Afterglow Peak Research Articles

X-ray Afterglow limits on the viewing angles of short gamma-ray bursts

Abstract The behavior of a short gamma-ray burst (sGRB) afterglow lightcurve can reveal the angular structure of the relativistic jet and constrain the observer’s viewing angle θobs. The observed deceleration time of the jet, and, therefore, the time of the afterglow peak, depends on the observer’s viewing angle. A larger viewing angle leads to a later peak of the afterglow and a lower flux at peak. We utilize the earliest afterglow detections of 58 sGRBs detected with the Neil Gehrels Swift Observatory X-ray Telescope to constrain the ratio of the viewing angle θobs to the jet’s core θc. We adopt a power-law angular jet structure in both energy E(θ)∝θ−a and Lorentz factor Γ(θ)∝θ−b beyond the core. We find that either sGRBs are viewed within θobs/θc < 1 or the initial Lorentz factor of material in their jet’s core is extremely high (Γ0 > 500). If we consider tophat jets, we constrain 90% of our sample to be viewed within θobs/θc < 1.06 and 1.15 for our canonical and conservative afterglow scenarios. For a subset of events with measurements of the jet break, we can constrain Γ0θc ≳ 30. This confirmation that cosmological sGRBs are viewed either on-axis or very close to their jet’s core has significant implications for the nature of the prompt gamma-ray production mechanism and for the rate of future sGRB detections coincident with gravitational waves (GWs), implying that they are extremely rare.

GRB 221009A: Revealing a Hidden Afterglow during the Prompt Emission Phase with Fermi-GBM Observations

Recently, LHAASO reported the detection of the brightest-of-all-time GRB 221009A, revealing the early onset of a TeV afterglow. We analyze the spectral evolution of the X-ray/gamma-ray emission of GRB 221009A measured by the Fermi Gamma-ray Burst Monitor (GBM) during the dips of two prompt emission pulses (i.e., intervals T 0 + [300–328] s and T 0 + [338–378] s, where T 0 is the GBM trigger time). We find that the spectra at the dips transit from the Band function to a power-law function, indicating a transition from the prompt emission to the afterglow. After ∼T 0 + 660 s, the spectrum is well described by a power-law function, and the afterglow becomes dominant. Remarkably, the underlying afterglow emission at the dips smoothly connect with the afterglow after ∼T 0 + 660 s. The entire afterglow emission measured by GBM can be fitted by a power-law function F ∼ t −0.95±0.05, where t is the time since the first main pulse at T* = T 0 + 226 s, consistent with the TeV afterglow decay measured by LHAASO. The start time of this power-law decay indicates that the afterglow peak of GRB 221009A should be earlier than T 0 + 300 s. We also test the possible presence of a jet break in the early afterglow light curve, finding that both the jet break model and single power-law decay model are consistent with the GBM data. The two models cannot be distinguished with the GBM data alone because the inferred jet break time is quite close to the end of the GBM observations.

First results of a new quadrupole minimum-B permanent magnet electron cyclotron resonance ion source

The first experimental results of a novel permanent magnet electron cyclotron resonance ion source (ECRIS) with a minimum-B quadrupole magnetic field topology are presented. Bremsstrahlung measurements indicate that the electrons can reach energies of 150–200 keV. Ion charge states up to Ar11+ and Kr15+ were detected in the charge state distributions of the extracted beams. Measurements in pulsed operation mode reveal an afterglow peak, which implies that high charge state ions are confined electrostatically similar to a conventional ECRIS. The potential applications and future development of the ion source are discussed.

