Showing papers on "Hypernova published in 2005"

Chemistry and Star Formation in the Host Galaxies of Type Ia Supernovae

Abstract: We study the effect of environment on the properties of Type Ia supernovae by analyzing the integrated spectra of 57 local Type Ia supernova host galaxies. We deduce from the spectra the metallicity, current star formation rate, and star formation history of the host and compare these to the supernova decline rates. Additionally, we compare the host properties to the difference between the derived supernova distance and the distance determined from the best-fit Hubble law. From this we investigate possible uncorrected systematic effects inherent in the calibration of Type Ia supernova luminosities using light-curve fitting techniques. Our results indicate a statistically insignificant correlation in the direction of higher metallicity spiral galaxies hosting fainter Type Ia supernovae. However, we present qualitative evidence suggesting that progenitor age is more likely to be the source of variability in supernova peak luminosities than is metallicity. We do not find a correlation between the supernova decline rate and host galaxy absolute B magnitude, nor do we find evidence of a significant relationship between decline rate and current host galaxy star formation rate. A tenuous correlation is observed between the supernova Hubble residuals and host galaxy metallicities. Further host galaxy observations will be needed to refine the significance of this result. Finally, we characterize the environmental property distributions for Type Ia supernova host galaxies through a comparison with two larger, more general galaxy distributions using Kolmogorov-Smirnov tests. The results show the host galaxy metallicity distribution to be similar to the metallicity distributions of the galaxies of the NFGS and SDSS. Significant differences are observed between the SN Ia distributions of absolute B magnitude and star formation histories and the corresponding distributions of galaxies in the NFGS and SDSS. Among these is an abrupt upper limit observed in the distribution of star formation histories of the host galaxy sample, suggesting a Type Ia supernovae characteristic delay time lower limit of approximately 2.0 Gyr. Other distribution discrepancies are investigated and the effects on the supernova properties are discussed.

Binary Merger Progenitors for Gamma-Ray Bursts and Hypernovae

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.

GRB 050509B: Constraints on Short Gamma-Ray Burst Models

Abstract: We have obtained deep optical images with the Very Large Telescope at ESO of the first well-localized short-duration gamma-ray burst, GRB 050509b. We observed in the V and R bands at epochs starting at {approx}2 days after the GRB trigger and lasting up to three weeks. We detect no variable objects inside the small Swift/XRT X-ray error circle down to 5{sigma} limiting magnitudes of V = 26.5 and R = 25.2. The X-ray error circle includes a giant elliptical galaxy at z = 0.225, which has been proposed as the likely host of this GRB. Our limits indicate that if the GRB originated at z = 0.225, any supernova-like event accompanying the GRB would have to be over 100 times fainter than normal Type Ia SNe or Type Ic hypernovae, 5 times fainter than the faintest known Ia or Ic SNe, and fainter than the faintest known Type II SNe. Moreover, we use the optical limits to constrain the energetics of the GRB outflow, and conclude that there was very little radioactive material produced during the GRB explosion. These limits strongly constrain progenitor models for this short GRB.

The Unique Type Ib Supernova 2005bf: A WN Star Explosion Model for Peculiar Light Curves and Spectra

Abstract: Observations and modeling for the light curve (LC) and spectra of supernova (SN) 2005bf are reported. This SN showed unique features: the LC had two maxima, and declined rapidly after the second maximum, while the spectra showed strengthening He lines whose velocity increased with time. The double-peaked LC can be reproduced by a double-peaked 56 Ni distribution, with most 56 Ni at low velocity and a small amount at high velocity. The rapid postmaximum decline requires a large fraction of the g-rays to escape from the 56 Ni-dominated region, possibly because of low-density “holes.” The presence of Balmer lines in the spectrum suggests that the He layer of the progenitor was substantially intact. Increasing g-ray deposition in the He layer due to enhanced g-ray escape from the 56 Ni-dominated region may explain both the delayed strengthening and the increasing velocity of the He lines. The SN has massive ejecta (∼6–7 M,), normal kinetic energy [∼(1.0–1.5) # 10 51 ergs], a high peak bolometric luminosity (∼ ergs s 1 ) for an epoch as late as ∼ 40 days, and a large 56 Ni mass 42 5 # 10 (∼0.32 M,). These properties and the presence of a small amount of H suggest that the progenitor was initially massive ( M,) and had lost most of its H envelope, and was possibly a WN star. The double-peaked M ∼ 25–30 56 Ni distribution suggests that the explosion may have formed jets that did not reach the He layer. The properties of SN 2005bf resemble those of the explosion of Cassiopeia A. Subject headings: stars: Wolf-Rayet — supernovae: general — supernovae: individual (Cassiopeia A, SN 2005bf)

On the light curve and spectrum of SN 2003dh separated from the optical afterglow of GRB 030329

