High-Energy Astrophysics American and Soviet Perspectives/Proceedings from the U.S.-U.S.S.R. Workshop on High-Energy Astrophysics (1991) / Chapter Skim
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OBSERVING SN 1987A WITH THE INTERNATIONAL ULTRAVIOLET EXPLORER
OBSERVING SN 1987A WITH THE INTERNATIONAL ULTRAVIOLET EXPLORER
Pages 237-250
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From page 237... ...
IVE observations of SN 1987A began promptly after the discovery and have been frequent through 1988 and 1989, using the FES for photometry, low dispersion spectra for the supernova spectrum as described in the next section, high dispersion observations for the interstellar medium when the supernova was bright (see below) , and for circumstellar gas surrounding the supernova as the initial event faded (see below)
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From page 238... ...
Future observations will include a UV observation of the light echo, monitoring the decay of the circumstellar emission, and perhaps a glimpse into the enriched material that was formerly the interior of Sanduleak ~9 20Z Supernova 1987A in the Large Magellanic Cloud has moved the subject of supernovae from plausible argument to observational demonstration ~ a number of areas and the IUE observations have helped in essential ways. While the supernova was the first visible to the unaided eye since Kepler's 16~ supernova, retinal observations have not proved the most novel Instead, the advances in technology, including geosynchronous satellites, have provided the data for real insight.
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From page 239... ...
The indirect effects of the energy release are seen in the light curve, measured with the Fine Error Sensor on IUE, as presented in in the first section, but the direct measurement of the interior composition through ultraviolet lines will occur only after the opaque atmosphere turns transparent Clues to a possible neutron star remnant may also be embedded in the light curio for SN 1987A, but the resolution of these tantalizing questions lies in the future. OBSERVATIONS The first IUE spectra of SN1987A were taken from Goddard on the afternoon of Tuesday, February 24, about 4 hours after the report from the Central Bureau for Astronomical Telegrams.
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The product of velocity and age requires a temperature of order 100,000 K to produce the observed flub 1b press the UV obsenations back to the earliest possible moment, we have begun to examine the badly over-exposed images taken in the first attempts to get IUE spectra of SN 1987A In the depths of the absorption lines, and in the regions of the spectrum where {UK has the least sensitivity, some reliable measurements may be recovered which will help trace the arrival of the shock at the surface of the Sanduleak star. Following the dramatic changes of the first days, the IUE spectrum of SN 1987A has remained remarkably constant.
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From page 241... ...
These elements are important in comparing the observed composition for SN 1987A with the theoretical results for massive star evolution, and they are difficult to observe at optical wavelengths. Measurements from the Fine Error Sensor have proved surprisingly accurate and useful in monitoring the flux from SN 1987N Even though the FES was never intended as an accurate photometer, we have found that careful attention to calibration by a standard star during the same observing session produces a marked decrease in the random errors of FES measurements.
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From page 242... ...
The brightness of the supernova as a background source allowed much shorter exposures than previous studies of the ISM toward the LMC were compelled to use, and the resulting particle background in the data was much lower. Because the dine span for obtaining these exquisite data was
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From page 243... ...
short, there was little opportunity to study the time-dependent effects of the ionizing flash from SN 1987A, but the very high quality of the data that were obtained not only allowed them to confirm kinematic results obtained at higher resolution from the ground but to extend them by providing the chemical composition of the intervening absorbers. Several velocity components were detected in a wide range of ionization stages ranging from neutral gas to triply ionized carbon (de Boer et al.
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CIRCUMSTELLAR MATTERS Blue supergiants like SK -69 202 often have low density, high velocity stellar winds, but IUE observations of SN 1987A show that this star had a dense circumstellar shell that resulted from an interesting stellar history. The weak radio emission from SN 1987A ~Ibrtle et al.
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find N/C = 7.8 it 4 and N/O = 1.6 ~ 0.8. These are respectively factors of 37 and 12 higher man the solar values, implying that the gas has undergone substantial CNO processing.
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Key ingredients seem to be the lower heavy element abundance in the LMC, thorough mixing of hydrogen-burning products, and substantial mass loss as a red supergiant. One prediction based on the presence of a circumstellar shell is that the rapidly expanding debris, moving at 1/10 c, will strike the shell, at 1/2 light year, in the next several years.
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, then equal observed flmes would imptr that me integrated UV luminosity was about 10% of the bolometric luminosity radiated near the SN peak If this observation Is confirmed, it will provide a useful constraint on theoretical models of the outburst. While the case is not yet proven, the IUE results provide the tantalizing possibility of detecting a signal which was emitted two days before the IUE first pointed at SN 1987A' and which may prove useful in understanding the physics of supernova explosions.
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From page 248... ...
Employing the FES as an accurate photometer was not anticipated, but new calibration methods make those measurements quite helpful. No one predicted that IUE short-wavelength observations of narrow emission lines from a fluorescent circumstellar shell would be a major constraint on the late stages of stellar evolution for the EMC supernova, but a careful background subtraction technique has made this a reality.
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From page 249... ...
1989. Neutrino Astrophysics Cambridge University Press, Cambridge.
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From page 250... ...
250 AMERICAN AND SOYIET PERSPECTIVES McNaught, RH.
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