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NASA NTRS1993

Is PSR 1509-58 the remnant of supernova AD 185?

Thorsett has recently advanced the proposal that the counterpart of the supernova recorded by Chinese astronomers in AD 185 is the pulsar PSR 1509-58 in the supernova remnant MSH 15-52. This proposal is attractive since it was claimed to better fit the visibility contraints that plagued earlier identifications and since the spin-down age of the pulsar is 1690 years. I have examined in detail the question of the visibility of a supernova at the proposed position and find that the reported dates of visibility can be matched only if the supernova appeared substantially brighter than Venus at its peak. For the distance and extinction to the pulsar, this implies M(sub V) (max) was brighter than -21.4 mag, whereas the brightest known absolute magnitude of a Type II supernova is -19.65 (H(sub 0) = 75 km/s/Mpc). Thus, the high required luminosity can be used as good evidence against the identification of SN 185 with PSR 1509-58. However, if the identification is retained, then Hubble's Constant would have to have a small value and/or the supernova had to have been a type IIP event with exceptional brilliance. The earlier identification of SN 185 with MSH 14-63 by Clark and Stephenson can also be reconciled with the visibility data.

Schaefer, Bradley E.↗
NASA NTRS1988

Ejecta in SN 1006: The knotty issue

The 1988 IUE SWP observations of a faint sdOB star situated behind the remnant of the supernova of AD 1006 are presented. These spectra along with IUE spectra of the star taken between 1982 and 1986 provide a detailed look at the elemental composition and dynamical properties of the SN 1006 remnant. Over the 6 years there were no significant changes in the absorption features associated with the remnant at 1281, 1330, or 1420 A. While the lack of variability in these absorption lines makes it impossible to decide whether the ejecta is distributed smoothly or in knots, it is clear that the 1281 A feature is a blend, requiring either S II absorption redshifted at 6000 km/sec plus Si II 1260 at 5200 km/sec, or else 2 individual Si absorbing regions.

Fesen, Robert A.↗
NASA NTRS2020

RGS Observations of Ejecta Knots in Tycho's Supernova Remnant

We present results from XMM-Newton/RGS observations of prominent knots in the southest portion of Tycho's supernova remnant, known to be the remnant of a Type Ia SN in 1572 C.E. By dispersing the photons from these knots out of the remnant with very little emission in front of or behind them, we obtained the nearly uncontaminated spectra of the knots. In the southernmost knot, the RGS successfully resolved numerous emission lines from Si, Ne, O He-alpha and Ly-alpha, and Fe L-shell. This is the first clear detection of O lines in Tycho's SNR. Line broadening was measured to be ~ 3 eV for the O He-alpha and ~ 4:5 eV for Fe L lines. If we attribute the broadening to pure thermal Doppler effects, then we obtain kTO and kTFe to be ~ 400 keV and 1.5 MeV, respectively. These temperatures can be explained by heating in a reverse shock with a shock velocity of ~ 3500 km/s. The abundances obtained from fitting the RGS and MOS data together imply substantially elevated amounts of these materials, confi rming previous studies that the knots are heated by a reverse shock, and thus contain ejecta material from the supernova. We are unable to fi nd a Type Ia explosion model that reproduces these abundances, but this is likely the result of this knot being too small to extrapolate to the entire remnant.

Brian J. Williams↗
NASA NTRS1992

Oriented Scintillation Spectrometer Experiment observations of Co-57 in SN 1987A

The Oriented Scintillation Spectrometer Experiment (OSSE) on the Compton Gamma Ray Observatory has observed SN 1987A for two 2 week periods during the first 9 months of the mission. Evidence for gamma-ray line and continuum emission from Co-57 is observed with an intensity of about 10 exp -4 gamma/sq cm/s. This photon flux between 50 and 136 keV is demonstrated by Monte Carlo calculations to be independent of the radial distribution of Co-57 for models of low optical depth, viz., models having photoelectric absorption losses of 122 keV photons no greater than several percent. For such models the observed Co-57 flux indicates that the ratio Ni-57/Ni-56 produced in the explosion was about 1.5 times the solar system ratio of Fe-57/Fe-56. When compared with nearly contemporaneous bolometric estimates of the luminosity for SN 1987A, our observations imply that Co-57 radioactivity does not account for most of the current luminosity of the supernova remnant in low optical depth models. We suggest alternatives, including a large optical depth model that is able to provide the SN 1987A luminosity and is consistent with the OSSE flux. It requires a 57/56 production ratio about twice solar.

Kurfess, J. D.↗
NASA NTRS1979

X-ray iron-line emission from the SN 185 remnant

Radio and optical research was carried out in order to show that the supernova remnant RCW86 is a remnant of the earliest supernova event ever recorded in history (185 AD). The results are as follows: (1) an iron-line emission was found at 6.7 keV; (2) the temperature measured from HEAO-1 was approximately 6 keV; and (3) the equivalent width was consistent within the uncertainties with a cosmic iron abundance. These results support the identification of the supernova remnant RCW86 (it's X-ray source) with the historic supernova event.

