Peak Photon Energy Research Articles

Deep neural networks for estimation of gamma-ray burst redshifts

Abstract While the available set of Gamma-ray Burst (GRB) data with known redshift is currently limited, a much larger set of GRB data without redshift is available from different instruments. This data includes well-measured prompt gamma-ray flux and spectral information. We estimate the redshift of a selection of these GRBs detected by Fermi-GBM and Konus-Wind using Machine Learning techniques that are based on spectral parameters. We find that Deep Neural Networks with Random Forest models employing non-linear relations among input parameters can reasonably reproduce the pseudo-redshift distribution of GRBs, mimicking the distribution of GRBs with spectroscopic redshift. Furthermore, we find that the pseudo-redshift samples of GRBs satisfy (i) Amati relation between the peak photon energy of the time-averaged energy spectrum in the cosmological rest frame of the GRB Ei, p and the isotropic-equivalent radiated energy Eiso during the prompt phase; and (ii) Yonetoku relation between Ei, p and isotropic-equivalent luminosity Liso, both measured during the peak flux interval.

The short gamma-ray burst population in a quasi-universal jet scenario

We present a model of the short gamma-ray burst (SGRB) population under a ‘quasi-universal jet’ scenario in which jets can differ somewhat in their on-axis peak prompt emission luminosity, Lc, but share a universal angular luminosity profile, ℓ(θv) = L(θv)/Lc, as a function of the viewing angle, θv. The model was fitted, through a Bayesian hierarchical approach inspired by gravitational wave (GW) population analyses, to three observed SGRB samples simultaneously: the Fermi/GBM sample of SGRBs with spectral information available in the catalogue (367 events); a flux-complete sample of 16 Swift/BAT SGRBs that are also detected by the GBM and have a measured redshift; and a sample of SGRBs with a binary neutron star (BNS) merger counterpart, which only includes GRB 170817A at present. Particular care was put into modelling selection effects. The resulting model, which reproduces the observations, favours a narrow jet ‘core’ with half-opening angle θc = 2.1−1.4+2.4 deg (uncertainties hereon refer to 90% credible intervals from our fiducial ‘full sample’ analysis) whose peak luminosity, as seen on-axis, is distributed as a power law, p(Lc) ∝ Lc−A with A = 3.2−0.4+0.7, above a minimum isotropic-equivalent luminosity, Lc⋆ = 5−2+11 × 1051 erg s−1. For viewing angles larger than θc, the luminosity profile scales as a single power law, l ∝ θv−αL with αL = 4.7−1.4+1.2, with no evidence of a break, despite the model allowing for it. While the model implies an intrinsic ‘Yonetoku’ correlation between L and the peak photon energy, Ep, of the spectral energy distribution, its slope is somewhat shallower, Ep ∝ L0.4 ± 0.2, than the apparent one, and the normalisation is offset towards larger Ep due to selection effects. The implied local rate density of SGRBs (regardless of the viewing angle) is between about one hundred up to several thousand events per cubic gigaparsec per year, in line with the BNS merger rate density inferred from GW observations. Based on the model, we predict 0.2 to 1.3 joint GW+SGRB detections per year by the advanced GW detector network and Fermi/GBM during the O4 observing run.

Magnetar Giant Flare Origin for GRB 210410A?

In general, giant flares (GFs) produced by magnetars have a very short-hard initial spike that is followed by a weak oscillatory phase. GFs from a nearby galaxy would appear as cosmic short-hard gamma-ray bursts (GRBs), such as GRB 200415A. In this paper, we search for GF-originated bursts in the Fermi GRB category and report GRB 210410A, which is presented with a very short-hard spike followed by an extended tail emission. In the E p,z − E iso plane, GRB 210410A with a duration of T 90 ∼ 48 s differs from long GRBs, might be classified as a short GRB with a redshift of z ∼ 0.28, and could be regarded as a GF with a distance of ∼2.7 Mpc. Here, E p,z , E iso, and L iso denote the rest-frame peak photon energy, the isotropic energy, and the isotropic luminosity of the burst, respectively. The radiation spectrum of GRB 210410A, similar to that of GRB 200415A, can be well fitted with a non-dissipative photospheric emission. However, GRB 210410A in the E p,z − L iso plane is beyond the death line of cosmic GRBs for non-dissipated photospheric emission with a general initial size of the fireball. Since the E p,z − L iso relation of GFs is far beyond the death line of cosmic GRBs, GRB 210410A may have originated from the same channel that produces GFs. We also perform the analysis and discuss both the highest photon energy event (4.2 GeV) and the extended tail emission in this burst.

