SN 1998A: explosion of a blue supergiant

We present spectroscopic and photometric observations of the peculiar Type II supernova (SN) 1998A. The light curves and spectra closely resemble those of SN 1987A, suggesting that the SN 1998A progenitor exploded when it was a compact blue supergiant. However, the comparison with SN 1987A also highlights some important differences: SN 1998A is more luminous and the spectra show bluer continua and larger expansion velocities at all epochs. These observational properties indicate that the explosion of SN 1998A is more energetic than SN 1987A and more typical of Type II supernovae. Comparing the observational data with simulations, we deduce that the progenitor of SN 1998A was a massive star  (∼25 M_⊙)  with a small pre-supernova radius  (≲6 × 10¹² cm)  . The Ba  ii lines, unusually strong in SN 1987A and some faint II-P events, are almost normal in the case of SN 1998A, indicating that the temperature plays a key role in determining their strength.     

A study of the Type II-P supernova 2003gd in M74

We present photometric and spectroscopic data of the Type II-P supernova (SN II-P) 2003gd, which was discovered in M74 close to the end of its plateau phase. SN 2003gd is the first Type II supernova (SN) to have a directly confirmed red supergiant (RSG) progenitor. We compare SN 2003gd to SN 1999em, a similar SN II-P, and estimate an explosion date of 2003 March 18. We determine a reddening towards the SN of   E ( B − V ) = 0.14 ± 0.06  , using three different methods. We also calculate three new distances to M74 of  9.6 ± 2.8, 7.7 ± 1.7  and  9.6 ± 2.2 Mpc  . The former was estimated using the standard candle method (SCM), for Type II supernovae (SNe II), and the latter two using the brightest supergiants method (BSM). When combined with existing kinematic and BSM distance estimates, we derive a mean value of  9.3 ± 1.8 Mpc  . SN 2003gd was found to have a lower tail luminosity compared with other normal Type II-P supernovae (SNe II-P) bringing into question the nature of this SN. We present a discussion concluding that this is a normal SN II-P, which is consistent with the observed progenitor mass of  8⁺⁴₋₂ M_⊙  .     

Type IIP supernova SN 2004et: a multiwavelength study in X-ray, optical and radio

We present X-ray, broad-band optical and low-frequency radio observations of the bright type IIP supernova SN 2004et. The Chandra X-ray Observatory observed the supernova at three epochs, and the optical coverage spans a period of ∼470 d since explosion. The X-ray emission softens with time, and we characterize the X-ray luminosity evolution as   L _X∝ t ^−0.4  . We use the observed X-ray luminosity to estimate a mass-loss rate for the progenitor star of  ∼2 × 10⁻⁶ M_⊙ yr⁻¹  . The optical light curve shows a pronounced plateau lasting for about 110 d. Temporal evolution of photospheric radius and colour temperature during the plateau phase is determined by making blackbody fits. We estimate the ejected mass of ⁵⁶Ni to be  0.06 ± 0.03 M_⊙  . Using the expressions of Litvinova & Nadëzhin we estimate an explosion energy of  (0.98 ± 0.25) × 10⁵¹ erg  . We also present a single epoch radio observation of SN 2004et. We compare this with the predictions of the model proposed by Chevalier, Fransson & Nymark. These multiwavelength studies suggest a main-sequence progenitor mass of  ∼20 M_⊙  for SN 2004et.     

Supernova 1994aj: a probe for pre-supernova evolution and mass-loss from the progenitor

Extensive photometric and spectroscopic observations of SN 1994aj until 540 d after maximum light have been obtained. The photometry around maximum suggests that the SN belongs to the Type II Linear class, with a peak absolute magnitude of M _V∼−17.8 (assuming H ₀=75 km s⁻¹ Mpc⁻¹). The spectra of SN 1994aj were unusual, with the presence of a narrow line with a P Cygni profile on top of the broad Balmer line emission. This narrow feature is attributed to the presence of a dense superwind surrounding the SN. At 100–120 d after maximum light the SN ejecta start to interact with this circumstellar material. The SN luminosity decline rates slowed down [γ _R =0.46 mag (100 d)⁻¹], becoming less steep than the average late luminosity decline of normal SN II [∼1 mag (100 d)⁻¹]. This dense ( ˙M / u _W∼10¹⁵ g cm⁻¹) wind was confined to a short distance from the progenitor ( R _out=∼5×10¹⁶ cm), and results from a very strong mass-loss episode ( ˙M =10⁻³ M⊙ yr⁻¹), which terminated shortly before explosion (∼5–10 yr).     

