Radio observations of supernova 1987A

Proceedings of The Life Cycle of Dust in the Universe: Observations, Theory, and Laboratory Experiments — PoS(LCDU2013), 2014

The Astrophysical Journal, 2006

We present new (2004 July) G750L and G140L Space Telescope Imaging Spectrograph (STIS) data of the H and Ly emission from supernova remnant (SNR) 1987A. With the aid of earlier data, from 1997 October to 2002 October, we track the local evolution of Ly emission and both the local and global evolution of H emission. The most recent observations allow us to directly compare the H and Ly emission from the same slit position and at the same epoch. Consequently, we find clear evidence that, unlike H, Ly is reflected from the debris by resonant scattering. In addition to emission that we can clearly attribute to the surface of the reverse shock, we also measure comparable emission, in both H and Ly, that appears to emerge from supernova debris interior to the surface. New observations taken through slits positioned slightly eastward and westward of a central slit show a departure from cylindrical symmetry in the H surface emission. Using a combination of old and new observations, we construct a light curve of the total H flux, F, from the reverse shock, which has increased by a factor of $4 over about 8 yr. However, due to large systematic uncertainties, we are unable to discern between the two limiting behaviors of the flux: F / t (self-similar expansion) and F / t 5 (halting of the reverse shock). Such a determination is important for constraining the rate of hydrogen atoms crossing the shock, which is relevant to the question of whether the reverse shock emission will vanish in P7 yr. Future deep, low-or moderate-resolution spectra are essential for accomplishing this task. Subject headingg s: circumstellar matter -shock waves -supernova remnantssupernovae: individual (SN 1987A)

We present Murchison Widefield Array observations of the supernova remnant (SNR) 1987A between 72 and 230 MHz, representing the lowest frequency observations of the source to date. This large lever arm in frequency space constrains the properties of the circumstellar medium created by the progenitor of SNR 1987A when it was in its red supergiant phase. As of late-2013, the radio spectrum of SNR 1987A between 72 MHz and 8.64 GHz does not show any deviation from a non-thermal power-law with a spectral index of −0.74 ± 0.02. This spectral index is consistent with that derived at higher frequencies, beneath 100 GHz, and with a shock in its adiabatic phase. A spectral turnover due to free-free absorption by the circumstellar medium has to occur below 72 MHz, which places upper limits on the optical depth of ≤ 0.1 at a reference frequency of 72 MHz, emission measure of 13,000 cm −6 pc, and an electron density of 110 cm −3. This upper limit on the electron density is consistent with the detection of prompt radio emission and models of the X-ray emission from the supernova. The electron density upper limit implies that some hydrodynamic simulations derived a red supergiant mass loss rate that is too high, or a wind velocity that is too low. The mass loss rate of ∼ 5 × 10 −6 solar mass yr −1 and wind velocity of 10 km s −1 obtained from optical observations are consistent with our upper limits, predicting a current turnover frequency due to free-free absorption between 5 and 60 MHz.

The Astrophysical Journal, 2003

We present two-dimensional line profiles of high-velocity ($AE12,000 km s À1 ) Ly and H emission from supernova remnant 1987A obtained with the Space Telescope Imaging Spectrograph between 1997 September and 2001 September (days 3869-5327 after the explosion). This emission comes from hydrogen in the debris that is excited and ionized as it passes through the remnant's reverse shock. We use these profiles to measure the geometry and development of the reverse-shock surface. The observed emission is confined within $AE30 about the remnant's equatorial plane. At the equator, the reverse shock has a radius of $75% of the distance to the equatorial ring. We detect marginal differences (6% AE 3%) between the location of the reverse-shock front in the northeast and southwest parts of the remnant. The radius of the reverse shock surface increases for latitudes above the equator, a geometry consistent with a model in which the supernova debris expands into a bipolar nebula. Assuming that the outer supernova debris has a power-law density distribution, we can infer from the reverse-shock emission light curve an expansion rate (in the northeast part of the remnant) of 3700 AE 900 km s À1 , consistent with the expansion velocities determined from observations in radio (Manchester et al.) and X-ray (Park et al.; Michael et al.) wavelengths. However, our most recent observation (at day 5327) suggests that the rate of increase of mass flux across the northeast sector of the reverse shock has accelerated, perhaps because of deceleration of the reverse shock caused by the arrival of a reflected shock created when the blast wave struck the inner ring. Resonant scattering within the supernova debris causes Ly photons created at the reverse shock to be directed preferentially outward, resulting in a factor of $5 difference in the observed brightness of the reverse shock in Ly between the near and far sides of the remnant. Accounting for this effect, we compare the observed reverse-shock Ly and H fluxes to infer the amount of interstellar extinction by dust as EðB À V Þ ¼ 0:17 AE 0:01 mag. We also notice extinction by dust in the equatorial ring with EðB À V Þ % 0:02-0.08 mag, which implies dust-to-gas ratios similar to that of the LMC. Since H photons are optically thin to scattering, the observed asymmetry in brightness of H from the near and far sides of the remnant represents a real asymmetry in the mass flux through the reverse shock of $30%. We discuss future observational strategies that will permit us to further investigate the reverse-shock dynamics and resonant scattering of the Ly line and to constrain better the extinction by dust within and in front of the remnant.

