Gamma-ray Burst Photons Research Articles

Observations of GRB 221009A by the MAVEN-SEP Instrument at Mars

We report on the detection of the Brightest Of All Time (the BOAT) gamma-ray burst (GRB) 221009A by the MAVEN Solar Energetic Particle (SEP) silicon (Si) detectors. The SEP instrument on board the MAVEN spacecraft at Mars is designed to measure charged particle fluxes and energies. In this work, we show that the SEP Si detectors have detected populations of secondary charged particles and low-energy primary photons from the GRB. Our analysis relies on a series of simplified Geant4 Monte Carlo simulations. We show that electromagnetic and hadronic interactions between the GRB photons and the spacecraft’s passive material and Si detectors produced the detected secondary particles.

GRB 221009A: Spectral Signatures Based on ALPs Candidates

GRB 221009A has posed a significant challenge to our current understanding of the mechanisms that produce TeV photons in gamma-ray bursts (GRBs). On one hand, the Klein–Nishina (KN) effect of the inverse Compton scattering leads to less efficient energy losses of high-energy electrons. On the other hand, at a redshift of 0.151, the TeV spectrum of GRB 221009A undergoes significant absorption by the extragalactic background light (EBL). Therefore, the observation of a 13 TeV photon in this event implies the presence of enormous photon fluxes at the source, which the synchrotron self-Compton mechanism in external shocks cannot easily generate. As an alternative, some authors have suggested the possibility of converting the TeV photons into axion-like particles (ALPs) at the host galaxy, in order to avoid the effects of EBL absorption, and then reconverting them into photons within the Milky Way. While this solution relaxes the requirement of very high photon fluxes, the KN effect still poses a challenge. Previously, we have shown that the injections of ALPs could explain the observation of 13 TeV photons. Here, we include the energy dependence of the probability of survival and the amount of energy carried to determine the ALP candidates, which could potentially explain the TeV photons observed by the Large High Altitude Air Shower Observatory and their hard spectrum. We found that the allowed candidates are generally clustered around masses of 10−7 eV. We also considered different EBL models, for the one predicting larger attenuation tends to reject ALP candidates with the lowest coupling factor. For some hypotheses of the EBL model, these candidates are found below a region of the parameter space in which, if detected, ALPs could account for all of the cold dark matter in the Universe.

Probing for Lorentz Invariance Violation in Pantheon Plus Dominated Cosmology

The Hubble tension in cosmology is not showing signs of alleviation and thus, it is important to look for alternative approaches to it. One such example would be the eventual detection of a time delay between simultaneously emitted high-energy and low-energy photons in gamma-ray bursts (GRB). This would signal a possible Lorentz Invariance Violation (LIV) and in the case of non-zero quantum gravity time delay, it can be used to study cosmology as well. In this work, we use various astrophysical datasets (BAO, Pantheon Plus and the CMB distance priors), combined with two GRB time delay datasets with their respective models for the intrinsic time delay. Since the intrinsic time delay is considered the largest source of uncertainty in such studies, finding a better model is important. Our results yield as quantum gravity energy bound EQG≥1017 GeV and EQG≥1018 GeV respectively. The difference between standard approximation (constant intrinsic lag) and the extended (non-constant) approximations is minimal in most cases we conside. However, the biggest effect on the results comes from the prior on the parameter cH0rd, emphasizing once again that at current precision, cosmological datasets are the dominant factor in determining the cosmology. We estimate the energies at which cosmology gets significantly affected by the time delay dataset.

Single extra dimension from \u03ba-Poincar\xe9 and gauge invariance

We show that κ-Poincaré invariant gauge theories on κ-Minkowski space with physically acceptable commutative (low energy) limit must be 5-d. The gauge invariance requirement of the action fixes the dimension of the κ-Minkowski space to d = 5 and selects the unique twisted differential calculus with which the construction can be achieved. We characterize a BRST symmetry related to the 5-d noncommutative gauge invariance though the definition of a nilpotent operation, which is used to construct a gauge-fixed action. We also consider standard scenarios assuming (compactification of) flat extra dimension, for which the 5-d deformation parameter κ can be viewed as the bulk 5-d Planck mass. We study physical properties of the resulting 4-d effective theories. Recent data from collider experiments require κ ≳ mathcal{O} (1013) GeV. The use of standard test of in-vacuo dispersion relations of Gamma Ray Burst photons increases this lower bound by 4 orders of magnitude. The robustness of this bound is discussed in the light of possible new features of noncommutative causal structures.