An analytic derivation of the empirical correlations of gamma-ray bursts

Empirical correlations between various key parameters have been extensively explored ever since the discovery of gamma-ray bursts (GRBs) and have been widely used as standard candles to probe the Universe. The Amati relation and the Yonetoku relation are two good examples that enjoyed special attention. The former reflects the connection between the peak photon energy (Ep) and the isotropic γ-ray energy release (Eiso), while the latter links Ep with the isotropic peak luminosity (Lp), both in the form of a power-law function. Most GRBs are found to follow these correlations well, but a theoretical interpretation is still lacking. Some obvious outliers may be off-axis GRBs and may follow correlations that are different from those at the on-axis. Here we present a simple analytical derivation for the Amati relation and the Yonetoku relation in the framework of the standard fireball model, the correctness of which is then confirmed by numerical simulations. The off-axis Amati relation and Yonetoku relation are also derived. They differ markedly from the corresponding on-axis relation. Our results reveal the intrinsic physics behind the radiation processes of GRBs, and they highlight the importance of the viewing angle in the empirical correlations of GRBs.

Hadronic supercriticality in spherically expanding sources: application to GRB prompt emission

ABSTRACT Relativistic hadronic plasmas can become, under certain conditions, supercritical, abruptly and efficiently releasing the energy stored in protons through photon outbursts. Past studies have tried to relate the features of such hadronic supercriticalities (HSCs) to the phenomenology of gamma-ray burst (GRB) prompt emission. In this work we investigate, for the first time, HSC in adiabatically expanding sources. We examine the conditions required to trigger HSC, study the role of expansion velocity, and discuss our results in relation to GRB prompt emission. We find multipulse light curves from slowly expanding regions (≲ 0.01c) that are a manifestation of the natural HSC quasi-periodicity, while single-pulse light curves with a fast rise and slow decay are found for higher velocities. The formation of the photon spectrum is governed by an in-source electromagnetic cascade. The peak photon energy is approximately $1 \cdot \frac{\Gamma }{100} \frac{1+z}{3}$ MeV for maximum proton energies $(1-10) \cdot \frac{\Gamma }{100} \frac{1+z}{3}$ PeV, while the peak γ-ray luminosities are in the range $(10^{49}-10^{52}) \cdot (\frac{\Gamma }{100})^4$ erg s−1. HSC bursts peaking in the MeV energy band are also copious neutrino emitters with peak energies $\sim 10 \cdot \frac{\Gamma }{100} \frac{1+z}{3}$ TeV and an all-flavour neutrino fluence $\sim 10~{{\ \rm per\ cent}}$ of the γ-ray one. The hypothesis that long-duration GRBs are powered by HSCs could be applied therefore only to the most luminous GRBs observed assuming bulk Lorentz factors Γ ≤ 100.

Detection of a Prompt Fast-variable Thermal Component in the Multipulse Short Gamma-Ray Burst 170206A

We report the detection of a strong thermal component in the short gamma-ray burst 170206A with three intense pulses in its light curves, throughout which the fluxes of this thermal component exhibit fast temporal variability the same as that of the accompanying nonthermal component. The values of the time-resolved low-energy photon index in the nonthermal component are between about −0.79 and −0.16, most of which are harder than the −2/3 expected in the synchrotron emission process. In addition, we found a common evolution between the thermal component and the nonthermal component, and , where E p,CPL and F CPL are the peak photon energy and corresponding flux of the nonthermal component, and kT BB and F BB are the temperature and corresponding flux of the thermal component, respectively. Finally, we proposed that the photospheric thermal emission and the Comptonization of thermal photons may be responsible for the observational features of GRB 170206A.