Monthly Notices of The Royal Astronomical Society, 1998

We report the detection of the slow moving wind into which the compact supernova remnant SN 1997ab is expanding. Echelle spectroscopy provides clear evidence for a well resolved narrow (Full Width at Zero Intensity, FWZI ~ 180 km/s) P-Cygni profile, both in Ha and Hb, superimposed on the broad emission lines of this compact supernova remnant. From theoretical arguments we know that the broad and strong emission lines imply a circumstellar density (n ~ 10^7 cm^-3). This, together with our detection, implies a massive and slow stellar wind experienced by the progenitor star shortly prior to the explosion.

The Astrophysical Journal, 2011

We present the most sensitive ultraviolet observations of Supernova 1987A to date. Imaging spectroscopy from the Hubble Space Telescope-Cosmic Origins Spectrograph shows many narrow (∆v ∼ 300 km s −1) emission lines from the circumstellar ring, broad (∆v ∼ 10-20 × 10 3 km s −1) emission lines from the reverse shock, and ultraviolet continuum emission. The high signal-to-noise (> 40 per resolution element) broad Lyα emission is excited by soft X-ray and EUV heating of mostly neutral gas in the circumstellar ring and outer supernova debris. The ultraviolet continuum at λ > 1350Å can be explained by H I 2-photon (2s 2 S 1/2-1s 2 S 1/2) emission from the same region. We confirm our earlier, tentative detection of N V λ1240 emission from the reverse shock and present the first detections of broad He II λ1640, C IV λ1550, and N IV] λ1486 emission lines from the reverse shock. The helium abundance in the high-velocity material is He/H = 0.14 ± 0.06. The N V/Hα line ratio requires partial ion-electron equilibration (T e /T p ≈ 0.14-0.35). We find that the N/C abundance ratio in the gas crossing the reverse shock is significantly higher than that in the circumstellar ring, a result that may be attributed to chemical stratification in the outer envelope of the supernova progenitor. The N/C abundance ratio may have been stratified prior to the ring expulsion, or this result may indicate continued CNO processing in the progenitor subsequent to the expulsion of the circumstellar ring. Subject headings: supernovae: individual (SN 1987A)-shock waves-circumstellar matter * Based on observations made with the NASA/ESA Hubble Space T elescope, obtained from the data archive at the Space Telescope Science Institute. STScI is operated by the Association of Universities for Research in Astronomy, Inc. under NASA contract NAS 5-26555.

2008

We propose to use the unique instrumental capabilities of SOFIA to conduct imaging and spectroscopic studies of supernovae (SNe), of young supernova remnants (SNRs) for which the ejecta have not yet fully mixed with the ISM, and select regions in older remnants which are interacting with the ambient ISM. These observations will address key issues within NASA’s Visions for Science quest for discovering the origin, structure, evolution and destiny of the universe: What is the origin of dust in early universe? How efficient are supernovae in producing interstellar dust? How efficient are their blast waves in destroying, processing, or even forming dust as they expand into the circumstellar and interstellar medium? How do interstellar shocks facilitate chemical reaction on the surfaces of dust grains? The answers to these questions are crucial for understanding the evolutionary cycle of interstellar dust, the role of dust in the processing of starlight and in determining the thermal bal...

