SN1987A's Twentieth Anniversary (Forwarded)
- From: Andrew Yee <ayee@xxxxxxxxxxxxxxxxxxxxxx>
- Date: Sun, 25 Feb 2007 05:20:37 GMT
ESO Education and Public Relations Dept.
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Contacts
Roberto Gilmozzi, Bruno Leibundgut, Jason Spyromilio
ESO
Phone: +49 89 3200 6667, +49 89 3200 6295, +49 89 3200 6411
John Danziger
OAT-INAF, Trieste, Italy
Phone: +39 040 3199 223
Patrice Bouchet
Observatoire de Paris, France
Email: pbouchet (at) mesiog.obspm.fr
ESO Science Release 08/07
For Immediate Release: 24 February 2007
SN1987A's Twentieth Anniversary
Looking back at 20 Years of Observations of this Supernova with ESO
telescopes
The unique supernova SN 1987A has been a bonanza for astrophysicists. It
provided several observational 'firsts,' like the detection of neutrinos
from an exploding star, the observation of the progenitor star on archival
photographic plates, the signatures of a non-spherical explosion, the
direct observation of the radioactive elements produced during the blast,
observation of the formation of dust in the supernova, as well as the
detection of circumstellar and interstellar material.
Today, it is exactly twenty years since the explosion of Supernova 1987A
in the Large Magellanic Cloud was first observed, at a distance of 163,000
light-years. It was the first naked-eye supernova to be seen for 383
years. Few events in modern astronomy have met with such an enthusiastic
response by the scientists and now, after 20 years, it continues to be an
extremely exciting object that is further studied by astronomers around
the world, in particular using ESO's telescopes.
When the first signs of Supernova 1987A, the first supernova of the year
1987, were noticed early on 24 February of that year, it was clear that
this would be an unusual event. It was discovered by naked-eye and on a
panoramic photographic plate taken with a 10-inch astrograph on Las
Campanas in Chile by Oscar Duhalde and Ian Shelton, respectively. A few
hours earlier, still on 23 February, two large underground detectors:- in
Japan and the USA:- had registered the passage of high-energy neutrinos.
Since SN 1987A exploded in the Large Magellanic Cloud (LMC), it was only
accessible to telescopes in the Southern Hemisphere, more particularly in
Australia, South Africa, and South America. In Chile, ESO's observatory at
La Silla with its armada of telescopes with sizes between 0.5 and 3.6-m,
played an important role.
Astronomers John Danziger and Patrice Bouchet, who were there at the time,
recall: "When astronomers at La Silla arrived for the ritual afternoon tea
at 4pm on the 24th February 1987 after the previous night's clear
observing, they were greeted by the news that a supernova had been
detected in the LMC the previous night. The tea-time ritual of groggy
astronomers quietly sipping their tea was transformed, to be succeeded by
flurries of excited but still to some extent uncoordinated planning.
Nobody doubted for one second that the sky would be clear and there would
be excitement galore in the days and nights ahead. And indeed there was!
A large observatory such as La Silla with its many telescopes can be
considered like a naval fleet consisting of many ships from torpedo boats
to cruisers and even aircraft carriers. La Silla had them all. All
observers were encouraged to plan for observing SN1987A by whatever means
at their disposal."
"Ironically, the supernova was too bright for the state-of-the-art
4m-class telescopes and some of them had to be stopped down, e.g. by
half-closed telescope covers," says Jason Spyromilio (ESO). Some of the
smaller telescopes took their chance. The 61-cm Bochum telescope on La
Silla was used, on a nearly daily basis for more than a year, to measure
optical spectroscopy with photometric accuracy. Since the LMC is
circumpolar for most southern observatories, this also meant that there
exists an uninterrupted record of the photometry and spectroscopy; else
part of the peak phase, which lasted into May of 1987, would have been
missed.
