Chun Shing Jason Pun

The Axisymmetric Ejecta of Supernova 1987A

Extensive early observations proved that the ejecta of supernova 1987A (SN 1987A) are aspherical. The most important of these early observations include (1) the Bochum event that revealed small-scale spectroscopic structure indicating chemical inhomogeneities of the ejecta, (2) spectropolarimetry that showed deviations from spherical symmetry, and (3) speckle observations that revealed both the asymmetry of the ejecta and the mystery spot manifested as a secondary source off center from the bulk of the supernova ejecta. Fifteen years after the supernova explosion, the Hubble Space Telescope has resolved the rapidly expanding ejecta. The late-time images and spectroscopy provide a geometrical picture that is consistent with early observations and suggests a highly structured, axially symmetric geometry. We present here a new synthesis of the old and new data. We show that the Bochum event, presumably a clump of 56Ni, and the late-time image, the locus of excitation by 44Ti, are most naturally accounted for by sharing a common position angle of about 14°, the same as the mystery spot and early speckle data on the ejecta, and that they are both oriented along the axis of the inner circumstellar ring at 45° to the plane of the sky. We also demonstrate that the polarization represents a prolate geometry with the same position angle and axis as the early speckle data and the late-time image, and hence that the geometry has been fixed in time and throughout the ejecta. The Bochum event and the Doppler kinematics of the [Ca II]/[O II] emission in spatially resolved Hubble Space Telescope spectra of the ejecta can be consistently integrated into this geometry. The radioactive clump is deduced to fall approximately along the axis of the inner circumstellar ring and therefore to be redshifted in the north, whereas the [Ca II]/[O II] 7300 A emission is redshifted in the south. We present a jet-induced model for the explosion and argue that such a model can account for many of the observed asymmetries. In the jet models, the oxygen and calcium are not expected to be distributed along the jet but primarily in an expanding torus that shares the plane and northern blue shift of the inner circumstellar ring.

Preliminary Spectral Analysis of the Type II Supernova 1999em

We have calculated fast direct spectral model fits to two early-time spectra of the Type II plateau SN 1999em, using the SYNOW synthetic spectrum code. The first is an extremely early blue optical spectrum and the second a combined Hubble Space Telescope and optical spectrum obtained one week later. Spectroscopically this supernova appears to be a normal Type II, and these fits are in excellent agreement with the observed spectra. Our direct analysis suggests the presence of enhanced nitrogen. We have further studied these spectra with the full non-LTE general model atmosphere code PHOENIX. While we do not find confirmation for enhanced nitrogen (nor do we rule it out), we do require enhanced helium. An even more intriguing possible line identification is complicated Balmer and He I lines, which we show falls naturally out of the detailed calculations with a shallow density gradient. We also show that very early spectra such as those presented here combined with sophisticated spectral modeling allow an independent estimate of the total reddening to the supernova, since when the spectrum is very blue, dereddening leads to changes in the blue flux that cannot be reproduced by altering the temperature of the emitted radiation. These results are extremely encouraging since they imply that detailed modeling of early spectra can shed light on both the abundances and total extinction of SNe II, the latter improving their utility and reliability as distance indicators.

Spatially resolved STIS spectroscopy of SN 1987A: Evidence for shock interaction with circumstellar gas

Visual and ultraviolet spatially resolved (~01) spectra of SN 1987A obtained on days 3715 and 3743 with the Space Telescope Imaging Spectrograph on the Hubble Space Telescope show that the high-velocity supernova debris is colliding with circumstellar gas. Very broad Lyα emission with velocities extending to ~±20,000 km s-1 originates inside the inner circumstellar ring and appears to fill most of the surface area within 067 ± 003 (0.14 pc at a distance of 50 kpc) of the rings center. The observed Lyα flux from the shocked ejecta is (1.85±0.53) × 10−13 and (1.25±0.51) × 10−12 ergs cm-2 s-1 after correcting for extinction. A spatially unresolved blueshifted emission feature was discovered in Hα (and other lines) on the inner ring at position angle 31°±8°. The Hα emission extends to -250 km s-1 with no corresponding redshifted emission. This highly localized interaction appears to be the initial contact of the supernova blast wave with an inward protrusion of the inner ring. The broad Lyα emission and the hot spot are separate interaction phenomena associated with the reverse and forward shocks, respectively. We also find that the size of the inner ring in forbidden lines of oxygen has a dependence on ionization potential, in agreement with photoionization models of the ring.

Analysis of Type IIn SN 1998S: Effects of Circumstellar Interaction on Observed Spectra

We present spectral analysis of early observations of the Type IIn supernova 1998S using the general non-local thermodynamic equilibrium atmosphere code PHOENIX. We model both the underlying supernova spectrum and the overlying circumstellar interaction region and produce spectra in good agreement with observations. The early spectra are well fitted by lines produced primarily in the circumstellar region itself, and later spectra are due primarily to the supernova ejecta. Intermediate spectra are affected by both regions. A mass-loss rate of order ~ 0.0001-0.001 M☉ yr-1 is inferred for a wind speed of 100-1000 km s-1. We discuss how future self-consistent models will better clarify the underlying progenitor structure.

[ITAL]Hubble Space Telescope[/ITAL] Spectroscopy of Spot 1 on the Circumstellar Ring of SN 1987A

We present ultraviolet and optical spectra of the first bright spot (P.A. = 29°) on SN 1987As equatorial circumstellar ring taken with the Space Telescope Imaging Spectrograph. We interpret this spot as the emission produced by radiative shocks that occur where the supernova blast wave strikes an inward protrusion of the ring. The observed line widths and intensity ratios indicate the presence of radiative shocks with velocities ranging from 100 to 250 km s-1 entering dense (104 cm-3) gas. These observations, and future observations of the development of the spectra and line profiles, provide a unique opportunity to study the hydrodynamics of radiative shocks.