GRB 180325A: dust grain-size distribution and interstellar iron nanoparticles contribution

ABSTRACT We modelled dust grain-size distributions for carbonaceous and silicates dust, as well as for free-flying iron nanoparticles in the environment of a γ-ray burst (GRB) afterglow, GRB 180325A. This GRB, at a redshift ($z$) of 2.2486, has an unambiguous detection of the 2175 Å extinction feature with RV = 4.58 and AV = 1.58 mag. In addition to silicates, polycyclic aromatic hydrocarbons (PAH), and graphite, we used iron nanoparticles grain-size distributions for the first time to model the observed extinction curve of GRB 180325A. We fit the observed extinction for four model permutations, using 232 sets of silicates, graphite, carbon abundance in hydrocarbon molecules (bC), and fraction of iron abundance in free-flying nanoparticles (YFe). These four different permutations were chosen to test iron nanoparticles significance and carbon abundance in hydrocarbons. Our results indicate that iron nanoparticles contribution is insignificant and there is a degeneracy of carbon abundances, with the range (0.0 ≤ bC ≤ 0.7) × 10−5 providing the best-fit to the observed extinction curve of GRB 180325A. We therefore favour the simplest model of silicates and PAHs. The silicates are dominant and contribute to the entire wavelength range of the GRB extinction curve while graphite contributes towards both the 2175 Å bump and the ultraviolet (UV) extinction. The afterglow peak luminosity (1.5 × 1051 erg s−1) indicates dust destruction may have taken place. We conclude that further investigations into other potential contributors of extinction are warranted, particularly for steep UV extinction.

Status and prospects of the 60 GHz SEISM ion source

SEISM is a unique ECR ion source operating at a frequency of 60 GHz. The prototype is based on a simple magnetic geometry, the cusp, allowing the use of polyhelix coils (developed with LNCMI, Grenoble) to generate the closed ECR surface at 2.14T. The plasma is sustained by a high intensity HF pulse (up to 300kW). Previous experiments at LNCMI have successfully demonstrated the establishment of the nominal magnetic field and the extraction of ion beams with a current density up to 1 A cm-2. The presence of afterglow peaks was also observed, proving the existence of ion confinement in a CUSP ECR source. An experimental campaign is carried out in 2021 using a new transport line designed to improve the transmission of the beam to the new detectors. Short and long-term research plans are presented to transform this high current density into a high intensity ion beam that can be used for accelerators of the future.

The early afterglow of GRB 190829A

ABSTRACT GRB 190829A at z = 0.0785 is the fourth closest long GRB ever detected by the Neil Gehrels Swift observatory, and the third confirmed case with a very high-energy component. We present our multiwavelength analysis of this rare event, focusing on its early stages of evolution, and including data from Swift, the MASTER global network of optical telescopes, ALMA, and ATCA. We report sensitive limits on the linear polarization of the optical emission, disfavouring models of off-axis jets to explain the delayed afterglow peak. The study of the multiwavelength light curves and broad-band spectra supports a model with at least two emission components: a bright reverse shock emission, visible at early times in the optical and X-rays and, later, in the radio band; and a forward shock component dominating at later times and lower radio frequencies. A combined study of the prompt and afterglow properties shows many similarities with cosmological long GRBs, suggesting that GRB 190829A is an example of classical GRBs in the nearby universe.

Radio afterglows of binary neutron star mergers: a population study for current and future gravitational wave observing runs

Following the historical observations of GW170817 and its multi-wavelength afterglow, more radio afterglows from neutron star mergers are expected in the future as counterparts to gravitational wave inspiral signals. Our aim is to describe these events using our current knowledge of the population of neutron star mergers based on gamma-ray burst science, and taking into account the sensitivities of current and future gravitational wave and radio detectors. We combined analytical models for the merger gravitational wave and radio afterglow signals to a population model prescribing the energetics, circum-merger density and other relevant parameters of the mergers. We reported the expected distributions of observables (distance, orientation, afterglow peak time and flux, etc.) for future events and studied how these can be used to further probe the population of binary neutron stars, their mergers and related outflows during future observing campaigns. In the case of the O3 run of the LIGO-Virgo Collaboration, the radio afterglow of one third of gravitational-wave-detected mergers should be detectable (and detected if the source is localized thanks to the kilonova counterpart) by the Very Large Array. Furthermore, these events should have viewing angles similar to that of GW170817. These findings confirm the radio afterglow as a powerful insight into these events, although some key afterglow-related techniques, such as very long baseline interferometry imaging of the merger remnant, may no longer be feasible as the gravitational wave horizon increases.

