Showing papers on "Hypernova published in 2003"

A very energetic supernova associated with the |[gamma]|-ray burst of 29 March 2003

Abstract: Over the past five years evidence has mounted that long-duration (greater than 2s) gamma-ray bursts (GRBs), the most brilliant of all astronomical explosions, signal the collapse of massive stars in our Universe. This evidence, originally based on the probable association of one unusual GRB with a supernova, now includes the association of GRBs with regions of massive star-formation in distant galaxies, tantalizing evidence of supernova-like light-curve 'bumps' in the optical afterglows of several bursts, and lines of freshly synthesized elements in the spectra of a few X-ray afterglows. These observations support, but do not yet conclusively validate, models based upon the deaths of massive stars, presumably associated with core collapse. Here we report evidence for a very energetic supernova (a hypernova), temporally and spatially coincident with a GRB at redshift z=0.1685. The timing of the supernova indicates that it exploded within a few days of the GRB, strongly suggesting that core-collapse events can give rise to GRBs. Amongst the GRB central engine models proposed to-date, the properties of this supernova thus favour the collapsar model.

Spectroscopic Discovery of the Supernova 2003dh Associated with GRB 030329

Abstract: We present early observations of the afterglow of GRB 030329 and the spectroscopic discovery of its associated supernova SN 2003dh. We obtained spectra of the afterglow of GRB 030329 each night from March 30.12 (0.6 days after the burst) to April 8.13 (UT) (9.6 days after the burst). The spectra cover a wavelength range of 350-850 nm. The early spectra consist of a power-law continuum (Fν ν-0.9) with narrow emission lines originating from H II regions in the host galaxy, indicating a low redshift of z = 0.1687. However, our spectra taken after 2003 April 5 show broad peaks in flux characteristic of a supernova. Correcting for the afterglow emission, we find that the spectrum of the supernova is remarkably similar to the Type Ic hypernova SN 1998bw. While the presence of supernovae has been inferred from the light curves and colors of gamma-ray burst afterglows in the past, this is the first direct, spectroscopic confirmation that a subset of classical gamma-ray bursts originate from supernovae.

Observed and Physical Properties of Core-Collapse Supernovae

Abstract: I use photometry and spectroscopy data for 24 Type II plateau supernovae (SNe IIP) to examine their observed and physical properties This data set shows that these objects encompass a wide range of ~5 mag in their plateau luminosities, their expansion velocities vary by a factor of 5, and the nickel masses produced in these explosions go from 00016 to 026 M☉ From a subset of 16 objects I find that the explosion energies vary between 06 × 1051 and 55 × 1051 ergs, the ejected masses encompass the range 14-56 M☉, and the progenitors' radii go from 80 to 600 R☉ Despite this great diversity, several regularities emerge, which reveal that there is a continuum in the properties of these objects from the faint, low-energy, nickel-poor SNe 1997D and 1999br, to the bright, high-energy, nickel-rich SN 1992am This study provides evidence that more massive progenitors produce more energetic explosions, thus suggesting that the outcome of the core collapse is somewhat determined by the envelope mass I also find that SNe with greater energies produce more nickel Similar relationships appear to hold for SNe Ib/c, which suggests that both SNe II and SNe Ib/c share the same core physics When the whole sample of core-collapse objects is considered, there is a continuous distribution of energies below 8 × 1051 ergs Far above in energy scale and nickel production lies the extreme hypernova 1998bw, the only SN firmly associated with a gamma-ray burst

An asymptotic-giant-branch star in the progenitor system of a type Ia supernova.

Abstract: Stars that explode as supernovae come in two main classes A type Ia supernova is recognized by the absence of hydrogen and the presence of elements such as silicon and sulphur in its spectrum; this class of supernova is thought to produce the majority of iron-peak elements in the Universe They are also used as precise ‘standard candles’ to measure the distances to galaxies While there is general agreement that a type Ia supernova is produced by an exploding white dwarf star1, no progenitor system has ever been directly observed Significant effort has gone into searching for circumstellar material to help discriminate between the possible kinds of progenitor systems2, but no such material has hitherto been found associated with a type Ia supernova3 Here we report the presence of strong hydrogen emission associated with the type Ia supernova SN2002ic, indicating the presence of large amounts of circumstellar material We infer from this that the progenitor system contained a massive asymptotic-giant-branch star that lost several solar masses of hydrogen-rich gas before the supernova explosion