Massive stars exploding in a He-rich circumstellar medium – III. SN 2006jc: infrared echoes from new and old dust in the progenitor CSM

We present near- (NIR) and mid-infrared (MIR) photometric data of the Type Ibn supernova (SN) 2006jc obtained with the United Kingdom Infrared Telescope (UKIRT), the Gemini North Telescope and the Spitzer Space Telescope between days 86 and 493 post-explosion. We find that the IR behaviour of SN 2006jc can be explained as a combination of IR echoes from two manifestations of circumstellar material. The bulk of the NIR emission arises from an IR echo from newly condensed dust in a cool dense shell (CDS) produced by the interaction of the ejecta outward shock with a dense shell of circumstellar material ejected by the progenitor in a luminous blue variable (LBV)-like outburst about two years prior to the SN explosion. The CDS dust mass reaches a modest  3.0 × 10⁻⁴ M_⊙  by day 230. While dust condensation within a CDS formed behind the ejecta inward shock has been proposed before for one event (SN 1998S), SN 2006jc is the first one showing evidence for dust condensation in a CDS formed behind the ejecta outward shock in the circumstellar material. At later epochs, a substantial and growing contribution to the IR fluxes arises from an IR echo from pre-existing dust in the progenitor wind. The mass of the pre-existing circumstellar medium (CSM) dust is at least  ∼8 × 10⁻³ M_⊙  . This paper therefore adds to the evidence that mass-loss from the progenitors of core-collapse SNe could be a major source of dust in the Universe. However, yet again, we see no direct evidence that the explosion of an SN produces anything other than a very modest amount of dust.     

SN 2005cs in M51 – II. Complete evolution in the optical and the near-infrared

We present the results of the one-year long observational campaign of the type II plateau SN 2005cs, which exploded in the nearby spiral galaxy M51 (the Whirlpool galaxy). This extensive data set makes SN 2005cs the best observed low-luminosity, ⁵⁶Ni-poor type II plateau event so far and one of the best core-collapse supernovae ever. The optical and near-infrared spectra show narrow P-Cygni lines characteristic of this SN family, which are indicative of a very low expansion velocity (about  1000 km s⁻¹  ) of the ejected material. The optical light curves cover both the plateau phase and the late-time radioactive tail, until about 380 d after core-collapse. Numerous unfiltered observations obtained by amateur astronomers give us the rare opportunity to monitor the fast rise to maximum light, lasting about 2 d. In addition to optical observations, we also present near-infrared light curves that (together with already published ultraviolet observations) allow us to construct for the first time a reliable bolometric light curve for an object of this class. Finally, comparing the observed data with those derived from a semi-analytic model, we infer for SN 2005cs a ⁵⁶Ni mass of about  3 × 10⁻³ M_⊙  , a total ejected mass of  8–13 M_⊙  and an explosion energy of about  3 × 10⁵⁰ erg  .     

Optical and infrared photometry of the Type IIn SN 1998S: days 11–146

We present contemporaneous optical and infrared (IR) photometric observations of the Type IIn SN 1998S covering the period between 11 and 146 d after discovery. The IR data constitute the first ever IR light curves of a Type IIn supernova. We use blackbody and spline fits to the photometry to examine the luminosity evolution. During the first 2–3 months, the luminosity is dominated by the release of shock-deposited energy in the ejecta. After ∼100 d the luminosity is powered mostly by the deposition of radioactive decay energy from 0.15±0.05 M_⊙ of ⁵⁶Ni which was produced in the explosion. We also report the discovery of an astonishingly high IR excess, K − L '=2.5, that was present at day 130. We interpret this as being due to thermal emission from dust grains in the vicinity of the supernova. We argue that to produce such a high IR luminosity so soon after the explosion, the dust must be pre-existing and so is located in the circumstellar medium of the progenitor. The dust could be heated either by the UV/optical flash (IR echo) or by the X-rays from the interaction of the ejecta with the circumstellar material.     