Abstract: The net optical light curves and spectra of the supernova (SN) 2003dh are obtained from the published spectra of GRB 030329, covering about 6 days before SN maximum to about 60 days after. The bulk of the U-band flux is subtracted from the observed spectra using early-time afterglow templates, because strong line blanketing greatly depresses the UV and U-band SN flux in a metal-rich, fast-moving SN atmosphere. The blue-end spectra of the gamma-ray burst (GRB) connected hypernova SN 1998bw is used to determine the amount of subtraction. The subtraction of a host galaxy template affects the late-time results. The derived SN 2003dh light curves are narrower than those of SN 1998bw, rising as fast before maximum, reaching a possibly fainter maximum, and then declining ~ 1.2-1.4 times faster. We then build UVOIR bolometric SN light curve. Allowing for uncertainties, it can be reproduced with a spherical ejecta model of Mej ~ 7 ± 3 M☉, EK ~ 3.5 ± 1.5 × 1052 ergs, with EK/Mej ~ 5 following previous spectrum modeling, and M(56Ni) ~ 0.4 M☉. This suggests a progenitor main-sequence mass of ~25-40 M☉, lower than SN 1998bw but significantly higher than normal Type Ic SNe and the GRB-unrelated hypernova SN 2002ap.

Broad‐band colours and overall photometric properties of template galaxy models from stellar population synthesis

Abstract: We present here a new set of evolutionary population synthesis models for template galaxies along the Hubble morphological sequence. The models, which account for the individual evolution of the bulge, disc, and halo components, provide basic morphological features, along with bolometric luminosity and colour evolution (including Johnson/Cousins, Gunn g, r, i, and Washington C, M, T1, T2 photometric systems) between 1 and 15 Gyr. The luminosity contribution from residual gas is also evaluated, both in terms of nebular continuum and Balmer-line enhancement. Our theoretical framework relies on the observed colours of present-day galaxies, coupled with a minimal set of physical assumptions related to simple stellar population (SSP) evolution theory, to constrain the overall distinctive properties of galaxies at earlier epochs. A comparison with more elaborate photometric models, and with empirical sets of reference spectral energy distributions (SEDs) for early- and late-type galaxies is accomplished, in order to test output reliability and investigate the internal uncertainty of the models. The match with observed colours of present-day galaxies tightly constrain the stellar birth rate, b, which smoothly increases from E to Im types. The comparison with the observed supernova (SN) rate in low-redshift galaxies shows, as well, a pretty good agreement, and allows us to tune up the inferred star formation activity and the SN and hypernova rates among the different galaxy morphological types. Among others, these results could find useful application also in cosmological studies, given for instance the claimed relationship between hypernova events and gamma-ray bursts. One outstanding feature of the back-in-time evolution model is the prevailing luminosity contribution of the bulge at early epochs. As a consequence, the current morphological look of galaxies might drastically change when moving to larger distances, and we discuss here how sensibly this bias could affect the observation (and the interpretation) of high-redshift surveys. In addition to broad-band colours, the modelling of Balmer line emission in disc-dominated systems shows that striking emission lines, like Hα, can very effectively track stellar birth rate in a galaxy. For these features to be useful age tracers as well, however, one should first assess the real change of b versus time on the basis of supplementary (and physically independent) arguments.

Low-Mass Star Formation Triggered by Supernovae in Primordial Clouds

Abstract: The evolution of a gas shell, swept up by the supernova remnant of a massive first-generation star, is studied with H2 and HD chemistry taken into account and with the use of a semianalytical approximation to the dynamics. When a first-generation star, formed in a parent pregalactic cloud, explodes as a supernova with explosion energy in the range of 1051-1052 ergs at redshifts of z = 10-50, H2 and HD molecules are formed in the swept up gas shell at fractional abundances of ~10-3 and ~10-5, respectively, and effectively cool the gas shell to temperatures of 32-154 K. If the supernova remnant can sweep to gather the ambient gas of mass 6 × 104 to 8 × 105 M☉, the gas shell comes to be dominated by its self-gravity and, hence, is expected to fragment. The amount of swept up gas necessary for fragmentation increases with the explosion energy and decreases with the interstellar gas density (or redshift) of the host cloud, which provides a lower boundary to the mass of the host cloud in which star formation is triggered by the first-generation supernova. Also, the condition for fragmentation is very sensitive to the thermal state of interstellar gas. Our result shows that for a reasonable range of temperatures (200-1000 K) of interstellar gas, the formation of second-generation stars can be triggered by a single supernova or hypernova with explosion energy in the above range in a primordial cloud of total (dark and baryonic) mass as low as a few times 106 M☉. For higher temperatures in the interstellar gas, however, the condition for the fragmentation in the swept up gas shell demands a larger supernova explosion energy. We also follow the subsequent contraction of the fragment pieces assuming their geometry (sphere and cylinder) and demonstrate that the Jeans masses in the fragments decrease to well below 1 M☉ by the time the fragments become optically thick to the H2 and HD lines. The fragments are then expected to break up into dense cores whose masses are comparable to the Jeans masses and collapse to form low-mass stars that can survive to the present. If the material in the gas shell is mixed well with the ejecta of the supernova, the shell and low-mass stars thus formed are likely to have metals of abundance [Fe/H] -3 on average. This metallicity is consistent with those of the extremely metal-poor stars found in the Galactic halo. Stars with low metallicities of [Fe/H] < -5 such as HE 0107-5240, recently discovered in the Galactic halo, are difficult to form by this mechanism and must be produced in different situations.

