Showing papers on "Hypernova published in 2004"
TL;DR: In this paper, the abundance analysis of an homogeneous sample of 35 giants selected from the HK survey of Beers et al. was presented, emphasizing stars of extremely low metallicity: 30 of the 35 stars are in the range −4.1 < (Fe/H) < −2.7, and 22 stars have (Fe /H) ≥ −3.0.
Abstract: In the framework of the ESO Large Programme "First Stars", very high-quality spectra of some 70 very metal-poor dwarfs and giants were obtained with the ESO VLT and UVES spectrograph. These stars are likely to have descended from the first generation(s) of stars formed after the Big Bang, and their detailed composition provides constraints on issues such as the nature of the first supernovae, the efficiency of mixing processes in the early Galaxy, the formation and evolution of the halo of the Galaxy, and the possible sources of reionization of the Universe. This paper presents the abundance analysis of an homogeneous sample of 35 giants selected from the HK survey of Beers et al. (1992, 1999), emphasizing stars of extremely low metallicity: 30 of our 35 stars are in the range −4.1 < (Fe/H) < −2. 7, and 22 stars have (Fe/H) < −3.0. Our new VLT/UVES spectra, at a resolving power of R ∼ 45 000 and with signal-to-noise ratios of 100-200 per pixel over the wavelength range 330-1000 nm, are greatly superior to those of the classic studies of McWilliam et al. (1995) and Ryan et al. (1996). The immediate objective of the work is to determine precise, comprehensive, and homogeneous element abundances for this large sample of the most metal-poor giants presently known. In the analysis we combine the spectral line modeling code "Turbospectrum" with OSMARCS model atmospheres, which treat continuum scattering correctly and thus allow proper inter- pretation of the blue regions of the spectra, where scattering becomes important relative to continuous absorption ( λ< 400 nm). We obtain detailed information on the trends of elemental abundance ratios and the star-to-star scatter around those trends, en- abling us to separate the relative contributions of cosmic scatter and observational/analysis errors. Abundances of 17 elements from C to Zn have been measured in all stars, including K and Zn, which have not previously been detected in stars with (Fe/H) < −3.0. Among the key results, we discuss the oxygen abundance (from the forbidden (OI) line), the different and sometimes complex trends of the abundance ratios with metallicity, the very tight relationship between the abundances of certain elements (e.g., Fe and Cr), and the high (Zn/Fe) ratio in the most metal-poor stars. Within the error bars, the trends of the abundance ratios with metallicity are consistent with those found in earlier literature, but in many cases the scatter around the average trends is much smaller than found in earlier studies, which were limited to lower-quality spectra. We find that the cosmic scatter in several element ratios may be as low as 0.05 dex. The evolution of the abundance trends and scatter with declining metallicity provides strong constraints on the yields of the first supernovae and their mixing into the early ISM. The abundance ratios found in our sample do not match the predicted yields from pair-instability hypernovae, but are consistent with element production by super- novae with progenitor masses up to 100 M� . Moreover, the composition of the ejecta that have enriched the matter
1,192 citations
TL;DR: A critical comparison of estimates for the rates of hypernovae (HNe) and gamma-ray bursts (GRBs) is presented in this paper, which gives a galactic rate of 10-6 to 10-5 yr-1 for both events.
Abstract: A critical comparison of estimates for the rates of hypernovae (HNe) and gamma-ray bursts (GRBs) is presented. Within the substantial uncertainties, the estimates are shown to be quite comparable and give a galactic rate of 10-6 to 10-5 yr-1 for both events. These rates are several orders of magnitude lower than the rate of core-collapse supernovae, suggesting that the evolution leading to an HN/GRB requires special circumstances, very likely due to binary interactions. Various possible binary channels are discussed, and it is shown that these are generally compatible with the inferred rates.
284 citations
TL;DR: In this paper, the first stars were not very massive stars (VMSs; M > 140 M), and the existence of VMSs is not necessary to meet existing constraints commonly taken to motivate them.
