Progenitors Of Long Gamma-ray Bursts Research Articles

Using the COSMIC Population Synthesis Code to Investigate How Metallicity Affects the Rates of Interacting Binaries

We use COSMIC, a galaxy population synthesis code, to investigate how metallicity affects the rate of formation of massive stars with a closely orbiting compact object companion. Metallicity—a crucial component to stellar evolution and binary system formation—can affect how and when these systems form. We present the formation time of these systems at different metallicities, and the anti-correlation the rates have with metallicity. In particular, these systems occur about 10 times more frequently at metallicities between Z = 2 × 10−4 and 2 × 10−3, compared to those between Z = 2 × 10−3 and 2 × 10−2. This work serves as a prerequisite to predicting global rates of these systems as a function of redshift, ultimately giving crucial insight into our understanding of the progenitors of long gamma-ray bursts and their evolution over cosmic time.

The Dependence of Gamma-Ray Burst Jet Collimation on Black Hole Spin

Gamma-ray bursts (GRBs) are the most luminous events in the Universe and are excellent laboratories to study extreme physical phenomena in the cosmos. Despite a long trajectory of progress in understanding these highly energetic events, there are still many observed features that are yet to be fully explained. Observations of the jet opening angle of long gamma-ray bursts (LGRBs) suggest that LGRB jets are narrower for those GRBs at higher redshift. This phenomenon has been explained in the context of collimation by the stellar envelope, with denser (lower metallicity) stars at higher redshifts able to collimate the jet more effectively. However, until now, the dependence of the jet opening angle on the properties of the central engine has not been explored. We investigate the effect of black hole spin on the jet collimation angle for a magnetically launched jet, using the general relativistic radiation magnetohydrodynamical code ν bhlight. We present 3D results for a range of spin values. The simulations show that higher-spinning black holes tend to create narrower jets. If indeed LGRB progenitors in the early Universe are able to produce black hole central engines with higher spin, this could account for at least some of the observed jet opening angle-redshift correlation.

The internal metallicity distributions of simulated galaxies from EAGLE, Illustris, and IllustrisTNG at z = 1.8–4 as probed by gamma-ray burst hosts

ABSTRACT Massive stars are thought to be progenitors of long gamma-ray bursts (GRBs), most likely with a bias favouring low-metallicity progenitors. Because galaxies do not have a constant metallicity throughout, the combination of line-of-sight absorption metallicity inferred from GRB afterglow spectroscopy and of host galaxy global metallicity derived from emission lines diagnostics represents a powerful way to probe both the bias function for GRB progenitors and the chemical inhomogeneities across star-forming regions. In this study, we predict the relationship between Zabs and Zemiss using three different hydrodynamical cosmological simulations: Illustris, EAGLE, and IllustrisTNG. We find that while the qualitative shape of the curve relating emission versus absorption metallicity remains the same, the predicted relationship between these two observables is significantly different between the simulations. Using data for the host galaxy of GRB121024A for which both Zabs and Zemiss have been measured, we find marginal support for the Illustris simulation as producing the most-realistic internal metallicity distributions within star-forming galaxies at cosmic noon. Overall, all simulations predict similar properties for the bulk of the GRB host galaxy population, but each has distinct features in the tail of the Zabs-Zemiss distribution that in principle allow to discriminate between models if a sufficiently large sample of observations are available (i.e. N ≳ 11 on average). Substantial progress is expected in the near future, with upcoming JWST/NIRspec observations of 10 GRB host galaxies for which absorption metallicity from the afterglow spectra exists.