Light cone in a quantum spacetime

Noncommutative spacetimes are a proposed effective description of the low-energy regime of Quantum Gravity. Defining the microcausality relations of a scalar quantum field theory on the κ-Minkowski noncommutative spacetime allows us to define for the first time a notion of light-cone in a quantum spacetime. This allows us to reach two conclusions. First, the majority of the literature on κ-Minkowski suggests that this spacetime allows superluminal propagation of particles. The structure of the light-cone we introduced allows to rule this out, thereby excluding the possibility of constraining the relevant models with observations of in-vacuo dispersion of Gamma Ray Burst photons. Second, we are able to reject a claim made in Neves et al. (2010) [33], according to which the light-cone of the κ-Minkowski spacetime has a ‘blurry’ region of Planck-length thickness, independently of the distance of the two events considered. Such an effect would be hopeless to measure. Our analysis reveals that the thickness of the region where the notion of timelike and spacelike separations blurs grows like the square root of the distance. This magnifies the effect, e.g. in the case of cosmological distances, by 30 orders of magnitude.

Lorentz violation from gamma-ray burst neutrinos

The Lorentz violation (LV) effect of ultra-relativistic particles can be tested by gamma-ray burst (GRB) neutrinos and photons. The IceCube Collaboration has observed plenty of ultra-high energy neutrinos, including four PeV scale neutrinos. Recent studies suggested a possible energy dependent speed variation of GRB neutrinos in a similar way to that of GRB photons. Here we find that all four PeV neutrinos with associated GRB candidates can satisfy a regularity found from TeV neutrinos about a linear form correlation between the observed time difference and the LV factor. Such regularity indicates a Lorentz violation scale ELV = (6.5 ± 0.4) × 1017 GeV, which is comparable with that determined by GRB photons. We also suggest that neutrinos and anti-neutrinos can be superluminal and subluminal respectively due to opposite signs of LV correction.

In vacuo dispersion features for gamma-ray-burst neutrinos and photons

Over the last 15 years there has been considerable interest in the possibility of quantum-gravity-induced in-vacuo dispersion, the possibility that spacetime itself might behave essentially like a dispersive medium for particle propagation. Two very recent studies have exposed what might be in-vacuo dispersion features for GRB (gamma-ray-burst) neutrinos of energy in the range of 100 TeV and for GRB photons with energy in the range of 10 GeV. We here show that these two features are roughly compatible with a description such that the same effects apply over 4 orders of magnitude in energy. We also characterize quantitatively how rare it would be for such features to arise accidentally, as a result of (still unknown) aspects of the mechanisms producing photons at GRBs or as a result of background neutrinos accidentally fitting the profile of a GRB neutrino affected by in-vacuo dispersion.

CONSTRAINTS ON THE HADRONIC CONTENT OF GAMMA RAY BURSTS

The IceCube high-energy neutrino telescope has been collecting data since 2006. Conversely, hundreds of Gamma Ray Bursts (GRBs) have been detected by the GBM on board Fermi, since its launch in 2008. So far no neutrino event has been associated with a GRB, despite many models predicting the generation of high energy neutrinos through GRB photon interaction with PeV protons in the GRB jet. We use the non-detection of neutrinos to constrain the hadronic content of GRB jets independent of jet model parameters. Assuming a generic particle spectrum of $E^{-\alpha}$ with $\alpha = 2$, we find that the ratio of the energy carried by pions to that in electrons has to be small $f_\pi / f_e \lesssim 0.24$ at 95\% confidence level. A distribution of spectral slopes can lower $f_\pi / f_e$ by orders of magnitude. Another limit, independent of neutrinos, is obtained if one ascribes the measured Fermi/LAT GeV gamma-ray emission to pair-photon cascades of high-energy photons resulting from (the same photon-hadronic interactions and subsequent) neutral pion decays. Based on the generally observed MeV to GeV GRB fluence ratio of $\approx 10$, we show that $f_\pi / f_e \lesssim 0.3$. In some bursts, where this ratio is as low as unity, $f_\pi / f_e \lesssim 0.03$. These findings add to the mounting doubts regarding the presence of PeV protons in GRB jets.

