Abstract
The recent discovery of a kilonova from the long-duration gamma-ray burst (GRB) GRB 211211A challenges classification schemes based on temporal information alone. Gamma-ray properties of GRB ...211211A reveal an extreme event, which stands out among both short and long GRBs. We find very short variations (few milliseconds) in the lightcurve of GRB 211211A and estimate ∼1000 for the Lorentz factor of the outflow. We discuss the relevance of the short variations in identifying similar long GRBs resulting from compact mergers. Our findings indicate that in future gravitational-wave follow-up campaigns, some long-duration GRBs should be treated as possible strong gravitational-wave counterparts.
Abstract
Multiwavelength campaigns have been carried out to study the correlation between the very high-energy (VHE) γ-ray and the X-ray emissions in blazars but no conclusive results have been ...achieved yet. In this paper, we add Milagro data to the existing VHE γ-ray data from HEGRA-CT1 and Whipple and test the consistency and robustness of the reported correlation between VHE γ-ray and X-ray fluxes in Mrk 421. We found that on a monthly time-scale the correlation is robust, consistent between instruments, and described as a linear function. Furthermore, most of the fluxes on shorter time-scales are consistent with the correlation within 3σA even, where σA is an estimated intrinsic scatter. However, a break-down of the correlation becomes clearly evident at high states of activity with fluxes $\rm \gtrsim \! 2.5\times 10^{-10}\, cm^{-2}\, s^{-1}$ at energies above 400 GeV independently of the time-scale, observational period, or instrument; even for single flares, the X-ray and VHE γ-ray emissions lie on the correlation until the VHE γ-ray flux reaches values higher than the one mentioned above. We have interpreted our results within the one-zone synchrotron self-Compton model. We found that describing a single and unique γ-ray/X-ray correlation strongly narrows the range of possible values of the magnetic field B when a constant value of the spectral index along the correlation is assumed.
ABSTRACT
GRB 210704A is a burst of intermediate duration (T90 ∼ 1–4 s) followed by a fading afterglow and an optical excess that peaked about 7 d after the explosion. Its properties, and in ...particular those of the excess, do not easily fit into the well-established classification scheme of gamma-ray bursts (GRBs) as being long or short, leaving the nature of its progenitor uncertain. We present multiwavelength observations of the GRB and its counterpart, observed up to 160 d after the burst. In order to decipher the nature of the progenitor system, we present a detailed analysis of the GRB high-energy properties (duration, spectral lag, and Amati correlation), its environment, and late-time optical excess. We discuss three possible scenarios: a neutron star merger, a collapsing massive star, and an atypical explosion possibly hosted in a cluster of galaxies. We find that traditional kilonova and supernova models do not match well the properties of the optical excess, leaving us with the intriguing suggestion that this event was an exotic high-energy merger.
We present the afterglow light curves produced by the deceleration of a nonrelativistic ejecta mass in a stratified circumstellar medium with a density profile n(r) ∝ r−k with k = 0, 1, 1.5, 2, and ...2.5. Once the ejecta mass is launched with equivalent kinetic energy parameterized by E(>β) ∝ β− (where β is the ejecta velocity) and propagates into the surrounding circumstellar medium, it first moves with constant velocity (the free-coasting phase), and later it decelerates (the Sedov-Taylor expansion). We present the predicted synchrotron and synchrotron self-Compton light curves during the free-coasting phase and the subsequent Sedov-Taylor expansion. In particular cases, we show the corresponding light curves generated by the deceleration of several ejecta masses with different velocities launched during the coalescence of binary compact objects and the core collapse of dying massive stars, which will contribute at distinct timescales, frequencies, and intensities. Finally, using the multiwavelength observations and upper limits collected by a large campaign of orbiting satellites and ground telescopes, we constrain the parameter space of both the kilonova (KN) afterglow in GW170817 and the possibly generated KN afterglow in S190814bv. Further observations on timescales of years post-merger are needed to derive tighter constraints.
The detection of high-energy astrophysical neutrinos and ultra-high-energy cosmic rays (UHECRs) provides a new way to explore sources of cosmic rays. One of the highest energy neutrino events ...detected by IceCube, tagged as IC35, is close to the UHECR anisotropy region detected by Pierre Auger Observatory. The nearby starburst (SB) galaxy, NGC 4945, is close to this anisotropic region and inside the mean angular error of the IC35 event. Considering the hypernovae contribution located in the SB region of NGC 4945, which can accelerate protons up to ~ 1017 eV and inject them into the interstellar medium, we investigate the origin of this event around this starburst galaxy. We show that the interaction of these protons with the SB region's gas density could explain Fermi-LAT gamma-ray and radio observations if the magnetic field's strength in the SB region is the order of ~ mG. Our estimated PeV neutrino events, in ten years, for this source is approximately 0.01 (4 × 10−4) if a proton spectral index of 2.4 (2.7) is considered, which would demonstrate that IC35 is not produced in the central region of this SB galaxy. Additionally, we consider the superwind region of NGC 4945 and show that protons can hardly be accelerated in it up to UHECRs.