On LGRB progenitors: An approach from thermally-produced neutrinos

Gamma-ray bursts (GRB) are the most intense electromagnetic (EM) sources in the Universe. Long GRB (LGRB) correspond to those events with a typical prompt emission of more than a few seconds. It is generally assumed that they are originated after an implosion of a very massive star within a central compact object engine that can be either a black hole (BH) or a rapidly-spinning highly-magnetized neutron star (NS). Nevertheless, one of the most challenging aspects of defining a unique model is that the progenitor remains initially hidden for direct EM observation. In this work, we investigate the evolution of thermally-produced neutrino properties in both GRB progenitors to provide an alternative solution. We consider the characteristics of both progenitors and the fireball scenario to calculate the oscillation probabilities within a three-flavor admixture regime. Then we obtain the expected neutrino ratio and we also estimate the number of events from these sources that could be detected in the future Hyper-Kamiokande (Hyper-K) detector, considering a sample of previously observed GRB with remarkably signs of being magnetar-produced. Our findings indicate that examining the predicted neutrino rates result in an additional mechanism to determine the type of progenitor associated with these events. This is especially useful when, for instance, we cannot directly observe an electromagnetic counterpart, such as so-called “failed” GRB with hidden jets, or when light curve analysis is inconclusive.

Contribution to the extragalactic neutrino background from dense environment of GRB jets

Long gamma-ray bursts (GRBs) are at present well confirmed sites of acceleration of particles to relativistic energies due to observations of gamma-ray emission in the GeV-TeV energy range. We consider a scenario in which the mechanism accelerating electrons is also responsible for acceleration of hadrons in the GRB jets to multi-PeV energies. Since progenitors of long GRBs are massive stars still immersed in dense stellar clusters, these hadrons can efficiently interact with the matter after escaping from the jet. We calculate the spectra of neutrinos from the interaction of those hadrons with the matter of a huge cloud surrounding GRB. Those neutrinos form an afterglow on a time scale determined by their diffusion time scale in the cloud. Due to this long delay, their identification with any specific GRB is not possible. We estimate contribution of neutrinos from such afterglows to the extragalactic neutrino background recently reported by the IceCube Observatory.

Magnetorotational core collapse of possible GRB progenitors – II. Formation of protomagnetars and collapsars

ABSTRACT 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 protoneutron star (PNS) formed after the 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 protomagnetars (PMs). Some of our PM candidates have been run for $\lesssim 10\,$ 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 ($M_\rm {\small PNS}\approx 1.85{-}2.5\, \mathrm{M}_{\odot }$, $\bar{P}_\rm {\small PNS}\approx 1.5 {-} 4\,$ ms, and $b^{\rm surf}_\rm {\small PNS}\lesssim 10^{15}\,$ G) and their very collimated supernova ejecta have nearly reached the stellar surface with (still growing) explosion energies $\gtrsim {2} \times 10^{51}\, \textrm {erg}$.

Implications of the Low Binary Black Hole Aligned Spins Observed by LIGO

Abstract We explore the implications of the low-spin components along the orbital axis observed in an Advanced LIGO O1 run on binary black hole (BBH) merger scenarios in which the merging BBHs have evolved from field binaries. The coalescence time determines the initial orbital separation of BBHs. This, in turn, determines whether the stars are synchronized before collapse, and hence determines their projected spins. Short coalescence times imply synchronization and large spins. Among known stellar objects, Wolf–Rayet (WR) stars seem to be the only progenitors consistent with the low aligned spins observed in LIGO’s O1, provided that the orbital axis maintains its direction during the collapse. We calculate the spin distribution of BBH mergers in the local universe, and its redshift evolution for WR progenitors. Assuming that the BBH formation rate peaks around a redshift of ∼2–3, we show that BBH mergers in the local universe are dominated by low-spin events. The high-spin population starts to dominate at a redshift of ∼0.5–1.5. WR stars are also progenitors of long gamma-ray bursts that take place at a comparable rate to BBH mergers. We discuss the possible connection between the two phenomena. Additionally, we show that hypothetical Population III star progenitors are also possible. Although WR and Population III progenitors are consistent with the current data, both models predict a non-vanishing fraction of high positive values of the BBHs’ aligned spin. If those are not detected within the coming LIGO/Virgo runs, it will be unlikely that the observed BBHs formed via field binaries.