Supernova 2002ap: the first month

Supernova (SN) 2002ap in M74 was discovered on 2002 January 29. Being one of the nearest (10 Mpc) SN events in the last decades, and spectroscopically similar to the so-called 'hypernovae' 1997ef and 1998bw, both possibly associated with gamma-ray bursts (GRBs), it is of great interest. Shortly after its discovery, we launched an intensive photometric and spectroscopic monitoring campaign of this event, and here we report the results of the first month of observations. We use our UBVRI photometry to estimate the magnitudes at, and dates of, peak brightness. Our data suggest that this object reached its peak B -band luminosity on February     . Based on its similarity to SN 1998bw, we estimate the range of possible dates for a GRB that may have been associated with SN 2002ap. We find that it may include dates outside the time frame for which all available gamma-ray data have been intensively scanned, according to recent reports. The absolute magnitude at peak brightness of SN 2002ap  ( M _B =-16.9)  shows that it was significantly fainter than SN 1998bw, or normal Type Ia SNe, but similar to SN 1997ef. Our spectroscopic observations confirm that SN 2002ap is strikingly similar to SNe 1998bw and 1997ef. We briefly describe the spectral evolution of this object. To assist other observers and to stimulate theoretical models, we make our entire data set publicly available in digital form (http://wise-obs.tau.ac.il/∼avishay/local.html).     

A search for the progenitors of two Type Ia Supernovae in NGC 1316

Recent evidence of a young progenitor population for many Type Ia supernovae (SNe Ia) raises the possibility that evolved intermediate-mass progenitor stars may be detected in pre-explosion images. NGC 1316, a radio galaxy in the Fornax cluster, is a prolific producer of SNe Ia, with four detected since 1980. We analyse Hubble Space Telescope ( HST ) pre-explosion images of the sites of two of the SNe Ia that exploded in this galaxy, SN2006dd (a normal Type Ia) and SN2006mr (likely a subluminous, 1991bg-like, SN Ia). Astrometric positions are obtained from optical and near-infrared ground-based images of the events. We find no candidate point sources at either location, and set upper limits on the flux in B, V and I from any such progenitors. We also estimate the amount of extinction that could be present, based on analysis of the surface-brightness inhomogeneities in the HST images themselves. At the distance of NGC 1316, the limits correspond to absolute magnitudes of  ∼−5.5, −5.4  and −6.0 mag in   M _B , M _V   and   M _I   , respectively. Comparison to stellar evolution models argues against the presence at the supernova sites, 3 yr prior to the explosion, of normal stars with initial masses  ≳6 M_⊙  at the tip of their asymptotic-giant branch (AGB) evolution, young post-AGB stars that had initial masses  ≳4 M_⊙  and post-red giant stars of initial masses  ≳9 M_⊙  .     

Hubble Space Telescope imaging of the progenitor sites of six nearby core-collapse supernovae

The search for the progenitors of six core-collapse supernovae (CCSNe) in archival Hubble Space Telescope ( HST ) WFPC2 pre-explosion imaging is presented. These SNe are 1999an, 1999br, 1999ev, 2000ds, 2000ew and 2001B. Post-explosion imaging of the SNe, with the HST ACS/WFC, has been utilized with the technique of differential astrometry to identify the progenitor locations on the pre-explosion imaging. SNe 1999br, 1999ev, 2000ew and 2001B are recovered in late-time imaging, and estimates of the progenitor locations on the pre-explosion imaging, with subpixel accuracy, have been made. Only the progenitor of the Type II-P SN 1999ev has been recovered, on pre-explosion F555W imaging, at a 4.8σ significance level. Assuming a red supergiant progenitor, the pre-explosion observation is consistent with   M _ZAMS= 15–18 M_⊙  . The progenitors of the other five SNe were below the 3σ detection threshold of the pre-explosion observations. The detection thresholds were translated to mass limits for the progenitors by comparison with stellar evolution models. Pre-explosion observations of the peculiarly faint SN 1999br limit the mass of a red supergiant progenitor to   M _ZAMS < 12 M_⊙  . Analysis has been extended, from previous studies, to include possible detections of high- T _eff, high-mass stars by conducting synthetic photometry of model Wolf–Rayet star spectra. The mass limits for the Type II-P SNe 1999an and 1999br are consistent with previously determined mass limits for this type of SN. The detection limits for the progenitors of the Type Ibc SNe (2000ds, 2000ew and 2001B) do not permit differentiation between high-mass Wolf–Rayet progenitors or low-mass progenitors in binaries.     