Bipolar Supernova Explosions: Nucleosynthesis and Implications for Abundances in Extremely Metal-Poor Stars

Abstract: Hydrodynamics and explosive nucleosynthesis in bipolar supernova explosions are examined to account for some peculiar properties of hypernovae as well as peculiar abundance patterns of metal-poor stars. The explosion is assumed to be driven by bipolar jets that are powered by accretion onto a central remnant. The energy injection rate by the jets is assumed to be proportional to the accretion rate, i.e., ?jet = ?c2. We explore the features of the explosions with varying progenitors' masses and jet properties. The outcomes are different from conventional spherical models. (1) In the bipolar models, Fe-rich materials are ejected at high velocities along the jet axis, while O-rich materials occupy the central region, whose density becomes very high as a consequence of continuous accretion from the side. This configuration can explain some peculiar features in the light curves and the nebular spectra of hypernovae. (2) Production of 56Ni tends to be smaller than in spherical thermal bomb models. To account for a large amount of 56Ni observed in hypernovae, the jets should be initiated when the compact remnant mass is still smaller than 2-3 M?, or they should be very massive and slow. (3) Ejected isotopes are distributed as follows in order of decreasing velocities: 64Zn, 59Co, 56Fe, 44Ti, and 4He at the highest velocities; 55Mn, 52Cr, 32S, and 28Si at the intermediate velocities; and 24Mg and 16O at the lowest velocities. (4) The abundance ratios (Zn, Co)/Fe are enhanced while the ratios (Mn, Cr)/Fe are suppressed. This can account for the abundance pattern of extremely metal-poor stars. These agreements between the models and observations suggest that hypernovae are driven by bipolar jets and have significantly contributed to the early Galactic chemical evolution.

Bipolar Supernova Explosions: Nucleosynthesis & Implication on Abundances in Extremely Metal-Poor Stars

Abstract: Hydrodynamics and explosive nucleosynthesis in bipolar supernova explosions are examined to account for some peculiar properties of hypernovae as well as peculiar abundance patterns of metal-poor stars. The explosion is supposed to be driven by bipolar jets which are powered by accretion onto a central remnant. We explore the features of the explosions with varying progenitors' masses and jet properties. The outcomes are different from conventional spherical models. (1) In the bipolar models, Fe-rich materials are ejected at high velocities along the jet axis, while O-rich materials occupy the central region whose density becomes very high as a consequence of continuous accretion from the side. This configuration can explain some peculiar features in the light curves and the nebular spectra of hypernovae. (2) Production of $^{56}$Ni tends to be smaller than in spherical thermal bomb models. To account for a large amount of $^{56}$Ni observed in hypernovae, the jets should be initiated when the compact remnant mass is still smaller than $2-3\msun$, or the jets should be very massive and slow. (3) Ejected isotopes are distributed as follows in order of decreasing velocities: $^{64}$Zn, $^{59}$Co, $^{56}$Fe, $^{44}$Ti, and $^{4}$He at the highest velocities, $^{55}$Mn, $^{52}$Cr, $^{32}$S, and $^{28}$Si at the intermediate velocities, and $^{24}$Mg, $^{16}$O at the lowest velocities. (4) The abundance ratios (Zn, Co)/Fe are enhanced while the ratios (Mn, Cr)/Fe are suppressed. This can account for the abundance pattern of extremely metal-poor stars. These agreements between the models and observations suggest that hypernovae are driven by bipolar jets and have significantly contributed to the early Galactic chemical evolution.

