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At least 325 records · Page 18
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NASA NTRS1997

A comparative modeling of supernova 1993J

The light curve of Supernova 1993J is calculated using two computational radiation transport approaches. The two approaches are represented by the computer codes STELLA and EDDINGTON. The emphasis is on the shock breakout and the photometry in the U, B and V bands during the first 120 days of the supernova. The STELLA model includes implicit hydrodynamics and is able to model early supernova evolution before the expansion is homologous. The STELLA model employs multi-group photonics and is able to follow the radiation as it decouples from the matter. The EDDINGTON code uses an algorithm for integrating the transport equation which assumes homologous expansion and uses a finer frequency resolution. The agreement between the two codes is considered to be satisfactory only in the case where compatible physical assumptions are made concerning the opacity. The assumptions are justified. The continuum spectrum for SN 1993J is predicted near the shock breakout to be superior to that predicted by standard single energy group hydrocodes. The uncertainties involved in current time dependent models of supernova light curves are discussed.

Blinnikov, Sergei↗
NASA NTRS1991

Hot gas metallicity and the history of supernova activity in elliptical galaxies

Calculations of the dynamical evolution of the hot interstellar medium (ISM) in a massive elliptical galaxy are described, with a variety of past variations of the SN rate being assumed. The investigation focuses on iron enrichment in the ISM. The equivalent widths of the 6.7-keV iron line are calculated as a function of redshift and of galactic projected radius. The present-day interstellar gas in elliptical galaxies contains a fossil record of past SN activity that can be determined from measurements of iron line equivalent widths at several projected radii in the galaxy. It is proposed that the ISM iron abundance is likely to be quite inhomogeneous. The hydrogen-free ejecta of type Ia SN also result in pronounced ISM abundance inhomogeneities that probably eventually cool and move in pressure equilibrium with the local ISM flow velocity. The 6.7-keV iron line emission is greater if the iron is confined to ionized regions of pure iron.

Loewenstein, Michael↗
NASA NTRS1989

Signatures of particle acceleration at SN 1987A

At least eight experiments are currently monitoring SN 1987A for photons or neutrinos with energies in the TeV range or higher. Observation of such signals would indicate that the supernova is the site of acceleration of charged particles to even higher energies. The way that the acceleration might occur is discussed, and the prospects for detection of such signals in light of current limits on power in the supernova from sources other than the nickel-cobalt-iron decay chain are evaluated. It is pointed out that signals of particle acceleration may show up in continuum MeV gamma rays as well as in the 100 MeV range.

Gaisser, T. K.↗
NASA NTRS2012

Multi-wavelength Observations of the Enduring Type IIn Supernovae 2005ip and 2006jd1

We present an observational study of the Type IIn supernovae (SNe IIn) 2005ip and 2006jd. Broad-band UV, optical and near-IR photometry, and visual-wavelength spectroscopy of SN 2005ip complement and extend upon published observations to 6.5 years past discovery. Our observations of SN 2006jd extend from UV to mid-infrared wavelengths, and like SN 2005ip, are compared to reported X-ray measurements to understand the nature of the progenitor. Both objects display a number of similarities with the 1988Z-like subclass of SN IIn including: (i) remarkably similar early- and late-phase optical spectra, (ii) a variety of high ionization coronal lines, (iii) long-duration optical and near-IR emission and, (iv) evidence of cold and warm dust components. However, diversity is apparent including an unprecedented late-time r-band excess in SN 2006jd. The observed di erences are attributed to di erences between the mass-loss history of the progenitor stars. We conclude that the progenitor of SN 2006jd likely experienced a signi cant mass-loss event during its pre-SN evolution akin to the great 19th century eruption of eta Carinae. Contrarily, as advocated by Smith et al. (2009), we nd the circumstellar environment of SN 2005ip to be more consistent with a clumpy wind progenitor.

Stritzinger, Maximilian↗
NASA NTRS1989

Late emission from supernovae - A window on stellar nucleosynthesis

Monte Carlo techniques are used to study the energy deposition of gamma rays from the radioactive decay of Co-56 in Type Ib and Type II SN. It is found that above an electron fraction of about 0.1, direct excitations are negligible, and the line emission arises from thermal processes. The results indicate that the emission is dominated by neutral and singly ionized lines, including forbiden O I, forbidden Ca II, forbidden C I, and forbidden Si I. The late spectrum is shown to be useful as a diagnostic of the nucleosynthetic structure of the ejecta. The present model has been applied to observations of the Type Ib SN 1985F, and it is suggested that Type Ib SN come from stars of greater than 25 solar masses.