Molecular Superbubbles in the Starburst Galaxy NGC 253

Abstract: The central 2x1 kpc of the starburst galaxy NGC 253 has been imaged using the Submillimeter Array at a 60 pc resolution in the J=2-1 transitions of 12CO, 13CO, and C18O as well as in the 1.3 mm continuum. Molecular gas and dust are mainly in the circumnuclear disk of ~500 pc radius, with warm (~40 K) and high area-filling factor gas in its central part. Two gas shells or cavities have been discovered in the circumnuclear disk. They have ~100 pc diameters and have large velocity widths of 80-100 km/s, suggestive of expansion at ~50 km/s. Modeled as an expanding bubble, each shell has an age of ~0.5 Myr and needed kinetic energy of ~1E46 J as well as mean mechanical luminosity of ~1E33 W for its formation. The large energy allows each to be called a superbubble. A ~10^6 Msun super star cluster can provide the luminosity, and could be a building block of the nuclear starburst in NGC 253. Alternatively, a hypernova can also be the main source of energy for each superbubble, not only because it can provide the mechanical energy and luminosity but also because the estimated rate of superbubble formation and that of hypernova explosions are comparable. Our observations indicate that the circumnuclear molecular disk harboring the starburst is highly disturbed on 100 pc or smaller scales, presumably by individual young clusters and stellar explosions, in addition to globally disturbed in the form of the well-known superwind.

Deep Photometry of GRB 041006 Afterglow: Hypernova Bump at Redshift z=0.716

Abstract: We present deep optical photometry of the afterglow of gamma-ray burst (GRB) 041006 and its associated hypernova obtained over 65 days after detection (55 R-band epochs on 10 different nights). Our early data (t<4 days) joined with published GCN data indicates a steepening decay, approaching F_nu ~t^{-0.6} at early times (<<1 day) and F_nu ~t^{-1.3} at late times. The break at t_b=0.16+-0.04 days is the earliest reported jet break among all GRB afterglows. During our first night, we obtained 39 exposures spanning 2.15 hours from 0.62 to 0.71 days after the burst that reveal a smooth afterglow, with an rms deviation of 0.024 mag from the local power-law fit, consistent with photometric errors. After t~4 days, the decay slows considerably, and the light curve remains approximately flat at R~24 mag for a month before decaying by another magnitude to reach R~25 mag two months after the burst. This ``bump'' is well-fitted by a k-corrected light curve of SN1998bw, but only if stretched by a factor of 1.38 in time. In comparison with the other GRB-related SNe bumps, GRB 041006 stakes out new parameter space for GRB/SNe, with a very bright and significantly stretched late-time SN light curve. Within a small sample of fairly well observed GRB/SN bumps, we see a hint of a possible correlation between their peak luminosity and their ``stretch factor'', broadly similar to the well-studied Phillips relation for the type Ia supernovae.

Deep Photometry of GRB 041006 Afterglow: Hypernova Bump at Redshift z = 0.716*

Abstract: We present deep optical photometry of the afterglow of gamma-ray burst (GRB) 041006 and its associated hypernova obtained over 65 days after detection (55 R-band epochs on 10 different nights). Our early data (t < 4 days) joined with published GCN data indicate a steepening decay, approaching Fν t-0.6 at early times (t 1 day) and Fν t-1.3 at late times. The break at tb = 0.16 ± 0.04 days is the earliest reported jet break among all GRB afterglows. During our first night, we obtained 39 exposures spanning 2.15 hr from 0.62 to 0.71 days after the burst that reveal a smooth afterglow, with an rms deviation of 0.024 mag from the local power-law fit, consistent with photometric errors. After t ~ 4 days, the decay slows considerably, and the light curve remains approximately flat at R ~ 24 mag for a month before decaying by another magnitude to reach R ~ 25 mag 2 months after the burst. This bump is well fit by a k-corrected light curve of supernova SN 1998bw, but only if stretched by a factor of 1.38 in time. In comparison with the other GRB-related SN bumps, GRB 041006 stakes out new parameter space for GRBs/SNe, with a very bright and significantly stretched late-time SN light curve. Within a small sample of fairly well observed GRB/SN bumps, we see a hint of a possible correlation between their peak luminosity and their stretch factor, broadly similar to the well-studied Phillips relation for the Type Ia supernovae.

Radio Afterglows of Gamma-Ray Bursts and Hypernovae at High Redshift and Their Potential for 21 Centimeter Absorption Studies

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.