A Two-Component Model for the Light Curves of Hypernovae

Abstract: The light curves of hypernovae, i.e., very energetic supernovae with E51 ≡ E/1051 ergs 5-10, are characterized by a phase of linear decline at epochs of a few months. Classical, one-dimensional explosion models fail to simultaneously reproduce the light curve near peak and at the linear decline phase. The evolution of these light curves may, however, be explained by a simple model consisting of two concentric components. The outer component is responsible for the early part of the light curve and for the broad absorption features observed in the early spectra of hypernovae, similar to the one-dimensional models. In addition, a very dense inner component is added, which reproduces the linear decline phase in the observed magnitude versus time relation for SN 1998bw, SN 1997ef, and SN 2002ap. This simple approach does contain one of the main features of jet-driven, asymmetric explosion models, namely, the presence of a dense core. Although the total masses and energies derived with the two-component model are similar to those obtained in previous studies that also adopted spherical symmetry, this study suggests that the ejecta are aspherical, and thus, the real energies and masses may deviate from those derived assuming spherical symmetry. The supernovae that were modeled are divided into two groups according to the prominence of the inner component: the inner component of SN 1997ef is denser and more 56Ni-rich, relative to the outer component, than the corresponding inner components of SN 1998bw and SN 2002ap. These latter objects have a similar inner-to-outer component ratio, although they have very different global values of mass and energy.

The Type Ic Hypernova SN 2003dh/GRB 030329

Abstract: The spectra of SN 2003dh, identified in the afterglow of GRB 030329, are modeled using radiation transport codes. It is shown that SN 2003dh had a high explosion kinetic energy (~4 × 1052 ergs in spherical symmetry), making it one of the most powerful hypernovae observed so far and supporting the case for association between hypernovae and gamma-ray bursts. However, the light curve derived from fitting the spectra suggests that SN 2003dh was not as bright as SN 1998bw, ejecting only ~0.35 M☉ of 56Ni. The spectra of SN 2003dh resemble those of SN 1998bw around maximum, but later they look more like those of the less energetic hypernova SN 1997ef. The spectra and the inferred light curve can be modeled adopting a density distribution similar to that used for SN 1998bw at v > 25,000 km s-1 but more like that of SN 1997ef at lower velocities. The mass of the ejecta is ~8 M☉, somewhat less than in the other two hypernovae. The progenitor must have been a massive star (M ~ 35-40 M☉), as for other hypernovae. The need to combine different one-dimensional explosion models strongly indicates that SN 2003dh was an asymmetric explosion.

Supernovae and Gamma-Ray Bursters

Abstract: Supernovae.- Historical Supernovae.- Classification of Supernovae.- Supernova Rates.- Optical Spectra of Supernovae.- Optical Light Curves of Supernovae.- X-Ray Supernovae.- Ultraviolet Supernovae.- Radio Supernovae.- Supernova Interaction with a Circumstellar Medium.- Measuring Cosmology with Supernovae.- Supernova 1987A.- Supernovae to ?-Ray Bursters.- SN1998bw and Hypernovae.- Supernovae and ?-Ray Bursters.- ?-Ray Bursters.- Observational Properties of Cosmic ?-Ray Bursts.- X-Ray Observations of ?-Ray Burst Afterglows.- Optical Observations of ?-Ray Burst Afterglows.- Radio Observations of ?-Ray Burst Afterglows.- Gamma-Ray Bursts: The Underlying Model.- Ambient Interaction Models for ?-Ray Burst Afterglows.- Cosmological Studies with ?-Ray Bursts.

The Type Ic Hypernova SN 2003dh/GRB 030329

Abstract: The spectra of SN 2003dh, identified in the afterglow of GRB030329, are modeled using radiation transport codes. It is shown that SN 2003dh had a high explosion kinetic energy ($\sim 4 \times 10^{52}$ erg in spherical symmetry), making it one of the most powerful hypernovae observed so far, and supporting the case for association between hypernovae and Gamma Ray Bursts. However, the light curve derived from fitting the spectra suggests that SN 2003dh was not as bright as SN 1998bw, ejecting only $\sim 0.35\Msun$ of \Nifs. The spectra of SN 2003dh resemble those of SN 1998bw around maximum, but later they look more like those of the less energetic hypernova SN 1997ef. The spectra and the inferred light curve can be modeled adopting a density distribution similar to that used for SN 1998bw at $ v > 25,000$\kms but more like that of SN 1997ef at lower velocities. The mass of the ejecta is $\sim 8\Msun$, somewhat less than in the other two hypernovae. The progenitor must have been a massive star ($M \sim 35-40\Msun$), as for other hypernovae. The need to combine different one-dimensional explosion models strongly indicates that SN 2003dh was an asymmetric explosion.