Abstract: We critique the hypothesis that the first stars were very massive stars (VMSs; M > 140 M☉). We review the two major lines of evidence for the existence of VMSs: (1) that the relative metal abundances of extremely metal-poor Galactic halo stars show evidence of VMS enrichment and (2) that the high electron-scattering optical depth (τe) to the cosmic microwave background found by the Wilkinson Microwave Anisotropy Probe (WMAP) requires VMSs for reionization in a concordance ΛCDM cosmology. The yield patterns of VMSs exploding as pair-instability supernovae are incompatible with the Fe-peak and r-process abundances in halo stars. Models including Type II supernovae and/or "hypernovae" from zero-metallicity progenitors with M = 8-40 M☉ can better explain the observed trends. We use the nucleosynthesis results and stellar evolution models to construct an initial mass function (IMF) for reionization. With a simple metal transport model, we estimate that halo enrichment curtails metal-free star formation after ~108 yr at z ~ 20. Because the lifetime-integrated ionizing photon efficiency of metal-free stars peaks at ~120 M☉ and declines at higher mass, an IMF with an approximate lower bound at M ~ 10-20 M☉ and no VMS can maximize the ionizing photon budget and still be consistent with the nucleosynthetic evidence. An IMF devoid of low-mass stars is justified independently by models of the formation of primordial stars. Using a semianalytic model for H I and He II reionization, we find that such an IMF can reproduce τe 0.10-0.14, consistent with the range from WMAP, without extreme astrophysical assumptions, provided that metal-free star formation persists 107-108 yr after star formation begins. Because stars in the mass range 50-140 M☉ are the most efficient sources of ionizing photons but are expected to collapse to black holes without releasing metals, this IMF effectively decouples early metal enrichment and early ionization. Such an IMF may allow the unique properties of the zero-metallicity IMF to persist longer than they would in the pure VMS case and to contribute significantly to the global ionizing photon budget before halo self-enrichment and/or interhalo metal transport truncates metal-free star formation. We conclude, on the basis of these results, that VMSs are not necessary to meet the existing constraints commonly taken to motivate them.
136 citations
TL;DR: The TeV neutrino signatures expected from such slower jets are explored, and the expected detection rates with upcoming Gigaton Cherenkov experiments are calculated, concluding that individual jetted supernovae may be detectable from nearby galaxies.
Abstract: A fraction of core-collapse supernovae of type Ib/c are associated with gamma-ray bursts, which are thought to produce highly relativistic jets. Recently, it has been hypothesized that a larger fraction of core-collapse supernovae produce slower jets, which may contribute to the disruption and ejection of the supernova envelope, and explain the unusually energetic hypernovae. We explore the TeV neutrino signatures expected from such slower jets, and calculate the expected detection rates with upcoming Gigaton Cherenkov experiments. We conclude that individual jetted supernovae may be detectable from nearby galaxies.
115 citations
TL;DR: The X-Ray Flash (XRF) is the closest γ-Ray Burst (GRB) or XRF known to date as mentioned in this paper, with a host galaxy at z = 0.1055, and a significant increase and subsequent decrease in the apparent brightness of the host, peaking between 10 and 33 days after the GRB.
Abstract: The X-Ray Flash (XRF), 031203 with a host galaxy at z = 0.1055, is, apart from GRB 980425, the closest γ-Ray Burst (GRB) or XRF known to date. We have monitored its host galaxy from 1-100 days after the burst. In spite of the high extinction to the source and the bright host, a significant increase and subsequent decrease has been detected in the apparent brightness of the host, peaking between 10 and 33 days after the GRB. The only convincing explanation is a supernova (SN) associated with the XRF, SN2003lw. This is the earliest time at which a SN signal is clearly discernible in a GRB/XRF (apart from SN1998bw). SN2003lw is extremely luminous with a broad peak and can be approximately represented by the lightcurve of SN1998bw brightened by ∼0.55 mag, implying a hypernova, as observed in most GRB-SNe. The XRF-SN association firmly links XRFs with the deaths of massive stars and further strengthens their connection with GRBs. The fact that SNe are also associated with XRFs implies that Swift may detect a significant population of intermediate redshift SNe very soon after the SN explosions, a sample ideally suited for detailed studies of early SN physics.
91 citations
TL;DR: In this paper, the properties of core-collapse supernovae have been studied and the best known object in this class is SN 1998bw, which owes its fame to its likely association with the gamma-ray burst GRB 980425.