Cosmic explosions : on the 10th anniversary of SN1993J (IAU Colloquium 192)

Abstract: Supernovae: Individual.- A Decade of Radio and X-ray Observations of SN 1993J.- Imaging of SN 1993J.- Nine Years of VLBI Imaging of Supernova 1993J.- On the SN 1993J Radio Shell Structure.- Optical, Ultraviolet, and Infrared Observations of SN 1993J.- Simulated Radio Images and Light Curves of SN 1993J.- X-ray Observations of SN 1993J.- Modeling the Radio and X-ray Emission of SN 1993J and SN 2002ap.- Detection of the Binary Companion to the Progenitor of SN 1993J.- Supernova 1987A: The Birth of a Supernova Remnant.- SN 1987A at Radio Wavelengths.- High-Resolution Radio Imaging of Young Supernovae: SN 1979C, SN 1986J, and SN 2001gd.- VLBI Observations of SN 1979C and SN 1986J.- SN 1994W: Evidence of Explosive Mass Ejection a Few Years Before Explosion.- A Most Energetic Type Ic Supernova: SN 2003L.- Radio Monitoring of Supernova 2001ig: The First Year.- Synthetic Spectra of the Type Ia SN 2002bo.- Supernovae: Observations.- Radio Supernovae.- Low Frequency Radio and X-ray Properties of Core-Collapse Supernovae.- Supernova Spectra.- Optical Spectroscopy of Type Ia Supernovae.- The Early Spectroscopy of Supernovae.- Optical Light Curves of Supernovae.- Late Light Curves of Type Ia SNe.- Photometric Observations of Recent Supernovae.- Observational Properties of Type II Plateau Supernovae.- X-ray Spectra of Young Supernovae.- Supernovae: Progenitors/Remnants.- Pre-Supernova Evolution of Rotating Massive Stars.- Radiation Bursts from a Presupernova Collapsar.- Radio Observations of Supernova Remnants in the M82 Starburst.- Deep Radio Imaging with MERLIN of the Supernova Remnants in M82.- Thermonuclear Supernova Explosions and Their Remnants: The Case of Tycho.- Supernovae: Models.- Models of Supernova Explosions: Where Do We Stand?.- Core-Collapse Supernovae at the Threshold.- Two New Possible Mechanisms of Supernova-Like Explosions.- Tests for Supernova Explosion Models: from Light Curves to X-ray Emission of Supernova Remnants.- Understanding Type II Supernovae.- Magnetorotational Mechanism of Supernova Type II Explosion.- Nucleosynthesis in Black-Hole-Forming Supernovae.- Nucleosynthesis in Multi-Dimensional Simulations of SNII.- 56Ni Mass in Type IIP SNe: Light Curves and H? Luminosity Diagnostics.- Effects of Small-Scale Fluctuations of Neutrino Flux in Supernova Explosions.- Neutrino Gas in Equilibrium with Self-Interaction.- Weak Interaction Processes in Core-Collapse Supernovae.- Synthetic Spectra for Type Ia Supernovae at Early Epochs.- On the Stability of Thermonuclear Burning Fronts in Type Ia Supernovae.- Explosion Models for Thermonuclear Supernovae Resulting from Different Ignition Conditions.- Supernovae: Searches/Statistics.- Supernova Statistics.- The Infrared Supernova Rate.- The Rate and the Origin of Type Ia SNe in Radio Galaxies.- Supernovae in Galaxy Clusters.- Using Multi-Band Photometry to Classify Supernovae.- Supernova and Gamma-Ray Burst Connections.- Optical and Near-IR Observations of SN 1998bw.- SN 1998bw and Other Hyperenergetic Type Ic Supernovae.- The Supernova/GRB Connection.- Optical Bumps in Cosmological GRBs as Supernovae.- Long GRBs and Supernovae from Collapsars.- How Common are Engines in Ib/c Supernovae?.- Gamma-Ray Bursters.- Cosmic Gamma-Ray Bursts: The Big Picture.- The Surroundings of Gamma-Ray Bursts: Constraints on Progenitors.- The Radio Afterglows of Gamma-Ray Bursts.- Gamma-ray Bursts.- X-ray Emission from Gamma-Ray Bursts.- Particle Acceleration in Gamma-Ray Bursts.- The First Steps in the Life of a GRB.- Physical Restrictions to Cosmological Gamma-Ray Burst Models.- Dynamical Evolution of ?-cooled Disks Following Compact Binary Mergers.- On the Central Engine of Short Gamma-ray Bursts.- Supernovae, Gamma-Ray Bursters, and Cosmology.- The Expanding and Accelerating Universe.- Observations of Type Ia Supernovae and Challenges for Cosmology.- The Standard Candle Method for Type II Supernovae and the Hubble Constan.- Observing the First Stars, One Star at a Time.- The Host Galaxies of High-Redshift Type Ia Supernovae.- Constraints on SN Ia Progenitors and ICM Enrichment from Field and Cluster SN Rates.- Expected Changes of SNe with Redshift due to Evolution of Their Progenitors.- Dark Energy: Nature and Robustness.- Brane Universes Tested by Supernovae.- A Geometric Determination of the Distance to SN 1987A and the LMC.