The chemical enrichment of long gamma-ray bursts nurseries up to z = 2

Aims. We investigate the existence of a metallicity threshold for the production of long gamma-ray bursts (LGRBs). Methods. We used the host galaxies of the Swift/BAT6 sample of LGRBs. We considered the stellar mass, star formation rate (SFR), and metallicity determined from the host galaxy photometry and spectroscopy up to z = 2 and used them to compare the distribution of host galaxies to that of field galaxies in the mass-metallicity and fundamental metallicity relation plane. Results. We find that although LGRBs also form in galaxies with relatively large stellar masses, the large majority of host galaxies have metallicities below log (O/H) ~ 8.6. The extension to z = 2 results in a good sampling of stellar masses also above Log(M∗/M⊙) ~ 9.5 and provides evidence that LGRB host galaxies do not follow the fundamental metallicity relation. As shown by the comparison with dedicated numerical simulations of LGRB host galaxy population, these results are naturally explained by the existence of a mild (~0.7 Z⊙) threshold for the LGRB formation. The present statistics does not allow us to discriminate between different shapes of the metallicity cutoff, but the relatively high metallicity threshold found in this work is somewhat in disagreement to most of the standard single-star models for LGRB progenitors.

Gamma-ray burst cosmology: Hubble diagram and star formation history

We briefly introduce the disadvantages for Type Ia supernovae (SNe Ia) as standard candles to measure the universe, and suggest Gamma-ray bursts (GRBs) can serve as a powerful tool for probing the properties of high redshift universe. We use GRBs as distance indicators in constructing the Hubble diagram at redshifts beyond the current reach of SNe Ia observations. Since the progenitors of long GRBs (LGRBs) are confirmed to be massive stars, they are deemed as an effective approach to study the cosmic star formation rate (SFR). A detailed representation of how to measure high-[Formula: see text] SFR using GRBs is presented. Moreover, first stars can form only in structures that are suitably dense, which can be parametrized by defining the minimum dark matter halo mass [Formula: see text]. [Formula: see text] must play a crucial role in star formation. The association of LGRBs with the collapses of massive stars also indicates that the GRB data can be applied to constrain the minimum halo mass [Formula: see text] and to investigate star formation in dark matter halos.

Short-Duration Gamma-Ray Bursts

Gamma-ray bursts (GRBs) display a bimodal duration distribution with a separation between the short- and long-duration bursts at about 2 s. The progenitors of long GRBs have been identified as massive stars based on their association with Type Ic core-collapse supernovae (SNe), their exclusive location in star-forming galaxies, and their strong correlation with bright UV regions within their host galaxies. Short GRBs have long been suspected on theoretical grounds to arise from compact object binary mergers (neutron star–neutron star or neutron star–black hole). The discovery of short GRB afterglows in 2005 provided the first insight into their energy scale and environments, as well as established a cosmological origin, a mix of host-galaxy types, and an absence of associated SNe. In this review, I summarize nearly a decade of short GRB afterglow and host-galaxy observations and use this information to shed light on the nature and properties of their progenitors, the energy scale and collimation of the relativistic outflow, and the properties of the circumburst environments. The preponderance of the evidence points to compact object binary progenitors, although some open questions remain. On the basis of this association, observations of short GRBs and their afterglows can shed light on the on- and off-axis electromagnetic counterparts of gravitational wave sources from the Advanced LIGO/Virgo experiments.

A method for quantifying the gamma-ray burst bias. Application in the redshift range of 0–1.1