Abstract: During the last few years, a number of exceptional core-collapse supernovae (SNe) have been discovered. Although their properties are rather diverse, they have the common feature that at least some of their basic parameters (kinetic energy of the explosion, mass of the ejecta, mass of the synthesized 56Ni), and sometimes all of them, are larger, sometimes by more than an order of magnitude, than the values typically found for this type of SNe. Therefore, these SNe have been given the collective classification of ‘Hypernovae’ . The best known object in this class is SN 1998bw, which owes its fame to its likely association with the gamma-ray burst GRB 980425. In this paper, we first describe how the basic parameters of SN 1998bw can be derived from observations and modeling, and discuss the properties of other hypernovae individually. These hypernovae seem to come from rather massive stars, being more massive than ~ 20 – 25 M ⊙ on the main-sequence, thus forming black holes. On the other hand, there are some examples of massive SNe with only a small kinetic energy. We suggest that stars with non-rotating black holes are likely to collapse “quietly” ejecting a small amount of heavy elements (Faint supernovae). In contrast, stars with rotating black holes are likely to give rise to very energetic supernovae (Hypernovae). We present distinct nucleosynthesis features of these two types of “black-holeforming” supernovae. Nucleosynthesis in Hypernovae are characterized by larger abundance ratios (Zn,Co,V,Ti)/Fe and smaller (Mn,Cr)/Fe. Nucleosynthesis in Faint supernovae is characterized by a large amount of fall-back. We show that the abundance pattern of the recently discovered most Fe deficient star, HE0107 – 5240, and other extremely metal-poor carbon-rich stars are in good accord with those of black-hole-forming supernovae, but not pair-instability supernovae. This suggests that black-hole-forming supernovae made important contributions to the early Galactic (and cosmic) chemical evolution. Finally we discuss the nature of First (Pop III) Stars.
67 citations
TL;DR: In this article, the evolution of a gas shell, swept by the supernova remnant of a massive first generation star, is studied with H_2 and HD chemistry taken into account, and it is shown that for a reasonable range of temperatures (200 K - 1000 K) of interstellar gas, the formation of second-generation stars can be triggered by a single supernova or hypernova.
Abstract: The evolution of a gas shell, swept by the supernova remnant of a massive first generation star, is studied with H_2 and HD chemistry taken into account. When a first-generation star explodes as a supernova, H_2 and HD molecules are formed in the swept gas shell and effectively cool the gas shell to temperatures of 32 K - 154 K. If the supernova remnant can sweep to gather the ambient gas, the gas shell comes to be dominated by its self-gravity, and hence, is expected to fragment. Our result shows that for a reasonable range of temperatures (200 K - 1000 K) of interstellar gas, the formation of second-generation stars can be triggered by a single supernova or hypernova.
65 citations
TL;DR: In this paper, the two peculiar Type Ic supernovae (SNe 1997ef and 1997dq) are shown to have very similar photometric and spectral evolution in the epochs when both SNe are observed (i.e., beyond ~80 days after the explosion).
Abstract: The two peculiar Type Ic supernovae (SNe) 1997ef and 1997dq are shown to have very similar photometric and spectral evolution in the epochs when both SNe are observed (i.e., beyond ~80 days after the explosion). The early light curves and spectra of SN 1997ef suggested that this was a "hypernova," or "SN 1998bw-like Type Ic supernova." The fact that the two SNe are very similar allows us to extend the time coverage of this type of event, since SN 1997dq, unlike SN 1997ef, was observed well into the nebular phase. In contrast to SN 1998bw, the spectra of these two SNe did not become fully nebular until almost 1 yr after the explosion. During a long transition phase, lasting at least 6 months, the SNe developed nebular emission in lines of [O I] and [Ca II], but at the same time they retained an underlying, photospheric-type spectrum, originating at very low velocities. Spectral synthesis techniques are used to model the spectrum of SN 1997dq, suggesting that it produced ~0.16 M☉ of 56Ni, and that a significant fraction of this is located in a dense, low-velocity inner region.
61 citations
TL;DR: In this article, Zhang et al. examined the evolution of an expanding relativistic blob of gas intended to be representative of a jet associated with ejecta from an extremely energetic event such as a hypernova, that produces a gamma-ray burst.
Abstract: Utilizing 3D relativistic hydrodynamical calculations, we have examined the evolution of an expanding relativistic blob of gas intended to be representative of a jet associated with ejecta from an extremely energetic event such as a hypernova, that produces a gamma-ray burst (Aloy et al. 2000; Tan, Matzner, & McKee 2001; MacFadyen, Woosley, & Heger 2001, Zhang, Woosley, & Heger 2003, Zhang, Woosley, & MacFadyen 2003). Since these are the first such calculations applied to the blob during the time in which the afterglow radiation is produced, we have purposely kept them simple in an effort to concentrate on the most fundamental aspects of the physics. We restrict our attention to the transition from spherical to jetlike expansion that occurs during the time that the Lorentz factor becomes less than the reciprocal of the jet spreading angle. We have not yet attached specific numbers to our results. From the SRHD equations, one sees that the relevant quantities are the ratios of pressure to density, and of distance to time. If we specify either one of these two sets of numbers, the other one is also determined.
