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Swift Newsletter
Issue 6/January 2007
Welcome Message from PI Neil Gehrels
The last six months of Swift gamma-ray burst science have been what I would call a  swirl of complexity. In conference talks and
hallway conversations, the discussion inevitably turned to new questions raised by Swift observations. Quite a few seem to be coming to a head at this time.
What is the distance to short gamma-ray bursts?
The first distance measurements in 2005
pointed toward low distances - much less
than long bursts. Now it appears that there
is a wide range from low to high.
- How can long and short bursts be distinguished
from each other? It sounds easy - use the
duration of the event to decide. However,
we are finding that a good fraction of short
bursts have long-lasting tails that can easily
be confused with long bursts.
- Do long gamma-ray bursts all have
accompanying supernovae? Models
predict that when the core of a massive
star collapses to a black hole and produces
a gamma-ray burst, there is enough energy
deposited in the star to explode it. Also,
there is observational evidence of four
nearby bursts with coincident supernovae.
However, this summer Swift detected two
nearby bursts that appear to be in the long
category but have no supernovae detected
to stringent limits.
- Are the gamma rays in a burst beamed in
narrow jets toward us? Prior to Swift there
seemed to be strong evidence for beaming
in the fading optical light after bursts. We
still believe there must be collimation,
but the Swift X-ray and optical afterglow
data are complex and are resisting simple
interpretations.
Is this a cause for alarm? No, it is precisely
the way progress is made. The data are
guiding us down the crooked path toward
correct answers and ultimate understanding.
Also, what could be more fun than having
new mysteries to unravel!
One of the venues for discussing the above
topics was the gamma-ray burst meeting
in London this September. It was a Royal
Society Discussion meeting and was expertly
organized by Alan Wells, Keith Mason, and
Martin Rees. It was a fabulous conference
with scientists of many different areas of
interest and expertise discussing the new
findings from Swift and other observatories.
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Burst of Controversy May Signal New Class of GRBs
By: Derek Fox, Penn State University
A gamma-ray burst detected by Swift on June 14, 2006, has been stirring up controversy within the GRB research community. The burst lasted for 100 seconds, which should easily qualify it for membership in the class of "long bursts" that have been subject to detailed study for more than nine years. At the same time, though, it exhibits some properties of the "short bursts" that were first identified and studied in detail last year. The unique combination of characteristics has theorists and observers scratching their heads, and has caused them to dub this burst, GRB 060614, the possible first example of a new class of "hybrid gamma-ray bursts."
Observations from Swift raised the first questions
about this event. In a paper for the magazine Nature,
led by Neil Gehrels, the satellite team describes
one paradoxical aspect of the burst. If we think of a
gamma-ray burst as a short piece of music, then the
more energetic gamma-rays in the burst correspond
to higher notes, and the less energetic gamma-rays
correspond to lower notes. For a typical long burst,
the lower notes lag the higher notes by a fraction of a
second - a slight asynchrony. The 100 second-long
piece that was GRB 060614, however, was played
in strictest unison across the whole gamma-ray keyboard.
Bursts from the short class - those lasting
less than two seconds - typically exhibit this sort of
synchrony, but it had never before been seen from
such a long burst.
Subsequent observations by ground-based telescopes
and the Hubble Space Telescope added
further wrinkles. First, the burst was found to lie
within a bright, relatively nearby galaxy, 1.6 billion
light-years away in the constellation Indus. GRBs
at such a close distance are rare, and whenever
one can be identified, astronomers like to study it
closely. In every previous case where a long burst
was subjected to such study, it rewarded astronomers
by blossoming, two weeks after the event,
into a brilliant and long-lived supernova. Not so
GRB 060614 - it was seen instead to disappear
without a trace. This too, although a novel behavior
for long bursts, has been the typical pattern
for short ones - a point made by the authors of
three additional papers in Nature, led by Massimo
Della Valle, Johan Fynbo, and Avishay Gal-Yam.
The difference between long and short bursts is a
deep one. Because of their habit of turning into
supernovae, the long bursts are considered to result
from the collapse and explosion of a shortlived
massive star, ten or so times the mass of the
Sun. Meanwhile, the occurrence of some short
bursts in old, red galaxies has demonstrated that
they cannot be produced by such massive stars - rather, they are thought to be due to the inspiral
and merger of two old, dead stellar remnants, either
neutron stars or black holes.