Detectability of neutron star merger afterglows

ABSTRACT VLBI and JVLA observations revealed that GW170817 involved a narrow jet (θj ≈ 4°) that dominated the afterglow peak at our viewing angle, θobs ≈ 20°. This implies that at the time of the afterglow peak, the observed signal behaved like an afterglow of a top-hat jet seen at θobs ≫ θj, and it can be modelled by analytic expressions that describe such jets. We use a set of numerical simulations to calibrate these analytic relations and obtain generic equations for the peak time and flux of such an afterglow as seen from various observing angles. Using the calibrated equations and the estimated parameters of GW170817, we estimate the detectability of afterglows from future double neutron star mergers during the Advanced LIGO/Virgo observation run O3. GW170817 took place at a relatively low-density environment. Afterglows of similar events will be detectable only at small viewing angles, θobs ≲ 20°, and only 20 per cent of the GW detections of these events will be accompanied by a detectable afterglow. At higher densities, more typical to sGRB sites, up to $70\,\rm{per\,cent}$ of the GW detections are expected to be followed by a detectable afterglow, typically at θobs ∼ 30°. We also provide the latest time one should expect an afterglow detection. We find that for typical parameters, if the jet emission had not been detected within about a year after the merger, it is unlikely to be ever detected.

Optical properties of Mn2+ doped CsCdF3: A potential real-time and retrospective UV and X-ray dosimeter material

Luminescence measurements of CsCdF3:Mn reveal material properties suitable for UV and X-ray sensing. Mn2+ substitutes for Cd2+ with octahedral crystal field parameters 10Dq = 7020 ± 120 cm−1 and B = 773 ± 13 cm−1. UV stimulation at 250 nm results in intense Mn2+ emission and also in the production of F-centers and additional defects. Continuous 250 nm stimulation charges the material, enhancing the Mn2+ emission intensity over time due to the filling of shallow traps that contribute to persistent luminescence. When the stimulation is ceased, Mn2+ emission is observed as an afterglow. F-centers give rise to optically stimulated luminescence (OSL) that is temporally stable and can be stimulated at wavelengths near 300 nm. We propose a model that describes these effects, where UV stimulation results in electron transfer from Mn2+ to the conduction band and subsequent electron trapping in various defect states. X-ray stimulation produces Mn2+ radioluminescence that varies in intensity by 0.004%/Gy after a 300 Gy priming dose. The X-ray irradiation also produces OSL-active F-centers and the defects that cause the afterglow. Thermoluminescence measurements reveal low-temperature peaks that are correlated with the afterglow and high-temperature peaks that are correlated with the OSL, after both X-ray and UV irradiations. The luminescence of Mn2+ in CsCdF3:Mn may be useful for radiation sensing, where the real-time changes in Mn2+ emission under X-ray and UV stimulation allow for real-time dose measurements, and the OSL induced by each irradiation allows for retrospective dose monitoring.

The trap bag concept of afterglow luminescence

This article explains the behavior of afterglow luminescence using the trap bag concept, in which a constant phosphor dose contains a presumed bag with the ability to capture or release electrons through its opening. Luminescence is emitted as the bag releases the captured electrons. The electron-holding capacity is determined by the irradiation conditions, the width of the opening, and the electron activation; these factors are inherent properties of the long persistent luminescence (PLUM) dose and are affected by the thermal status. During the afterglow stage, higher temperatures may result in a wider opening and increased activation of electrons released from the bag, thus creating a higher light intensity and leading to the quicker exhaustion of the electrons within. In contrast, the opposite phenomenon will occur at lower temperatures. This article provides a detailed explanation of the trap bag concept at various thermal statuses and provides a method for delaying the afterglow peak profile through temperature change. Experimental tests were performed to confirm the proposed concept.