Long Gamma Ray Bursts (LGRBs) are related to the final stages of evolution of massive stars. As such, they should follow the star formation rate (SFR) of galaxies. We can use them to probe for star-forming galaxies (SFGs) in the distant universe following this assumption. The relation between the rate of LGRBs in a given galaxy and its SFR (that we call the LGRB "bias") may be complex, as we have indications that the LGRB hosts are not perfect analogues to the general population of SFGs. In this work, we try to quantify the dependence of the LGRB bias on physical parameters of their host galaxy such as the SFR or the stellar mass. We propose an empirical method based on the comparison of stellar mass functions (and SFR distributions) of LGRB hosts and of SFGs in order to find how the bias depends on the stellar mass or the SFR. By applying this method to a sample of LGRB hosts at redshifts lower than 1.1, where the properties of SFGs are well established, and where the properties of LGRB host galaxies can be deduced from observations (for stellar masses larger than 10**9.25 Msun and SFR larger than 1.8 Msun / yr), we find that the LGRB bias depends on both the stellar mass and SFR. We find that the bias decreases with the SFR, i.e. we see no preference for highly SFGs, once taken into account the larger number of massive stars in galaxies with larger SFR. We do not find any trend with the specific star formation rate (SSFR) but the dynamical range in SSFR in our study is narrow. Although through an indirect method, we relate these trends to a possible decrease of the LGRBs rate / SFR ratio with the metallicity. The method we propose suggests trends that may be useful to constrain models of LGRB progenitors, showing a clear decrease of the LGRB bias with the metallicity. This is promising for the future as the number of LGRB hosts studied will increase.

Collapse of rotating very massive stellar core to a black hole and a disk

Recent studies of modeling a progenitor of long gamma-ray bursts (LGRBs) suggest that progenitors of LGRBs might have a core with higher entropy than that of ordinary presupernove. Based on the above suggestion, we performed fully general relativistic, two-dimensional simulations of collapse of higher entropy core to a black hole and an accretion disk taking account of important microphysics. The initial core is simply modeled by a equilibrium configuration with constant entropy and electron fraction. We clarified that the formation dynamics depends even qualitatively on the amount of angular momentum. As a novel feature, we discovered that accretion disks formed after collapse can be convectively unstable.

Can massive Be/Oe stars be progenitors of long gamma ray bursts?

<i>Context. <i/>The identification of long-gamma-ray-bursts (LGRBs) is still uncertain, although the collapsar engine of fast-rotating massive stars is gaining a strong consensus.<i>Aims. <i/>We propose that low-metallicity Be and Oe stars, which are massive fast rotators, as potential LGRBs progenitors.<i>Methods. <i/>We checked this hypothesis by 1) testing the global specific angular momentum of Oe/Be stars in the ZAMS with the SMC metallicity; 2) comparing the ZAMS (Ω/Ω<sub>c<sub/>,<i>M<i/>/) parameters of these stars with the area predicted theoretically for progenitors with metallicity <i>Z<i/> = 0.002; and 3) calculating the expected rate of LGRBs/year/galaxy and comparing them with the observed ones. To this end, we determined the ZAMS linear and angular rotational velocities for SMC Be and Oe stars using the observed <i>V<i/> sin <i>i<i/> parameters, corrected from the underestimation induced by the gravitational darkening effect.<i>Results. <i/>The angular velocities of SMC Oe/Be stars are on average Ω/Ω<sub>c<sub/> = 0.95 in the ZAMS. These velocities are in the area theoretically predicted for the LGRBs progenitors. We estimated the yearly rate per galaxy of LGRBs and the number of LGRBs produced in the local Universe up to <i>z<i/> = 0.2. We have considered that the mass range of LGRB progenitors corresponds to stars hotter than spectral types B0-B1 and used individual beaming angles from 5 to 15°. We thus obtain ~ 10<sup>-7<sup/> to ~10<sup>-6<sup/> LGRBs/year/galaxy, which represents on average 2 to 14 LGRB predicted events in the local Universe during the past 11 years. The predicted rates could widely surpass the observed ones [(0.2–3)×10<sup>-7<sup/> LGRBs/year/galaxy; 8 LGRBs observed in the local Universe during the last 11 years] if the stellar counts were made from the spectral type B1-B2, in accordance with the expected apparent spectral types of the appropriate massive fast rotators.<i>Conclusions. <i/>We conclude that the massive Be/Oe stars with SMC metallicity could be LGRBs progenitors. Nevertheless, other SMC O/B stars without emission lines, which have high enough specific angular momentum, can enhance the predicted <i>R<i/><sub>LGRB<sub/> rate.

