FIVE YEARS OF MID-INFRARED EVOLUTION OF THE REMNANT OF SN 1987A: THE ENCOUNTER BETWEEN THE BLAST WAVE AND THE DUSTY EQUATORIAL RING
- Observational Cosmology Lab., Code 665, NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States)
- CRESST/UMBC, Code 665, NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States)
- DSM/DAPNIA/Service d'Astrophysique, CEA/Saclay, F-91191 Gif-sur-Yvette (France)
- Department of Astronomy and Astrophysics, Pennsylvania State University, 525 Davey Laboratory, University Park, PA 16802 (United States)
- Harvard-Smithsonian, CfA, 60 Garden Street, MS-19, Cambridge, MA 02138 (United States)
- Osservatorio Astronomico di Trieste, Via Tiepolo 11, Trieste (Italy)
- Gemini Observatory, Southern Operations Center, c/o AURA, Casilla 603, La Serena (Chile)
- Department of Astronomy, University of Minnesota, 116 Church Street, SE, Minneapolis, MN 55455 (United States)
We have used the Spitzer satellite to monitor the mid-IR evolution of SN 1987A over a five year period spanning the epochs between days {approx}6000 and 8000 since the explosion. The supernova (SN) has evolved into a supernova remnant and its radiative output is dominated by the interaction of the SN blast wave with the pre-existing equatorial ring (ER). The mid-IR spectrum is dominated by emission from {approx}180 K silicate dust, collisionally heated by the hot X-ray emitting gas with a temperature and density of {approx}5 x 10{sup 6} K and {approx}3 x 10{sup 4} cm{sup -3}, respectively. The mass of the radiating dust is {approx}1.2 x 10{sup -6} M{sub sun} on day 7554 and scales linearly with IR flux. Comparison of the IR data with the soft X-ray flux derived from Chandra observations shows that the IR-to-X-ray flux ratio, IRX, is roughly constant with a value of 2.5. Gas-grain collisions therefore dominate the cooling of the shocked gas. The constancy of IRX is most consistent with the scenario that very little grain processing or gas cooling has occurred throughout this epoch. The shape of the dust spectrum remained unchanged during the observations while the total flux increased by a factor of {approx}5 with a time dependence of t'{sup 0.87{+-}0.20}, t' being the time since the first encounter between the blast wave and the ER. These observations are consistent with the transitioning of the blast wave from free expansion to a Sedov phase as it propagates into the main body of the ER, as also suggested by X-ray observations. The constant spectral shape of the IR emission provides strong constraints on the density and temperature of the shocked gas in which the interaction takes place. Silicate grains, with radii of {approx}0.2 {mu}m and temperature of T {approx} 180 K, best fit the spectral and temporal evolution of the {approx}8-30 {mu}m data. The IR spectra also show the presence of a secondary population of very small, hot (T {approx}> 350 K), featureless dust. If these grains spatially coexist with the silicates, then they must have shorter lifetimes. The data show slightly different rates of increase of their respective fluxes, lending some support to this hypothesis. However, the origin of this emission component and the exact nature of its relation to the silicate emission is still a major unsolved puzzle.
- OSTI ID:
- 21464694
- Journal Information:
- Astrophysical Journal, Vol. 722, Issue 1; Other Information: DOI: 10.1088/0004-637X/722/1/425; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
COSMOLOGY AND ASTRONOMY
COSMIC X-RAY SOURCES
DUSTS
EXPLOSIONS
INFRARED SPECTRA
SATELLITES
SILICATES
SOFT X RADIATION
STAR EVOLUTION
SUPERNOVA REMNANTS
TIME DEPENDENCE
COSMIC RADIO SOURCES
COSMIC RAY SOURCES
ELECTROMAGNETIC RADIATION
EVOLUTION
IONIZING RADIATIONS
OXYGEN COMPOUNDS
RADIATIONS
SILICON COMPOUNDS
SPECTRA
X RADIATION