So: was GRB 060614 produced by a single massive
star, by two merging stellar remnants, or by
something else entirely? It's an important question,
and without a clear answer at this time. All
that can be said is that this event is the best candidate
in a long time for something totally new, a "hybrid burst" that might just represent
the most exotic class of them all.
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Swift in the News
8/30/06 - Caught in the Act, Scientists Watch
Supernova Explode - Scientists using NASAs Swift satellite and a combination of orbiting and ground-based observatories have for the first time caught a supernova in the act of exploding. +More
HEAD Meeting News
10/4/06 - Mug Shots of Supernovas Reveal Two
Key Findings -
Scientists using NASAs Swift satellite have observed
two dozen recent star explosions, called
supernovae, quickly after the event and have
discovered never-before-seen properties. +More
10/5/06 - NASA Performs Headcount of Local
Black Holes
NASA scientists using the Swift satellite have
conducted the first complete census of galaxies
with active, central black holes, a project that
scanned the entire sky several times over a ninemonth
period. +More
10/5/06 - Scientists Determine The Nature
of Black Hole Jets - NASA and Italian scientists using Swift have provided
the most compelling evidence to date that
black hole jets are made of protons. +More
11/6/06 - Monster Stellar Flare
Dwarfs All Others -
Swift detected a flare with one hundred million
times the energy of a typical solar flare from a
star in the binary system II Pegasi. +More
11/21/06 -Twin Star Explosions Fascinate
Astronomers -
A galaxy that has produced four supernovae since
1980 lit up with two at once, in an amusing image
taken by the Swift UVOT and featured in a
Penn State release.
12/21/06 -Swift Finds New Kind of Black Hole
Explosion -
Studies of two bursts that appear to be a new kind
of explosion resulted in four papers in the December
21, 2006 issue of Nature. +More
For links to all of these press releases and images, see: http://swift.gsfc.nasa.gov/docs/swift/news/
By: Lynn Cominsky
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By: John Nousek, Penn State University
Swift continues operating smoothly and efficiently.
We have gained better understanding of the observatory
and the instruments, so we have been able to
make upgrades to their performances.
By the time you read this, we will have crossed the
milestones of discovering more than 200 new GRBs
(with prompt observations of more than 75%). We
will have conducted more than 60,000 slews of the
observatory (a slew is when we move from one target
to the next). Approximately 98% of the usable
observing time (i.e. when we are outside the South
Atlantic Anomaly) has been spent collecting BAT
data for the detection of new GRBs and for the
BAT hard X-ray all-sky survey.
Our Italian colleagues have continued their excellent
support by providing more than 9000 ground
passes from their Malindi tracking station in Africa
at better than 98% success rate. Our Penn State
mission operations center has successfully captured
more than 99% of the total data generated by Swift.
Our Goddard Space Flight Center Swift Science Center and Swift Data Center have continuously
processed data and supported user requests for all
the Swift data. The United Kingdom continues
with its active support of the UVOT and XRT
teams and the UK Data Center. Italy also provides
a Data Center and support for the XRT team.
Goddard has supported the BAT team and the allsky
BAT survey data analysis.
In addition to GRBs, Swift has conducted a vigorous
Target of Opportunity program with more
than 200 approved targets. These targets range
from observations of comets with the XRT and
UVOT, to nearby supernova, to distant AGNs,
and previously unknown sources of gamma rays
and ultra-high energy (TeV) photons discovered
by INTEGRAL, HESS and VERITAS.
Approximately one out of every three days the
Flight Operations Team responds outside normal
working hours to command the spacecraft for commanding
Swift to chase new science targets (usually
new GRBs), to capture data missed by the routine
downloads, or to respond to instrument or spacecraft
anomalies. We have reduced the incidence of anomalies by operational procedures and software
patches. The BAT operated more than 300 days
on a continuous basis, and the UVOT for 92 days.
The XRT, however, has never had a software crash.
Overall the Swift science uptime is about 97%.