SN 2005cs in M51 – I. The first month of evolution of a subluminous SN II plateau

Early-time optical observations of supernova (SN) 2005cs in the Whirlpool Galaxy (M51) are reported. Photometric data suggest that SN 2005cs is a moderately underluminous Type II plateau SN (SN IIP). The SN was unusually blue at early epochs (   U − B ≈−0.9  about three days after explosion) which indicates very high continuum temperatures. The spectra show relatively narrow P Cygni features, suggesting ejecta velocities lower than observed in more typical SNe IIP. The earliest spectra show weak absorption features in the blue wing of the He  i 5876-Å absorption component and, less clearly, of Hβ and Hα. Based on spectral modelling, two different interpretations can be proposed: these features may either be due to high-velocity H and He  i components, or (more likely) be produced by different ions (N  ii , Si  ii ). Analogies with the low-luminosity, ⁵⁶Ni-poor, low-velocity SNe IIP are also discussed. While a more extended spectral coverage is necessary in order to determine accurately the properties of the progenitor star, published estimates of the progenitor mass seem not to be consistent with stellar evolution models.     

The type IIn supernova 1995G: interaction with the circumstellar medium

We present the photometric and spectroscopic evolution of the type IIn SN 1995G in NGC 1643, on the basis of 4 years of optical and infrared observations. This supernova shows very flat optical light curves similar to SN 1988Z, with a slow decline rate at all times. The spectra are characterized by strong Balmer lines with multiple components in emission and with a P Cygni absorption component blueshifted by only 700 km s⁻¹. This feature indicates the presence of a slowly expanding shell above the SN ejecta as in the case of SNe 1994aj and 1996L. As in other SNe IIn, the slow luminosity decline cannot be explained only with a radioactive energy input, and an additional source of energy is required, most likely that produced by the interaction between supernova ejecta and a pre-existent circumstellar medium (CSM). It was estimated that the shell material has a density   n _H≫10⁸ cm^-3  , consistent with the absence of forbidden lines in the spectra. About 2 years after the burst the low-velocity shell is largely overtaken by the SN ejecta and the luminosity drops at a faster rate.     

Observational characteristics and possible asphericity of overluminous Type Ia supernovae

A few Type Ia supernovae (SNe Ia) have been suggested to be an explosion of a super-Chandrasekhar-mass white dwarf (WD) in order to account for their large luminosities, requiring a large amount of ⁵⁶Ni. However, the candidate overluminous SNe Ia 2003fg, 2006gz and (moderately overluminous) SN 1991T have very different observational features: the characteristic time-scale and velocity are very different. We examine if and how the diversity can be explained, by one-dimensional spherical radiation transport calculations covering a wide range of model parameters (e.g. WD mass). The observations of SN 2006gz are naturally explained by the super-Chandrasekhar-mass model. SN 1991T represents a marginal case, which may either be a Chandrasekhar or a super-Chandrasekhar-mass WD explosion. In contrast, the low velocity and short time-scale seen in SN 2003fg indicate that the ejecta mass is smaller than the Chandrasekhar mass, which is in apparent contradiction to the large luminosity. We suggest that the problem is solved if the progenitor WD, and thus the SN explosion, is aspherical. This may reflect a rapid rotation of the progenitor star, likely a consequence of the super-Chandrasekhar-mass WD progenitor. The observed differences between SNe 2003fg and 2006gz may be attributed to different viewing orientations.     

