A Search for Radio-Loud Supernovae

Elaine M. Sadler, Duncan Campbell--Wilson, PASA, 14 (2), in press.

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A five-year survey of southern spiral galaxies with MOST

Following on from the pilot study, we have now begun a five-year program to search a larger sample of galaxies for radio supernovae. To have the best chance of detecting RSNe, and hence determining their true frequency, we restrict the search to galaxies which are sufficiently nearby that most RSNe should be detectable above our nominal MOST detection limit of 10mJy.

We therefore chose a subset of the RSA galaxy sample (also monitored by Evans), using the following criteria:

  • The galaxy is in the RSA Catalog.
  • It is a spiral or irregular, i.e. type Sa or later (in general, E and S0 galaxies produce only Type Ia SNe, whereas all the known RSNe appear to be Type II or Type Ib SNe).
  • It is nearby (vtex2html_wrap_inline582 1400 km/s).
  • It lies south of tex2html_wrap_inline584 declination (set by the declination limit of the MOST).
  • The LMC and SMC are excluded because they are too large for us to cover effectively.

This gives us 81 target galaxies, of which 75 are also in the Evans et al. (1989) sample of RSA galaxies monitored optically and 33 have already been observed at least once with MOST (9 of them in our pilot study). We aim to observe each of these galaxies at least twice over the 5-year period 1993-98.

What kind of limits should this study set on the radio supernova rate? Scaling from the pilot study, we should reach total surveillance times of at least 2500tex2html_wrap_inline474 years/10tex2html_wrap_inline392Ltex2html_wrap_inline394 for objects like 1986J and 625tex2html_wrap_inline474 years/10tex2html_wrap_inline392Ltex2html_wrap_inline394 for objects like 1978K.

If no RSNe were actually detected, our upper limit for the RSN rate would be roughly tex2html_wrap_inline598 /century/10tex2html_wrap_inline392Ltex2html_wrap_inline394 for objects like 1986J and tex2html_wrap_inline604 /century/10tex2html_wrap_inline392Ltex2html_wrap_inline394 for objects like 1978K. This would allow us to say that no more than 3% and 12% respectively of Type II SNe are RSNe at the levels of 1986J and 1978K.

It is likely that the detection limits adopted for the pilot study (10mJy and 20% variation in flux density) are over-cautious, and that careful subtraction would allow us to reach detection limits of perhaps 2-3mJy. In this case, the surveillance time associated with each observation would of course be correspondingly higher.

A byproduct of this search will be a uniform set of radio images of southern spiral galaxies, most of which have not previously been mapped by any radio telescope.


Next Section: References
Title/Abstract Page: A Search for Radio-Loud
Previous Section: Optical supernovae in the
Contents Page: Volume 14, Number 2

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