Gamma-ray bursts from tidally spun-up Wolf-Rayet stars?

Context. The collapsar model requires rapidly rotating Wolf-Rayet stars as progenitors of long gamma-ray bursts. However, Galactic Wolf-Rayet stars rapidly lose angular momentum due to their intense stellar winds.

The circumstellar medium around a rapidly rotating, chemically homogeneously evolving, possible gamma-ray burst progenitor

Context. Rapidly rotating, chemically homogeneously evolving massive stars are considered to be progenitors of long gamma-ray bursts. Aims. We present numerical simulations of the evolution of the circumstellar medium around a rapidly rotating 20 Mstar at a metal- licity of Z = 0.001. Its rotation is fast enough to produce quasi-chemically homogeneous evolution. While conventionally, a star of 20 Mwould not evolve into a Wolf-Rayet stage, the considered model evolves from the main sequence directly to the helium main sequence. Methods. We use the time-dependent wind parameters, such as mass loss rate, wind velocity and rotation-induced wind anisotropy from the evolution model as input for a 2D hydrodynamical simulation. Results. While the outer edge of the pressure-driven circumstellar bubble is spherical, the circumstellar medium close to the star shows strong non-spherical features during and after the periods of near-critical rotation. Conclusions. We conclude that the circumstellar medium around rapidly rotating massive stars differs considerably from the sur- rounding material of non-rotating stars of similar mass. Multiple blue-shifted high velocity absorption components in gamma-ray burst afterglow spectra are predicted. As a consequence of near critical rotation and short stellar evolution time scales during the last few thousand years of the star's life, we find a strong deviation of the circumstellar density profile in the polar direction from the 1/R 2 density profile normally associated with stellar winds close to the star.

Modeling GRB 050904: Autopsy of a Massive Stellar Explosion atz = 6.29

GRB 050904 at redshift z=6.29, discovered and observed by Swift and with spectroscopic redshift from the Subaru telescope, is the first gamma-ray burst to be identified from beyond the epoch of reionization. Since the progenitors of long gamma-ray bursts have been identified as massive stars, this event offers a unique opportunity to investigate star formation environments at this epoch. Apart from its record redshift, the burst is remarkable in two respects: first, it exhibits fast-evolving X-ray and optical flares that peak simultaneously at t~470 s in the observer frame, and may thus originate in the same emission region; and second, its afterglow exhibits an accelerated decay in the near-infrared (NIR) from t~10^4 s to t~3 10^4 s after the burst, coincident with repeated and energetic X-ray flaring activity. We make a complete analysis of available X-ray, NIR, and radio observations, utilizing afterglow models that incorporate a range of physical effects not previously considered for this or any other GRB afterglow, and quantifying our model uncertainties in detail via Markov Chain Monte Carlo analysis. In the process, we explore the possibility that the early optical and X-ray flare is due to synchrotron and inverse Compton emission from the reverse shock regions of the outflow. We suggest that the period of accelerated decay in the NIR may be due to suppression of synchrotron radiation by inverse Compton interaction of X-ray flare photons with electrons in the forward shock; a subsequent interval of slow decay would then be due to a progressive decline in this suppression. The range of acceptable models demonstrates that the kinetic energy and circumburst density of GRB 050904 are well above the typical values found for low-redshift GRBs.