Thermal energy effect on optoelectronic characteristics of InGaAsN/GaAs laser diode under the variation of quantum well number

A laser device based on InGaAsN quantum well active regions emitting at 1.26 mm is reported. The performances of the laser under the effect of thermal energy are investigated in terms of threshold current, Ith, gain parameter, gt, photon energy, hn, and cavity length, Lc. Four structures with one, two, and three quantum wells along with a structure that have three quantum wells with tensile strained barriers are proposed to study the relation between the peak gain, gpeak, and photon energy. The founds show that structures with one and two quantum wells operating at room temperature and under pulse wave condition, exhibit a linear dependence of gpeak on both Lc and photon energy. It is shown that the threshold current density, Jth, increases at any temperature with the cavity length Lc ranging from 250 nm to 1000 nm. Also, the investigation of the proposed structures shows that gt decreases with increasing temperature, while the ratio of the cur-rent density parameter to internal efficiency, Jt/hi, per well increases with the quantum well number. A comparison was carried out for two particular structures with three quantum wells and GaAsP barriers, the results show a decrease in the threshold current per well.

Temperature Characterization of Unipolar-Doped Electroluminescence in Vertical GaN/AlN Heterostructures

An electroluminescence (EL) phenomenon in unipolar-doped GaN/AlN/GaN double-barrier heterostructures—without any p-type contacts—was investigated from 4.2 K to 300 K. In the range of 200–300 K, the extracted peak photon energies agree with the Monemar formula. In the range of 30 to 200 K, the photon energies are consistent with A-exciton emission. At 4.2 K, the exciton type likely transforms into B-exciton. These studies confirm that the EL emission comes from a cross-bandgap (or band-to-band) electron-hole radiative recombination and is excitonic. The excitons are formed by the holes generated through interband tunneling and the electrons injected into the GaN emitter region of the GaN/AlN heterostructure devices.

Group-IV-semiconductor quantum-dots in thermal SiO2 layer fabricated by hot-ion implantation technique: different wavelength photon emissions

We experimentally studied three types of group-IV-semiconductor quantum-dots (IV-QDs) of Si-, SiC-, and C-QDs in a thermal SiO2 layer that were fabricated using a very simple hot-ion implantation technique for Si+, double Si+/C+, and C+ into the SiO2 layer, respectively, to realize a different wavelength photoluminescence (PL) emission from near-IR to near-UV ranges. TEM analyses newly confirmed both Si- and C-QDs with a diameter of approximately 2–4 nm in addition to SiC-QDs in SiO2. We successfully demonstrated very strong PL emission from three IV-QDs, and the peak photon energies (E PH) (peak PL-wavelength) of Si-, and SiC-, and C-QDs were approximately 1.56 eV (800 nm), 2.5 eV (500 nm), and 3.3 eV (380 nm), respectively. IV-QDs showed that the PL properties strongly depend on the hot-ion doses of Si and C atoms and the post N2 annealing processes. Consequently, it is easy to design peak PL wavelengths by controlling the ion doses of Si+ and C+ implanted into the SiO2 layer.

Constraints on cosmological parameters from gamma-ray burst peak photon energy and bolometric fluence measurements and other data

ABSTRACT We use measurements of the peak photon energy and bolometric fluence of 119 gamma-ray bursts (GRBs) extending over the redshift range of 0.3399 ≤ z ≤ 8.2 to simultaneously determine cosmological and Amati relation parameters in six different cosmological models. The resulting Amati relation parameters are almost identical in all six cosmological models, thus validating the use of the Amati relation in standardizing these GRBs. The GRB data cosmological parameter constraints are consistent with, but significantly less restrictive than, those obtained from a joint analysis of baryon acoustic oscillation and Hubble parameter measurements.

