X-ray Emission from the Type Ic Supernova 1994I Observed with Chandra

We present two high-resolution Chandra X-ray observations of supernova (SN) 1994I which show, for the first time, that the interaction of the blast wave from a Type Ic SN with its surrounding circumstellar material (CSM) can give rise to soft X-ray emission. Given a 0.3-2 keV band X-ray luminosity of L_x ~ 1 x 10^{37} ergs/s between six and seven years after the outburst of SN 1994I, and assuming the X-ray emission arises from the shock-heated CSM, we derive a pre-SN mass-loss rate of \dot{M} ~ 1 x 10^{-5} M_sun/yr (v_w/10 km/s). Combining the results with earlier ROSAT observations, we construct the X-ray lightcurve of SN 1994I. A best-fit X-ray rate of decline of L_x \propto t^{-s} with index s~1 and a CSM density profile of rho_csm \propto r^{-1.9\pm0.1} are inferred, consistent with what is expected for a constant mass-loss rate and constant wind velocity profile for the SN progenitor (rho_csm \propto r^{-2}).Comment: 5 pages, 3 figures, accepted for publication in the Astrophysical Journal Letter

Strong Evolution of X-Ray Absorption in the Type IIn Supernova SN 2010jl

We report two epochs of Chandra-ACIS X-ray imaging spectroscopy of the nearby bright Type IIn supernova SN 2010jl, taken around 2 months and then a year after the explosion. The majority of the X-ray emission in both the spectra is characterized by a high temperature (\ga 10 keV) and is likely to be from the forward shocked region resulting from circumstellar interaction. The absorption column density in the first spectrum is high, ~ 10^{24} cm^{-2}, more than 3 orders of magnitude higher than the Galactic absorption column, and we attribute it to absorption by circumstellar matter. In the second epoch observation, the column density has decreased by a factor of 3, as expected for shock propagation in the circumstellar medium. The unabsorbed 0.2-10 keV luminosity at both epochs is ~7 x 10^{41} erg/s. The 6.4 keV Fe line clearly present in the first spectrum is not detected in the second spectrum. The strength of the fluorescent line is roughly that expected for the column density of circumstellar gas, provided the Fe is not highly ionized. There is also evidence for an absorbed power law component in both the spectra, which we attribute to a background ultraluminous X-ray source.Comment: 14 pages, 4 figures, resubmitted to ApJL after responding to referee's comment

SN 1996cr: Confirmation of a Luminous Type IIn Supernova in the Circinus Galaxy

We have recently confirmed SN 1996cr as a late-time type IIn supernova (SN) via VLT spectroscopy and isolated its explosion date to ~1 yr using archival optical imaging. We briefly touch upon here the wealth of optical, X-ray, and radio archival observations available for this enigmatic source. Due to its relative proximity (3.8 +/-0.6 Mpc), SN 1996cr ranks among the brightest X-ray and radio SNe ever detected and, as such, may offer powerful insights into the structure and composition of type IIn SNe. We also find that SN 1996cr is matched to GRB 4B 960202 at a 2-3 sigma confidence level, making it perhaps the third GRB to be significantly associated with a type II SN. We speculate on whether SN 1996cr could be an off-axis or ``failed'' GRB.Comment: 3 pages, 1 figure, poster proceeding for "Supernova 1987A: 20 Years After: Supernovae and Gamma-Ray Bursters" AIP, New York, eds. S. Immler, K.W. Weiler, and R. McCra

Ultraviolet Observations of Supernovae

The motivations to make ultraviolet (UV) studies of supernovae (SNe) are reviewed and discussed in the light of the results obtained so far by means of IUE and HST observations. It appears that UV studies of SNe can, and do lead to fundamental results not only for our understanding of the SN phenomenon, such as the kinematics and the metallicity of the ejecta, but also for exciting new findings in Cosmology, such as the tantalizing evidence for "dark energy" that seems to pervade the Universe and to dominate its energetics. The need for additional and more detailed UV observations is also considered and discussed.Comment: 10 pages, 5 figures - Invited talk at the "Supernova 1987A: 20 Years after: Supernovae and Gamma-Ray Bursters" Conference, February 19-23, 2007, Aspen, CO, (AIP Conf. Proc.), eds. S. Immler, R. McCray and K.W. Weiler, in press. Slightly revised version that clarifies some confusing statement

Observations of extremely thin clouds in the tropical tropopause region by a ship based lidar.