Fransson, Claes↗
NASA NTRS1993

The cosmic gamma-ray background from Type Ia supernovae

We present an improved calculation of the cumulative gamma-ray spectrum of Type Ia supernovae during the history of the universe. We follow Clayton & Ward (1975) in using a few Friedmann models and two simple histories of the average galaxian nucleosynthesis rate, but we improve their calculation by modeling the gamma-ray scattering in detailed numerical models of SN Ia's. The results confirm that near 1 MeV the SN Ia background may dominate, and that it is potentially observable, with high scientific importance. A very accurate measurement of the cosmic background spectrum between 0.1 and 1.0 MeV may reveal the turn-on time and the evolution of the rate of Type Ia supernova nucleosynthesis in the universe.

The, Lih-Sin↗
NASA NTRS2017

The Origin of the Iron-Rich Knot in Tycho's Supernova Remnant

X-ray observations of supernova remnants (SNRs) allow us to investigate the chemical inhomogeneity of ejecta, offering unique insight into the nucleosynthesis in supernova explosions. Here we present detailed imaging and spectroscopic studies of the Fe knot located along the eastern rim of the Type Ia SNR Tycho ( SN 1572) using Suzaku and Chandra long-exposure data. Surprisingly, the Suzaku spectrum of this knot shows no emission from Cr, Mn, or Ni, which is unusual for the Fe-rich regions in this SNR. Within the framework of the canonical delayed-detonation models for SN Ia, the observed mass ratios M(sub Cr)/M(sub Fe) is less than 0.023, M(sub Mn)/M(sub Fe) is less than 0.012, and M(sub Ni)/M(sub Fe) is less than 0.029 (at 90% confidence) can only be achieved for a peak temperature of (5.3 - 5.7) x 10(exp. 9) K and a neutron excess of approximately less than 2.0 x 10(exp. -3). These constraints rule out the deep, dense core of a Chandrasekhar-mass white dwarf as the origin of the Fe knot and favor either incomplete Si burning or an Alpha-rich freeze-out regime, probably close to the boundary. An explosive He burning regime is a possible alternative, although this hypothesis is in conflict with the main properties of this SNR.

ISM supernova remnants↗
NASA NTRS1985

The destruction of dust grains in collisions of a supernova with a circumstellar medium

Dust grains exist, if not abundantly, in systems composed of a Type II supernova and a circumstellar medium (CSM). The grains, however, may subsequently suffer intense sputtering by X-ray emitting plasmas during the collision of the supernova ejecta with the CSM. An approximate expression is obtained for the amount of grain erosion in both the blast-shocked CSM and the reverse-shocked ejecta, assuming their self-similar interaction. The distortion of the grain size distribution is also calculated. In the remnant of SN 1979c, the population of the grains of radius 0.1 micron, for example, will be diminished substantially in both the ejecta and the CSM, while in the remnant of SN 1980k, it will be affected considerably only in the ejecta. The infrared fluxes expected from the blast-shocked CSM are roughly estimated. The present destruction mechanism may be responsible for the severe under-abundance of dust in the Cassiopeia A supernova remnant.

Itoh, H.↗
NASA NTRS1993

Gamma ray constraints on the Galactic supernova rate

Most Galactic optical supernovae are hidden due to severe extinction in the disk, but could be detectable through their gamma-ray afterglow. Ti-44 is among the potentially detectable isotopes in supernova ejecta. HEAO 3 and SMM sky surveys have not detected gamma-ray lines from the decay of Ti-44, thus constraining SN rates and nucleosynthesis. We perform Monte Carlo simulations of the gamma-ray signatures of SN occurring during the last millenium to interpret the gamma-ray paucity.