Peaks of optical and X-ray afterglow light curves

The peaks of 30 optical afterglows and 14 X-ray light-curves display a good anticorrelation of the peak flux with the peak epoch: F_p ~ t_p^{-2.0} in the optical, F_p ~ t_p^{-1.6} in the X-ray, the distributions of the peak epochs being consistent with each other. We investigate the ability of two forward-shock models for afterglow light-curve peaks -- an observer location outside the initial jet aperture and the onset of the forward-shock deceleration -- to account for those peak correlations. For both models, the slope of the F_p - t_p relation depends only on the slope of the afterglow spectrum. We find that only a conical jet seen off-aperture and interacting with a wind-like medium can account for both the X-ray peak relation, given the average X-ray spectral slope beta_x = 1.0, and for the larger slope of the optical peak relation. However, any conclusion about the origin of the peak flux - peak epoch correlation is, at best, tentative, because the current sample of X-ray peaks is too small to allow a reliable measurement of the F_p - t_p relation slope and because more than one mechanism and/or one afterglow parameter may be driving that correlation.

GRB early afterglow observations with the REM robotic telescope

Gamma-ray bursts (GRBs) are thought to be produced by highly relativistic outflows. Although upper and lower limits for the outflow initial Lorentz factor Γ0 are available, observational efforts to derive a direct determination of Γ0 have so far failed or have provided ambiguous results. As a matter of fact, the shape of the early-time afterglow light curve is very sensitive to Γ0, which determines the time of the afterglow peak, i.e., when the outflow and the shocked circumburst material share a comparable amount of energy. We now comment on the early-time observations of the near-infrared afterglows of GRB060418 and GRB060607A performed by the (REM) robotic telescope. For both events, the afterglow peak was singled out, which allowed us to determine the initial fireball Lorentz, Γ0 ∼ 400.

The onset of the GeV afterglow of GRB 090510

We study the emission of the short/hard GRB 090510 at energies > 0.1 GeV as observed by the Large Area Telescope (LAT) onboard the Fermi satellite. The GeV flux rises in time as t^2 and decays as t^-1.5 up to 200 s. The peak of the high energy flux is delayed by 0.2 s with respect to the main ~MeV pulse detected by the Fermi Gamma Burst Monitor (GBM). Its energy spectrum is consistent with F(E)=E^-1. The time behavior and the spectrum of the high energy LAT flux are strong evidences of an afterglow origin. We then interpret it as synchrotron radiation produced by the forward shock of a fireball having a bulk Lorentz factor Gamma ~ 2000. The afterglow peak time is independent of energy in the 0.1-30 GeV range and coincides with the arrival time of the highest energy photon (~ 30 GeV). Since the flux detected by the GBM and the LAT have different origins, the delay between these two components is not entirely due to possible violation of the Lorentz invariance. It is the LAT component by itself that allows to set a stringent lower limit on the quantum-gravity mass of 4.7 times the Planck mass.

GRB060614: a “fake” short GRB from a merging binary system

(Shortened) CONTEXT: [...] GRB060614 is the first nearby long duration GRB clearly not associated to a bright Ib/c supernova. Moreover, its duration (T_{90} ~ 100s) makes it hardly classifiable as a short GRB. It presents strong similarities with GRB970228, the prototype of the new class of fake short GRBs that appear to originate from the coalescence of binary neutron stars or white dwarfs spiraled out into the galactic halo. AIMS: Within the GRB scenario based on the model, we test if GRB060614 can be a fake or disguised short GRB. [...] METHODS: We fit GRB060614 light curves in Swift's BAT (15-150keV) and XRT (0.2-10keV) energy bands. Within the fireshell model, light curves are formed by two well defined and different components: the Proper-GRB (P-GRB), emitted at the fireshell transparency, and the extended afterglow, due to the interaction between the leftover accelerated baryonic and leptonic shell and the CBM. RESULTS: We determine the two free parameters describing the GRB source within the fireshell model. [...] A small average CBM density [...] is inferred, typical of galactic halos. The first spikelike emission is identified with the P-GRB and the following prolonged emission with the extended afterglow peak.[...] CONCLUSIONS: The anomalous GRB060614 finds a natural interpretation within our canonical GRB scenario: it is a disguised short GRB. [...] This result points to an old binary system, likely formed by a white dwarf and a neutron star, as the progenitor of GRB060614 and well justify the absence of an associated SN Ib/c. Particularly important for further studies of the final merging process are the temporal structures in the P-GRB down to 0.1s.