DEEP PHOTOMETRY OF GRB 041006 AFTERGLOW: HYPERNOVA BUMP AT REDSHIFT z p 0.716 1

Abstract: We present deep optical photometry of the afterglow of gamma-ray burst (GRB) 041006 and its associated hypernova obtained over 65 days after detection (55 R-band epochs on 10 different nights). Our early data ( days) joined t ! 4 with published GCN data indicate a steepening decay, approaching at early times ( day) and 0.6 F ∝ tt K 1 F ∝ nn at late times. The break at days is the earliest reported jet break among all GRB afterglows. 1.3 tt p 0.16 0.04 b During our first night, we obtained 39 exposures spanning 2.15 hr from 0.62 to 0.71 days after the burst that reveal a smooth afterglow, with an rms deviation of 0.024 mag from the local power-law fit, consistent with photometric errors. After days, the decay slows considerably, and the light curve remains approximately flat at mag t ∼ 4 R ∼ 24 for a month before decaying by another magnitude to reach mag 2 months after the burst. This “bump” is R ∼ 25 well fi t by ak-corrected light curve of supernova SN 1998bw, but only if stretched by a factor of 1.38 in time. In comparison with the other GRB-related SN bumps, GRB 041006 stakes out new parameter space for GRBs/SNe, with a very bright and significantly stretched late-time SN light curve. Within a small sample of fairly well observed GRB/ SN bumps, we see a hint of a possible correlation between their peak luminosity and their “stretch factor,” broadly similar to the well-studied Phillips relation for the Type Ia supernovae. Subject headings: galaxies: distances and redshifts — gamma rays: bursts — supernovae: general Online material: color figures, machine-readable table

The Σ D relation for supernova remnants in nearby galaxies

Abstract: This paper examines relations between the radio surface brightness £ and the diameter D (also known as Σ-D relations) for a sample of extragalactic supernova remnants (SNRs) as constructed from a combination of published data and data from our own surveys. Our sample of extragalactic SNRs is the largest ever devised for the purpose of analyzing Σ-D relations. The main results of this paper may be summarized as follows: (i) the empirical relations for SNRs in 10 of the 11 nearby galaxies studied have the approximately trivial Σ D -2 form, therefore limiting their interpretation as physically meaningful relations. In addition, these relations are subject to selection effects rendering them even less useful. Further Monte Carlo simulations suggest that the effect of survey sensitivity has the opposite effect of volume selection (e.g. Malinquist bias, a volume selection effect that shapes the Galactic sample) by tending to flatten the slopes toward a trivial relation. In this case, the true slopes may be steeper than the observed slopes; (ii) compact M 82 SNRs appear to follow a uniquely different Σ-D relation in comparison to the larger, older SNRs in the other 10 galaxies. Monte Carlo simulations suggest that the probability of this difference arising by chance is 1% to 10%, depending on what is assumed regarding the underlying SNR population; (iii) three candidate hypernova remnants were identified in our sample of 11 nearby galaxies.

M74 X-1 (CXOU J013651.1+154547): An Extremely Variable Ultraluminous X-Ray Source

Abstract: Ultraluminous X-ray sources (ULXs) have been described variously as the most luminous normal X-ray binaries, hypernovae, and ‘‘intermediate-mass’’ black holes with masses of hundreds to thousands of solar masses. We present results on M74 X-1 (CXOU J013651.1+154547), a ULX in the nearby spiral galaxy M74 (NGC 628), from observations by Chandra and XMM-Newton. M74 X-1 is a persistent source that exhibits extreme variability and changesinspectralstateontimescalesofseveralthousandseconds.Itsvariabilitytimescalesandbehaviorresemble some Galactic microquasars. This suggests that the emission mechanism may be related to relativistically beamed jets and that M74 X-1 could be an extragalactic ‘‘microblazar’’—a microquasar whose jet axis is aligned with our line of sight. We also note that its spectrum is consistent with the presence of a low-temperature disk blackbody component, which, assuming it is due to radiation from an accretion disk, could indicate that M74 X-1 contains an intermediate-mass black hole. Subject heading gs: galaxies: individual (NGC 628, M74) — X-rays: individual (CXOU J013651.1+154547)

Infrared mergers and infrared quasi-stellar objects with galactic winds – III. Mrk 231: an exploding young quasi-stellar object with composite outflow/broad absorption lines (and multiple expanding superbubbles)