Hartmann, D.↗
NASA NTRS1993

A multiwavelength study of the Eridanus soft X-ray enhancement

We present soft X-ray, N(H), and IR maps of the Eridanus soft X-ray enhancement. Soft X-ray maps from the HEAO 1 A-2 LED experiment, processed with a maximum entropy method (MEM) algorithm, show that the enhancement consists of two distinct components: a large hook-shaped component and a small circular component at different temperatures. Both of these are located in 'holes' in the IR emission, and they correspond to N(H) features at very different velocities. The dust surrounding the X-ray enhancements appears to be associated with several high-latitude molecular clouds, which allow us to obtain a probable distance of about 130 pc to the near edge of the main enhancement. The total power emitted by the hot gas is then about 10 exp 35 to 10 exp 36 ergs/s. We consider alternative interpretations of these objects as adiabatic supernova remnants or as stellar wind bubbles and conclude that they are more likely to be stellar wind bubbles, possibly reheated by a SN explosion in the case of the main, hook-shaped object.

Burrows, D. N.↗
NASA NTRS2020

Early Ultraviolet Observations of Type IIn Supernovae Constrain the Asphericity of Their Circumstellar Material

We present a survey of the early evolution of 12 Type IIn supernovae (SNe IIn) at ultraviolet and visible light wavelengths. We use this survey to constrain the geometry of the circumstellar material (CSM) surrounding SN IIn explosions, which may shed light on their progenitor diversity. In order to distinguish between aspherical and spherical CSM, we estimate the blackbody radius temporal evolution of the SNe IIn of our sample, following the method introduced by Soumagnac et al. We find that higher-luminosity objects tend to show evidence for aspherical CSM. Depending on whether this correlation is due to physical reasons or to some selection bias, we derive a lower limit between 35% and 66% for the fraction of SNe IIn showing evidence for aspherical CSM. This result suggests that asphericity of the CSM surrounding SNe IIn is common—consistent with data from resolved images of stars undergoing considerable mass loss. It should be taken into account for more realistic modeling of these events.

Maayane T Soumagnac↗
NASA NTRS1999

The Impact of SN1987A with its Circumstellar Ring

Following is final report on the study "The Impact of SN1987A with its Circumstellar Ring", which is now complete. In 1994, it was predicted that the blast wave from SN1987A would strike the circumstellar ring in AD1999+/-3, and that the ring would brighten by several hundreds optically as the shock entered the ring. It was also predicted that the emission lines from the shocked ring would have linewidths of a few hundred km/s. Today, we see a "hot spot" on the ring that first appeared in Hubble Space Telescope (HST) images in 1995 and has doubled in brightness between August 1997 and February 1998. Moreover, spectra from STIS show that the emission lines from the hot spot have widths and blue shifts of order 200 km/s, just as we predicted in 1994. Our guess of 1999+/-3 for the impact time was lucky, because we assumed that the hot gas in the bubble between the supernova and the ring had a low density (approximately 10 cm(exp -3)). But it was pointed out that the ROSAT observations of soft X-rays from SN 1987A implied that the intervening gas had a higher density, (approximately 100 cm(exp -3)), which would delay the impact until ca. 2007. Others developed hydrodynamic models to fit the ROSAT X-ray emission spectrum and came to the same conclusion. But these models were oversimplified in that they assumed that the ring was perfectly round. Now we see clearly that the hot spot is a peninsula that protrudes inward from the ring -- the first spot on the ring to be struck by the blast wave. No doubt there are other protrusions on the ring, which we may expect to light up in the next few years until they finally merge to set the entire ring ablaze, probably within 5 - 10 years. It was also predicted that the X-ray emission must be accompanied by optical and ultraviolet emission from atoms in the supernova debris and in the circumstellar gas that cross the reverse shock and the blast wave, respectively, and that the Lyman-alpha and NV emission lines should be bright enough to see with the STIS.

McCray, Richard↗
NASA NTRS1988

Ultraviolet observations of SN 1987A - Clues to mass loss

Evidence for a circumstellar shell surrounding SN 1987A is presented, based on UV observations. In May 1987, narrow (less than 1500 km/s) emission lines began to appear in the short wavelength IUE spectra (Wamsteker et al., 1987 and Kirshner et al., 1987) It is suggested that the narrow UV emission lines are due to photoionization of the circumstellar shell by the UV emission expected when the shock hits the surface of the star SK -69 deg 202. Because the gas is N-rich, has a low velocity, and may be located a light-year from the supernova, it is suggested that it was ejected from the progenitor during a red supergiant phase. Also, it is found that the hydrogen mass above a velocity of 6,000 km/s for SN 1987A is between 1 and 6 solar masses.