Direct GRB fireball Lorentz factor measurements through REM early afterglow observations

The huge energies involved in gamma-ray bursts (GRBs) coupled with the short emission time scales unavoidably imply that the emitting source is moving relativistically, with a speed close to that of light. Here we present the REM telescope observations of the early-time near-infrared light curves of the GRB 060418 and GRB 060607A afterglows. The detection of the afterglow peak provides for the first time a direct measurement of the initial Lorentz factor Γ0 of the radiating material. We find that the emitting region was indeed highly relativistic in the first seconds after the explosions, with Γ0∼400. Comparison with the Lorentz factor as determined at later epochs provides direct evidence that the emitting shell is decelerating and confirms that the afterglow emission is powered by the dissipation of bulk kinetic energy. The deceleration radius was inferred to be R dec≈1017 cm. This is much larger than the internal shocks radius (believed to power the prompt emission), thus providing further evidence for a different origin of the prompt and afterglow stages of the GRB.

REM observations of GRB 060418 and GRB 060607A: the onset of the afterglow and the initial fireball Lorentz factor determination

Context. Gamma-ray burst (GRB) emission is believed to originate in highly relativistic fireballs. Aims. Currently, only lower limits were securely set to the initia l fireball Lorentz factor 0. We aim to provide a direct measure of 0. Methods. The early-time afterglow light curve carries information about 0, which determines the time of the afterglow peak. We have obtained early observations of the near-infrared afte rglows of GRB 060418 and GRB 060607A with the REM robotic telescope. Results. For both events, the afterglow peak could be clearly singled out, allowing a firm determination of the fireball Lorentz of 0∼ 400, fully confirming the highly relativistic nature of GRB fi reballs. The deceleration radius was inferred to be Rdec≈ 10 17 cm. This is much larger than the internal shocks radius (believed to power the prompt emission), thus providing further evidence for a different origin of the prompt and afterglow stages of the GRB.

ON THE STRUCTURE OF THE BURST AND AFTERGLOW OF GAMMA-RAY BURSTS I: THE RADIAL APPROXIMATION

We have recently proposed three paradigms for the theoretical interpretation of gamma-ray bursts (GRBs). (1) The relative space–time transformation (RSTT) paradigm emphasizes how the knowledge of the entire world-line of the source from the moment of gravitational collapse is a necessary condition in order to interpret GRB data.1 (2) The interpretation of the burst structure (IBS) paradigm differentiates in all GRBs between an injector phase and a beam-target phase.2 (3) The GRB-supernova time sequence (GSTS) paradigm introduces the concept of induced supernova explosion in the supernovae-GRB association.3 The RSTT and IBS paradigms are enunciated and illustrated using our theory based on the vacuum polarization process occurring around an electromagnetic black hole (EMBH) theory. The results are summarized using figures, diagrams and a complete table with the space–time grid, the fundamental parameters and the corresponding values of the Lorentz gamma factor for GRB 991216 used as a prototype. In the following sections the detailed treatment of the EMBH theory needed to understand the results of the three above paradigms is presented. We start from the considerations on the dyadosphere formation. We then review the basic hydrodynamic and rate equations, the equations leading to the relative space–time transformations as well as the adopted numerical integration techniques. We then illustrate the five fundamental eras of the EMBH theory: the self acceleration of the e+e- pair-electromagnetic plasma (PEM pulse), its interaction with the baryonic remnant of the progenitor star, the further self acceleration of the e+e- pair-electromagnetic radiation and baryon plasma (PEMB pulse). We then study the approach of the PEMB pulse to transparency, the emission of the proper GRB (P-GRB) and its relation to the "short GRBs". Particular attention is given to the free parameters of the theory and to the values of the thermodynamical quantities at transparency. Finally the three different regimes of the afterglow are described within the fully radiative and radial approximations: the ultrarelativistic, the relativistic and the nonrelativistic regimes. The best fit of the theory leads to an unequivocal identification of the "long GRBs" as extended emission occurring at the afterglow peak (E-APE). The relative intensities, the time separation and the hardness ratio of the P-GRB and the E-APE are used as distinctive observational test of the EMBH theory and the excellent agreement between our theoretical predictions and the observations are documented. The afterglow power-law indexes in the EMBH theory are compared and contrasted with the ones in the literature, and no beaming process is found for GRB 991216. Finally, some preliminary results relating the observed time variability of the E-APE to the inhomogeneities in the interstellar medium are presented, as well as some general considerations on the EMBH formation. The issue of the GSTS paradigm will be the object of a forthcoming publication while the relevance of the iron-lines observed in GRB 991216 is shortly reviewed. The general conclusions are then presented based on the three fundamental parameters of the EMBH theory: the dyadosphere energy, the baryonic mass of the remnant, the interstellar medium density. An in depth discussion and comparison of the EMBH theory with alternative theories is presented as well as indications of further developments beyond the radial approximation, which will be the subject of paper II in this series. Future needs for specific GRB observations are outlined.