The Astrophysical Journal, 2008

Multiwavelength observations of supernova remnant (SNR) 1987A show that its morphology and luminosity are rapidly changing at X-ray, optical, infrared, and radio wavelengths as the blast wave from the explosion expands into the circumstellar equatorial ring, produced by mass loss from the progenitor star. The observed infrared (IR) radiation arises from the interaction of dust grains that formed in mass outflow with the soft X-ray emitting plasma component of the shocked gas. Spitzer IRS spectra at 5 -30 µm taken on day 6190 since the explosion show that the emission arises from ∼ 1.1 × 10 −6 M ⊙ of silicate grains radiating at a temperature of ∼ 180± 20 15 K. Subsequent observations on day 7137 show that the IR flux had increased by a factor of 2 while maintaining an almost identical spectral shape. The observed IR-to-X-ray flux ratio (IRX) -2is consistent with that of a dusty plasma with standard Large Magellanic Cloud dust abundances. IRX has decreased by a factor of ∼ 2 between days 6190 and 7137, providing the first direct observation of the ongoing destruction of dust in an expanding SN blast wave on dynamic time scales. Detailed models consistent with the observed dust temperature, the ionization timescale of the soft X-ray emission component, and the evolution of IRX suggest that the radiating silicate grains are immersed in a 3.5×10 6 K plasma with a density of (0.3−1)×10 4 cm −3 , and have a size distribution that is confined to a narrow range of radii between 0.023 and 0.22 µm. Smaller grains may have been evaporated by the initial UV flash from the supernova.

Nature, 2003

Large amounts of dust (>10 8 M ( ) have recently been discovered in high-redshift quasars 1,2 and galaxies 3-5 corresponding to a time when the Universe was less than one-tenth of its present age. The stellar winds produced by stars in the late stages of their evolution (on the asymptotic giant branch of the Hertzsprung-Russell diagram) are thought to be the main source of dust in galaxies, but they cannot produce that dust on a short enough timescale 6 (<1 Gyr) to explain the results in the high-redshift galaxies. Supernova explosions of massive stars (type II) are also a potential source, with models predicting 0.2-4M ( of dust 7-10 . As massive stars evolve rapidly, on timescales of a few Myr, these supernovae could be responsible for the high-redshift dust. Observations 11-13 of supernova remnants in the Milky Way, however, have hitherto revealed only 10 27 -10 23 M ( each, which is insufficient to explain the high-redshift data. Here we report the detection of ,2-4M ( of cold dust in the youngest known Galactic supernova remnant, Cassiopeia A. This observation implies that supernovae are at least as important as stellar winds in producing dust in our Galaxy and would have been the dominant source of dust at high redshifts.

AIP Conference Proceedings, 2009

Study of radio supernovae over the past 27 years includes more than three dozen detected objects and more than 150 upper limits. From this work it is possible to identify classes of radio properties, demonstrate conformance to and deviations from existing models, estimate the density and structure of the circumstellar material and, by inference, the evolution of the presupemova stellar wind, and reveal the last stages of stellar evolution before explosion. It is also possible to detect ionized hydrogen along the line of sight, to demonstrate binary properties of the presupemova stellar system, and to detect dumpiness of the circumstellar material. Along with reviewing these general properties of the radio emission from supernovae, we present our extensive observations of the radio emission from supemova (SN) 1993J in M 81 (NGC 3031) made with the Very Large Array and other radio telescopes. The SN 1993J radio emission evolves regularly in both time and frequency, and the usual interpretation in terms of shock interaction with a circumstellar medium (CSM) formed by a pre-supernova stellar wind describes the observations rather well considering the complexity of the phenomenon. However: 1) The highest frequency measurements at 85 -110 GHz at early times (< 40 days) are not well fitted by the parameterization which describes the cm wavelength measurements rather well. 2) At mid-cm wavelengths there is often deviation from the fitted radio light curves, particularly near the peak flux density, and considerable shorter term deviations in the declining portion when the emission has become optically thin. 3) At a time -^3100 days after shock breakout, the decline rate of the radio emission steepens from (t+^)/3 -^ -0.7to/3 -^ -2.7 without change in the spectral index (v+"; a-^ -0.81). However, this decline is best described not as a power-law, but as an exponential decay starting at day -^ 3100 with an e-folding time of -^ 1100 days. 4) The best overall fit to all of the data is a model including both non-thermal synchrotron self-absorption (SSA) and a thermal free-free absorbing (FFA) components at early times, evolving to a constant spectral index, optically thin decline rate, until a break in that decline rate at day -^3100, as mentioned above. Moreover, neither a purely SSA nor a purely FFA absorbing model can provide a fit that simultaneously reproduces the light curves, the spectral index evolution, and the brightness temperature evolution.