Visual Discovery of SN 1996X in NGC 5061.

(Robert Evans)

It was not until the IAU Circular was issued that we found out there had been an independent amateur photographic discovery of this supernova by Kesao Takamizawa of Japan. Attempts to verify our discovery operated without this knowledge.

Earlier in the week, 660 galaxies had been observed during two nights we had use of the 40 inch telescope at Siding Spring. These galaxies did not include either NGC 4027, site of the SN1996W or NGC 5061. So I had to try to cover the remaining galaxies in my search with the 41cm telescope at home.

The supernova in NGC 5061 was first seen with the smaller telescope about 10pm local time on Friday, April 12 (April 12.5 UT). My comparison photos were from the ESO "B" survey and the southern "J" survey, so it was easy to show the star was new.

Some years earlier I had heard about an asteroid that the Berkeley Automated Supernova Search had seen near this galaxy, so I was careful about the possibility of this new object being an asteroid, as well. As a result, I watched this star for three hours looking for any movement. I was afraid that this possible asteroid might be stationary or moving very slowly.

It was not easy to check for slight movements by the new star, and I thought there might have been a very slight movement of a few seconds of arc during the three hours. I also rang Queensland amateur Brendan Downes, and he took two CCD exposures. This enabled him to prove the star was a new object by comparison with the digitized sky survey on the internet, but could not solve the problem of any slight movement. Concern about the "stationary asteroid" possibility meant that I did not suggest to Brendan that we continue these CCD observations through the night, in order to eliminate the question of movement by that means. In this way we could, perhaps, have been in contact with the Central Bureau at least fifteen hours earlier than what actually happened.

It was not untill late next day that Rob McNaught told me asteroids at opposition generally move at about thirty seconds of arc per hour. This alone showed that the new object was most probably a supernova, but it was the wrong time of the day for me to try leaving phone messages at the Central Bureau. Therefore it was planned that Gordon Garradd would use his CCD the next night, work out an exact position for the supernova, and would report e-mail all the details to the Central Bureau. This would also doubly check against any movement.

The galaxy is a normal elliptical galaxy, the kind that does not produce very many supernovae by comparison. Thus the supernova would contribute to the exploration of several theories about peculiarities of supernovae in this kind of galaxy.

The position of supernova in relation to the parent galaxy is that the supernova is a long way out from the nucleus, even outside what it appears to be the edge of the galaxy in some photos. Because of its position outside the galaxy, the supernova can be more easily observed with spectograph or photometer, isolating it from the background glare of the galaxy, and should also be observable for a longer period than objects closer to the middle of the galaxy.

Very prompt spectral observations, made at a number of places, showed that this is a classical Type Ia supernova around maximum light at magnitude 13.3.

This report is issued on April 22, and the supernova still remains at the same brightness as when it was first found.

Here are some images from supernova observers:

  • Kesao Takamizawa discovery image was made with a 10cm f/4.0 Pentax lens and TMax 400 film, on April 12, 1996.
  • Brendan Downs was the first to confirm the discovery on April 13. His image was taken with a Meade 12inch LX200 and a ST-7 CCD from his backyard observatory located at Ipswich, Queensland, Australia.
  • Diego Rodriguez of Madrid, Spain, has imaged 1996X on April 15. His image is here visible.
  • Marcel Geltner of Steward Observatory Campus Station in Arizona, USA, has imaged 1996X on April 16. His image was made with a 21" f/6.1 telescope and an ST6 CCD camera.
  • Giulio Scarfi' and Luciano Zannoni have imaged 1996X on April 19. Their image was made at Mt. Visseggi observatory near La Spezia (Italy) with a 40cm Ritchey-Cretien f/8 telescope and ST-6 CCD camera.
  • Mark Armstrong of Rolvenden, UK, has imaged 1996X on April 23. His image was taken with a with a Meade 10inch LX200 and a CCD Starlight Xpress.
  • Spectrum of 1996X obtained with 1.2 meter telescope at the Harvard-Smithsonian Center for Astrophysics during April.
  • Image of 1996x obtained with 1.2 meter telescope at the Harvard-Smithsonian Center for Astrophysics on April 16.