Abstract: We present a study of outflow (OF) and broad absorption line (BAL) systems in Mrk 231, and in similar infrared (IR) quasi-stellar objects (QSOs). This study is based mainly on one-dimensional and two-dimensional spectroscopy (obtained at La Palma/William Herschel Telescope, Hubble Space Telescope, International Ultraviolet Explorer, European Southern Observatory/New Technology Telescope, Kitt Peak National Observatory, Apache Point Observatory and Complejo Astronomico El Leoncito observatories) plus Hubble Space Telescope images. For Mrk 231, we report evidence that the extreme nuclear OF process has at least three main components on different scales, which are probably associated with: (i) the radio jet, at parsec scale; (ii) the extreme starburst at parsec and kiloparsec scale. This OF has generated at least four concentric expanding superbubbles and the BAL systems. Specifically, inside and very close to the nucleus the two-dimensional spectra show the presence of an OF emission bump in the blend Hα+[N ii], with a peak at the same velocity of the main BAL-I system (VEjection BAL-I∼−4700 km s−1). This bump was more clearly detected in the area located at 0.6–1.5 arcsec (490–1220 pc), to the south-west of the nucleus core, showing a strong and broad peak. In addition, in the same direction [at position angle (PA) ∼−120°, i.e. close to the PA of the small-scale radio jet] at 1.7–2.5 arcsec, we also detected multiple narrow emission-line components, with ‘greatly’ enhanced [N ii]/Hα ratio (very similar to the spectra of jets bow shocks). These results suggest that the BAL-I system is generated in OF clouds associated with the parsec-scale jet. The Hubble Space Telescope images show four (or possibly five) nuclear superbubbles or shells with radii r∼ 2.9, 1.5, 1.0, 0.6 and 0.2 kpc. For these bubbles, the two-dimensional Hα velocity field map and two-dimensional spectra show the following. (i) At the border of the more extended bubble (S1), a clear expansion of the shell with blueshifted velocities (with circular shape and at a radius r∼ 5.0 arcsec). This bubble shows a rupture arc – to the south – suggesting that the bubble is in the blowout phase. The axis of this rupture or ejection (at PA ∼ 00°) is coincident with the axis of the intermediate and large-scale structures detected at radio wavelengths. (ii) In addition, in the three more external bubbles (S1, S2, S3), the two-dimensional William Herschel Telescope spectra show multiple emission-line components with OF velocities, of 〈VOF Bubble〉 S1, S2 and S3 =[−(650 − 420) ± 30], [−500 ± 30] and [−230 ± 30] km s−1. (iii) In the whole circumnuclear region (1.8 0.8), which are consistent with low-ionization nuclear emission-line region/OF processes associated with fast velocity shocks. Therefore, we suggest that these giant bubbles are associated with the large-scale nuclear OF component, which is generated – at least in part – by the extreme nuclear starburst: giant supernova/hypernova explosions. The variability of the short-lived BAL-III Na i D system was studied, covering almost all the period in which this system appeared (between ∼1984 and 2004). We have found that the BAL-III light curve is clearly asymmetric with a steep increase, a clear maximum and an exponential fall (similar to the shape of a supernova light curve). The origin of this BAL-III system is discussed, mainly in the framework of an extreme explosive event, probably associated with giant supernova/hypernova explosions. Finally, the IR colour diagram and the ultraviolet BAL systems of IR + GW/OF + Fe ii QSOs are analysed. This study shows two new BAL IR QSOs and suggests/confirms that these objects could be nearby young BAL QSOs, similar to those detected recently at z∼ 6.0. We propose that the phase of young QSOs is associated with accretion of a large amount of gas (by the supermassive black hole) + extreme starbursts + extreme composite OFs/BALs.

Late-epoch optical and near-infrared observations of the GRB000911 afterglow and its host galaxy

Abstract: We present the results of an optical and near-infrared (NIR) monitoring campaign of the counterpart of Gamma-Ray Burst (GRB) 000911, located at redshift z=1.06, from 5 days to more than 13 months after explosion. Our extensive dataset is a factor of 2 larger and spans a time interval about 4 times longer than the ones considered previously for this GRB afterglow; this allows a more thorough analysis of its light curve and of the GRB host galaxy properties. The afterglow light curves show a single power-law temporal decline, modified at late times by light from a host galaxy with moderate intrinsic extinction, and possibly by an emerging supernova (SN). The afterglow evolution is interpreted within the classical "fireball" scenario as a weakly collimated adiabatic shock propagating in the interstellar medium. The presence of a SN light curve superimposed on the non-thermal afterglow emission is investigated: while in the optical bands no significant contribution to the total light is found from a SN, the NIR J-band data show an excess which is consistent with a SN as bright as the known hypernova SN1998bw. If the SN interpretation is true, this would be the farthest GRB-associated SN, as well as the farthest core-collapse SN, discovered to date. However, other possible explanations of this NIR excess are also investigated. Finally, we studied the photometric properties of the host, and found that it is likely to be a slightly reddened, subluminous, extreme starburst compact galaxy, with luminosity about 0.1 L*, an age of about 0.5 Gyr and a specific Star Formation Rate (SFR) of approximately 30 Msol yr-1 (L/L*)-1. This is the highest specific SFR value for a GRB host inferred from optical/NIR data.

Precursors and Main Bursts of Gamma-Ray Bursts in a Hypernova Scenario

Abstract: We investigate a "hypernova" model for gamma-ray bursts (GRBs), i.e., a massive C+O star model with relativistic jets. In this model, nonthermal precursors can be produced by the "first" relativistic shell ejected from the star. Main GRBs are produced behind the first shell by the collisions of several relativistic shells. They become visible to distant observers after the colliding region becomes optically thin. We examine six selected conditions using relativistic hydrodynamical simulations and simple analyses. Interestingly, our simulations show that subrelativistic (v ~ 0.8c) jets from the central engine are sufficient to produce highly relativistic (Γ > 100) shells. We find that the relativistic shells from such a star can reproduce observed GRBs with certain conditions. Two conditions are especially important. One is the sufficiently long duration of the central engine, 100 s. The other is the existence of a dense shell somewhere behind the first shell. Under these conditions, both the existence and nonexistence of precursors, and the long delay between precursors and main GRBs, can be explained.

