Evaporation and condensation of corundum and silicon carbide grains around the supernova SN1987A in the large magellanic cloud

We investigate the evaporation and condensation of corundum and silicon carbide grains around the supernova SN1987A. We predict the time after outburst of the interaction of the condensed dust with pre-existing dust, with a view to undertaking observations with future instrumentation such as the Infra-Red Space Observatory.     

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.     

Visible and Infrared Images of C/1999 S4 (LINEAR) during the Disruption of Its Nucleus

An analysis of the behavior of the dust coma of the Comet C/1999 S4 (LINEAR) from visible and infrared images acquired shortly before and after the disruption of the comet's nucleus is presented. During the predisruption phase, the overall dust production increased by a factor of 11 in two steps; an initial outburst occurred between July 18 and 19 and a second stronger one occurred between July 20 and 21. Postdisruption images obtained on July 26 and 27 suggest that most of the dust was released in the huge outburst produced during the disruption of the nucleus a few days before. The color of the dust coma did not show any measurable day-to-day variation and was also very uniform throughout the coma. The latter is an indication of the homogeneity of the dust component of the nucleus.     

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.     

Penetration of nearby supernova dust in the inner solar system

We investigate the method by which nearby supernovae – within a few tens of pc of the solar system – can penetrate the solar system and deposit live radioactivities on earth. The radioactive isotopic signatures that could potentially leave an observable geological imprint are in the form of refractory metals; consequently, it is likely they would arrive in the form of supernova-produced dust grains. Such grains can penetrate into the solar system more easily than the bulk supernova plasma, which gets stalled and deflected near the solar system due to the solar wind plasma pressure. We therefore examine the motion of charged grains as they decouple from the supernova plasma and are influenced by the solar magnetic, radiation, and gravitational fields. We characterize the dust trajectories with analytical approximations which display the roles of grain size, initial velocity, and surface voltage. These results are verified with full numerical simulations for wide ranges of dust properties. We find that supernova dust grains traverse the inner solar system nearly undeflected, if the incoming grain velocity – which we take to be that of the incident supernova remnant – is comparable to the solar wind speeds and much larger than the escape velocity at 1 AU. Consequently, the dust penetration to 1 AU has essentially 100% transmission probability and the dust capture onto the earth should have a geometric cross section. Our results cast in a new light the terrestrial deposition of radioisotopes from nearby supernovae in the geological past. For explosions beyond ～10 pc from earth, dust grains can still deliver supernova ejecta to earth, and thus the amount of supernova material deposited is set by the efficiency of dust condensation and survival in supernovae. Turning the problem around, we use observations of live ⁶⁰Fe in both deep-ocean and lunar samples to infer a conservative lower bound iron condensation efficiency of M_dust,Fe/M_tot,Fe ? 4  × 10^?4 for the supernova which apparently produced these species 2–3 Myr ago.     

The next galactic supernova

It is pointed out that there is a better than even chance that a galactic supernova will occur during the lifetime of the present generation of astronomers. A brief discussion is given of a number of types of observations that could be made of such a unique event. It would be particularly important to obtain speckle interferometry of the expanding supernova. High time-resolution spectroscopy and photometry should be obtained during the early phases of the outburst.     

Upper limit on dimming of cosmological sources by intergalactic grey dust from the soft X-ray background

Active galactic nuclei (AGN) produce a dominant fraction  ( F _AGN∼ 80 per cent)  of the soft X-ray background (SXB) at photon energies  0.5 < E < 2 keV  . If dust pervaded throughout the intergalactic medium, its scattering opacity would have produced diffuse X-ray haloes around AGN. Taking account of known galaxies and galaxy clusters, only a fraction   F _halo≲ 10 per cent  of the SXB can be in the form of diffuse X-ray haloes around AGN. We therefore limit the intergalactic opacity to optical/infrared photons from large dust grains, with radii in the range   a = 0.2–2.0 μm  , to a level  τ_GD≲ 0.15( F _halo/10 per cent)(F_AGN/80 per cent)⁻¹  to a redshift   z ∼ 1  . Our results are only weakly dependent on the grain size distribution in this size range or the redshift evolution of the intergalactic dust. Stacking X-ray images of AGN can be used to improve our constraints and diminish the importance of dust as a source of systematic uncertainty for future supernova surveys which aim to improve the precision on measuring the redshift evolution of the dark energy equation-of-state.     