57 citations
TL;DR: In this paper, it was shown that a rate of about 0.02 SN 2003dh-like events per century in the central region of the Galaxy is sufficient to explain the positron flux detected by INTEGRAL/SPI.
Abstract: The observation of a strong and extended positron-electron line annihilation emission in the central regions of the Galaxy by the SPectrometer on the International Gamma-Ray Astrophysical Laboratory (INTEGRAL/SPI), consistent with the Galactic bulge geometry and without any counterpart in the gamma-ray range, neither at high energy nor in the 1809 keV 26Al decay line, is challenging. Leaving aside the geometrical question, we address the problem of the adequate positron sources, showing the potentiality of a new category of Type Ic supernovae (SNe Ic), exemplified by SN 2003dh, that is associated with a gamma-ray burst (GRB). This kind of supernova/hypernova/GRB event is interpreted as the result of a bipolar Wolf-Rayet explosion, which produces a large amount of 56Ni and ejects it at high velocity along the rotation axis. The bulk of positrons resulting from 56Co decay escapes in the surrounding medium as a result of the rapid thinning of the ejecta in the polar direction. We show that a rate of about 0.02 SN 2003dh-like events per century in the central region of the Galaxy is sufficient to explain the positron flux detected by INTEGRAL/SPI. In order to explain this flux by SN Ia events alone, a rate of 0.5 per century is necessary, much higher than indicated by Galactic evolutionary models applied to the bulge. Further observations of late light curves of SNe Ia and SNe Ic in the bulge of spiral galaxies, together with three-dimensional hydrodynamic calculations of anisotropic ejections of 56Ni in SN Ic/GRB events, will allow us to estimate the separate contributions of SNe Ia and SNe Ic to positron injection.
57 citations
TL;DR: In this paper, the two peculiar Type Ic supernovae (SNe) 1997ef and 1997dq are shown to have very similar photometric and spectral evolution in the epochs when both SNe are observed (i.e. beyond $\sim 80$ days after the explosion).
Abstract: The two peculiar Type Ic supernovae (SNe) 1997ef and 1997dq are shown to have very similar photometric and spectral evolution in the epochs when both SNe are observed (i.e. beyond $\sim 80$ days after the explosion). The early light curves and spectra of SN 1997ef suggested that this was a ``hypernova,'' or ``SN 1998bw-like Type Ic supernova.'' The fact that the two SNe are very similar allows us to extend the time coverage of this type of event, since SN 1997dq, unlike SN 1997ef, was observed well into the nebular phase. In contrast to SN 1998bw, the spectra of these two SNe did not become fully nebular until almost one year after the explosion. During a long transition phase, lasting at least 6 months, the SNe developed nebular emission in lines of [\OI] and [\CaII], but at the same time they retained an underlying, photospheric-type spectrum, originating at very low velocities. Spectral synthesis techniques are used to model the spectrum of SN 1997dq, suggesting that it produced $\sim 0.16 \Msun$ of \Nifs, and that a significant fraction of this is located in a dense, low-velocity inner region.
TL;DR: In this article, the radio afterglows of gamma-ray bursts (GRBs) and hypernovae (HNe) at high redshifts and quantify their detectability, as well as their potential usefulness for 21 cm absorption line studies of the intergalactic medium and intervening structures.
Abstract: We investigate the radio afterglows of gamma-ray bursts (GRBs) and hypernovae (HNe) at high redshifts and quantify their detectability, as well as their potential usefulness for 21 cm absorption line studies of the intergalactic medium (IGM) and intervening structures. We examine several sets of source and environment model parameters that are physically plausible at high redshifts. The radio afterglows of GRBs would be detectable out to z ~ 30, while the energetic HNe could be detectable out to z ~ 20 even by the current Very Large Array (VLA). We find that the 21 cm absorption line due to the diffuse neutral IGM is difficult to detect even by the proposed Square Kilometer Array (SKA), except for highly energetic sources. We also find that the 21 cm line due to collapsed gas clouds with high optical depth may be detected on rare occasions.
TL;DR: In this article, the authors investigate nucleosynthesis inside both a gamma-ray burst accretion disk and a wind launched from an inner region of the disk using one-dimensional models of the disks and wind.
