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Four snapshots of the rest-mass density evolution of the RM. The rest-mass density is normalized to the EM density ρ ext = 8 × 10 − 14 g cm − 3 . The time displayed in each panel refers to the laboratory frame time. In the upper-left panel, we show the
Source publication
We extend an existing theoretical model to explain the class of Black-Body
Dominated GRBs, namely long lasting events characterized by the presence of a
notable thermal component trailing the GRB prompt emission, and a rather weak
traditional afterglow. GRB 101225A, the Christmas Burst (CB), is a prototype of
such class. It has been suggested that...
Contexts in source publication
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... Fig. 2, we show four snapshots of the RM evolution. Shortly after the start of the jet injection, within the first few seconds, the jet starts to hit the inner boundary of the CE shell (Fig. 2, upper-left panel). As a result a pair of shocks form that rapidly heat the plasma to temperatures of up to ∼ few × 10 6 K. The properties of these ...
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... Fig. 2, we show four snapshots of the RM evolution. Shortly after the start of the jet injection, within the first few seconds, the jet starts to hit the inner boundary of the CE shell (Fig. 2, upper-left panel). As a result a pair of shocks form that rapidly heat the plasma to temperatures of up to ∼ few × 10 6 K. The properties of these shocks are not the standard ones expected for the forward and reverse shocks in relativistic ejecta associated with GRB afterglows. Instead, they are propagating at Newtonian speeds, start- ...
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... Instead, they are propagating at Newtonian speeds, start- ing at the funnel walls and moving laterally towards the jet axis. In the process, the shocks are also penetrating the CE shell and moving sideways, in a direction almost perpendic- ular to the jet propagation and, hence, to the line of sight (the shock can be seen as white shades in Fig. 2, upper-right ...
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... we have seen in the previous section, the X-ray flux den- sity in our models peaks too late with respect to the obser- vations. In Fig. 20, we display the X-ray light curves of all the models (except D3) in Table 1. The peak flux is model dependent: broader jets (T20) peak earlier (t X,peak (T20) 0.35 d) than the RM (t X,peak (RM) 0.48 d) or narrower jets (t X,peak (T14) 0.6 d). The model which peaks latest is G2 (previously discussed in Section 5.1). The model D2 is the ...
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... The model D2 is the one with the lowest X-ray flux density. This is easy to understand since it is the model where the mass of the CE-early-interaction wedge is smaller, and where the CE- shell/jet interaction converts the smallest amount of kinetic into thermal energy. Changing only the stratification of the CE shell (compare models GS and RM in Fig. 20) we realize that a stratified CE shell only increases the flux by factors of 2 at early times, but after 0.5 d the flux is very similar to that of the RM. G0 model shows a similar behaviour at early times since we decreased the innermost radius of the CE shell (keeping the opening angle of the funnel constant). Thus, as we have ...
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... radius of the CE shell (keeping the opening angle of the funnel constant). Thus, as we have increased the CE-early-interaction wedge, the emission grows at early times. However, even more im- portant than the small increase of the X-ray flux at early times is the fact that at late times, the X-ray light curve of model G0 (also of model M2; Fig. 20) does not flatten, as a result of the 10 times smaller EM rest-mass density than in the ...
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... shocks, the prop- erties of which are very similar in the standard and high- resolution runs, or the thermal emission, dominated by the jet/CE-shell interaction. To show that the thermal emission is roughly the same in all three cases we have explicitly com- puted the light curves due to thermal emission processes for the different resolutions (Fig. B2). The fact that the syn- thetic emission depends only weakly on the resolution is be- cause the jet/CE-shell interaction region is sufficiently well resolved in all cases. Therefore, we are justified in choosing a mesh size nr × n θ = 5400 × 270 (standard resolution) for all our simulations, because it gives the best trade-off between ...
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... density Jy Figure B2. Light curves for the RM considering only the (ther- mal) bremsstrahlung-BB contribution, comparing the conver- gence of the results employing different mesh sizes, nr × n θ : 5400 × 270 (standard; solid lines), 10800 × 540 (high; thick dashed lines) and 2700 × 135 (low; thin dashed lines). ...