Lsyn – Esyn, p – δ relation in active galactic nucleus jets and implication for the physical origin of the Lp − Ep,z − Γ0 relation of gamma-ray bursts

High energy photon radiations of gamma-ray bursts (GRBs) and active galactic nuclei (AGNs) are dominated by their jet radiations. We examine whether the synchrotron radiations of jets in BL Lacs, flat spectrum radio quasars (FSRQs), and Narrow Line Seyfert 1 galaxies (NLS1s) follow the relation between the prompt gamma-ray emission and the initial Lorentz factor (Γ0) of GRBs. It is shown that the AGN sample does not agree with the Lp − Ep,z − Γ0 relation of GRBs. In addition, we obtain a tight relation of for FSRQs and NLS1 galaxies, where Lsyn is the luminosity at peak photon energy Esyn, p of the synchrotron radiations. This relation is different from the Lp − Ep,z − Γ0 relation of GRBs. The dependence of Lsyn to δ is consistent with the expectation of the Doppler boosting effect for the FSRQs and NLS1 galaxies, but it is not for GRBs. We argue that Γ0 may be a representative of the kinetic power of the radiating region and the tight Lp − Ep, z − Γ0 relation is shaped by the radiation physics and the jet power together.

Carrier localization structure combined with current micropaths in AlGaN quantum wells grown on an AlN template with macrosteps

The microscopic structural and optical characteristics of AlGaN-based light-emitting diodes grown on AlN templates with macrosteps were evaluated. Cross-sectional transmission electron microscopy in the high-angle annular dark field scanning mode and microscopic energy dispersive X-ray spectroscopy reveal that the AlGaN cladding layer under the AlGaN quantum wells (QWs) has microscopic compositional modulations originating from the macrosteps at the AlN template surface. The Ga-rich oblique zones in the cladding layer likely behave as current micropaths. These micropaths are connected to the carrier localization structure, which is formed by the modulation of both the well widths and the compositions of the QWs. In-plane spatially-resolved cathodoluminescence (CL) spectroscopy indicated significant inhomogeneity of the CL characteristics: the brighter emission with a lower peak photon energy confirms the existence of the carrier localization structure in the QWs. Carrier localization in the QWs along with the current micropaths in the AlGaN cladding layer appears to increase the external quantum efficiency of AlGaN LEDs.

A Comprehensive Analysis of Fermi Gamma-Ray Burst Data. IV. Spectral Lag and its Relation to Ep Evolution

Abstract The spectral evolution and spectral lag behavior of 92 bright pulses from 84 gamma-ray bursts observed by the Fermi Gamma-ray Burst Monitor (GBM) telescope are studied. These pulses can be classified into hard-to-soft pulses (H2S; 64/92), H2S-dominated-tracking pulses (21/92), and other tracking pulses (7/92). We focus on the relationship between spectral evolution and spectral lags of H2S and H2S-dominated-tracking pulses. The main trend of spectral evolution (lag behavior) is estimated with ( ), where E p is the peak photon energy in the radiation spectrum, t + t 0 is the observer time relative to the beginning of pulse −t 0, and is the spectral lag of photons with energy E with respect to the energy band 8–25 keV. For H2S and H2S-dominated-tracking pulses, a weak correlation between and k E is found, where W is the pulse width. We also study the spectral lag behavior with peak time of pulses for 30 well-shaped pulses and estimate the main trend of the spectral lag behavior with . It is found that is correlated with k E . We perform simulations under a phenomenological model of spectral evolution, and find that these correlations are reproduced. We then conclude that spectral lags are closely related to spectral evolution within the pulse. The most natural explanation of these observations is that the emission is from the electrons in the same fluid unit at an emission site moving away from the central engine, as expected in the models invoking magnetic dissipation in a moderately high-σ outflow.