By July, the first conference on SN 1987A, organised by John Danziger, had
already taken place at ESO in Garching to be followed by several others
during that year and following years.
The optical light curve of SN 1987A was rather different from those of
previously observed core-collapse supernovae. The old models of spherical
explosions had to be revised. The spectroscopic evolution provided further
evidence for asymmetries in the explosion. The 'Bochum event' was a rapid
change in the line profile observed with the Bochum telescope on La Silla.
It is the signature of a radioactive blob rising from the inner ejecta to
the surface. "The picture emerging from the observations of the first
several weeks was certainly more complex than what had ever been assumed
of supernovae before," says Bruno Leibundgut (ESO).
The 1-m telescope at La Silla was also extensively used in daytime
observing the supernova in the near- and mid-infrared for more than one
year after the explosion. A clear excess emission developed in the
near-infrared already 10 days after the explosion, the origin of which is
still not fully understood. It was most probably due to circumstellar
material that was lighted up by the explosion.
Dust condensation in the ejecta was discovered by spectroscopy about 500
days after the explosion. Macroscopic dust grains partially covered the
ejecta, and most probably still do. They might explain why no compact
object is seen at the location of the supernova.
In 1989, when the NTT came into operation, it imaged for the first time
the circumstellar ring around SN 1987A. And, about three years after the
explosion, NTT images revealed a circumstellar structure around SN 1987A
which resembled the triangular hat which Napoleon wore. Napoleon's hat
gave the first opportunity for a 3-dimensional view of SN 1987A.
"The existence of the ring presents an unsolved puzzle for SN 1987A," says
Roberto Gilmozzi (ESO). "Even though it is not clear how to construct such
a ring, it is likely that the star that exploded as SN 1987A had a
companion."
When ESO's Very Large Telescope came into operation, the interest in the
supernova had not faded away. Far from it! Observations were done with the
VLT's many instruments, including FORS, UVES, ISAAC, and VISIR, to probe
in more detail the surroundings of the explosion. More recently, adaptive
optics instruments, which compensate for the blurring effect of the
atmosphere, and so can see as if they were in space, have also been used.
The NACO instrument has obtained amazing images of the rings, while
SINFONI has been used to study the changes in the rings' appearances and
the evolution of the spectral lines.
"SN 1987A was full of surprises and it remains unique amongst the known
supernovae," says Leibundgut. "Not only was it the closest supernova for
several centuries, it was also very peculiar, coming from a blue
supergiant progenitor, with a circumstellar environment unlike any other
supernova known. We will certainly continue to monitor its evolution for
many years to come."
One goal will be to find the possible compact object that should have
survived the dramatic explosion. But until now, this remnant has proved
elusive.
More Information
Two articles in the forthcoming issue of ESO's Messenger discuss SN 1987A:
* "SN1987A at La Silla: The early days", by Ivan John Danziger and Patrice
Bouchet.
* "Twenty Years of Supernova 1987A" by Claes Fransson, Roberto Gilmozzi,
Per Gröningsson, Reinhard Hanuschik, Karina Kjær, Bruno Leibundgut, and
Jason Spyromilio
National contacts for the media:
Belgium: Dr. Rodrigo Alvarez, +32-2-474 70 50
Finland: Ms. Tiina Raivo, +358 9 7748 8369
Denmark: Dr. Michael Linden-Vørnle, +45-33-18 19 97
France: Dr. Daniel Kunth, +33-1-44 32 80 85
Germany: Dr. Jakob Staude, +49-6221-528229
Italy: Dr. Leopoldo Benacchio, +39-347-230 26 51
The Netherlands: Ms. Marieke Baan, +31-20-525 74 80
Portugal: Prof. Teresa Lago, +351-22-089 833
Sweden: Dr. Jesper Sollerman, +46-8-55 37 85 54
Switzerland: Dr. Martin Steinacher, +41-31-324 23 82
United Kingdom: Mr. Peter Barratt, +44-1793-44 20 25
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