On the Spectrum and Spectropolarimetry of Type Ic Hypernova SN 2003dh/GRB 030329*

Abstract: Spectroscopic and spectropolarimetric observations of SN 2003dh/GRB 030329 obtained in 2003 May using the Subaru 8.2 m Telescope are presented. The properties of the supernova (SN) are investigated through a comparison with spectra of the Type Ic hypernovae SN 1997ef and SN 1998bw (hypernovae being a tentatively defined class of SNe with very broad absorption features: these features suggest a large velocity of the ejected material and possibly a large explosion kinetic energy). Comparison with spectra of other hypernovae shows that the spectrum of SN 2003dh obtained on 2003 May 8 and 9, i.e., 34-35 rest-frame days after the gamma-ray burst (GRB; for z = 0.1685), are similar to those of SN 1997ef obtained ~34-42 days after the fiducial time of explosion of that SN. The match with SN 1998bw spectra is not as good (at rest 7300-8000 A), but again spectra obtained ~33-43 days after GRB 980425 are preferred. This indicates that the SN may have intermediate properties between SNe 1997ef and 1998bw. On the basis of the analogy with the other hypernovae, the time of explosion of SN 2003dh is then constrained to be between -8 and +2 days of the GRB. The Si and O P Cygni lines of SN 2003dh seem comparable to those of SN 1997ef, which suggests that the ejected mass in SN 2003dh may match that in SN 1997ef. Polarization was marginally detected at optical wavelengths. This is consistent with measurements of the late afterglow, implying that it originated mostly in the interstellar medium of the host galaxy.

A Two-Component Model for the Light Curves of Hypernovae

Abstract: The light curves of 'hypernovae', i.e. very energetic supernovae with $E_{51} \equiv E/10^{51}$ergs $\gsim 5-10$ are characterized at epochs of a few months by a phase of linear decline. Classical, one-dimensional explosion models fail to simultaneously reproduce the light curve near peak and at the linear decline phase. The evolution of these light curves may however be explained by a simple model consisting of two concentric components. The outer component is responsible for the early part of the light curve and for the broad absorption features observed in the early spectra of hypernovae, similar to the one-dimensional models. In addition, a very dense inner component is added, which reproduces the linear decline phase in the observed magnitude-versus-time relation for SNe 1998bw, 1997ef, and 2002ap. This simple approach does contain one of the main features of jet-driven, asymmetric explosion models, namely the presence of a dense core. Although the total masses and energies derived with the two-component model are similar to those obtained in previous studies which also adopted spherical symmetry, this study suggests that the ejecta are aspherical, and thus the real energies and masses may deviate from those derived assuming spherical symmetry. The supernovae which were modeled are divided into two groups, according to the prominence of the inner component: the inner component of SN 1997ef is denser and more $^{56}$Ni-rich, relative to the outer component, than the corresponding inner components of SNe 1998bw and 2002ap. These latter objects have a similar inner-to-outer component ratio, although they have very different global values of mass and energy.

On The Spectrum and Spectropolarimetry of Type Ic Hypernova SN 2003dh/GRB 030329

Abstract: Spectroscopic and spectropolarimetric observations of SN 2003dh/GRB 030329 obtained in 2003 May using the Subaru 8.2 m telescope are presented. The properties of the SN are investigated through a comparison with spectra of the Type Ic hypernovae SNe 1997ef and 1998bw. (Hypernovae being a tentatively defined class of SNe with very broad absorption features: these features suggest a large velocity of the ejected material and possibly a large explosion kinetic energy.) Comparison with spectra of other hypernovae shows that the spectrum of SN 2003dh obtained on 2003 May 8 and 9, i.e., 34-35 rest-frame days after the GRB (for z=0.1685), are similar to those of SN 1997ef obtained ~34-42 days after the fiducial time of explosion of that SN. The match with SN 1998bw spectra is not as good (at rest 7300-8000 A, but again spectra obtained ~33-43 days after GRB 980425 are preferred. This indicates that the SN may have intermediate properties between SNe 1997ef and 1998bw. Based on the analogy with the other hypernovae, the time of explosion of SN 2003dh is then constrained to be between -8 and +2 days of the GRB. The Si and O P-Cygni lines of SN 2003dh seem comparable to those of SN 1997ef, which suggests that the ejected mass in SN 2003dh may match that in SN 1997ef. Polarization was marginally detected at optical wavelengths. This is consistent with measurements of the late afterglow, implying that it mostly originated in the interstellar medium of the host galaxy.