Binary star progenitors of long gamma-ray bursts

Context: The collapsar model for long gamma-ray bursts requires a rapidly rotating Wolf-Rayet star as progenitor. Aims: We test the idea of producing rapidly rotating Wolf-Rayet stars in massive close binaries through mass accretion and consecutive quasi-chemically homogeneous evolution - the latter had previously been shown to provide collapsars below a certain metallicity threshold. Methods: We use a 1D hydrodynamic binary evolution code to simulate the evolution of a 16+15 Mo binary model with an initial orbital period of 5 days and SMC metallicity (Z=0.004). Internal differential rotation, rotationally induced mixing and magnetic fields are included in both components, as well as non-conservative mass and angular momentum transfer, and tidal spin-orbit coupling. Results: The considered binary system undergoes early Case B mass transfer. The mass donor becomes a helium star and dies as a type Ib/c supernova. The mass gainer is spun-up, and internal magnetic fields efficiently transport accreted angular momentum into the stellar core. The orbital widening prevents subsequent tidal synchronization, and the mass gainer rejuvenates and evolves quasi-chemically homogeneously thereafter. The mass donor explodes 7 Myr before the collapse of the mass gainer. Assuming the binary to be broken-up by the supernova kick, the potential gamma-ray burst progenitor would become a runaway star with a space velocity of 27 km s-1, traveling about 200 pc during its remaining lifetime. Conclusions: .The binary channel presented here does not, as such, provide a new physical model for collapsar production, as the resulting stellar models are almost identical to quasi-chemically homogeneously evolving rapidly rotating single stars. However, it may provide a means for massive stars to obtain the required high rotation rates. Moreover, it suggests that a possibly large fraction of long gamma-ray bursts occurs in runaway stars.

Single star progenitors of long gamma-ray bursts

We present grids of massive star evolution models at four different metallicities (Z=0.004, 0.002, 0.001, 0.00001). The effects of rotation on the stellar structure and the transport of angular momentum and chemical elements through the Spruit-Tayler dynamo and rotationally induced instabilities are considered. After discussing uncertainties involved with the adopted physics, we elaborate the final fate of massive stars as a function of initial mass and spin rate, at each considered metallicity. In particular, we investigate for which initial conditions long gamma-ray bursts (GRBs) are expected to be produced in the frame of the collapsar model. Then, using an empirical spin distribution of young massive metal-poor stars and a specified metallicity-dependent history of star-formation, we compute the expected GRB rate as function of metallicity and redshift based on our stellar evolution models. The GRB production in our models is limited to metallicities of Z \lsim 0.004, with the consequence that about 50 % of all GRBs are predicted to be found at redshifts above z = 4, with most supernovae occurring at redshifts below z\simeq 2.2. The average GRB/SN ratio predicted by our model is about 1/200 globally, and 1/1250 at low redshift. Future strategies for testing the considered GRB progenitor scenario are briefly discussed.

Study of Gamma‐Ray Burst Binary Progenitors

Recently much work in studying gamma-ray bursts (GRBs) has been devoted to revealing the nature of outburst mechanisms and to studies of GRB afterglows. These issues have also been closely followed by the quest to identify GRB progenitors. Several types of progenitors have been proposed for GRBs: the most promising objects seem to be collapsars, compact object binaries, mergers of compact objects with helium cores of evolved stars in common envelope episodes, and also the recently discussed connection of GRBs with supernovae. In this paper we consider the binary star progenitors of GRBs: white dwarf-neutron star (WD-NS) binaries, white dwarf-black hole (WD-BH) binaries, helium core-neutron star (He-NS) mergers, helium core-black hole (He-BH) mergers, and double neutron star (NS-NS) and neutron star-black hole binaries (NS-BH). Using population synthesis methods we calculate merger rates of these binary progenitors and compare them to the observed BATSE GRB rate. For the binaries considered, we also calculate the distribution of merger sites around host galaxies and compare them to the observed locations of GRB afterglows with respect to their hosts. We find that the rates of binary GRB progenitors in our standard model are lower than the observed GRB rates if GRBs are highly collimated. However, the uncertainty in the population synthesis results is too large to make this a firm conclusion. Although some observational signatures seem to point to collapsars as progenitors of long GRBs, we find that mergers of WD-NS, He-NS, He-BH, and NS-NS systems also trace the star formation regions of their host galaxies, as it is observed for long GRBs. We also speculate about possible progenitors of short-duration GRBs. For these, the most likely candidates are still mergers of compact objects. We find that the locations of NS-NS and NS-BH mergers with respect to their hosts are significantly different. This may allow us to distinguish between these two progenitor models once current and near future missions, such as HETE-2 or Swift, measure the locations of short GRBs.