Simulations of gamma-ray burst afterglows with a relativistic kinetic code

This paper introduces a kinetic code that simulates gamma-ray burst (GRB) afterglow emission from the external forward shock and presents examples of some of its applications. One interesting research topic discussed in the paper is the high-energy radiation produced by Compton scattering of the prompt GRB photons against the shock-accelerated electrons. The difference between the forward shock emission in a wind-type and a constant-density medium is also studied, and the emission due to Maxwellian electron injection is compared to the case with pure power-law electrons. The code calculates the time-evolving photon and electron distributions in the emission region by solving the relativistic kinetic equations for each particle species. For the first time, the full relativistic equations for synchrotron emission/absorption, Compton scattering, and pair production/annihilation were applied to model the forward shock emission. The synchrotron self-absorption thermalization mechanism, which shapes the low-energy end of the electron distribution, was also included in the electron equation. The simulation results indicate that inverse Compton scattering of the prompt GRB photons can produce a luminous TeV emission component, even when pair production in the emission region is taken into account. This very high-energy radiation may be observable in low-redshift GRBs. The test simulations also show that the low-energy end of a pure power-law distribution of electrons can thermalize owing to synchrotron self-absorption in a wind-type environment, but without an observable impact on the radiation spectrum. Moreover, a flattening in the forward shock X-ray light curve may be expected when the electron injection function is assumed to be purely Maxwellian instead of a power law.

Origin of highly energetic photons in gamma ray bursts

This article deals with the generation of highly energetic photons at the Gamma Ray Bursts. The model of bursts followed by gravity induced natural bremsstrahlung for decelerated mass during the core collapse following supernova. For short duration bursts using Fourier transformation of induced radiation field gives the conception of creation of energetic photons. The theoretical result somehow gives the detectable maximum energetic photons in a good extent implying the experimentally observed values of the parameters for some short duration bursts.

On the Prompt Signals of Gamma Ray Bursts

We introduce a new model of gamma ray burst (GRB) that explains its observed prompt signals, namely, its primary quasi-thermal spectrum and high energy tail. This mechanism can be applied to either assumption of GRB progenitor: coalescence of compact objects or hypernova explosion. The key ingredients of our model are: (1) The initial stage of a GRB is in the form of a relativistic quark-gluon plasma "lava"; (2) The expansion and cooling of this lava results in a QCD phase transition that induces a sudden gravitational stoppage of the condensed non-relativistic baryons and form a hadrosphere; (3) Acoustic shocks and Alfven waves (magnetoquakes) that erupt in episodes from the epicenter efficiently transport the thermal energy to the hadrospheric surface and induce a rapid detachment of leptons and photons from the hadrons; (4) The detached $e^+e^-$ and $\gamma$ form an opaque, relativistically hot leptosphere, which expands and cools to $T \sim mc^2$, or 0.5 MeV, where $e^+e^- \to 2\gamma$ and its reverse process becomes unbalanced, and the GRB photons are finally released; (5) The "mode-conversion" of Alfven waves into electromagnetic waves in the leptosphere provides a "snowplow" acceleration and deceleration that gives rise to both the high energy spectrum of GRB and the erosion of its thermal spectrum down to a quasi-thermal distribution. According to this model, the observed GRB photons should have a redshifted peak frequency at $E_p \sim \Gamma(1 + \beta/2)mc^2/(1 + z),$ where $\Gamma\sim {\cal{O}}(1)$ is the Lorentz factor of the bulk flow of the lava, which may be determined from the existing GRB data.