Optical and near-infrared observations of the GRB020405 afterglow ?

Abstract: We report on photometric, spectroscopic and polarimetric monitoring of the optical and near-infrared (NIR) afterglow of GRB020405. Ground-based optical observations, performed with 8 different telescopes, started about 1 day after the high-energy prompt event and spanned a period of ∼10 days; the addition of archival HST data extended the coverage up to ∼150 days after the GRB. We report the first detection of the afterglow in NIR bands. The detection of Balmer and oxygen emission lines in the optical spectrum of the host galaxy indicates that the GRB is located at redshift z = 0.691. Fe II and Mg II absorption systems are detected at z = 0.691 and at z = 0.472 in the afterglow optical spectrum. The latter system is likely caused by absorbing clouds in the galaxy complex located ∼2" southwest of the GRB020405 host. Hence, for the first time, the galaxy responsible for an intervening absorption line system in the spectrum of a GRB afterglow is spectroscopically identified. Optical and NIR photometry of the afterglow indicates that, between 1 and 10 days after the GRB, the decay in all bands is consistent with a single power law of index a = 1.54 ′0.06. The late-epoch VLT J-band and HST optical points lie above the extrapolation of this power law, so that a plateau (or "bump") is apparent in the VRIJ light curves at 10-20 days after the GRB. The light curves at epochs later than day ∼20 after the GRB are consistent with a power-law decay with index α' = 1.85 ′ 0.15. While other authors have proposed to reproduce the bump with the template of the supernova (SN) 1998bw, considered the prototypical "hypernova", we suggest that it can also be modeled with a SN having the same temporal profile as the other proposed hypernova SN2002ap, but 1.3 mag brighter at peak, and located at the GRB redshift. Alternatively, a shock re-energization may be responsible for the rebrightening. A single polarimetric R-band measurement shows that the afterglow is polarized, with P = 1.5 ′ 0.4% and polarization angle 0 = 172° ′8°. Broad-band optical-NIR spectral flux distributions show, in the first days after the GRB, a change of slope across the J band which we interpret as due to the presence of the electron cooling frequency v c . The analysis of the multiwavelength spectrum within the standard fireball model suggests that a population of relativistic electrons with index p ∼ 2.7 produces the optical-NIR emission via synchrotron radiation in an adiabatically expanding blastwave, with negligible host galaxy extinction, and the X-rays via Inverse Compton scattering off lower-frequency afterglow photons.

Theory and astrophysical consequences of a magnetized torus around a rapidly rotating black hole

Abstract: We analyze the topology, lifetime, and emissions of a torus around a black hole formed in hypernovae and black hole-neutron star coalescence. The torus is ab initio uniformly magnetized, represented by two counteroriented current rings, and develops a state of suspended accretion against a magnetic wall around the black hole. Magnetic stability of the torus gives rise to a new fundamental limit /k < 0.1 for the ratio of poloidal magnetic field energy to kinetic energy, corresponding to a maximum magnetic field strength Bc (1016 G) (7 M☉/MH) (6MH/R)2 (MT/0.03MH)1/2. The lifetime of rapid spin of the black hole, effectively defined by the timescale of dissipation of spin energy Erot in the horizon, hereby satisfies T (40 s) (MH/7 M☉)(R/6MH)4(0.03MH/MT) for a black hole of mass MH surrounded by a torus of mass MT and radius R. The torus converts a major fraction Egw/Erot ~ 10% into gravitational radiation through a finite number of multipole mass moments and a smaller fraction into MeV neutrinos and baryon-rich winds. At a source distance of 100 Mpc, these emissions over N = 2 × 104 periods give rise to a characteristic strain amplitude N1/2hchar 6 × 10-21. We argue that torus winds create an open magnetic flux tube on the black hole, which carries a minor fraction Ej/Erot 10-3 in baryon-poor outflows to infinity. We conjecture that these are not high-σ outflows, owing, in part, to magnetic reconnection in surrounding current sheets. The fraction Ej/Erot ~ (MH/R)4 is standard for a universal horizon half-opening angle θH MH/R of the open flux tube. We identify this baryon-poor output of tens of seconds with gamma-ray bursts with contemporaneous and strongly correlated emissions in gravitational radiation, conceivably at multiple frequencies. Ultimately, this leaves a black hole binary surrounded by a supernova remnant.

