We derive basic analytical results for the timing and decay of the gamma-ray burst (GRB) counterpart and delayed afterglow light curves for a brief emission episode from a relativistic surface ...endowed with angular structure, consisting of a uniform core of size (Lorentz factor and surface emissivity are angle independent) and an axially symmetric power-law envelope ( ). In this "large-angle emission" model, radiation produced during the prompt emission phase (GRB) at angles arrives at the observer well after the burst (delayed emission). The dynamical time range of the very fast decaying GRB "tail" and of the flat afterglow "plateau" and the morphology of the GRB counterpart/afterglow are all determined by two parameters: the core's parameter and the envelope's Lorentz factor index g, leading to three types of light curves that display three post-GRB phases (type 1: tail, plateau/slow decay, post-plateau/normal decay), two post-GRB phases (type 2: tail and fast decay), or just one (type 3: normal decay). We show how X-ray light-curve features can be used to determine core and envelope dynamical and spectral parameters. Testing of the large-angle emission model is done using the Swift/XRT X-ray emission of two afterglows of type 1 (GRB 060607A, GRB 061121), one of type 2 (GRB 061110A), and one of type 3 (GRB 061007). We find that the X-ray afterglows with plateaus require an envelope Lorentz factor and a comoving-frame emissivity ; thus, for a typical afterglow spectrum , the lab-frame energy release is uniform over the emitting surface.
We present the light curves and spectra of 24 afterglows that have been monitored by Fermi-LAT at 0.1-100 GeV over more than a decade. All light curves (except 130427) are consistent with a single ...power law starting from their peaks, which occur in most cases before the burst end. The light curves display a brightness-decay rate correlation, with all but one (130427) of the bright afterglows decaying faster than the dimmer afterglows. We attribute this dichotomy to the quick deposition of relativistic ejecta energy in the external shock for the brighter/faster-decaying afterglows and to an extended energy injection in the afterglow shock for the dimmer/slower-decaying light curves. The spectra of six afterglows (090328, 100414, 110721, 110731, 130427, 140619B) indicate the existence of a harder component above a spectral dip or ankle at energies of 0.3-3 GeV, offering evidence for inverse-Compton emission at higher energies and suggesting that the harder power-law spectra of five other LAT afterglows (130327B, 131231, 150523, 150627, 160509) could also be inverse-Compton, while the remaining, softer LAT afterglows should be synchrotron emission. Marginal evidence for a spectral break and softening at higher energies is found for two afterglows (090902B and 090926).
We investigate the adiabatic and radiative (synchrotron and inverse-Compton) cooling of relativistic electrons whose injected or initial distribution with energy is a power law. Analytical and ...numerical results are presented for the cooling-tail and the cooled-injected distribution that develop below and above the typical energy of injected electrons, for the evolution of the peak energy Ep of the synchrotron emission spectrum. The pulse shape resulting from an episode of electron injection is also analyzed. The synchrotron emission calculated numerically is compared with the spectrum and shape of Gamma-ray burst (GRB) pulses. Both adiabatic and radiative cooling processes lead to a softening of the pulse spectrum, and both types of cooling processes lead to pulses peaking earlier and lasting shorter at higher energy, quantitatively consistent with observations. For adiabatic-dominated electron cooling, a power-law injection rate Ri suffices to explain the observed power-law GRB low-energy spectra. Synchrotron-dominated cooling leads to power-law cooling-tails that yield the synchrotron standard slope = −3/2 provided that Ri ∼ B2, which is exactly the expectation if the magnetic field is a constant fraction of the post-shock energy density. Increasing (decreasing) Ri and decreasing (increasing) B(t) lead to harder (softer, respectively) slopes than the standard value and to nonpower-law (curved) cooling-tails. Inverse-Compton cooling yields four values for the slope but, as for synchrotron, other Ri or B histories yield a wider range of slopes and curved low-energy spectra. Feedback between the power-law segments that develop below and above the typical injected electron leads to a synchrotron spectrum with many breaks.
Mechanisms for electron injection, trapping, and loss in the near‐Earth space environment are investigated during the October 2012 “double‐dip” storm using our ring current‐atmosphere interactions ...model with self‐consistent magnetic field (RAM‐SCB). Pitch angle and energy scattering are included for the first time in RAM‐SCB using L and magnetic local time (MLT)‐dependent event‐specific chorus wave models inferred from NOAA Polar‐orbiting Operational Environmental Satellites (POES) and Van Allen Probes Electric and Magnetic Field Instrument Suite and Integrated Science observations. The dynamics of the source (approximately tens of keV) and seed (approximately hundreds of keV) populations of the radiation belts simulated with RAM‐SCB is compared with Van Allen Probes Magnetic Electron Ion Spectrometer observations in the morning sector and with measurements from NOAA 15 satellite in the predawn and afternoon MLT sectors. We find that although the low‐energy (E< 100 keV) electron fluxes are in good agreement with observations, increasing significantly by magnetospheric convection during both SYM‐H dips while decreasing during the intermediate recovery phase, the injection of high‐energy electrons is underestimated by this mechanism throughout the storm. Local acceleration by chorus waves intensifies the electron fluxes at E≥50 keV considerably, and RAM‐SCB simulations overestimate the observed trapped fluxes by more than an order of magnitude; the precipitating fluxes simulated with RAM‐SCB are weaker, and their temporal and spatial evolutions agree well with POES/Medium Energy Proton and Electron Detectors data.