The circumstellar material around SN IIn 1997eg: another detection of a very narrow P Cygni profile

We report the detection of a very narrow P Cygni profile on top of the broad emission H α and H β lines of the Type IIn Supernova 1997eg. A similar feature has been detected in SN 1997ab, SN 1998S and SN 1995G . The detection of the narrow P Cygni profile indicates the existence of a dense circumstellar material (CSM), into which the ejecta of the supernova is expanding. From the analysis of the spectra of SN 1997eg we deduce (i) that such CSM is very dense  ( n ≳5×10⁷ cm^-3)  , (ii) that it has a low expanding velocity of about 160 km s⁻¹. The origin of such dense CSM can be either a very dense progenitor wind  ( M˙ ∼10^-2 M_⊙ yr^-1)  or a circumstellar shell product of the progenitor wind expanding into a high-pressure environment.     

Consequences for some dark energy candidates from the type Ia supernova SN 1997ff

We examine the status of various dark energy models in light of the recently observed SN 1997ff at   z ≈1.7  . The modified data still fit a pure cosmological constant Λ or a quintessence with an equation of state similar to that of Λ. The kinematical Λ models,  Λ∼ S ^-2  and  Λ∼ H ²  , also fit the data reasonably well and require less dark energy density (hence more matter energy density) than is required by the constant Λ model. However, the model  Λ∼ S ^-2  with low energy density becomes unphysical as it cannot accommodate higher redshift objects.
We also examine an alternative explanation of the data, namely the absorption by the intervening whisker-like dust, and find that the quasi-steady state (QSS) model and the Friedmann–Robertson–Walker (FRW) model  Ω_m0=0.33  without any dark energy also fit the data reasonably well.
We notice that the addition of SN 1997ff to the old data has worsened the fit to most of the models, except a closed FRW model with a constant Λ and a closed quintessence model with   ω _φ =-0.82  , and the models have started departing from each other as we go above   z =1  . However, to make a clear discrimination possible, a few more supernovae with   z >1  are required.
We have also calculated the age of the Universe in these models and find that, in the models with a constant Λ, the expansion age is uncomfortably close to the age of the globular clusters. Quintessence models show even lower age. The kinematical Λ models are, however, interesting in this connection (especially the model  Λ∼ H ²)  , as they give a remarkably large age of the Universe.     

Nucleosynthesis of 56Ni in wind-driven supernova explosions and constraints on the central engine of gamma-ray bursts

Theoretically expected natures of a supernova (SN) driven by a wind/jet are discussed. Approximate analytical formulations are derived to clarify basic physical processes involved in the wind/jet-driven explosions, and it is shown that the explosion properties are characterized by the energy injection rate     and the mass injection rate     . To explain observations of Supernova 1998bw associated with gamma-ray burst (GRB) 980425, the following conditions are required:     and     (if the wind Lorentz factor  Γ_w∼ 1  ) or     (if  Γ_w≫ 1  ). In Supernova 1998bw, ⁵⁶Ni  (∼0.4 M_⊙)  is probably produced in the shocked stellar mantle, not in the wind. The expected natures of SNe, e.g. ejected ⁵⁶Ni mass and ejecta mass, vary depending on     and     . The sequence of the SN properties from high     and     to low     and     is as follows: Supernova 1998bw-like – intermediate case – low mass ejecta  (≲1 M_⊙)  where ⁵⁶Ni is from the wind – whole collapse. This diversity may explain the diversity of SNe associated with GRBs. Our result can be used to constrain natures of the wind/jet, which are linked to the central engine of GRBs, by studying properties of the associated SNe.     

Optical photometry and spectroscopy of the Type Ibn supernova SN 2006jc until the onset of dust formation

We present optical UBVRI photometric and spectroscopic data of the Type Ibn supernova SN 2006jc, until the onset of the dust-forming phase. The optical spectrum shows a blue continuum and is dominated by the presence of moderately narrow (velocity ∼2500 km s⁻¹) He  i emission lines superimposed over a relatively weak supernova spectrum. The helium lines are produced in a pre-existing He-rich circumstellar shell. The observed helium line fluxes indicate the circumstellar shell is dense, with a density of  ∼10⁹–10¹⁰ cm⁻³  . The helium mass in this shell is estimated to be  ≲0.07 M_⊙  . The optical light curves show a clear signature of dust formation, indicated by a sharp decrease in the magnitudes around day 50, accompanied by a reddening of the colours. The evolution of the optical light curves during the early phase and that of the uvoir bolometric light curve at all phases is reasonably similar to normal Ib/c supernovae.     