Infrared emission from interstellar grains heated by supernovae

The infrared emission from interstellar grains heated by a supernova in eruption is investigated. The dependence of the emission on various physical parameters, such as the depth of the supernova into the dust plane of the parent galaxy, the inclination of the galaxy to the line-of-sight, are investigated. The possibility of detecting this emission is discussed. The prospects are hopeful as far as cryogenically-cooled instruments in Earth orbit are concerned.     

Cassiopeia A: dust factory revealed via submillimetre polarimetry

If Type II supernovae – the evolutionary end points of short-lived, massive stars – produce a significant quantity of dust  (>0.1 M_⊙)  then they can explain the rest-frame far-infrared emission seen in galaxies and quasars in the first Gyr of the Universe. Submillimetre (submm) observations of the Galactic supernova remnant, Cas A, provided the first observational evidence for the formation of significant quantities of dust in Type II supernovae. In this paper, we present new data which show that the submm emission from Cas A is polarized at a level significantly higher than that of its synchrotron emission. The orientation is consistent with that of the magnetic field in Cas A, implying that the polarized submm emission is associated with the remnant. No known mechanism would vary the synchrotron polarization in this way and so we attribute the excess polarized submm flux to cold dust within the remnant, providing fresh evidence that cosmic dust can form rapidly. This is supported by the presence of both polarized and unpolarized dust emission in the north of the remnant where there is no contamination from foreground molecular clouds. The inferred dust polarization fraction is unprecedented  ( f _pol∼ 30 per cent)  which, coupled with the brief time-scale available for grain alignment (<300 yr), suggests that supernova dust differs from that seen in other Galactic sources (where   f _pol= 2−7  per cent) or that a highly efficient grain alignment process must operate in the environment of a supernova remnant.     

The X-ray nuclei of intermediate-redshift radio sources

We re-assess the question of a systematic time delay between the formation of the progenitor and its explosion in a Type Ia supernova (SN Ia) using the Hubble Higher- z Supernova Search sample. While a previous analysis indicated a significant time delay, with a most likely value of 3.4 Gyr, effectively ruling out all previously proposed progenitor models, our analysis shows that the time-delay estimate is dominated by systematic errors, in particular due to uncertainties in the star formation history (SFH). We find that none of the popular progenitor models under consideration can be ruled out with any significant degree of confidence. The inferred time delay is mainly determined by the peak in the assumed SFH. We show that, even with a much larger supernova sample, the time-delay distribution cannot be reliably reconstructed without better constraints on the SFH.     

A Model of the Vela Supernova Remnant

A model of the Vela supernova remnant (SNR) based on a cavity explosion of a supernova (SN) star is proposed. It is suggested that the general structure of the remnant is determined by the interaction of the SN blast wave with a massive shell created by the SN progenitor (15-20 M_⊙) star. A possible origin of the nebula of hard X-ray emission detected around the Velapulsar is discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Near infrared coronal line emission in Nova Herculis 1991

Near infrared coronal line emission at 1.98 ± 0.02Μm due to [Si VI] detected in the spectrum of Nova Herculis 1991 about 17 days after optical maximum is reported. The early appearance of coronal emission is yet another unusual feature of this fast nova in which early onset of dust formation processes and X-ray detection five days after outburst have already been reported. The coronal line observations reported here are consistent with X-ray detection and support a hot shocked circumstellar envelope at the periphery of the dust formation zone in the nova.     