The knee in the Galactic cosmic ray spectrum and variety in Supernovae

Abstract: We calculate Galactic cosmic ray (GCR) flux averaged over Supernova explosion energies and types, applying only the formulae of standard model of CR acceleration in Supernova remnants (SNR) and using latest astronomical data on the variety in Supernovae In the presented model the cosmic ray flux in the whole energy range up to 10 18 eV is predominantly formed by the most energetic SN explosions The “knee” in GCR spectrum at energy around Eknee = 3 PeV can quantitatively be explained by the dominant contribution of Hypernovae The model sketches all-particle cosmic ray spectrum up to 10 18 eV

The Optical/Near-Infrared Light Curves of SN 2002ap for the First 140 Days after Discovery

Abstract: Supernova (SN) 2002ap in M74 was observed in the $UBVRIJHK$ bands for the first 40 days following its discovery (2002 January 29) until it disappeared because of solar conjunction, and then in June after it reappeared. The magnitudes and dates of peak brightness in each band were determined. While the rate of increase of the brightness before the peak is almost independent of wavelength, the subsequent rate of decrease becomes smaller with wavelength from the $U$ to the $R$ band, and is constant at wavelengths beyond $I$. The photometric evolution is faster than in the well-known ``hypernovae'' SNe~1998bw and 1997ef, indicating that SN 2002ap ejected less mass. The bolometric light curve of SN 2002ap for the full period of observations was constructed. The absolute magnitude is found to be much fainter than that of SN 1998bw, but is similar to that of SN 1997ef, which lies at the faint end of the hypernova population. The bolometric light curve at the early epochs was best reproduced with the explosion of a C+O star that ejects $2.5~M_\sun$ with kinetic energy $E_{\rm K}=4\times 10^{51}~{\rm ergs}$. A comparison of the predicted brightness of SN 2002ap with that observed after solar conjunction may imply that $\gamma$-ray deposition at the later epochs was more efficient than in the model. This may be due to an asymmetric explosion.

The optical/near-infrared light curves of SN 2002ap for the first 1.5 years after discovery

Abstract: Supernova (SN) 2002ap in M74 was observed in the UBVRIJHK bands for the first 40 days following its discovery (2002 January 29) until it disappeared as a result of solar conjunction and then in June after it reappeared. The magnitudes and dates of peak brightness in each band were determined. While the rate of increase of the brightness before the peak is almost independent of wavelength, the subsequent rate of decrease becomes smaller with wavelength from the U to the R bands and is constant at wavelengths beyond the I band. The photometric evolution is faster than in the well-known "hypernovae" SNe 1998bw and 1997ef, indicating that SN 2002ap ejected less mass. The bolometric light curve of SN 2002ap for the full period of observations was constructed. The absolute magnitude is found to be much fainter than that of SN 1998bw but is similar to that of SN 1997ef, which lies at the faint end of the hypernova population. The bolometric light curve at the early epochs was best reproduced with the explosion of a C + O star that ejects 2.5 M☉ with kinetic energy EK = 4 × 1051 ergs. A comparison of the predicted brightness of SN 2002ap with that observed after solar conjunction may imply that γ-ray deposition at the later epochs was more efficient than in the model. This may be due to an asymmetric explosion.

Hypernovae/GRB in the Galactic Center as possible sources of Galactic Positrons

Abstract: The observation of a strong and extended positron-electron line annihilation emission in the central regions of the Galaxy by INTEGRAL-SPI, consistent with the Galactic bulge geometry, without any counterpart in the gamma-ray range, neither at high energy nor in the 1809 keV $^{26}$Al 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 SN Ic, exemplified by SN2003dh, which is associated to a gamma-ray burst. This kind of supernova/hypernova/GRB event is interpreted as the result of a bipolar Wolf-Rayet explosion, which produces a large amount of $^{56}$Ni and ejects it at high velocity along the rotation axis. The bulk of positrons resulting from $^{56}$Co decay escapes in the surrounding medium due to the rapid thinning of the ejecta in the polar direction. We show that a rate of about 0.02 SN2003dh-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 3D hydrodynamic calculations of anisotropic ejections of $^{56}$Ni in SN Ic/GRB events, will allow to estimate the separate contributions of SNe Ia and SNe Ic to positron injection.