Magnetized relativistic jets and long-duration GRBs from magnetar spin-down during core-collapse supernovae

We use ideal axisymmetric relativistic magnetohydrodynamic simulations to calculate the spin-down of a newly formed millisecond,   B ∼ 10¹⁵ G  , magnetar and its interaction with the surrounding stellar envelope during a core-collapse supernova (SN) explosion. The mass, angular momentum and rotational energy lost by the neutron star are determined self-consistently given the thermal properties of the cooling neutron star's atmosphere and the wind's interaction with the surrounding star. The magnetar drives a relativistic magnetized wind into a cavity created by the outgoing SN shock. For high spin-down powers  (∼10⁵¹–10⁵² erg s⁻¹)  , the magnetar wind is superfast at almost all latitudes, while for lower spin-down powers  (∼10⁵⁰ erg s⁻¹)  , the wind is subfast but still super-Alfvénic. In all cases, the rates at which the neutron star loses mass, angular momentum and energy are very similar to the corresponding free wind values (≲30 per cent differences), in spite of the causal contact between the neutron star and the stellar envelope. In addition, in all cases that we consider, the magnetar drives a collimated  (∼5–10°)  relativistic jet out along the rotation axis of the star. Nearly all of the spin-down power of the neutron star escapes via this polar jet, rather than being transferred to the more spherical SN explosion. The properties of this relativistic jet and its expected late-time evolution in the magnetar model are broadly consistent with observations of long duration gamma-ray bursts (GRBs) and their associated broad-lined Type Ic SN.     

The impact of a supernova explosion in a very massive binary

We consider the effect of a supernova (SN) explosion in a very massive binary that is expected to form in a portion of Population III stars with the mass higher than  100 M_⊙  . In a Population III binary system, a more massive star can result in the formation of a black hole (BH) and a surrounding accretion disc. Such BH accretion could be a significant source of the cosmic reionization in the early Universe. However, a less massive companion star evolves belatedly and eventually undergoes a SN explosion, so that the accretion disc around a BH might be blown off in a lifetime of companion star. In this paper, we explore the dynamical impact of a SN explosion on an accretion disc around a massive BH, and elucidate whether the BH accretion disc is totally demolished or not. For the purpose, we perform three-dimensional hydrodynamic simulations of a very massive binary system, where we assume a BH of  10³ M_⊙  that results from a direct collapse of a very massive star and a companion star of  100 M_⊙  that undergoes a SN explosion. We calculate the remaining mass of a BH accretion disc as a function of time. As a result, it is found that a significant portion of gas disc can survive through three-dimensional geometrical effects even after the SN explosion of a companion star. Even if the SN explosion energy is higher by two orders of magnitude than the binding energy of gas disc, about a half of disc can be left over. The results imply that the Population III BH accretion disc can be a long-lived luminous source, and therefore could be an important ionizing source in the early Universe.     

Photometric study of type Ia supernova SN 2002hu

Optical UBVRI photometry of the type Ia supernova (SN Ia) SN 2002hu covering the period from −2 to +73 d since B maximum is presented. The supernova reached at maximum brightness in B on  JD 245 2591.78 ± 0.5  with an apparent magnitude of  16.83 ± 0.02 mag  and a relatively blue colour  ( B − V ) =−0.08 ± 0.04 mag  . The luminosity decline rate of  Δ m ₁₅( B ) = 1.00 ± 0.05  indicates an absolute B magnitude at maximum of   M ^max _B =−19.38 ± 0.3  . The estimated absolute B magnitude, together with the photometric evolution, indicate SN 2002hu was slightly overluminous compared to the average SNe Ia. The distance modulus to the parent galaxy is estimated to be  μ= 36.04 ± 0.20  .