Kirshner, Robert P.↗
NASA NTRS1991

The circumstellar shell of SN 1987A

An hourglass-shaped circumstellar shell, with radius about 0.65 lt-yr at the equator and about 2.4 lt-yr at the poles, surrounds SN 1987A. The shell is a bubble blown by the wind of the blue giant progenitor of SN 1987A into an equatorially concentrated wind of a prior red giant stage. The bubble was ionized by the initial UV flash of the supernova, and the emission-line region is concentrated in a ring at the waist of the hourglass. In about 2002 AD the supernova envelope will strike the shell. The resulting young supernova remnant will become a luminous source of soft X-rays and broad optical and ultraviolet emission lines.

Luo, Ding↗
NASA NTRS2004

Chandra Observations of the X-ray Environs of SN 1998 bw/GRB 980425

We report X-ray studies of the environs of SN 1998bw and GRB 980425 using the Chandra X-Ray Observatory 1281 days after the GRB. Eight X-ray point sources were localized, three and five each in the original error boxes--S1 and S2--assigned for variable X-ray counterparts to the GRB by BeppoSAX. The sum of the discrete X-ray sources plus continuous emission in S2 observed by CXO on day 1281 is within a factor of 1.5 of the maximum and the upper limits seen by BeppoSAX. We conclude that S2 is the sum of several variable sources that have not disappeared, and therefore is not associated with the GRB. Within S1, clear evidence is seen for a decline of approximately a factor of 12 between day 200 and day 1281. One of the sources in S1, S1a, is coincident with the well-determined radio location of SN 1998bw, and is certainly the remnant of that explosion. The nature of the other sources is also discussed. Combining our observation of the supernova with others of the GRB afterglow, a smooth X-ray light curve, spanning (approx) 1300 days, is obtained by assuming the burst and supernova were coincident at 35. 6 Mpc. When this X-ray light curve is compared with those of the X-ray 'afterglows' of ordinary GRBs, X-ray Flashes, and ordinary supernovae, evidence emerges for at least two classes of lightcurves, perhaps bounding a continuum.

X-RAY SOURCES↗
NASA NTRS1991

Emission processes and dynamics of hot gases in astrophysics

A detailed model was developed for Kepler's supernova remnant (SNR). Observations of the SNR revealed a strong interaction with the surrounding circumstellar medium, which was studied through both analytical and numerical calculations. Effects were studied of electron thermal conduction on the structure of radiative interstellar shock waves. An explanation is sought for the observed line emission from metal rich ejecta in SNR, incorporating atomic data. Light echoes around SN 1987A was also studied. Analysis of infrared and scattered circumstellar light echoes was accomplished with early observations to set limits on the mass of circumstellar dust. Work was completed on the emission from heavy element gas ejected in the supernova explosion of massive stars. It was assumed that a radioactive energy source was present and calculated the detailed heating and ionization of the gas. The evolution was studied of SNR in the very high pressure environment of a starburst galaxy.

Chevalier, Roger A.↗
NASA NTRS1974

A search for X-rays from supernova 1972e with Uhuru and OSO-7

The results of observations performed with X-ray detectors aboard OSO-7 and Uhuru at 13 different times ranging from 16 months before to 2 years after Sn 1972e maximum light are reported. Only one possible (3.2 sigma) positive result was found. The absence of any sizable flux contradicts the model of Shklovsky and imposes limitations on the model of Colgate and McKee.

Canizares, C. R.↗
NASA NTRS1990

A limit on the production of Ni-56 in a type I supernova

The data from the Gamma-Ray Spectrometer on the Solar Maximum Mission satellite have been searched for evidence of gamma-ray line emission from the decay of Co-56 in the type Ia SN, 1986G. No significant flux at either 847 or 1238 keV, the energies of the two strongest decay lines is found. Based on the data, a 3-sigma upper limit of 0.4 solar masses (D/3 Mpc)-squared on the amount of Ni-56 produced in the explosion is set. This value is consistent with radioactive models of type I light curves. For distances less than 3 Mpc, the limit is inconsistent with most models of SN Ia as thermonuclear explosions of white dwarfs.

Matz, Steven M.↗