Probing early cosmic magnetic fields through pair echoes from high-redshift GRBs

We discuss the expected properties of pair echo emission from gamma-ray bursts (GRBs) at high redshifts ($z \gtrsim 5$), their detectability, and the consequent implications for probing intergalactic magnetic fields (IGMFs) at early epochs. Pair echos comprise inverse Compton emission by secondary electron-positron pairs produced via interactions between primary gamma-rays from the GRB and low-energy photons of the diffuse intergalactic radiation, arriving with a time delay that depends on the nature of the intervening IGMFs. At sufficiently high $z$, the IGMFs are unlikely to have been significantly contaminated by astrophysical outflows, and the relevant intergalactic radiation may be dominated by the well-understood cosmic microwave background (CMB). Pair echoes from luminous GRBs at $z \sim 5-10$ may be detectable by future facilities such as the Cherenkov Telescope Array or the Advanced Gamma-ray Imaging System, as long as the GRB primary emission extends to multi-TeV energies, the comoving IGMFs at these redshifts are $B \sim 10^{-16}-10^{-15}~{\rm Gauss}$, and the non-CMB component of the diffuse intergalactic radiation is relatively low. Observations of pair echos from high-$z$ GRBs can provide a unique, in-situ probe of weak IGMFs during the epochs of early structure formation and cosmic reionization.

Extensive testing of Schottky CdTe detectors for the ECLAIRs X-/gamma-ray camera on board the SVOM mission

We report on an on-going test campaign of more than 5000 Schottky CdTe detectors (4×4 ×1 mm 3), over a sample of twelve thousands, provided by Acrorad Co., Ltd (Japan). Six thousand four hundred of these detectors will be used to build the detection plane of the ECLAIRs camera on the Chinese–French gamma-ray burst mission SVOM. These tests aim at eliminating, from the flight model, detectors showing high leakage current and unstable behaviors. They are mandatory to fulfill the prime requirement of ECLAIRs to detect gamma-ray burst photons down to 4 keV. For better functional performance and stability, the detectors will be operated at −20 °C under a reverse bias of 600 V. Under these conditions, we found that 78% of the detectors already tested could be considered for the flight model. They show a low initial leakage current (with a mean value around 20 pA), and remain stable below 100 pA within 2 h. Using a standard analog electronics chain, we measured a mean energy resolution of 1.8 keV at 59.6 keV using an 241Am source. Because the Schottky detectors are well known to be unstable due to the bias-induced polarization effect, the high voltage power supplies on ECLAIRs will have to be switched off at regular time intervals. We investigated the polarization effect first at room temperature and low bias voltage for faster analysis. We found that the spectroscopic degradation in quantum efficiency, gain and energy resolution, starts as soon as the bias is turned on: first slowly and then dramatically after a time t p which depends on the temperature and the voltage value. Preliminary tests under in-flight conditions (−20 °C, −600 V) showed that the detectors should remain stable over a timescale larger than a day. As a by product of our test campaign, we measured the mean activation energy of 170 Schottky CdTe detectors. We found evidence for two distinct populations of detectors: the main one centered at 0.64 eV, interpreted as due to cadmium vacancies in the crystal, and the second population centered at 0.54 eV, correlated with a lower apparent resistivity.

High-energy emission as a test of the prior emission model for gamma-ray burst afterglows

Abstract We study high-energy gamma-ray afterglow emission from gamma-ray bursts (GRBs) in the prior emission model, which is proposed to explain the plateau phase of the X-ray afterglow. This model predicts the high-energy gamma-ray emission when the prompt GRB photons from the main flow are up-scattered by relativistic electrons accelerated at the external shock due to the prior flow. The expected spectrum has the peak of ∼10–100 GeV at around the end time of the plateau phase for typical GRBs, and high-energy gamma-rays from nearby and/or energetic GRBs can be detected by the current and future Cherenkov telescopes such as MAGIC, VERITAS, CTA and possibly Fermi. Multiwavelength observations by ground-based optical telescopes as well as Fermi and/or Swift satellites are important to constrain the model. Such external inverse-Compton emission may even lead to GeV–TeV gamma-ray signals with the delay time of ∼10–100 s, only if the plateau phase is short lived.