Abstract: We investigate nucleosynthesis inside both a gamma-ray burst accretion disk and a wind launched from an inner region of the disk using one-dimensional models of the disk and wind. Far from a central black hole, the composition of accreting gas is taken to be that of an Si-rich or O-rich layer of a massive star before core collapse. We find that the inner region of the disk comprises five layers characterized by dominant elements: 16O, 28Si, 54Fe (and 56Ni), 4He, and nucleons. As the accretion rate decreases, the individual layers shift inward, retaining the overall profiles of compositions. A massive amount of 56Ni, over 0.1 M☉, is ejected through the wind from the disk where the electron fraction 0.5. The amount of 56Ni produced through the disk wind can be responsible for the light curves observed at the late stage in hypernovae (HNe). The yields of elements heavier than Ca produced via the disk wind are comparable to or greater than those of a normal supernova and their composition is similar to that of an aspherical HN explosion. A significant amount of Ga, Ge, and Se is ejected from the disk. A variety of neutron-rich elements, as well as p-nuclei, are also appreciably produced through the disk wind.
TL;DR: In this article, optical photometric and spectroscopic data of the bright hypernova SN 2002ap have been presented and the distance has been inferred by applying the Expanding Photosphere Method for the data around maximum.
Abstract: New optical photometric and spectroscopic data of the bright hypernova SN 2002ap are presented. The obtained BVRI light curves as well as the optical spectra agree well with other published data series. The distance has been inferred by applying the Expanding Photosphere Method for the data around maximum. The derived 6.7 Mpc is in good agreement with recent photometric distances of M 74. However, the total (random plus systematic) uncertainty of the EPM-distance is at least ±4.5 Mpc (about 70%). The physical parameters of the SN have been determined via simplified analytic models of the light and velocity curves. It is confirmed that SN 2002ap was a less energetic hypernova, the kinetic energy was 4−8 × 10 51 erg, and the reddening-free absolute bolometric magnitude reached −16.63 mag (corresponding to Lbol = 3.47 × 10 8 L� ), about 2 mag less than the prototype hypernova SN 1998bw.
TL;DR: In this paper, the authors compared the X-ray luminosity and colour distribution of the field of M74 in January 2003 with XMM-Newton, 11 months after the detection of SN 2002ap.
Abstract: We have re-observed the field of M74 in January 2003 with XMM-Newton, 11 months after the X-ray detection of SN 2002ap. From a comparison of the two XMM-Newton observations we obtain more accurate values for the X-ray luminosity and colours of the source five days after the event, and a limit on its decline rate. We compare its X-ray behaviour (prompt soft Xray emission, relatively low luminosity) with that of other type Ic SNe, and speculate that SN 2002ap may share some physical properties (low mass-loss rate and high-velocity stellar wind from the progenitor star) with the candidate hypernova/gamma-ray-burst progenitor SN 1998bw, but with a lower (non-relativistic) speed of the ejecta. We suggest that the X-ray emission observed in 2002 is likely to come from the radiatively-cooling reverse shock, at a temperature kT approximate to 0.8 keV, and that this soft component was already detected 5 d after the event because the absorbing column density of the cool shell between the forward and reverse shocks was only similar to10(20) cm(-2), i.e., the shell was optically thin in the soft X-ray band. The new XMM-Newton data also allowed us to continue monitoring two bright variable sources in M74 that had reached peak luminosities > 10(39) erg s(-1) in previous XMM-Newton and Chandra observations. Finally, we used two Chandra observations from 2001 to investigate the luminosity and colour distribution of the X-ray source population of M74, typical of moderately-active late-type spirals.
TL;DR: In this article, optical photometric and spectroscopic data of the bright hypernova SN 2002ap have been presented and the distance has been inferred by applying the Expanding Photosphere Method for the data around maximum.
Abstract: New optical photometric and spectroscopic data of the bright hypernova SN 2002ap are presented. The obtained BVRI light curves as well as the optical spectra agree well with other published data series. The distance has been inferred by applying the Expanding Photosphere Method for the data around maximum. The derived 6.7 Mpc is in good agreement with recent photometric distances of M74. However, the total (random plus systematic) uncertainty of the EPM-distance is at least 4.5 Mpc (about 70 %). The physical parameters of the SN have been determined via simplified analytic models of the light and velocity curves. It is confirmed that SN 2002ap was a less energetic hypernova, the kinetic energy was 4 - 8 10^51 erg, and the reddening-free absolute bolometric magnitude reached -16.63 mag (corresponding to L_bol = 3.47 10^8 L_solar), about 2 magnitude less than the prototype hypernova SN 1998bw.