Acceleration of a Young Supernova Remnant by an Associated Pulsar

We present a numerical model of the action of a pulsar on its associated supernova remnant. The expansion of the blast wave in the progenitor star has first been considered until radiation pressure within the ejected material becomes negligible due to expansion. By assuming that expansion is ballistic and that the ejecta is opaque to the pulsar 's magnetodipole radiation, the model produces a radiation-filled cavity which grows around the pulsar and contributes to power the dynamics of the forming supernova remnant. The interface between the cavity and the ejecta has been modelled as a thin shell which, depending on the initial spin frequency of the pulsar, can sweep through the ejecta and reach the blast wave. Results for the evolution of the shell indicate that it may strike the front most part of the shocked gas some 60 years after the explosion. Such pulsar-supernova remnant interactions are proposed to form the base of a new subclassification of pulsar-filled supernova remnants. This revised version was published online in July 2006 with corrections to the Cover Date.     

Dust formation in primordial Type II supernovae

We have investigated the formation of dust in the ejecta of Type II supernovae (SNe), mostly of primordial composition, to answer the question of where the first solid particles are formed in the Universe. However, we have also considered non-zero progenitor metallicity values up to Z = Z_⊙ . The calculations are based on standard nucleation theory, and the scheme has been tested for the first time on the well-studied case of SN1987A, yielding results that are in agreement with the available data. We find that: (i) the first dust grains are predominantly made of silicates, amorphous carbon (AC), magnetite and corundum; and (ii) the largest grains are the AC ones, with sizes around 300 Å, whereas the other grain types have smaller radii, around 10–20 Å . The grain size distribution depends somewhat on the thermodynamics of the ejecta expansion, and variations in the results by a factor ≈2 might occur within reasonable estimates of the relevant parameters. Also, and for the same reason, the grain size distribution is essentially unaffected by metallicity changes. The predictions on the amount of dust formed are very robust: for Z =0 , we find that SNe with masses in the range (12–35) M_⊙ produce about 0.08 M_⊙≲ M _d≲0.3 M_⊙ of dust per supernova. The above range increases by roughly three times as the metallicity is increased to solar values. We discuss the implications and the cosmological consequences of the results.     

Dust formation and survival in supernova ejecta

The presence of dust at high redshift requires efficient condensation of grains in supernova (SN) ejecta, in accordance with current theoretical models. Yet observations of the few well-studied supernovae (SNe) and supernova remnants (SNRs) imply condensation efficiencies which are about two orders of magnitude smaller. Motivated by this tension, we have (i) revisited the model of Todini & Ferrara for dust formation in the ejecta of core collapse SNe, and (ii) followed, for the first time, the evolution of newly condensed grains from the time of formation to their survival – through the passage of the reverse shock – in the SNR. We find that  0.1–0.6  M_⊙  of dust form in the ejecta of 12–40 M_⊙ stellar progenitors. Depending on the density of the surrounding interstellar medium, between 2 and 20 per cent of the initial dust mass survives the passage of the reverse shock, on time-scales of about  4–8 × 10⁴  yr  from the stellar explosion. Sputtering by the hot gas induces a shift of the dust size distribution towards smaller grains. The resulting dust extinction curve shows a good agreement with that derived by observations of a reddened QSO at   z = 6.2  . Stochastic heating of small grains leads to a wide distribution of dust temperatures. This supports the idea that large amounts (∼0.1 M_⊙) of cold dust  ( T ∼ 40   K)  can be present in SNRs, without being in conflict with the observed infrared emission.     

The effects of ion screening on neutrino-nucleus interactions in core-collapse supernova explosions

The effects of ion screening in stellar core collapses are investigated based on a new progenitor star model.Simulation results show that ion screening slightly affects the leptons and decreases explosion energy,which is a negative factor for energy transfer supernova explosions.We also investigate the effect on type Ⅱ-supernova explosions of neutrino-nucleus elastic scattering based on the new progenitor star model.It is shown that,compared with the previously calculated results,neutrinos-nucleus elastic scattering in stellar core collapses is more severe,leading to an obvious reduction of the neutrino leakage energy loss and an increase of supernova explosion energy.     