Winkler, P. F.↗
NASA NTRS1986

The optical light curve of SN 1985f in NGC 4618

The 4930-A optical light curve obtained for the bizarre 1985f supernova in NGC 4618 covers a six-month interval; care has been taken to eliminate contamination by bright underlying H II regions. The light curve is well approximated by a constant decline of 0.0153 mag/day. The spectroscopic work of Gaskell et al. (1986) suggests that this supernova is a Type Ib object; if so, the present observations represent the first light curve of an object of this type at late times in its evolution, furnishing a standard against which future sightings can be compared.

Filippenko, Alexei V.↗
NASA NTRS1991

Supernova remnant 1987 A

A dense circumstellar shell, with radius of about 0.5 lt-yr, surrounds SN 1987 A. In 16 yr or less after outburst, the expanding debris of SN 1987 A will strike this shell. When it does, the hot gas and relativistic electrons resulting from the forward and reverse shocks will radiate X-rays, infrared radiation, and nonthermal radio waves. The remnant of SN 1987 A will then become one of the brightest X-ray and radio sources in the LMC.

Luo, Ding↗
NASA NTRS2019

The Type II superluminous SN 2008es at late times: near-infrared excess and circumstellar interaction

SN 2008es is one of the rare cases of a Type II superluminous supernova (SLSN), showing no narrow features in its early-time spectra, and therefore, its powering mechanism is under debate between circumstellar interaction (CSI) and magnetar spin-down. Late-time data are required for better constraints. We present optical and near-infrared (NIR) photometry obtained from Gemini, Keck, and Palomar Observatories from 192 to 554 d after explosion. Only broad H α emission is detected in a Gemini spectrum at 288 d. The line profile exhibits red-wing attenuation relative to the early-time spectrum. In addition to the cooling SN photosphere, an NIR excess with blackbody temperature ∼1500 K and radius ∼1016 cm is observed. This evidence supports dust condensation in the cool dense shell being responsible for the spectral evolution and NIR excess. We favour CSI, with ∼2–3 Mꙩ of circumstellar material (CSM) and ∼10–20 Mꙩ of ejecta, as the powering mechanism, which still dominates at our late-time epochs. Both models of uniform density and steady wind fit the data equally well, with an effective CSM radius ∼1015 cm, supporting the efficient conversion of shock energy to radiation by CSI. A low amount (≲0.4 Mꙩ) of 56Ni is possible but cannot be verified yet, since the light curve is dominated by CSI. The magnetar spin-down powering mechanism cannot be ruled out, but is less favoured because it overpredicts the late-time fluxes and may be inconsistent with the presence of dust.

Kornpob Bhirombhakdi↗
NASA NTRS1994

SN 1991T: Reflections of past glory

We have obtained photometry and spectra of SN 1991T which extend more than 1000 days past maximum light, by far the longest of SN Ia has been followed. Although SN 1991T exhibited nearly photometric behavior in the first 400 days following maximum, by 600 days its decline had slowed, and by 950 days the supernova brightness was consistent with a constant apparent magnitude of m(sub B) = 21.30. Spectra near maximum showed minor variations on the SN Ia theme which grew less conspicuous during the exponential decline. At 270 days the nebular spectrum was composed of Fe and Co lines common to SN Ia. However, by 750 days past maximum light, these lines had shifted in wavelength, and were superposed on a strong blue continuum. The luminosity of SN 1991T at 950 days is more than (9.0 x 10(exp 38)(D/13 Mpc)(2) ergs/s with a rate of decline of less than 0.04 mag per 100 days. We show that this emission is likely to be light that was emitted by SN 1991T near maximum light which has reflected from foreground dust, much like the light echos observed around SN 1987A.

Schmidt, Brian P.↗
NASA NTRS1983

X-ray spectra of young supernova remnants

Einstein solid-state-spectrometer (SSS) spectra are presented for the Crab Nebula, Cas A, SN 1006, the Tycho SNR, and the Kepler SNR. The history of X-ray observations of SNRs is reviewed; the SSS instrument is briefly characterized; a reduction technique which accounts for all background sources in the 0.5-4.5-keV band is applied; and the physical models of SNRs constructed to reproduce the refined spectra are discussed. The limitations of the modeling methods and the need for further observations, especially of localized regions, are indicated.

Holt, S. S.↗
NASA NTRS1989

On the detectability of infrared echo arcs around supernova 1987A

The ring-like interstellar visual echoes of radii 33 and 54 arcsec detected around SN 1987A should coincide with infrared echoes (thermal reradiation) from dust at T approximately equal to 15 to 30 K. Whether these infrared echoes are detectable at present is considered. They will be brightest at approximately 100 microns, the range of the Texas infrared photometer. Detectability depends on the ratio zeta congruent to tan(sub a)/tan(sub s)P(theta), where tan(sub a) and tan(sub s) are the visual absorption and scattering optical thicknesses of the echo layer, and P is the phase function function for small-angle scattering (theta approximately equal to 2 to 4 degrees). Zeta approximately greater than 1 is needed for a detectable signal (approximately 0.3 Jy), but zeta cannot be much less than 1; otherwise the visual echoes could not be as bright as they are. Typical dust mixtures of Mathis-Rumpl-Nordsieck type have zeta much less than 1. Zeta remains small even if a population of very small grains with power-law index as steep as approximately 5.5 is added. A population with even more small grains and/or fewer large grains could have a zeta similar to 1 and be detectable at present, but this seems unlikely. The echoes will move, but should remain accessible for many years and should be detected eventually.