21 Mar 2004
TL;DR: In this paper, the authors used extensive X-ray, optical and radio observations of the bright afterglow of the gamma-ray burst GRB 030329 to construct the multifrequency evolution of the event.
Abstract: Extensive X-ray, optical and radio observations of the bright afterglow of the gamma-ray burst GRB 030329 are used to construct the multifrequency evolution the event. The data are fitted using the standard fireball shock model to provide estimates of the initial energy, e = 6.8 x 10 52 erg sr -1 , the density of the ambient medium, no = 1 cm -3 , the electron and magnetic energy density fractions, ∈ e = 0.24 and ∈ B = 0.0017, the power-law index of the relativistic electron spectrum, p = 2.25, and the opening angle of the jet, θ j = 3°. Deviations from the standard model seen in the optical and radio are most likely attributable to the concurrent hypernova SN2003dh. Peaks at 0.23 and 1.7 d in the R-band are much brighter than expected from a standard supernova (SN), and there is a large radio excess over the expected afterglow flux for t > 2 d. No deviation from the best-fitting afterglow model is seen in the X-ray decline, indicating that the excess optical and radio flux from 1-5 d arises from a later injection of slower electrons by the central engine.
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TL;DR: In this paper, a discussion of the possible role of rotation in supernova blast energetics and morphology, and the origin of Cas A's and SN1987A's ejecta fields are discussed.
Abstract: We review some of the reasons for believing that the generic core-collapse supernova is neutrino-driven, not MHD-jet driven We include a discussion of the possible role of rotation in supernova blast energetics and morphology, and speculate on the origin of Cas A's and SN1987A's ejecta fields Two "explosive" phenomena may be associated with most core collapses, the neutrino-driven supernova itself and an underenergetic jet-like ejection that follows The latter may be a magnetic wind that easily penetrates the debris created by the much more energetic supernova We predict that many core-collapse supernova remnants should have sub-dominant jet-like features In Cas A, we associate this sub-dominant collimated wind with the "jet/counter-jet" structure observed We suggest that the actual Cas A explosion itself is at nearly right angles to this jet, along a rotation axis that coincides with the bulk of the ejecta, the iron lobes, and the putative direction of motion of the point source It may be that when rotation becomes sufficiently rapid that the strong-neutrino-driven-supernova/weak-jet duality switches to a strong-MHD-jet scenario that might be associated with hypernovae, and in some cases GRBs Finally, we present a calculation using a new 2D multi-group, flux-limited radiation/hydrodynamics code we have recently developed for the simulation of core-collapse supernovae We discuss the rotation-induced anisotropy in the neutrino radiation field, neutrino heating, and the neutrino flux vectors and speculate on rotation's possible role in the supernova mechanism and in the overall supernova phenomenon
TL;DR: In this paper, the position of the knee in the Galactic cosmic ray (GCR) spectrum is shown to depend on the explosion energy distribution function of supernovae (SN), which can be quantitatively explained by the dominating contribution of hypernovae with explosion energies of (∼30−50)×1051 erg, the fraction of which must be no less than 1% of all SN.
Abstract: The position of the knee in the Galactic cosmic ray (GCR) spectrum is shown to depend on the explosion energy distribution function of supernovae (SN). The position of the knee in the GCR spectrum can be quantitatively explained by the dominating contribution of hypernovae with explosion energies of (∼30–50)×1051 erg, the fraction of which must be no less than 1% of all SN. The model reproduces the main features in the spectrum of all particles measured in extensive air shower (EAS) experiments: the knee in the spectrum of all particles at energy of about 3 PeV, the change in slope by δγ ∼ 0.3–0.5 after the knee point, and the steepening of the spectrum near 1018 eV. The model predicts a smooth knee if the SN explosion energy distribution is universal and a sharp knee if the hypernovae represent a separate class of events. The suggested model of the GCR spectrum is essentially based on the assumption that a spread in explosion energies exists and that the assumptions of the standard model for the CR acceleration in supernova remnants are valid.
01 Jan 2004
TL;DR: In this paper, the authors review the collapsar mechanism for gammaray bursts, hypernovae, and X-ray flashes from progenitor formation through jet propogation.
Abstract: For most collapsing stars, neutrinos from the proto-neutron star are able to drive a strong supernova explosion with a neutron star remnant. But very massive stars (>20M ⊙) will ultimately form black holes. These stars have the potential to drive enormous explosions by tapping the energy in a black hole accretion disk. The engine behind this black hole accretion disk explosion has been termed “collapsar”. In this chapter, we review the collapsar mechanism for gammaray bursts, hypernovae, and X-ray flashes from progenitor formation through jet propogation.