Hubble Space Telescope Spectroscopy of Spot 1 on the Circumstellar Ring of SN 1987A

We present ultraviolet and optical spectra of the first bright spot (P.A. = 29°) on SN 1987As equatorial circumstellar ring taken with the Space Telescope Imaging Spectrograph. We interpret this spot as the emission produced by radiative shocks that occur where the supernova blast wave strikes an inward protrusion of the ring. The observed line widths and intensity ratios indicate the presence of radiative shocks with velocities ranging from 100 to 250 km s-1 entering dense (104 cm-3) gas. These observations, and future observations of the development of the spectra and line profiles, provide a unique opportunity to study the hydrodynamics of radiative shocks.

New [ITAL]Hubble Space Telescope[/ITAL] Observations of High-Velocity L[CLC]y[/CLC]α and Hα in SNR 1987A

We describe and model high-velocity (≈ 15,000 km s-1) Lyα and Hα emission from the supernova remnant SNR 1987A seen in 1997 September and October with the Space Telescope Imaging Spectrograph. Part of this emission comes from a reverse shock located at ≈ 75% of the radius of the inner boundary of the inner circumstellar ring and confined within ±30° of the equatorial plane. Departure from axisymmetry in the Lyα and Hα emission correlates with that seen in nonthermal radio emission and reveals an asymmetry in the circumstellar gas distribution. We also see diffuse high-velocity Lyα emission from supernova debris inside the reverse shock that may be due to excitation by nonthermal particles accelerated by the shock.We describe and model high velocity (~15,000 km/s) Lyman alpha and Balmer alpha emission from supernova remnant 1987A seen in September and October 1997 with the Space Telescope Imaging Spectrograph. Part of this emission comes from a reverse shock located at ~75% of the radius of the inner boundary of the inner circumstellar ring and confined within 30 degrees of the equatorial plane. Departure from axisymmetry in the Lyman alpha and Balmer alpha emission correlates with that seen in nonthermal radio emission and reveals an asymmetry in the circumstellar gas distribution. We also see diffuse high velocity Lyman alpha emission from supernova debris inside the reverse shock that may be due to excitation by nonthermal particles accelerated by the shock.

HST Spectroscopy of Spot 1 on the Circumstellar Ring of SN 1987A

We present ultraviolet and optical spectra of the first bright spot (P.A. = 29°) on SN 1987As equatorial circumstellar ring taken with the Space Telescope Imaging Spectrograph. We interpret this spot as the emission produced by radiative shocks that occur where the supernova blast wave strikes an inward protrusion of the ring. The observed line widths and intensity ratios indicate the presence of radiative shocks with velocities ranging from 100 to 250 km s-1 entering dense (104 cm-3) gas. These observations, and future observations of the development of the spectra and line profiles, provide a unique opportunity to study the hydrodynamics of radiative shocks.

New Hubble Space Telescope Observations of High-Velocity Lyα and Hα in SNR 1987A

We describe and model high-velocity (≈ 15,000 km s-1) Lyα and Hα emission from the supernova remnant SNR 1987A seen in 1997 September and October with the Space Telescope Imaging Spectrograph. Part of this emission comes from a reverse shock located at ≈ 75% of the radius of the inner boundary of the inner circumstellar ring and confined within ±30° of the equatorial plane. Departure from axisymmetry in the Lyα and Hα emission correlates with that seen in nonthermal radio emission and reveals an asymmetry in the circumstellar gas distribution. We also see diffuse high-velocity Lyα emission from supernova debris inside the reverse shock that may be due to excitation by nonthermal particles accelerated by the shock.We describe and model high velocity (~15,000 km/s) Lyman alpha and Balmer alpha emission from supernova remnant 1987A seen in September and October 1997 with the Space Telescope Imaging Spectrograph. Part of this emission comes from a reverse shock located at ~75% of the radius of the inner boundary of the inner circumstellar ring and confined within 30 degrees of the equatorial plane. Departure from axisymmetry in the Lyman alpha and Balmer alpha emission correlates with that seen in nonthermal radio emission and reveals an asymmetry in the circumstellar gas distribution. We also see diffuse high velocity Lyman alpha emission from supernova debris inside the reverse shock that may be due to excitation by nonthermal particles accelerated by the shock.

New hst observations of high velocity lyman alpha and balmer alpha in snr 1987a

We describe and model high-velocity (≈ 15,000 km s-1) Lyα and Hα emission from the supernova remnant SNR 1987A seen in 1997 September and October with the Space Telescope Imaging Spectrograph. Part of this emission comes from a reverse shock located at ≈ 75% of the radius of the inner boundary of the inner circumstellar ring and confined within ±30° of the equatorial plane. Departure from axisymmetry in the Lyα and Hα emission correlates with that seen in nonthermal radio emission and reveals an asymmetry in the circumstellar gas distribution. We also see diffuse high-velocity Lyα emission from supernova debris inside the reverse shock that may be due to excitation by nonthermal particles accelerated by the shock.We describe and model high velocity (~15,000 km/s) Lyman alpha and Balmer alpha emission from supernova remnant 1987A seen in September and October 1997 with the Space Telescope Imaging Spectrograph. Part of this emission comes from a reverse shock located at ~75% of the radius of the inner boundary of the inner circumstellar ring and confined within 30 degrees of the equatorial plane. Departure from axisymmetry in the Lyman alpha and Balmer alpha emission correlates with that seen in nonthermal radio emission and reveals an asymmetry in the circumstellar gas distribution. We also see diffuse high velocity Lyman alpha emission from supernova debris inside the reverse shock that may be due to excitation by nonthermal particles accelerated by the shock.