The effect of neutrinos on the initial fireballs in gamma-ray bursts

Abstract: We investigate the fate of very compact, sudden energy depositions that may lie at the origin of gamma-ray bursts. Following on from the work of Cavallo and Rees (1978), we take account of the much higher energies now believed to be involved. The main effect of this is that thermal neutrinos are present and energetically important. We show that these may provide sufficient cooling to tap most of the explosion energy. However, at the extreme energies usually invoked for gamma-ray bursts, the neutrino opacity suffices to prevent dramatic losses, provided that the heating process is sufficiently fast. In a generic case, a few tens of percent of the initial fireball energy will escape as an isotropic millisecond burst of thermal neutrinos with a temperature of about 60MeV, which is detectable for nearby gamma-ray bursts and hypernovae. For parameters we find most likely for gamma-ray burst fireballs, the dominant processes are purely leptonic, and thus the baryon loading of the fireball does not affect our conclusions.

Hypernovae and Gamma-Ray Bursts

Abstract: The nature of very energetic supernovae (hypernovae) is discussed. They are the explosive death of stars more massive than ~20–25M ⊙, probably linked to the enigmatic Gamma-Ray Bursts. The optical properties of hypernovae indicate that they are significantly aspherical. Synthetic light curves and late-phase spectra of aspherical supernova/hypernova models are presented. These models can account for the optical observations of SNe 1998bw and 2002ap. The abundance patterns of hypernovae are characterized by large ratios (Zn, Co)/Fe and small ratios (Mn, Cr)/Fe, indicating a significant contribution of hypernovae to the early Galactic chemical evolution.

Numerical simulations of expanding supershells in dwarf irregular galaxies II. Formation of giant HI rings

Abstract: We perform numerical hydrodynamic modeling of various physical processes that can form an HI ring as is observed in Holmberg I (Ho I). Three energetic mechanisms are considered: multiple supernova explosions (SNe), a hypernova explosion associated with a gamma ray burst (GRB), and the vertical impact of a high velocity cloud (HVC). The total released energy has an upper limit of » 10 54 ergs. We find that multiple SNe are in general more eective in producing shells that break out of the disk than a hypernova explosion of the same total energy. As a consequence, multiple SNe form rings with a high ring-to-center contrast K » 100 in the HI column density, whereas single hypernova explosions form rings with K » 10. Only multiple SNe can reproduce both the size (diameter » 1.7 kpc) and the ring-to-center contrast (K » 15 i 20) of the HI ring in Ho I. High velocity clouds create HI rings that are much smaller in size ( » 0.8 kpc) and contrast (K » 4.5) than seen in Ho I. We construct model position-velocity (pV) diagrams and find that they can be used to distinguish among dierent HI ring formation mechanisms. The observed pV-diagrams of Ho I (Ott et al. 2001) are best reproduced by multiple SNe. We conclude that the giant HI ring in Ho I is most probably formed by multiple SNe. We also find that the appearance of the SNe-driven shell in the integrated HI image depends on the inclination angle of the galaxy. In nearly face-on galaxies, the integrated HI image shows a ring of roughly constant HI column density surrounding a deep central depression, whereas in considerably inclined galaxies (i > 45 - ) the HI image

Precursors and Main-bursts of Gamma Ray Bursts in a Hypernova Scenario

Abstract: We investigate a "hypernova" model for gamma-ray bursts (GRBs), i.e., massive C+O star model with relativistic jets. In this model, non-thermal precursors can be produced by the "first" relativistic shell ejected from the star. Main GRBs are produced behind the "first"-shell by the collisions of several relativistic shells. They become visible to distant observers after the colliding region becomes optically thin. We examine six selected conditions using relativistic hydrodynamical simulations and simple analyses. Interestingly, our simulations show that sub-relativistic $(v \sim 0.8c)$ jets from the central engine is sufficient to produce highly-relativistic $(\Gamma > 100)$ shells. We find that the relativistic shells from such a star can reproduce observed GRBs with certain conditions. Two conditions are especially important. One is the sufficiently long duration of the central engine $ \gsim 100$ sec. The other is the existence of a dense-shell somewhere behind the "first"-shell. Under these conditions, both the existence and non-existence of precursors, and long delay between precursors and main GRBs can be explained.