Explosive Nucleosynthesis Associated with Formation of Jet-induced GRBs in Massive Stars

Abstract: We perform 2-dimensional relativistic hydrodynamical simulations in the context of collapsar model. Calculations of explosive nucleosynthesis are also accomplished. We investigate the influence of the structure of the progenitor and energy deposition rate on the resulting explosive nucleosynthesis, assuming that 56Ni is mainly synthesized in the jet launched by the neutrino heating. We show the amount of 56Ni is very sensitive to the energy deposition rate. Thus we conclude that it is quite natural not to detect an underlying supernova in some X-ray afterglows as in GRB 010921. We also point out the possibility that the relative abundance of the elements with intermediate mass number such as Si and S in the X-ray afterglow of GRB 011211 may be naturally explained if the energy deposition rate at the central engine is relatively long because little amount of 56Ni should be synthesized under such an environment. If this discussion is true, there should be correlation between the line features in the X-ray afterglow and duration of the GRB. It should be noted that the duration of GRB 011211 is 270 seconds, making it the longest burst ever observed by Beppo-SAX although it suffers from the effect of red-shift (z_host=2.14), which supports our conclusion. Our results also suggest that the type I collapsar model in which the energy deposition rate is relatively low (\dot{E} \sim 10^{51} erg/s) might have difficulty in reproducing the observed amount of 56Ni in a hypernova such as SN 1998bw. This means that the mechanism of the central engine of a hypernova accompanying GRB may be constrained by the discussion of explosive nucleosynthesis.

Neutrino-driven Explosions in Gamma-Ray Bursts and Hypernovae

Abstract: We study the physics behind the neutrino-driven mechanism for gamma-ray bursts (GRBs) and hypernovae, deriving the critical density at which these outbursts occur in the collapsar model. The agreement between this derivation and results from past collapsar simulations (MacFadyen & Woosley) is excellent, implying that we have captured the essential physics. We then use this derivation to study a range of progenitors for collapsar GRBs. We derive how much of the star will accrete onto the black hole core before the infall density drops below this critical density, leading to an estimate of the remnant black hole mass for GRBs and hypernovae. We also estimate the time delays between gravity-wave or neutrino signals and the onset of the explosion or burst event. This derivation, combined with future observational constraints, provides a physical insight into the structure of the GRB progenitor.

Explosive Nucleosynthesis Associated with Formation of Jet-induced Gamma-Ray Bursts in Massive Stars

Abstract: We perform two-dimensional relativistic hydrodynamic simulations in the context of collapsar model. Calculations of explosive nucleosynthesis are also accomplished. We investigate the influence of the structure of the progenitor and energy deposition rate on the resulting explosive nucleosynthesis, assuming that 56Ni is mainly synthesized in the jet launched by the neutrino heating. We show that the amount of 56Ni is very sensitive to the energy deposition rate. Thus, we conclude that it is quite natural to detect no underlying supernova in some X-ray afterglows, such as GRB 010921. We also point out the possibility that the relative abundance of the elements with an intermediate mass number, such as Si and S, in the X-ray afterglow of GRB 011211 may be naturally explained if the energy deposition rate at the central engine is relatively long because little 56Ni should be synthesized under such an environment. If this discussion is true, there should be a correlation between the line features in the X-ray afterglow and the duration of the gamma-ray burst. It should be noted that the duration of GRB 011211 is 270 s, making it the longest burst ever observed by BeppoSAX, although it suffers from the effect of redshift (zhost = 2.14), and supporting our conclusion. Our results also suggest that the type I collapsar model, in which the energy deposition rate is relatively low ( ~ 1051 ergs s-1), might have difficulty in reproducing the observed amount of 56Ni in a hypernova such as SN 1998bw. This means that models of the mechanism of the central engine of a hypernova-accompanying gamma-ray burst may be constrained by the requirements of explosive nucleosynthesis.

