the thermal (during harder pulse) to non-thermal (during softer pulse) outflow. We examine the correlation between spectral parameters and find that both peak energy and αpt exhibit the flux tracking pattern. The late time broad-band photometric data set can be explained within the framework of the external forward shock model with νm &amp;lt; νc &amp;lt; νx (where νm, νc, and νx are the synchrotron peak, cooling-break, and X-ray frequencies, respectively) spectral regime supporting a rarely observed hard electron energy index (p &amp;lt; 2). We find moderate values of host extinction of E(B − V) = 0.14 ± 0.01 mag for the small magellanic cloud extinction law. In addition, we also report late-time optical observations with the 10.4 m Gran Telescopio de Canarias placing deep upper limits for the host galaxy (z = 1.937), favouring a faint, dwarf host for the burst.

Systematic quark/gluon identification with ratios of likelihoods

Discriminating between quark- and gluon-initiated jets has long been a central focus of jet substructure, leading to the introduction of numerous observables and calculations to high perturbative accuracy. At the same time, there have been many attempts to fully exploit the jet radiation pattern using tools from statistics and machine learning. We propose a new approach that combines a deep analytic understanding of jet substructure with the optimality promised by machine learning and statistics. After specifying an approximation to the full emission phase space, we show how to construct the optimal observable for a given classification task. This procedure is demonstrated for the case of quark and gluons jets, where we show how to systematically capture sub-eikonal corrections in the splitting functions, and prove that linear combinations of weighted multiplicity is the optimal observable. In addition to providing a new and powerful framework for systematically improving jet substructure observables, we demonstrate the performance of several quark versus gluon jet tagging observables in parton-level Monte Carlo simulations, and find that they perform at or near the level of a deep neural network classifier. Combined with the rapid recent progress in the development of higher order parton showers, we believe that our approach provides a basis for systematically exploiting subleading effects in jet substructure analyses at the Large Hadron Collider (LHC) and beyond.

Optically thick, nonlocal, inhomogeneous, stationary jet model for high-energy radiation from blazars: Application to Mrk 421

Context. There is an increasing number of observational evidence that very high energy γ-rays in radio-loud activ galactic nuclei are produced in the direct vicinity of a supermassive black hole (SMBH), close to the base of a relativistic jet. In the case of some blazars, the angle between the jet axis and the observer’s line of sight is smaller than the angular extent of the jet. γ-rays that are produced close to SMBH therefore have to propagate in the nonthermal radiation of the extended jet before reaching the observer. This γ-ray emission can be strongly absorbed in the extended jet radiation, producing a second generation of e± pairs that loses energy mainly via the synchrotron process. Aims. We developed a nonlocal, inhomogeneous, stationary jet model in order to describe the multiwavelength emission from blazars. With this advanced model, we investigated the impact of the extended jet radiation on the propagation of γ-rays that are ejected from the direct vicinity of SMBH toward an observer located within the solid angle of the jet. We determined the conditions under which γ-rays are absorbed in the jet radiation and explored the effect of this absorption process on the γ-ray spectra and on the hard X-ray emission observed from some blazars. Methods. We first developed an inhomogeneous, stationary jet model in which the radiation that is produced nonlocally in the jet was taken into account when we calculated the nonthermal emission in the broad energy range. This emission serves as a target on which γ-rays, produced close to SMBH, can be absorbed. As a result, the cascade is initiated within the jet through inverse Compton and synchrotron processes. Results. We show that this advanced inhomogeneous jet model can explain the multiwavelength spectrum of the BL Lac object Mrk 421 in a nonflaring state for reasonable parameters of the jet and the SMBH. Moreover, we argue that synchrotron emission from the secondary e± pairs, which appear as a result of absorption of γ-rays that are produced close to the SMBH within the jet radiation, is consistent with the concave hard X-ray emission observed from Mrk 421.