Sub-50-as isolated extreme ultraviolet continua generated by 1.6-cycle near-infrared pulse combined with double optical gating scheme

We demonstrate the generation of ultrabroad bandwidth attosecond continua extending to sub-50-as duration in the extreme ultraviolet (EUV) region based on a 1.6-cycle Ti:sapphire laser pulse. The combination of the amplitude gating scheme with a sub-two-cycle driver pulse and the double optical gating scheme achieves the continuum generation with a bandwidth of 70 eV at the full width at half maximum near the peak photon energy of 140 eV, which supports a Fourier-transform-limited pulse duration as short as 32 as. The carrier-envelope-phase (CEP) dependence of the attosecond continua shows a single-peak structure originating from the half-cycle cut-off at appropriate CEP values, which strongly indicates the generation of a single burst of an isolated attosecond pulse. Our approach suggests a possibility for isolated sub-50-as pulse generation in the EUV region by compensating for the intrinsic attosecond chirp with a Zr filter.

Lessons from the Short GRB 170817A: The First Gravitational-wave Detection of a Binary Neutron Star Merger

Abstract The first, long-awaited, detection of a gravitational-wave (GW) signal from the merger of a binary neutron star (NS–NS) system was finally achieved (GW170817) and was also accompanied by an electromagnetic counterpart—the short-duration gamma-ray burst (GRB) 170817A. It occurred in the nearby ( Mpc) elliptical galaxy NGC 4993 and showed optical, IR, and UV emission from half a day up to weeks after the event, as well as late-time X-ray (at days) and radio (at days) emission. There was a delay of between the GW merger chirp signal and the prompt GRB emission onset, and an upper limit of was set on the viewing angle w.r.t the jet’s symmetry axis from the GW signal. In this letter we examine some of the implications of these groundbreaking observations. The delay sets an upper limit on the prompt GRB emission radius, , for a jet with sharp edges at an angle . GRB 170817A’s relatively low isotropic equivalent γ-ray energy output may suggest a viewing angle slightly outside the jet’s sharp edge, , but its peak photon energy and afterglow emission suggest instead that the jet does not have sharp edges and the prompt emission was dominated by less energetic material along our line of sight, at . Finally, we consider the type of remnant that is produced by the NS–NS merger and find that a relatively long-lived ( s) massive NS is strongly disfavored, while a hyper-massive NS of lifetime appears to be somewhat favored over the direct formation of a black hole.

Turbulent Magnetic Relaxation in Pulsar Wind Nebulae

Abstract We present a model for magnetic energy dissipation in a pulsar wind nebula. A better understanding of this process is required to assess the likelihood that certain astrophysical transients may be powered by the spin-down of a “millisecond magnetar.” Examples include superluminous supernovae, gamma-ray bursts, and anticipated electromagnetic counterparts to gravitational wave detections of binary neutron star coalescence. Our model leverages recent progress in the theory of turbulent magnetic relaxation to specify a dissipative closure of the stationary magnetohydrodynamic (MHD) wind equations, yielding predictions of the magnetic energy dissipation rate throughout the nebula. Synchrotron losses are self-consistently treated. To demonstrate the model’s efficacy, we show that it can reproduce many features of the Crab Nebula, including its expansion speed, radiative efficiency, peak photon energy, and mean magnetic field strength. Unlike ideal MHD models of the Crab (which lead to the so-called σ-problem), our model accounts for the transition from ultra to weakly magnetized plasma flow and for the associated heating of relativistic electrons. We discuss how the predicted heating rates may be utilized to improve upon models of particle transport and acceleration in pulsar wind nebulae. We also discuss implications for the Crab Nebula’s γ-ray flares, and point out potential modifications to models of astrophysical transients invoking the spin-down of a millisecond magnetar.