We have just completed the second full year of Swift
operations (which satisfied the Swift minimum success
criteria), and we are very pleased by the recommendation
of the NASA Senior Review that Swift
plan for four more years of operations.
The observatory and instruments are all operating at
full science capability. Minor performance glitches
(very rare instances of loss of star tracker lock, loss
of three columns in the XRT CCD, passive temperature control due to loss of the XRT TEC, and BAT
noisy detectors) are all controlled by operational
procedures and/or software improvements. There
are no consumables on Swift and the orbit will last
well beyond this four year period. At this point we
see no reason not to expect Swift to continue on its
mission through at least 2010.
I want to announce that we plan to hold a workshop
at Penn State on May 1-2, 2007, to consider the top
level strategy for Swift science. Is the current emphasis
on GRBs and afterglows the right priority for the
future of Swift, or should we consider increasing the
time available for TOOs or other science programs?
More details on the workshop will be available early
in 2007.
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E/PO Update - Newton's Laws
By: Phil Plait, SSU E/PO
When making educational products for the classroom
(what educators call formal materials), the
Swift E/PO group keeps an eye on the National Science
Education Standards, a set of basic grade level
specific concepts that was put together by a large
group of educators, and funded by such groups as
the NSF, NASA, and the U.S. Department of Education.
In the middle school standards, Newtons Laws figure
prominently, as they should you can base the
rest of high school physics on them! So years ago the
E/PO group put together a series of three posters,
each one expounding upon one of Newtons Laws.
These posters were a hit with teachers, but over the
years we found they needed serious updating. So
we carefully examined the concepts and the posters,
and almost totally reworked them.
Each poster features beautiful and topic-appropriate
artwork by artist Aurore Simonnet, illustrating
concrete examples of each Law. Furthermore, the
posters were designed in such a way that if they are
mounted next to each other, the artwork flows organically
from each poster to the next.
On the back side of each poster is an explanation of
the given Law, a description of the illustrations on
the front of the poster, an example of the Law using
the Swift spacecraft itself as an example, and an
activity that will give students hands-on experience
with the Law.
For the First Law, the students roll a toy car down
a ramp and observe the results (we even worked in
a safety message about seat belts!). For the Second
Law, students examine a drawing of a moving car
and match the diagram to a series of simple plots
showing the velocity and acceleration. The Third
Law activity has them making simple balloon rockets
which they can race.
To the original set of three, we have added a fourth
poster for the Universal Law of Gravitation. In the
activity, they drop various objects to see if they fall at
the same rate or if heavier ones fall faster. They also
calculate the gravitational acceleration of the various
planets, and can use that to find what they would
weigh on Mercury and Pluto!
Amateur Corner
Once again members of the
Swift Education and Public
Outreach (E/PO) team were
present at the Astronomical
Imaging Conference (AIC)
in San Jose via the Global
Telescope Network (GTN).
Held in November, the AIC is
a formal gathering of amateur
astronomers whose instruments and observations
are nothing but professional. Accompanying the
astronomers at the conference were vendors of highquality
CCD cameras, telescopes, and astronomy
software.
From the joint Swift, GLAST, and XMM-Newton
booth, the E/PO team distributed GTN flyers, Swift
stickers, and other E/PO materials. Interest in active
galaxies and other gamma ray producing objects was
generated within the astronomer community as the
team explained how the GTN operated; specifically
its robotically automated interface and its connection
to the gamma rays detected
by Swift. As was the case last
year after attending the AIC,
the GTN membership grew,
signaling the importance of direct
contact with the amateur
astronomy community.
As a sponsor, the GTN sent Dr.
Phil Plait, Tim Graves and Logan
Hill to the conference this
year. They were excited to find
the community interested in robotic
telescopes used for both science and education;
notably Russ Croman and Rick Gilbert's Remote
Imaging talks. Thanks to Steve Mandel, the
conference coordinator, the AIC once again brought
together leading amateur astronomers and cutting
edge technology for three days of talks, lectures and
discussions. The GTN and Swift E/PO are honored
to have been involved with the AIC.
For more information about the GTN, go to http://
gtn.sonoma.edu, and the AIC 2006 web page can
be found at
http://www.galaxyimages.com/AIC2006.html. |
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