POLAR: Design of a novel X-ray polarimeter based on plastic scintillators and MAPMTs

POLAR is a space-borne hard X-ray polarimeter whose design has been optimized to measure the level of linear polarization of gamma-ray bursts (GRB) in the energy range of 50–500 keV. In POLAR, the GRB photons undergo Compton scattering in a target constituted by 1600 plastic scintillator bars. The light output from the whole target is read by 25 multi-anode photomultipliers (MAPMTs). The azimuthal distribution of the scattered photons inside the target provides the information on the GRB polarization. To be able to measure polarization of photons with energy as low as 50 keV, an energy threshold for each single channel of maximum 5 keV is required. This introduces strong constraints in the photon collection efficiency. To maximize it, detailed studies of the scintillator bar surfaces and the available wrapping materials have been performed using both Monte Carlo simulations and laboratory measurements. At present, a POLAR demonstration model (2 of the 25 units of the final design) is being tested in the laboratory. The engineering-qualification model will be ready in 2010.

Light transport in long, plastic scintillators

As a form of the input into the collaboration the group from the Andrzej Sołtan Institute for Nuclear Studies undertook a task of investigating the validity of the design of a compact detector for Gamma Ray Bursts photon polarization measurements, known as POLAR. The authors focused at the scintillation and light transport properties of ( 200 × 6 × 6 ) mm 3 BC400 plastic bars as well as of other samples of BC408 plastic in the attempt to determine whether the assembled instrument is going to achieve the performance criteria bestowed upon it by the project. The investigation revealed a strong dependence between the amplitude of a signal and distance between the precursor interaction in a scintillator and the photodetector. Accordingly to this finding an attempt has been made to determine the influence of the surface polishing quality on the overall scintillator performance. The authors consider that proper machining of scintillator pieces, adequate choice of their packaging, and proper software analysis may overcome the revealed disadvantages.

Polarization in the prompt emission of gamma-ray bursts and their afterglows

Synchrotron radiation is considered the dominant emission mechanism in the production of gamma-ray burst photons in the prompt as well as in the afterglow phase. Polarization is a characteristic feature of synchrotron radiation and its study can reveal a wealth of information on the properties of the magnetic field and of the energy distribution in gamma-ray burst jets. In this paper, I will review the theory and observations of gamma-ray burst polarization. While the theory is well established, observations have proven difficult to perform, due to the weakness of the signal. The discriminating power of polarization observations, however, cannot be overestimated.

Gamma-ray bursts and the origin of galactic positrons

A recent observation of the 511 keV electron–positron annihilation line from the Galactic bulge has prompted a debate on the origin of the galactic positrons responsible for this emission. Assuming equilibrium between annihilation and injection of positrons in the Galaxy, we investigate the possibility that positrons were produced by past gamma-ray bursts (GRBs). We compare the positron annihilation rate inferred by the observed 511 keV line, with the predicted injection rate due to e+e− pairs leaking out of individual GRBs and those pair produced by GRB photons in the dense molecular clouds at the Galactic center. We conclude that the proposed scenario is marginally consistent with observations, and can reproduce the observed normalization of the annihilation line only for higher-than-average values of the GRB rate in the Galaxy and/or of the molecular clouds optical depth for pair production.

POLAR, a compact detector for gamma-ray bursts photon polarization measurements

The design and the simulated performances of a compact detector dedicated to the measurement of GRB photon polarization is presented. Such a detector would permit to answer the question “are most of the GRB strongly polarized?” in a mission of one year in space.

The Compton trail of gamma-ray bursts: A long-after glow

As they travel through the gas of the host galaxy, some of the gamma-rays emitted in a Gamma-Ray Burst (GRB) may experience Compton scattering and reach an observer even if he is not located in the direction of the primary photon beam. Such a process will last until the GRB photons have left their host galaxy, and the ambient electron density becomes negligible. We investigate the observability of this indirect GRB light, which would be seen as a faint trail along the path of the GRB photons, long after the initial event. We find that the so-called Compton trail of a 10 51 erg GRB can easily be observed from Earth, wherever the explosion occurred in our Galaxy in the past few thousand years. Gamma-ray surveys of the Galaxy can therefore provide constraints on the true GRB rate (or number of GRBs per supernova), independently of the GRB beaming angle. We also calculate the expected light curve and shape of the emitting region as a function of time.