Cosmology with gamma-ray bursts

Gamma-ray bursts are the most energetic explosions in the Universe. They are detectable up to very high redshifts, therefore can be used to study the expansion rate of the Universe and to investigate the observational properties of dark energy, provided that empirical correlations between spectral and intensity properties are appropriately calibrated. We used the type Ia supernova luminosity distances to calibrate the correlation between the peak photon energy, $E_{p, i}$, and the isotropic equivalent radiated energy, $ E_{iso}$ in GRBs. With this correlation, we tested the reliability of applying GRBs to measure cosmological parameters and to obtain indications on the basic properties and evolution of dark energy. Using 162 GRBs with measured redshifts and spectra, we applied a local regression technique to calibrate the $E_{p, i}$-$E_{iso}$ correlation against the type Ia SN data to build a calibrated GRB Hubble diagram. We tested the possible redshift dependence of the correlation and its effect on the Hubble diagram. Finally, we used the GRB Hubble diagram to investigate the dark energy EOS. For this, we focused on the so-called Chevalier-Polarski-Linder (CPL) parametrization of the dark energy EOS and implemented the Markov chain Monte Carlo (MCMC) method to efficiently sample the space of cosmological parameters. Our analysis shows once more that the $E_{p, i}$-$E_{iso}$ correlation has no significant redshift dependence. Therefore the high-redshift GRBs can be used as a cosmological tool to determine the basic cosmological parameters and to test different models of dark energy in the redshift region ($z\geqslant 3$), which is unexplored by the SNIa and baryonic acoustic oscillations data. Our updated calibrated Hubble diagram of GRBs provides some marginal indication (at $1\sigma$ level) of an evolving dark energy EOS.

Doppler Boosting Effect on the Jet Radiation of Gamma-Ray Bursts and Active Galactic Nuclei

AbstractHigh energy photon radiations of gamma-ray bursts (GRBs) and active galactic nuclei (AGNs) are dominated by their jet radiations. It was suggested that relativistic jets powered by different mass-scale black holes may share the same physical laws. A tight relation among the peak luminosity, the peak photon energy in the νfν spectrum, and the initial Lorentz factor is found for GRBs. With samples of GeV-TeV BL Lacs, FSRQs, and NLS1 galaxies, we show that these sources do not follow this relation. This may be attributed to the jet geometry and continuous/episodic jet as well as radiation physics for different kinds of sources.

Measurement of angularly dependent spectra of betatron gamma-rays from a laser plasma accelerator with quadrant-sectored range filters

Measurement of angularly dependent spectra of betatron gamma-rays radiated by GeV electron beams from laser wakefield accelerators (LWFAs) are presented. The angle-resolved spectrum of betatron radiation was deconvolved from the position dependent data measured for a single laser shot with a broadband gamma-ray spectrometer comprising four-quadrant sectored range filters and an unfolding algorithm, based on the Monte Carlo code GEANT4. The unfolded gamma-ray spectra in the photon energy range of 0.1–10 MeV revealed an approximately isotropic angular dependence of the peak photon energy and photon energy-integrated fluence. As expected by the analysis of betatron radiation from LWFAs, the results indicate that unpolarized gamma-rays are emitted by electrons undergoing betatron motion in isotropically distributed orbit planes.

Experimental study on interface region of two-dimensional Si layers by forming gas annealing

We experimentally studied the SiO2/Si and Si/buried oxide (BOX) interface regions of a two-dimensional (2D) Si layer, by forming gas annealing (FGA). A photoluminescence (PL) result measured at various lattice temperature, TL, values shows that the PL intensity IPL of the 2D-Si layer rapidly increases and then saturates with increasing FGA temperature, TA, and time, tA. IPL also increases with decreasing TL. A one-dimensional (1D) Schroedinger equation simulator indicates that some of the electrons in the 2D-Si layer generated by a PL excitation laser are quantum–mechanically transmitted into Si interface regions. Actually, we experimentally confirmed that the PL spectra of the 2D-Si layer can be fitted by the PL emission from two regions with different PL peak photon energy values, EPH, which consist of a typical 2D-Si and the interface regions of both the surface SiO2/Si and Si/BOX. Thus, this forming gas dependence is probably attributable to the improved lifetime τ of electrons in the surface interface region, because the Si surface is terminated by H atoms. Moreover, the EPH of the interface region is higher than that of the 2D-Si layer, because of the graded increased bandgap in the interface regions. However, the EPH of 2D-Si is independent of both TA and TL, and this TL independence does not agree with that of a 3D-Si layer. Consequently, we experimentally verified the larger impact of the Si interface on the performance of 2D-Si layer.