Neutrino-Driven Explosions in GRBs and Hypernovae

Abstract: We study the physics behind the neutrino-driven mechanism for gamma-ray bursts and hypernovae, deriving the critical density at which these outbursts occur in the collapsar model. The agreement between this derivation and results from past collapsar simulations (MacFadyen & Woosley 2000) is excellent, implying that we have captured the essential physics. We then use this derivation to study a range of progenitors for collapsar gamma-ray bursts. We derive how much of the star will accrete onto the black hole core before the infall density drops below this critical density, leading to an estimate of the remnant black hole mass for GRBs and hypernovae. We also estimate the time delays between gravity wave or neutrino signals and the onset of the explosion or burst event. This derivation, combined with future observational constraints, provides a physical insight into the structure of the GRB progenitor.

Hypernovae and their nucleosynthesis

Abstract: We review the characteristics of nucleosynthesis in ‘hypernovae’, i.e., core-collapse supernovae with very large explosion energies (≳ 10 52 ergs). The hypernova yields show the following characteristics: ( i ) the mass ratio between the complete and incomplete Si burning regions is larger in hypernovae than normal supernovae. As a result, higher energy explosions tend to produce larger [(Zn, Co, V)/Fe] and smaller [(Mn, Cr)/Fe], which could explain the trend observed in very metal-poor stars; ( ii ) because of enhanced α-rich freeze-out, 44 Ca, 48 Ti, and 64 Zn are produced more abundantly than in normal supernovae. The large [(Ti, Zn)/Fe] ratios observed in very metal poor stars strongly suggest a significant contribution of hypernovae; and ( iii ) oxygen burning takes place in more extended regions in hypernovae to synthesize a larger amount of Si, S, Ar, and Ca (‘Si’), which makes the ‘Si’/O ratio larger. The abundance pattern of the starburst galaxy M 82 may be attributed to hypernova explosions. We thus suggest that hypernovae make important contribution to the early Galactic (and cosmic) chemical evolution.

A second glance at SN 2002ap and the M74 field with XMM-Newton

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 X-ray 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/GRB 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 ~ 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 ~ 10^{20} cm^{-2}, ie, 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.

The X-ray, optical and radio evolution of the GRB030329 afterglow and the associated SN2003dh

Abstract: Extensive X-ray, optical and radio observations of the bright afterglow of the Gamma Ray Burst GRB 030329 are used to construct the multi-frequency evolution of the event. The data are fitted using the standard fireball shock model to provide estimates of the initial energy, epsilon = 6.8 x 10^52 ergs sr^-1, the density of the ambient medium, n_0 = 1 cm^-3, the electron and magnetic energy density fractions, epsilon_e = 0.24 & epsilon_B = 0.0017, the power law index of the relativistic electron spectrum, p = 2.25, and the opening angle of the jet, theta_j = 3 degrees. 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 days in the R-band are much brighter than expected from a standard SN, and there is a large radio excess over the expected afterglow flux for t>2 days. No deviation from the best-fit afterglow model is seen in the X-ray decline, indicating that the excess optical and radio flux from 1-5 days arises from a later injection of slower electrons by the central engine.

Black-hole formation from stellar collapse

Abstract: I review the end-state of massive stellar evolution, following the evolution of these massive stars from the onset of collapse through the formation of a compact remnant and the possible supernova or hypernova explosion. In particular, I concentrate on the formation of black holes from stellar collapse: the fraction of stars that form black holes, the black-hole mass distribution and the velocities these black-hole remnants may receive during their formation process.

SN1998bw and Hypernovae

Abstract: SN1998bw is a peculiar type Ic supernova Its peak brightness is almost ten times greater than typical type Ic in optical and even 10 – 100 times brighter than other radio bright type Ib/c supernovae in radio bands The extremely broad features in the optical spectra indicate high velocities of ejected matter ∼ 3 × 104 km s−1 which, combined with the breadth of light curves, lead to an estimated kinetic energy of explosion of ∼ 2−5×1052 erg under the assumption of spherical symmetry This class of hyperenergetic supernovae is termed “hypernova” There are some observational indications of possible asymmetry, which might reduce this energy requirement However, it is still likely that SN1998bw is a hypernova SN1998bw is the first supernova for which a possible link to a γ-ray burst was suggested due to its angular and time coincidence with GRB980425 The high radio luminosity and fast evolution of the radio light curves suggest the existence of a relativistic blast wave in SN1998bw, which might be related to the γ-ray burst directly or indirectly Several other several hypernova candidates have been discovered or reinterpreted since SN1998bw The unusual properties of these objects may require reconsideration of theories of stellar explosion mechanisms