Felten, James E.↗
NASA NTRS1988

The complete visual light curve of SN 1987A: Thirteen months of FES observations

Visual brightness measurements of SN 1987A are being obtained with the IUE acquisition camera and star tracker Fine Error Sensor, (FES) as part of each ultraviolet observation. Due to IUE's around-the-clock operation and lack of clouds, the FES record of SN 1987A provides the most complete set of visual photometry of the supernova made by any single instrument. The data illustrate the photometric limitations of the FES (+ or - 0.03 mag). Use of differential photometric methods are recommended for IUE observers desiring accurate photometry from FES measurements made during their observing shifts.

Sonneborn, G.↗
NASA NTRS1988

Recent results on SN 1987A

The results from observational studies of SN 1987A are reviewed. The evolution of the blue supergiant pre-supernova star is examined, including the composition and core structure of the star and nitrogen enhancements. The study of heavy elements and isotopes in the ejecta is discussed. Also, consideration is given to possible mixing of supernova composition in velocity space, the profiles of observed IR lines and their red-shifted wings, and the question of what happened to the neutron star.

Woosley, S. E.↗
NASA NTRS1988

Late evolution of SN 1987A

Topics related to the late evolution of SN 1987A are examined. The characteristics of interstellar light echoes are reviewed and studies of light echoes and shock waves surrounding SN 1987A are discussed. The late emission and the structure of the supernova ejecta are described. In addition, the effects of a central neutron star are considered.

Chevalier, Roger A.↗
NASA NTRS1990

A new subclass of Type II supernovae?

Observations of Type II supernovae are reported, focusing on evidence supporting the need for a new SN subclass. The objects that are likely to consistute the new subclass are listed and the properties that separate these objects from the mass of SN II objects are described.

Schlegel, Eric M.↗
NASA NTRS1994

Hard X-rays from SN 1993J

The Oriented Scintillation Spectrometer Experiment (OSSE) on the Compton Observatory observed SN 1993J during three intervals centered approximately 12, 30, and 108 days after its outburst. Hard X-ray emission was detected in the first two of these intervals. No emission was seen in the third observation or in two earlier observations in 1991 and 1992. The coincidence of the observed excess with the outburst of SN 1993J and the consistency of the spectra and time evolution with those seen at lower energies by ROSAT and ASCA (Astro-D) argue that the observed emission is indeed from SN 1993J. It is probably due to the interaction of the fast supernova ejecta with circumstellar material. The luminosity, 5 x 10(exp 40) ergs/sec (50-150 keV) in the first interval, is significantly larger than predicted. Extrapolating the spectrum to a few keV accounts for most or all of the observed emission at low energy. The observed high temperature, 10(exp 9) K, is easily obtained in the shocked circumstellar matter, but a surprisingly high density is required there to give the observed luminosity, and little or no additional X-ray emission from denser shocked supernova ejecta is allowed. The hard emission might also be explained in terms of the shocked supernova ejecta itself with unexpectedly high temperature.

Leising, M. D.↗
NASA NTRS1993

Iron, Cobalt, and Nickel in SN 1987A

During the first several weeks after the explosion of SN 1987A, Fe/Co/Ni clumps, containing approx. 1% of the mass of the supernova envelope, absorbed most of the energy release by Ni-56 and Co-56 decay. As a result, the clumps expanded relative to the substrate, forming a 'nickel bubble' of low-density Fe/Co/Ni. Later the clumps captured approx. 10% of the radioactive luminosity of gamma rays and positrons. Assuming that these elements are not mixed microscopically with other elements, we find that the clumps must occupy approx. greater than 30% of the volume of the emitting region (radial velocity approx. less than 2500 km/s). The result indicates that the emission at late times is dominated by an extra source of heating and ionization, most likely photoionization by two-photon continuum from metastable helium in the gas surrounding the clumps. The resulting 'frothy' structure, consisting of bubbles of low-density Fe surrounded by higher-density filaments of H, He, and other elements, will persist and may be seen in the spectra and structure of supernova remnants.

Li, Hongwei↗
NASA NTRS1988

The interstellar light echoes around SN 1987A

The observed light echoes around SN 1987A are modeled by dust in planar clouds roughly 120 and 330 pc in front of the supernova. The expected echo profiles depend on the observed light curve and on the cloud thicknesses. The surface brightness and colors of the echoes are modeled using a mix of silicate and graphite grains appropriate to the Large Magellanic Cloud (LMC). The model colors approximately agree with the observed ones. The observed surface brightness suggests that the dust column density in the echo clouds is comparable to the total dust column density in the LMC toward SN 1987A. The model predicts the presence of a narrow ultraviolet echo outside the visual echo; it should be detectable with future ultraviolet observatories and will give information on the supernova near the phase of shock breakout.

Chevalier, Roger A.↗