The origin of cosmic rays

Abstract: It is generally regarded that the bulk of cosmic rays originate in the galaxy and that those below the 'knee' (the rapid steepening in the energy spectrum) at a few PeV, come from galactic supernovae, the particles being accelerated by the shocks in the supernova remnants. At higher energies, there are problems in that conventional SNR—which surely constitute the bulk of the sources—have a natural limit at a few tens of PeV (for iron nuclei). The question of the origin of particles above this limit is thus an open one. Here we examine a number of possibilities: a variety of supernovae and hypernovae, pulsars, a giant galactic halo and an extragalactic origin. A relevant property of any model is the extent to which it can provide the lack of significant irregularity of the energy spectrum, its intensity and shape together with structures such as the 'second knee' at the sub-EeV energy, in addition to the well-known 'knee' and 'ankle'. Although it is appreciated that spectral measurements are subject to systematic as well as random errors, we consider that contemporary data are good enough to allow at least some progress in this new field. These aspects are examined for particles of all energies and it is shown that they can constrain some parameters of the proposed models. In the search for origin above PeV energies, we conclude that shocks in the galactic halo, whatever their source (galactic wind, relativistic plasmoids—'cannonballs', multiple shocks from supernovae etc) are most likely, pulsars such as B0656+14 and hypernovae come a close second although such a suggestion is not without its difficulties. What is most important is that trapping of particles in the halo is needed to reduce irregularities of the energy spectra both below and above the 'knee' caused by the stochastic nature of supernova explosions and other potential (discrete) galactic sources. We argue that precise experimental studies of spectral 'irregularities' will provide considerable help in the search for cosmic ray origin.

Si Isotopic Ratios in Supernovae for Presolar Grains

Abstract: Primitive meteorites contain presolar grains that are considered to have traces of the nucleosynthesis at their birth as large isotopic anomalies. The isotopic signatures are important to identify the origin of the grains. Supernova-originating presolar grains, such as SiC type X and low-density graphite, have also been identified by the excesses of 28Si with respect to the solar Si isotopic ratios. At the same time, most of them are depleted in 30Si rather than in 29Si compared to the solar Si ratios. A small number of them show 29Si deficits. We investigate the Si isotopic ratios of supernova ejecta with different-mass progenitors considering inhomogeneous mixing. The mixture components consist of four layers of the supernova ejecta: the Ni, Si/S, He/C, and He/N layers. Detailed nucleosynthesis during stellar evolution and supernova explosion is calculated using 3.3, 4, 6, and 8 M☉ He star models. Supernova explosions for all of the stellar models and a hypernova explosion for the 8 M☉ He star model are considered. The 30Si deficits with respect to solar ratios found in most grains are explained by the mixtures of the 3.3 and 4 M☉ supernova models and the 8 M☉ hypernova model. The 29Si deficits are explained by the mixtures of the 6 and 8 M☉ supernova models. Although the Si abundance in the Ni layer is small, the Ni layer is important to reproduce the Si isotopic ratios of the grains. The Si isotopic ratios in the Ni layer largely depend on the stellar mass, because a shorter explosion timescale is more favorable to the production of 29Si than 30Si. Most presolar grains from supernovae with deficits of 30Si rather than of 29Si compared to the solar Si isotopic ratios would be from less massive supernovae whose progenitor masses are smaller than ~15 M☉ and hypernovae whose progenitor masses are heavier than ~20 M☉.

Supernovae shedding light on gamma-ray bursts

Abstract: We review the observational status of the Supernova (SN)/Gamma-Ray Burst (GRB) connection. In section 2 we provide a short summary of the observational properties of core-collapse SNe. In sections 3-6 we review the circumstantial evidences and the direct observations that support the existence of a deep connection between the death of massive stars and GRBs. Present data suggest that SNe associated with GRBs form a heterogeneous class of objects including both bright and faint Hypernovae and perhaps also `standard' Ib/c events. In section 7, we provide an empirical estimate of the rate of Hypernovae, for a ``MilkyWay-like'' galaxy, of about $\sim 2.6\times 10^{-4}$ yr$^{-1}$ that may imply the ratio GRB/Hypernovae to be in the range $\sim 0.03-0.7$. In the same framework we find the ratio GRB/SNe-Ibc to be $\sim 0.008\div 0.05$. In section 8 we discuss the possible existence of a lag between the SN explosion and the associated gamma-ray event. In the few SN/GRB associations so far discovered the SN explosions and GRB events appear to go off simultaneously. In section 9 we present the conclusions and highlight the open problems that Swift hopefully will allow us to solve.

The Star of Bethlehem: a type Ia/Ic supernova in the Andromeda galaxy?

Abstract: I shall argue that the account in Matthew’s Gospel suggests the Star of Bethlehem may have been a Type Ia supernova or a Type Ic hypernova, located either in the Andromeda Galaxy, or if Type Ia, in a globular cluster of this galaxy. Matthew’s account may give the SN remnant to within 1′ in declination, and should be detectable with current techniques: the remnant should be 6′ in radius, and if Type Ia, possibly visible in the Fe I absorption line at 3860 A.

Nucleosynthesis in Black-Hole-Forming Supernovae

Abstract: Stars more massive than ∼ 20 − 25 M⨀ form a black hole at the end of their evolution. 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-hole-forming” supernovae. Nucleosynthesis in hypernovae is characterized by larger abundance ratios (Zn,Co,V,Ti)/Fe and smaller (Mn,Cr)/Fe than normal supernovae, which can explain the observed trend of these ratios in extremely metal-poor stars. 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-poor 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.