We present magnetohydrodynamical simulations of a strong accretion on to magnetized proto-neutron stars for the Kesteven 79 (Kes 79) scenario. The supernova remnant Kes 79, observed with the Chandra ...ACIS-I instrument during approximately 8.3 h, is located in the constellation Aquila at a distance of 7.1 kpc in the galactic plane. It is a galactic and a very young object with an estimate age of 6 kyr. The Chandra image has revealed, for the first time, a point-like source at the centre of the remnant. The Kes 79 compact remnant belongs to a special class of objects, the so-called central compact objects (CCOs), which exhibits no evidence for a surrounding pulsar wind nebula. In this work, we show that the submergence of the magnetic field during the hypercritical phase can explain such behaviour for Kes 79 and others CCOs. The simulations of such regime were carried out with the adaptive-mesh-refinement code flash in two spatial dimensions, including radiative loss by neutrinos and an adequate equation of state for such regime. From the simulations, we estimate that the number of thermal neutrinos expected on the Hyper-Kamiokande Experiment is 733 ± 364. In addition, we compute the flavour ratio on Earth for a progenitor model.
Abstract
Sub-relativistic materials launched during the merger of binary compact objects and the core collapse of massive stars acquire velocity structures when expanding in a stratified environment. ...The remnant (either a spinning magnetized neutron star (NS) or a central black hole) from the compact object or core collapse could additionally inject energy into the afterglow via spin-down luminosity or/and by accreting fallback material, producing a refreshed shock, modifying the dynamics, and leading to rich radiation signatures at distinct timescales and energy bands with contrasting intensities. We derive the synchrotron light curves evolving in a stratified environment when a power-law velocity distribution parameterizes the energy of the shock, and the remnant continuously injects energy into the blast wave. As the most relevant case, we describe the latest multiwavelength afterglow observations (≳900 days) of the GW170817/GRB 170817A event via a synchrotron afterglow model with energy injection of a sub-relativistic material. The features of the remnant and the synchrotron emission of the sub-relativistic material are consistent with a spinning magnetized NS and the faster
blue
kilonova afterglow, respectively. Using the multiband observations of some short bursts with evidence of kilonovae, we provide constraints on the expected afterglow emission.
The production of both gravitational waves and short gamma-ray bursts (sGRBs) is widely associated with the merger of compact objects. Several studies have modeled the evolution of the ...electromagnetic emission using the synchrotron emission produced by the deceleration of both a relativistic top-hat jet seen off-axis, and a wide-angle quasi-spherical outflow (both using numerical studies). In this study, we present an analytical model of the synchrotron and synchrotron self-Compton (SSC) emission for an off-axis top-hat jet and a quasi-spherical outflow. We calculate the light curves obtained from an analytic model in which the synchrotron and SSC emission (in the fast- or slow-cooling regime) of an off-axis top-hat jet and a quasi-spherical outflow are decelerated in either a homogeneous or a wind-like circumburst medium. We show that the synchrotron emission of the quasi-spherical outflow is stronger than that of the off-axis jet during the first ∼10-20 days, and weaker during the next 80 days. Moreover, we show that if the off-axis jet is decelerated in a wind-like medium, then the SSC emission is very likely to be detected. Applying an MCMC code to our model (for synchrotron emission only), we find the best-fit values for the radio, optical and X-ray emission of GRB 170817A that are in accordance with observations. For GRB 170817A, we find, using our model, that the synchrotron emission generated by the quasi-spherical outflow and off-axis top-hat jet increase as F ∝ t with 0.8 and > 3, respectively. Finally, we obtain the corresponding SSC light curves that are in accordance with the very-high-energy gamma-ray upper limits derived with the GeV-TeV observatories.
Recent X-ray observations in the central compact remnant of Puppis A and other young pulsars have provided convincing evidence about the anti-magnetar nature of the so-called central compact objects ...(CCOs). The measured period derivative, corrected by the proper movement, provides exceptionally low superficial magnetic fields for such sources. Using the dipole radiation canonical model, the superficial magnetic field of the CCO (RX J0822-4300) in Puppis A was estimated to be B 2.9 × 1010 G. In this paper, we present a numerical model to interpret the unusual magnetic-field behavior in RX J0822-4300. Using the magnetohydrodynamic simulations during the hypercritical accretion phase, we propose that a variety of MeV neutrinos is created given evidence about the submergence of the magnetic field in the pulsar. We investigate the production, propagation, oscillations, and detection of MeV neutrinos from this source. The detection of neutrino events with their flavor ratios would be a compelling signature of the decreasing evolution of the magnetic field not only in RX J0822-4300 but also in CCO candidates.
ABSTRACT
We collected the optical light-curve data of 227 gamma-ray bursts (GRBs) observed with the TAROT, COATLI, and RATIR telescopes. These consist of 133 detections and 94 upper limits. We ...constructed average light curves in the observer and rest frames in both X-rays (from Swift/X-Ray Telescope) and the optical. Our analysis focused on investigating the observational and intrinsic properties of GRBs. Specifically, we examined observational properties, such as the optical brightness function of the GRBs at T = 1000 s after the trigger, as well as the temporal slope of the afterglow. We also estimated the redshift distribution for the GRBs within our sample. Of the 227 GRBs analysed, we found that 116 had a measured redshift. Based on these data, we calculated a local rate of ρ0 = 0.2 Gpc−3 yr−1 for these events with z < 1. To explore the intrinsic properties of GRBs, we examined the average X-ray and optical light curves in the rest frame. We use the afterglowpy library to generate synthetic curves to constrain the parameters typical of the bright GRB jet, such as energy (〈E0〉 ∼ 1053.6 erg), opening angle (〈θcore〉 ∼ 0.2 rad), and density (〈n0〉 ∼ 10−2.1 cm−3). Furthermore, we analyse microphysical parameters, including the fraction of thermal energy in accelerated electrons (〈ϵe〉 ∼ 10−1.37) and in the magnetic field (〈ϵB〉 ∼ 10−2.26), and the power-law index of the population of non-thermal electrons (〈p〉 ∼ 2.2).
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