During the cruises ANT XVII/4 (Punta Arenas Bremerhaven, 2000) and ANT XX1/1 (Bremerhaven - Cape Town, 2003) continuous measurements of clouds and aerosol have been performed by a Mobile Aerosol Raman Lidar (MARL). This system measures backscatter of light at 355 nm and 532 nm and is able to detect even extremely thin layers of particles in the atmosphere. Cloud base and top height, depolarisation optical depth and color index can be deduced from this data. During the Polarstern cruises very thin layers of ice particles have been observed frequently in the tropical tropopause layer (TTL). Cases of persistent cloud layers with an optical depth below 10^-3 are reported. Based on the data of radiosondes which were launched daily aboard the vessel, the conditions at which these type of clouds form are analysed. It is shown, that these clouds form in a layer below the cold point, but above the lapse rate tropopause. The relation between cloud occurrence and temperature and wind in the TTL as well as state of the QBO are discussed

Circumstellar Interaction Around Type Ib/c Supernovae and the GRB Connection

Radio observations of Type Ib/c supernovae suggest that circumstellar interaction takes place with a wide range of wind densities, comparable to that seen in Galactic Wolf-Rayet stars. Efficient production of magnetic field in the shocked region is needed. The X-ray emission observed from some Type Ib/c supernovae is higher than would be expected by the thermal or inverse Compton mechanisms; a synchrotron interpretation requires a flattening of the electron energy spectrum at high energies, as might occur in a cosmic ray dominated shock wave. The wind density variations that are indicated in two supernovae may be due to a binary companion, although variable mass loss from a single star remains a possibility. Other than the optical supernova radiation, the emission from the nearby SN 2006aj/GRB 060218 appears to be powered by a central engine, while that from SN 1998bw/GRB 980425 could be powered by either a central engine or the outer supernova ejecta.Comment: 8 pages, to appear in Circumstellar Media and Late Stages of Massive Stellar Evolution, RevMexA

SN Shock Evolution in the Circumstellar Medium surrounding SN 1987A

We study the structure of the circumstellar medium surrounding SN 1987A in the equatorial plane. Furthermore, we study the evolution of the SN shock within this medium during the first 25 years, and the resulting hard X-ray and radio emission from the remnant.Comment: 5 pages, 3 Figures. To be published in the proceedings of the conference on "Supernova 1987A: 20 Years After: Supernovae and Gamma-Ray Bursters" AIP, New York, eds. S. Immler, K.W. Weiler, and R. McCra

The Radio Properties of Type Ibc Supernovae

Over the past few years, long-duration gamma-ray bursts (GRBs), including the subclass of X-ray flashes (XRFs), have been revealed to be a rare variety of Type Ibc supernova (SN Ibc). While all these events result from the death of massive stars, the electromagnetic luminosities of GRBs and XRFs exceed those of ordinary Type Ibc SNe by many orders of magnitude. The observed diversity of stellar death corresponds to large variations in the energy, velocity, and geometry of the explosion ejecta. Using multi-wavelength (radio, optical, X-ray) observations of the nearest GRBs, XRFs, and SNe Ibc, I show that while GRBs and XRFs couple at least 10^48 erg to relativistic material, SNe Ibc typically couple less than 10^48 erg to their fastest (albeit non-relativistic) outflows. Specifically, I find that less than 3% of local SNe Ibc show any evidence for association with a GRB or XRF. Recently, a new class of GRBs and XRFs has been revealed which are under-luminous in comparison with the statistical sample of GRBs. Owing to their faint high-energy emission, these sub-energetic bursts are only detectable nearby (z < 0.1) and are likely 10 times more common than cosmological GRBs. In comparison with local SNe Ibc and typical GRBs/XRFs, these explosions are intermediate in terms of both volumetric rate and energetics. Yet the essential physical process that causes a dying star to produce a GRB, XRF, or sub-energetic burst, and not just a SN, remains a crucial open question. Progress requires a detailed understanding of ordinary SNe Ibc which will be facilitated with the launch of wide-field optical surveys in the near future.Comment: 8 pages, Proceedings for "Supernova 1987A: 20 Years After: Supernovae and Gamma-Ray Bursters" AIP, New York, eds. S. Immler, K.W. Weiler, and R. McCra

Chandra and ASCA X-ray Observations of the Radio Supernova SN1979C IN NGC 4321

We report on the X-ray observation of the radio selected supernova SN1979C carried out with ASCA in 1997 December and serendipitously available from a Chandra Guaranteed Time Observation in 1999 November. The supernova, of type SN II-Linear (SN IIL), was first observed in the optical and occurred in the weakly barred, almost face on spiral galaxy NGC 4321 (M100). The galaxy, a member of the Virgo S cluster, is at a distance of 17.1 Mpc, and contains at least three other supernovae discovered in this century. The useful exposure time was ~25 ks for the Solid-State Imaging Spectrometer (SIS), ~28 ks for the Gas Scintillation Imaging Spectrometer (GIS), and ~2.5 ks for Chandra's Advanced CCD Imaging Spectrometer (ACIS). No point source was detected at the radio position of SN1979C in a 3' diameter half power response circle in the ASCA data. The background and galaxy subtracted SN signal had a 3sigma upper limit to the flux of 6.3x10^-14 ergs/s/cm^-2 in the full ASCA SIS band (0.4-10.0 keV) and a 3sigma upper limit of <3-4x10^-14 erg/s/cm^2 in the 2-10 keV band. In the Chandra data, a source at the position of SN1979C is marginally detected at energies below 2 keV at a flux consistent with the ROSAT HRI detection in 1995. At energies above 2 keV, no source is detected with an upper limit of ~3x10^-14 erg/s/cm^-2. These measurements give the first ever x-ray flux limit of a Type IIL SN above 2 keV which is an important diagnostic of the outgoing shock wave ploughing through the circumstellar medium.Comment: 8 pages, 2 figures, accepted A