Variability in the Nucleus of NGC 1068

The near-infrared output of the nucleus of NGC 1068 increased by a factor of two over the 18 years between 1976 and 1994 and has recently started to decline. It is not clear whether this event has been the response of an extended dusty region to a single outburst in the central engine or is the result of a continuous change in its XUV output. The integrated energy of the event amounts to well over 1052 erg and thus cannot be due to a single supernova. The variable part of the infrared flux from NGC 1068, observed through an aperture of constant diameter, is found to have a constant spectral shape. Comparison with similar data from other Seyfert galaxies shows that the variable infrared component in NGC 1068 is reddened by about 20 mag in Av if the emission mechanism is similar in all cases. This revised version was published online in July 2006 with corrections to the Cover Date.     

Limits on the X-ray and optical luminosity of the progenitor of the Type Ia supernova 2007sr

We present Hubble Space Telescope ( HST )/Wide Field Planetary Camera 2 (WFPC2), Galaxy Evolution Explorer ( GALEX ) and Chandra observations of the position of the Type Ia supernova 2007sr in the Antennae galaxy, taken before the explosion. No source is found in any of the observations, allowing us to put interesting constraints on the progenitor luminosity. In total there is about 450 ks of Chandra data, spread over seven different observations. Limiting magnitudes of far-ultraviolet (FUV) (23.7 AB mag), near-ultraviolet (NUV) (23.8 AB mag), F555W (26.5 Vega mag) and F814W (24.5–25 Vega mag) are derived. The distance to the Antennae galaxy is surprisingly poorly known, with almost a factor of 2 difference between the latest distance based on the tip of the red giant branch (13.3 Mpc) and the distance derived from the 2007sr light curve (25 Mpc). Using these distances we derive limits on absolute optical and UV magnitudes of any progenitor but these are still above the brightest (symbiotic) proposed progenitors. From the Chandra data a 3σ upper limit to the X-ray luminosity of  0.5–8.0 × 10³⁷ erg s⁻¹  in the 0.3–1 keV range is found. This is below the X-ray luminosity of the potential progenitor of the Type Ia supernova 2007on that we recently discovered and for which we report a corrected X-ray luminosity. If that progenitor is confirmed it suggests the two supernovae have different progenitors. The X-ray limit is comparable to the brightest supersoft X-ray sources in the Galaxy, the Large Magellanic Cloud (LMC) and the Small Magellanic Cloud (SMC) and significantly below the luminosities of the brightest supersoft and quasi-soft X-ray sources found in nearby galaxies, ruling out such sources as progenitors of this Type Ia supernova.     

Cosmic gamma-ray emission and comet collisions with compact stars

The probability that γ-ray bursts may be generated by the infall of comet-like objects on the neutron stars, as recently proposed by Harwit and Salpeter (1973), is reexamined. Although hypothetical cometary clouds around the parent star may survive the supernova outburst virtually untouched, the frequency of γ-outbursts due to the comet impact on the neutron star or white dwarf is only about 10^?3 of the observed occurrence. A considerably higher rate of comets passing per year at critical periastron distance must be assumed if the γ-ray outbursts are to be due to the collision of coments with compact stars.     

Large scale studies of the surroundings of GRS 1915+105

We have carried out radio studies of the surroundings of the superluminal microquasar GRS 1915+105. Our main goal was to understand the possible relation of GRS 1915+105 with two infrared/radio sources that appear symmetrically located with respect to GRS 1915+105 and aligned with the position angle of the relativistic ejecta. We have also studied a nearby supernova remnant to test if the event that created the remnant could have been the progenitor of this hard X-ray binary.