01 Oct 2004
TL;DR: In this paper, the authors identified two GRBs in which early emission is very different than late emission, and they briefly discuss these observations in terms of a current hypernova jet model.
Abstract: We have identified two GRBs in which early emission is very different than late emission Post‐quiescent pulses of BATSE GRBs 960530 and 980125 have long lags, smooth morphologies, and soft spectral evolution The early emission satisfies the standard internal shock paradigm, while the late emission is consistent with external shocks The peak luminosity ratio between early and late episodes is not in agreement with that predicated by the lag vs peak luminosity relationship We briefly discuss these observations in terms of a current hypernova jet model
TL;DR: In this paper, light curves and late phase spectra of aspherical supernova/hypernova models are presented, showing that the optical observations of SNe 1998bw and 2002ap can be well accounted for.
Abstract: Natures of very energetic supernovae, i.e., hypernovae, are discussed. They are the explosive deaths of stars more massive than ∼ 20-25M, probably being linked to enigmatic Gamma-Ray Bursts: Optical properties of hypernovae indicate that they are significantly aspherical, while so far no detailed modeling of such an explosion is available. We present light curves and late-phase spectra of aspherical supernova/hypernova models, showing that the optical observations of SNe 1998bw and 2002ap can be well accounted for. The abundance patterns of hypernovae are characterized by large ratios (Zn, Co)/Fe and small ratios (Mn, Cr)/Fe, indicating significant contribution to the early Galactic chemical evolution.
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TL;DR: In this article, the authors explore the possibility of positron production and escape by supernova events in the framework of an asymmetric model, in which a huge amount of $56}$Ni is ejected in a cone with a very high velocity; the ejected material becomes quickly transparent to positrons, which spread out in the interstellar medium.
Abstract: INTEGRAL/SPI has recently observed a strong and extended emission resulting from electron-positron annihilation located in the Galactic center region, consistent with the Galactic bulge geometry, without any counterpart at high gamma-ray energies, nor in the 1809 keV $^{26}$Al decay line. In order to explain the rate of positron injection in the Galactic bulge, estimated to more than 10$^{43}$ s$^{-1}$, the most commonly considered positron injection sources are type Ia supernovae. However, SN Ia rate estimations show that those sources fall short to explain the observed positron production rate, raising a challenging question about the nature of the Galactic positron source. In this context, a possible source of Galactic positrons could be supernova events of a new type, as the recently observed SN2003dh/GRB030329, an exploding Wolf-Rayet star (type Ic supernova) associated with a hypernova/gamma-ray burst; the question about the rate of this kind of events remains open, but could be problematically low.
In this paper, we explore the possibility of positron production and escape by such an event in the framework of an asymmetric model, in which a huge amount of $^{56}$Ni is ejected in a cone with a very high velocity; the ejected material becomes quickly transparent to positrons, which spread out in the interstellar medium.
TL;DR: The discovery of a supernova emerging at late times in the afterglow of GRB 030329 has apparently settled the issue on the nature of the progenitor of gamma-ray bursts.
Abstract: The discovery of a supernova emerging at late times in the afterglow of GRB 030329 has apparently settled the issue on the nature of the progenitor of gamma-ray bursts. We now know that at least a fraction of cosmological GRBs are associated with the death of massive stars, and that the two explosions are most likely simultaneous. Even though the association was already suggested for GRB 980425, the peculiarity of that burst did not allow to extend the association to all GRBs. The issue is now to understand whether GRB 030329 is a "standard burst" or not. I will discuss some peculiarities of GRB 030329 and its afterglow lightcurve showing how, rather than a classical cosmological GRB, it looks more like a transition object linking weak events like GRB 980425 to the classical long duration GRBs. I will also discuss the problems faced by the Hypernova scenario to account for the X-ray features detected in several GRBs and their afterglows.
01 Oct 2004
TL;DR: In this paper, the effects of mass and angularmomentum transfer between the component stars and the subsequent transport of angular momentum through one of the stars are investigated. But the authors focus on how the core of the hypernova progenitor retains or acquires sufficient angular momentum to produce the requisite axisymmetric collapse.