On the Structures in the Afterglow Peak Emission of Gamma-Ray Bursts

Using GRB 991216 as a prototype, it is shown that the intensity substructures observed in what is generally called the prompt emission in gamma ray bursts (GRBs) do originate in the collision between the accelerated baryonic matter (ABM) pulse with inhomogeneities in the interstellar medium (ISM). The initial phase of such process occurs at a Lorentz factor $\gamma\sim 310$. The crossing of ISM inhomogeneities of sizes $\Delta R\sim 10^{15}$ cm occurs in a detector arrival time interval of $\sim 0.4$ s implying an apparent superluminal behavior of $\sim 10^5c$. The long lasting debate between the validity of the external shock model vs. the internal shock model for GRBs is solved in favor of the first.

On a Possible Gamma-Ray Burst–Supernova Time Sequence

The data from the Chandra satellite on the iron emission lines in the afterglow of GRB 991216 are used to give further support to the theory that links the origin of the energy of gamma-ray bursts (GRBs) to the extractable energy of electromagnetic black holes (EMBHs), leading to an interpretation of the GRB-supernova correlation. Following the relative spacetime transformation paradigm and the interpretation of the burst structure paradigm, we introduce a paradigm for the correlation between GRBs and supernovae. The following sequence of events is shown as kinematically possible and consistent with the available data: (1) the GRB-progenitor star P1 first collapses into an EMBH; (2) the proper GRB and the peak of the afterglow (the extended afterglow peak emission) propagate in interstellar space until the impact on a supernova-progenitor star P2 at a distance ≤2.69 × 1017 cm, and they induce the supernova explosion; and (3) the accelerated baryonic matter pulse, originating the afterglow, reaches the supernova remnants 18.5 hr after the supernova explosion and gives rise to the iron emission lines. Some considerations of the dynamical implementation of the paradigm are presented. The concept of an induced supernova explosion, introduced here specifically for the GRB-supernova correlation, may have a more general application in relativistic astrophysics.

On the Interpretation of the Burst Structure of Gamma-Ray Bursts

Given the very accurate data from the BATSE and the Rossi X-Ray Timing Explorer and Chandra satellites, we use GRB 991216 as a prototypical case to test the theory that links the origin of the energy of gamma-ray bursts (GRBs) to the extractable energy of electromagnetic black holes (EMBHs). The fit of the afterglow fixes the only two free parameters of the model and leads to a new paradigm for the interpretation of the burst structure (the IBS paradigm). It leads as well to a reconsideration of the relative roles of the afterglow and burst in GRBs by defining two new phases in this complex phenomenon: (1) the injector phase, giving rise to the proper GRB, and (2) the beam-target phase, giving rise to the extended afterglow peak emission and to the afterglow. Such differentiation leads to a natural possible explanation of the bimodal distribution of GRBs observed by BATSE. The agreement with the observational data in regions extending from the horizon of the EMBH all the way out to the distant observer confirms the uniqueness of the model.