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... The radiation is ubiquitous in all high-energy astrophysical scenarios, and in many of them, radiative transference has large effects in the dynamics of the system, especially in scenarios where the radiation is strongly coupled with the matter. Examples of scenarios like these include corecollapse supernovae and supernova shock breakout (Shibata et al. 2011;Kuroda et al. 2012Kuroda et al. , 2016Roberts et al. 2016;Suzuki et al. 2016;Obergaulinger et al. 2018;Skinner et al. 2019), jets from active galactic nuclei (AGNs), microquasars, tidal disruption events and gamma-ray bursts (GRBs; Aloy & Rezzolla 2006;Cuesta-Martínez et al. 2015a, 2015bRivera-Paleo & Guzmán 2016;De Colle et al. 2017;Aloy et al. 2018;Rivera-Paleo & Guzmán 2018), accretion of material onto black holes (Zanotti et al. 2011;Fragile et al. 2012;Sadowski et al. 2013;Parfrey & Tchekhovsko 2017;Dai et al. 2018;Liska et al. 2018;Fernández et al. 2019), and merger and post-merger of compact objects (Foucart et al. 2015;Sekiguchi et al. 2016;Fujibayashi et al. 2017;Kyutoku et al. 2018). In the most complex cases, the numerical models that emulate the radiation field of these high-energy astrophysical phenomena should include the solution of the Boltzmann radiation transfer equation, for either photons or neutrinos. ...
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... In these proceedings, we describe the setup and results of our reference model (RM). Interested readers are encouraged to review the complete references of our work [7,8], where we perform an exhaustive parametric study of all the elements of the system. ...
... This gap is artificial and is created with the only purpose to let the jet accelerate before the interaction with the CE shell occurs. Furthermore we have checked that the presence of this gap has a negligible impact in our results [7]. At R 0 an ultrarelativistic jet with an initial Lorentz factor Γ i = 80 and a specific enthalpy h i = 5 is injected for t inj = 7000/(1 + z) s. ...
... During the CE phase the outer shells of the massive star are expelled into the external medium (mostly in the equatorial plane), with roughly the escape velocity, thus creating a highdensity enviroment. This debris forms the so-called CE shell of the system [7]. Eventually the NS will merge with the core of the companion and form a black hole/disk system (or even a magnetar), able to power an ultrarelativistic jet which will interact with the surrounding CE shell. ...
... In these proceedings, we describe the setup and results of our reference model (RM). Interested readers are encouraged to review the complete references of our work [7,8], where we perform an exhaustive parametric study of all the elements of the system. ...
... This gap is artificial and is created with the only purpose to let the jet accelerate before the interaction with the CE shell occurs. Furthermore we have checked that the presence of this gap has a negligible impact in our results [7]. At R 0 an ultrarelativistic jet with an initial Lorentz factor Γ i = 80 and a specific enthalpy h i = 5 is injected for t inj = 7000/(1 + z) s. ...
Blackbody-dominated (BBD) gamma-ray bursts (GRBs) are events characterized by
the absence of a typical afterglow, long durations and the presence of a
significant thermal component following the prompt gamma-ray emission. GRB
101225A (the `Christmas burst') is a prototype of this class. A plausible
progenitor system for it, and for the BBD-GRBs, is the merger of a neutron star
(NS) and a helium core of an evolved, massive star. Using relativistic
hydrodynamic simulations we model the propagation of an ultrarelativistic jet
through the enviroment created by such a merger and we compute the whole
radiative signature, both thermal and non-thermal, of the jet dynamical
evolution. We find that the thermal emission originates from the interaction
between the jet and the hydrogen envelope ejected during the NS/He merger.
The final collapse of the cores of massive stars can lead to a wide variety of outcomes in terms of electromagnetic and kinetic energies, nucleosynthesis, and remnants. The association of this wide spectrum of explosion and remnant types with the properties of the progenitors remains an open issue. The rotation and magnetic fields in Wolf–Rayet stars of subsolar metallicity may explain extreme events such as superluminous supernovae and gamma-ray bursts powered by proto-magnetars or collapsars. Continuing with numerical studies of magnetorotational core collapse, including detailed neutrino physics, we focus on progenitors with zero-age main-sequence masses in the range between 5 and 39 ${\rm M}_{\odot }$. The pre-collapse stars are 1D models employing prescriptions for the effects of rotation and magnetic fields. Eight of the 10 stars we consider are the results of chemically homogeneous evolution owing to enhanced rotational mixing . All but one of them produce explosions driven by neutrino heating (more likely for low-mass progenitors up to 8 ${\rm M}_{\odot }$) and non-spherical flows or by magnetorotational stresses (more frequent above 26 ${\rm M}_{\odot }$). In most of them and for the one non-exploding model, ongoing accretion leads to black hole formation. Rapid rotation makes subsequent collapsar activity plausible. Models not forming black holes show proto-magnetar-driven jets. Conditions for the formation of nickel are more favourable in magnetorotationally driven models, although our rough estimates fall short of the requirements for extremely bright events if these are powered by radioactive decay. However, the approximate light curves of our models suggest that a proto-magnetar or black hole spin-down may fuel luminous transients (with peak luminosities $\sim 10^{43-44}\, \textrm {erg}$).
