Astronomy and Astrophysics – Astrophysics
Scientific paper
Apr 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994pasau..11...83a&link_type=abstract
Astronomical Society of Australia, Proceedings, vol. 11, no. 1, p. 83-84
Astronomy and Astrophysics
Astrophysics
2
Emission Spectra, Magellanic Clouds, Radio Emission, Supernova Remnants, X Ray Sources, Astrophysics, Image Analysis, Radio Astronomy
Scientific paper
The source 1E0102.2-7219 was first identified as a possible supernova remnant (SNR) by Seward and Mitchell (1981, Astrophys. J., 243, 736) using the Einstein observatory, on the basis of its X-ray luminosity and spectral energy distribution. It is the second brightest X-ray source in the Small Magellanic Cloud. 1E0102.2-7219 was positively identified as a supernova remnant (SNR) by Dopita et al. (1981, Astrophys. J. Lett., 248, L105) who classified it as a member of the oxygen-rich class of SNRs. Narrow-band optical imaging with the Anglo-Australian Telescope revealed a large (O III)/H alpha ratio and a strong (O III) filamentary shell only 1.5 arcmin from the quoted X-ray position. Observations made with the Australia Telescope Compact Array (ATCA) at 4790 MHz by Amy and Ball (1993, Astrophys. J., 411, 761) revealed an almost complete shell of radio emission and a compact central component which contributes about 14% of the total flux density. The angular diameter of the outer shell of radio emission is around 40 sec which is consistent with the angular diameter of the 'emission-hole' discussed by Dopita et al. (1981) and with the high-resolution X-ray data. Using the ATCA data along with previously published data at 408 MHz and 843 MHz we determined the radio spectral index to be alpha = -(0.7 +/- 0.1). The compact central component has an angular diameter of approximately 18 sec determined by taking cross-cuts through the ATCA image at various position angles. There are at least two possible interpretations of this compact component: (1) it may be a bright spot on the surface of the radio shell (front or back), in which case it probably corresponds to a region of enhanced acceleration and is of no special interest; or (2) it may be a central or core component inside the radio shell. Such core components are often referred to as 'plerions' and are thought to be associated with a remnant pulsar produced in the supernova explosion. If this is the case, then SNR 1E0102.2-7219 would be only the second oxygen-rich SNR to exhibit a clear shell and plerionic component (see Staveley-Smith, these Proceedings). To determine the nature of this component, higher-frequency radio observations have been obtained which again clearly resolve the outer shell and compact component. As plerions typically have a flatter spectral index (alpha greater than or equal to -0.3) than SNR shells, we expect the relative flux contribution from the central component to increase with frequency if the plerionic interpretation is correct.
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