Key Points
First RAM‐SCB simulations with 2‐D (MLT‐ and L‐dependent) event‐specific chorus wave models inferred from LEO and RBSP data
The measured low‐energy trapped and precipitating electron fluxes are well reproduced by magnetospheric convection
Local acceleration by chorus waves intensifies the electron fluxes at energies E greater than approximately 50 keV and overestimates observations
ABSTRACT We develop a numerical formalism for calculating the distribution with energy of the (internal) pairs formed in a relativistic source from unscattered MeV-TeV photons. For gamma-ray burst ...(GRB) afterglows, this formalism is more suitable if the relativistic reverse shock that energizes the ejecta is the source of the GeV photons. The number of pairs formed is set by the source GeV output (calculated from the Fermi-LAT fluence), the unknown source Lorentz factor, and the unmeasured peak energy of the LAT spectral component. We show synchrotron and inverse-Compton light curves expected from pairs formed in the shocked medium and identify some criteria for testing a pair origin of GRB optical counterparts. Pairs formed in bright LAT afterglows with a Lorentz factor in the few hundreds may produce bright optical counterparts ( ) lasting for up to one hundred seconds. The number of internal pairs formed from unscattered seed photons decreases very strongly with the source Lorentz factor, thus bright GRB optical counterparts cannot arise from internal pairs if the afterglow Lorentz factor is above several hundreds.
We investigate numerically the ability of three models (jet, structured outflow and energy injection) to accommodate the optical light-curve breaks observed in 10 gamma-ray burst (GRB) afterglows ...(980519, 990123, 990510, 991216, 000301c, 000926, 010222, 011211, 020813 and 030226), as well as the relative intensities of the radio, optical and X-ray emissions of these afterglows. We find that the jet and structured outflow models fare much better than energy injection model in accommodating the multiwavelength data of the above 10 afterglows. For the first two models, a uniform circumburst medium provides a better fit to the optical light-curve break than a wind-like medium with a r−2 stratification. However, in the only two cases where the energy injection model may be at work, a wind medium is favoured (an energy injection is also possible in a third case, the afterglow 970508, whose optical emission exhibited a sharp rise, but not a steepening decay). The best-fitting parameters obtained with the jet model indicate an outflow energy of 2 × 1050 to 6 × 1050 ergs and a jet opening of 2°–3°. Structured outflows with a quasi-uniform core have a core angular size of –1° and an energy per solid angle of 0.5 × 1053 to 3 × 1053 erg sr−1, surrounded by an envelope where this energy falls off roughly as θ−2 with angle from the outflow axis, requiring thus the same energy budget as jets. Circumburst densities are found to be typically in the range 0.1–1 cm−3, for either model. We also find that the reverse shock emission resulting from the injection of ejecta into the decelerating blast wave at about 1 d after the burst can explain the slowly decaying radio light curves observed for the afterglows 990123, 991216 and 010222.
The novel coronavirus disease 2019 (COVID-19) pandemic has had a profound impact on antenatal care, forcing authorities to consider some medical services unessential in the pursuit of avoiding the ...valid risk of patient contamination. The oral glucose tolerance test (OGTT) has been in some cases overlooked for screening in pregnancy, with potential detrimental consequences in terms of not diagnosing and treating gestational diabetes mellitus (GDM). The number of tests has dropped by 35% in 2020 in our hospital. We make a plea for resuming OGTT at 24-28 weeks gestation at least for women considered at high risk.
The X-ray light curves of the gamma-ray burst (GRB) afterglows monitored by Swift display one to four phases of power-law decay. In the chronological order they are: the burst tail, the ‘hump’, the ...standard decay, and the post-jet-break decay. We compare the decay indices and spectral slopes measured during each phase with the expectations for the forward-shock model to identify the processes which may be at work and to constrain some of their properties. The large-angle emission produced during the burst, but arriving at observer later, is consistent with the GRB tail decay for less than half of bursts. Several afterglows exhibit a slow, unbroken power-law decay from burst end until 1 d, showing that the forward-shock emission is, sometimes, present from the earliest afterglow observations. In fact, the forward-shock synchrotron emission from a very narrow jet (half-angle less than 1°) is consistent with the decay of 75 per cent of GRB tails. The forward-shock inverse-Compton emission from a narrow jet that does not expand sideways also accommodates the decay of 80 per cent of GRB tails. The X-ray light curve hump can be attributed to an increasing kinetic energy per solid angle of the forward-shock region visible to the observer. This increase could be due to the emergence of the emission from an outflow seen from a location outside its opening. However, the correlations among the hump timing, flux, and decay index expected in this model are not confirmed by observations. Thus, the increase in the forward-shock kinetic energy is more likely caused by some incoming ejecta arriving at the shock during the afterglow phase. The jet interpretation for the burst tails and the energy injection scenario for the hump lead to a double-jet outflow structure consisting of a narrow GRB jet which precedes a wider afterglow outflow of lower kinetic energy per solid angle but higher total energy.
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