Supernova 1993J in M81
SN 1993J appeared in NGC 3031 (M81) , a galaxy located in Ursa Major ,
12 m.l.y. far away from us, has been one of the brightest an best studied
SNe of the modern Astronomy.
It has been the brightest SN appeared in the northern Hemisphere in the
latest 21 years.
This is probably the SN with a more exact knowledge about the right moment
of the explosion.
It has been monitored and studied by the most sophisticated professional
telescopes, this includes Hubble, M. palomar , Roque de los Muchachos ,
and VLA telescopes, and Rosat , Asca, IUE.... Satellites..
SN 1993J was discovered on the 28th of March , Sunday night , By Francisco
Garcia Díaz , amateur astronomer living in Lugo , Spain with a 10"
telescope. Francisco is an active member of M1.
This group was created five years ago by M.A.A. members Diego Rodriguez
, José Ripero and Francisco Pujol. Since the very begining we were
aware that to find a SN was an extremely difficult task, but there was
Robert Evans example , amateurs astronomer with 26 discoveries . This fact
encouraged us to keep observing and try to find a new small point not included
in the M. Palomar images or in the Thompson Bryan charts.
The group gathered botch , equipment and bibliography to do SN hunting
( RealSky Thompson-Bryan charts , CCD Buil-Thouvenot , and Lopez Alvarez
Atlases, etc...) We also own a computer program able to provide asteroid
appulses to deep-sky objects , and therefore , to clarify possible false
alarms due to asteroids.
Francisco Garcia , joined the group three years ago. In the five years
prior to the discovery we achieved 25.000 negative observations checking
650 different galaxies . We have also been able to observe and monitor
visually , photographically and with CCD , SN 1989 in M66 , (This SN was
one of the reasons to create the group ), SN 1991T in NGC 4527 , SN 1991X
in NGC 4902 and SN 1992G in NGC 3294.
Chronology of the discovery of SN 1993J in M 81
Sunday, 28th of March 1993
Francisco García , member of the SN Search Group M1 , observed a
suspected star in the galaxy NGC 3031 (M81) , located in Ursa Major , He
estimated it to be m=11.8 . He called inmediately Jose Carvajal , M1 member
also , asking him to verify in the Asteroids Appulses computer program
, whether there was an asteroid.While Francisco Observes again the galaxy
, Jose Carvajal calls Diego Rodriguez, another M1 members , asking him
to take a CCD image of the galaxy and thus , to confirm that the suspected
new star was present. In that position nothing appeared in the Thonson
Bryan , Buil-Thouvenot and Hubble Atlases. Diego Rodriguez called Enrique
Pérez, Spanish astronomer astronomer observing that night with 2.5
meters aperture Issaac Newton Telescope , in the Roque de los Muchachos
Observatory in Canary Island. Enrique replied he was not sure whether he
would be able to confirm the SN .
Monday, 29th of March 1993
The twilight of Monday 29th , found Diego Rodriguez , Francisco Pujol ,
Francisco Garcia , and José Ripero , waiting anxiously , the first
star of the night to confirm the suspected new SN... Actually , the star
was in the same position and showed a brightness of m=11 , estimations
were made both , visually and with CCD .
After this confirmation we called urgently Dr. Wamsteker , Scientific Director
of VILSPA , we also sent him by Fax a copy of the CCD image taken by Diego
Rodriguez. Afterwards we called Janet Mattei (AAVSO) to confirm the SN
. Finally we talked to our good Australian Friend Rovert Evans the amateur
with more SNe decoveries. In the same night , a few hours late , the first
spectrum of the SN was taken by Enrique Pérez in the 2.5 meters
aperture Isaac Newton Telescope.
Wednesday, 31th of March 1993
Early in the morning we received , at last , The IAU Circular 5731 announcing
the discovery of SN 1993J by Francisco Garcia -Diaz of Lugo Spain , and
the SN group M1 of Madrid Astronomical Association. El PAIS , the most
important Spanish newspaper , covers the information , and remarks the
importance of this event discovered by Madrid amateurs astronomers.
Important highlights of this covery
There are a few aspects to be pointed out related to this discovery:
1.-The very short time that elapsed between the visual discovery and the
CCD image.This became crucial to know the exact SN position , and thus
, to make easier the spectral confirmation by professional telescopes.
2.- We were also very fast confirming this was neither an asteroid , nor
a variable star lurking near the galaxy, Just a few minutes after the first
sight , it had already been confirmed by another observer.
3.- A second visual confirmation , performed 24h later by most M1 members
definitely assured this star was a real SN.
4.- All this was possible due to the existence of an organized team with
good experience and resources to go ahead without doubst in case a SN arises.
Importance and peculiarities of SN 1993J
The following reasons make SN 1993J very peculiar:
This SN appeared in very close galaxy . Whit the exception of SN 1987A
, found in the Large Magellenic Cloud , modern Astronomy has never aimed
its telescopes to a so near SN.
The explosion time is known with just a few hours of uncertainty . Actually
, there is a photographic observation performed on saturday ,27th of March
, at 21h45 (UT) . In the picture take by the French amateur J.C. Merlin
, nothing brigther than m=16 appeared in the SN position .
On Sunday 28th of March , A.W. Neely , American amateur took some CCD images
at 7h15 (UT) . At this time the SN was already present and showed a brightness
of m=13.7 .
On Sunday 28th of March , at 21h45 (UT) , Francisco Garcia made discovery
and estimated the SN to be at m=11.8
According to last news sent By Dr. de Vaucouleurs , professional astronomers
consider explosion began on the midday of saturday 27th of March. This
assumption is based on theoretical models about the evolution of the SN
brightness . For this calculation it is assumed that the initial brightness
of the progenitor
star should be m=20.8
SN 1993J showed twon maximum
of light. The first happened one day after the discovery , while the second
one occurred three weeks later.
A nearly unique spectral behaviour . SN 1987K appeared in NGC 4651 (Virgo)
, and SN 1993J in M81 , are the only ones that moved from type II when
the explosion , to type Ib , some time later . Therefore , SN 1993J represents
a repetition of very unusual behaviour.
SN 1987K was discovered by Berkeley Automated SN Search Group , led by
Pennypacker , in late July 1987 ; this SN achieved m=14.2 . Based on its
spectrum , it was initially classified as type II (plateau) to a type Ib
. Actually , in the spectrum taken on May 11 1993 , all alfa hydrogen lines
had vanished . According to Astrophysic theories , wide and clear oxigen
an calcium lines will fill the spectrum in the coming weeks.
Progenitor star mass has been estimated to be in the rage of 10-20 M.O.
To Dr. Wilhem Wamsteker , Director of Villafranca Tracking Station, (VILSPA),
and to all his team.
To Mrs. Janet Mattei , AAVSO Director , she helped us a lot spreading through
electronic-mails the new of our discovery to most Observatories and Universities.
To SNe Group ,of IAC (Intituto Astrofisica de Canarias), conducted by Dr
. Mr. Francisco Sánchez , and specially to Mr . Gaby Gómez
, member of this group , for the continuous information provided about
the behaviour of SN 1993J.
To all wives , mothers, girlfriens , sons and daughters ... of M1 group
members , to bear our madness until the new about the discovery arrived
. And obviously , to share their lives with us and with SN 1993J . We are
in debit for your understanding and help...
SN 1993J Light curve.
Progenitor of SN 1993J
Actualizado el 5 de Mayo de 1997