[vsnet-chat 631] from the record of SN 1993J

[Taichi Kato <tkato>]

Dear ISN people, the CBAT members, and vsnet-chat members,

    Just for the record.  I have successfully retrieved articles from my
log file of SN 1993J showing how efficiently the network worked at the
very earliest stage of discovery confirmation and observations.  Hope
this actual time sequence would help the discussion of SN discovery and
confirmation matters.

Best regards,
Taichi Kato
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    The first alert of SN 1993J reached me via Novanet, just before noon
of 1993 Mar. 30, local time.  J. Mattei of the AAVSO sent this alert
at around 01h 56m UT (Mar. 30), addressing the discovery of a possible
supernova in M81 by Francisco Garcia Diaz.  This article stated that
the object was detected visually by him on Mar. 28.86 UT, and confirmed
using a CCD by Diego Rodriguez on Mar. 29.1 UT.  So it took nearly a day
this first alert to be known by world-wide observers after Rodriguez's
confirmation.  This alert described the position of the object as "200
arcsec south and 210 arcsec west of the nucleus, and is about 25 arcsec
to the northeast of a 14.0 magnitude star shown on finder charts of this
galaxy by the AAVSO and those by G. D. Thompson and J. T. Bryan".

   About three hours after this alert, S. Starrfield forwarded a message
to Novanet that the supernova was "confirmed" visually by an ASU student.
He also relayed an updated relative position to the galaxy.

   At about 06h 02m UT, P. Garnavich posted to Novanet the first spectro-
scopic observation of the supernova, taken at 06h 00m UT, suggesting a
very early type-II.  This spectroscopic observation was also reported
(at the bottom lines) in IAUC No. 5731.

   A. Filippenko sent almost simultaneously (06h 03m UT) an alert article
calling special attention to this object, and suggested how to make
useful spectrophotometric and multiwavelength photometry.  He noted that
the chance of initial infrared observations at the Palomer 5-m was missed
due to the large positional error in the initial report [if only there
was WWW and a displayed image, this misfortune would not have occurred..]

   Thanks to these alert messages and adequate suggestions, many observers
could follow the earliest development of this supernova, and western
observers were given enough time to optimize their observations:
BVRI-photometry started on Mar. 30.19 UT (Richmond), well before the
discovery was announced in IAUC issues, and U-measurement on Mar. 30.89 UT
(Penny at La Palma) when the ultraviolet flux was dramatically decreasing.
The earliest (to my knowledge) visual observation outside the discoverer's
group was apparently done by T. McGrath on Mar. 30.17 UT, and a number of
experienced variable star observers just followed.

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