Abstract: If long γ-ray bursts are produced by hypernovae, a problem that must be confronted is how the core of the hypernova progenitor retains or acquires sufficient angular momentum to produce the requisite axisymmetric collapse. Physical processes during the evolution of an isolated massive star will tend to extract any initial angular momentum from the stellar core, rendering it difficult for such a star to become a hypernova. However, a substantial fraction of massive stars are members of binary systems. Tidal locking, mass transfer, or stellar merger in an evolved massive binary may lead to the transfer of orbital angular momentum to the core of one of the stars (or the merged star), sufficient to produce the progenitor of a hypernova. We have developed a new binary stellar-evolution code that includes the effects of mass and angular-momentum transfer between the component stars and the subsequent transport of angular momentum through one of the stars. This transport is affected by dynamical and secular shear instabilities, convective motions, the critical layer instability, and gravity waves. Our code treats in a self-consistent way the dynamical distortion of the star resulting from the induced rapid differential rotation. The results of our numerical computations indicate that late main-sequence or early post-mainsequence accretion from a binary companion onto a star with an initial mass ≥ 20M⊙ may produce a stellar core that is rotating sufficiently rapidly when it collapses to provide the initial conditions necessary for a hypernova event. Our results also indicate that the merger of a late post-main-sequence star with its binary companion, as considered by Ivanova, Podsiadlowski & Spruit (2002), may also lead to a hypernova event in the stellar core but is unlikely to produce an observable γ-ray burst.
TL;DR: The recent COSPAR workshop on γ-ray bursts as mentioned in this paper provided a rich photometric and spectroscopic record and perhaps the most direct evidence yet for the association of a specific γray burst with a massive star progenitor.
TL;DR: In this paper, the authors presented the first calculations of the helium-star/helium-star merger progenitors for the collapsar model, which invoked the merger of two helium cores during the common envelope inspiral phase of a binary system.
Abstract: The collapsar model, the now leading model for the engine behind gamma-ray bursts and hypernovae, requires that a star collapses to form a black hole surrounded by an accretion disk of high-angular momentum material. The current best theoretical stellar models, however, do not retain enough angular momentum in the core of the star to make a centrifugally supported disk. In this paper, we present the first calculations of the helium-star/helium-star merger progenitors for the collapsar model. These progenitors invoke the merger of two helium cores during the common envelope inspiral phase of a binary system. We find that, in some cases, the merger can produce cores that are rotating 3-10 times faster than single stars. He-star/He-star gamma-ray burst progenitors have a very different redshift distribution than their single-star gamma-ray burst progenitors and we discuss how gamma-ray burst observations can constrain these progenitors.
01 Jan 2004
01 Oct 2004
TL;DR: In this paper, the authors explore the possibility of positron production and escape by supernova events in the framework of an asymmetric model, in which a huge amount of $56}$Ni is ejected in a cone with a very high velocity; the ejected material becomes quickly transparent to positrons, which spread out in the interstellar medium.
Abstract: INTEGRAL/SPI has recently observed a strong and extended emission resulting from electron-positron annihilation located in the Galactic center region, consistent with the Galactic bulge geometry, without any counterpart at high gamma-ray energies, nor in the 1809 keV $^{26}$Al decay line. In order to explain the rate of positron injection in the Galactic bulge, estimated to more than 10$^{43}$ s$^{-1}$, the most commonly considered positron injection sources are type Ia supernovae. However, SN Ia rate estimations show that those sources fall short to explain the observed positron production rate, raising a challenging question about the nature of the Galactic positron source. In this context, a possible source of Galactic positrons could be supernova events of a new type, as the recently observed SN2003dh/GRB030329, an exploding Wolf-Rayet star (type Ic supernova) associated with a hypernova/gamma-ray burst; the question about the rate of this kind of events remains open, but could be problematically low.
In this paper, we explore the possibility of positron production and escape by such an event in the framework of an asymmetric model, in which a huge amount of $^{56}$Ni is ejected in a cone with a very high velocity; the ejected material becomes quickly transparent to positrons, which spread out in the interstellar medium.
01 Jun 2004
TL;DR: In this paper, the authors reported on combined X-ray and radio observations of SN 2002ap with XMM-Newton ToO observation and GMRT observations aided with VLA published results.
Abstract: Here we report on combined X-ray and radio observations of SN 2002ap with XMM-Newton ToO observation and GMRT observations aided with VLA published results. In deriving the X-ray flux of SN 2002ap we account for the contribution of a nearby source, found to be present in the pre-SN explosion images obtained with Chandra observatory. We also derive upper limits on the mass loss rate from X-ray and radio data. We suggest that the prompt X-ray emission is non-thermal in nature and due to the repeated compton boosting of optical photons. We also compare the SN’s early radiospheric properties with two other SNe at the same epoch.