We assess the variance of the post-collapse evolution remnants of compact, massive, low-metallicity stars, under small changes in the degrees of rotation and magnetic field of selected pre-supernova cores. These stellar models are commonly considered progenitors of long gamma-ray bursts. The fate of the proto-neutron star (PNS) formed after collapse, whose mass may continuously grow due to accretion, critically depends on the poloidal magnetic field strength at bounce. Should the poloidal magnetic field be sufficiently weak, the PNS collapses to a black hole (BH) within a few seconds. Models on this evolutionary track contain promising collapsar engines. Poloidal magnetic fields smooth over large radial scales (e.g. dipolar fields) or slightly augmented with respect to the original pre-supernova core yield long-lasting PNSs. In these models, BH formation is avoided or staved off for a long time, hence, they may produce proto-magnetars (PMs). Some of our PM candidates have been run for ≲ 10 s after core bounce, but they have not entered the Kelvin-Helmholtz phase yet. Among these models, some display episodic events of spin-down during which we find properties broadly compatible with the theoretical expectations for PMs (Mpns ≈ 1.85 M⊙ − 2.5 M⊙, $\bar{P}_{\rm \small PNS}\approx 1.5 - 4\,$ms, and $b^{\rm surf}_pns \lesssim 10^{15}\,$G) and their very collimated supernova ejecta has nearly reached the stellar surface with (still growing) explosion energies ≳ 2 × 1051 erg.
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Motivated by the many associations of $\gamma$-ray bursts (GRBs) with energetic supernova (SN) explosions, we study the propagation of relativistic jets within the progenitor star in which a SN shock wave may be launched briefly before the jets start to propagate. Based on analytic considerations and verified with an extensive set of 2D axisymmetric relativistic hydrodynamic simulations, we have estimated a threshold intrinsic jet luminosity, $L_{\rm j}^{\rm thr}$, for successfully launching a jet. This threshold depends on the structure of the progenitor and, thus, it is sensible to its mass and to its metallicity. For a prototype host of cosmological long GRBs, a low-metallicity star of 35$\,M_{\odot}$, it is $L_{\rm j}^{\rm thr} \simeq 1.35\times 10^{49}\,$erg$\,$s$^{-1}$. The observed equivalent isotropic $\gamma$-ray luminosity, $L_{\rm \gamma,iso,BO} \simeq 4 \epsilon_\gamma L_{\rm j} \theta_{\rm BO}^{-2}$, crucially depends on the jet opening angle after breakout, $\theta_{\rm BO}$, and on the efficiency for converting the intrinsic jet luminosity into $\gamma$-radiation, $\epsilon_\gamma$. Highly energetic jets can produce low-luminosity events if either their opening angle after the breakout is large, which is found in our models, or if the conversion efficiency of kinetic and internal energy into radiation is low enough. Beyond this theoretical analysis, we show how the presence of a SN shock wave may reduce this luminosity threshold by means of numerical simulations. We foresee that the high-energy transients released by jets produced near the luminosity threshold will be more similar to llGRBs or XRFs than to GRBs.
The various stages of baryonic gamma-ray burst afterglow blast waves are reviewed. These are responsible for the afterglow emission from which much of our understanding of gamma-ray bursts derives. Initially, the blast waves are confined to the dense medium surrounding the burster (stellar envelope or dense wind), giving rise to a jet-cocoon structure. A massive ejecta is released and potentially fed by ongoing energy release from the burster and a forward-reverse shock system is set up between ejecta and ambient density. Ultimately the blast wave spreads sideways and slows down, and the dominant afterglow emission shifts from X-rays down to radio. Over the past years significant progress has been made both observationally and theoretically/numerically in our understanding of these blast waves, unique in the universe due to their often incredibly high initial Lorentz factors of 100-1000. The recent discovery of a short gamma-ray burst counterpart to a gravitational wave detection (GW 170817) brings the promise of a completely new avenue to explore and constrain the dynamics of gamma-ray burst blast waves.
The early X-ray afterglows of gamma-ray bursts (GRBs) are usually well described by absorbed power laws. However, in some cases, additional thermal components have been identified. The origin of this emission is debated, with proposed explanations including supernova shock breakout, emission from a cocoon surrounding the jet, as well as emission from the jet itself. A larger sample of detections is needed in order to place constraints on these different models. Here we present a time-resolved spectral analysis of 74 GRBs observed by Swift XRT in a search for thermal components. We report six detections in our sample, and also confirm an additional three cases that were previously reported in the literature. The majority of these bursts have a narrow range of blackbody radii around ~ 2 x 10^{12} cm, despite having a large range of luminosities (L ~ 10^{47} - 10^{51} erg s^{-1}). This points to an origin connected to the progenitor stars, and we suggest that emission from a cocoon breaking out from a thick wind may explain the observations. For two of the bursts in the sample, an explanation in terms of late prompt emission from the jet is instead more likely. We also find that these thermal components are preferentially detected when the X-ray luminosity is low, which suggests that they may be hidden by bright afterglows in the majority of GRBs.
