Swift Year in Review - PI Neil Gehrels
I have been looking forward to tell
you about a profound change that is happening with Swift.
The observing program is evolving toward a broader range of
science topics. This is dramatically illustrated in
Figure 1 showing observing time fraction. The fraction
of time spent observing gamma-ray bursts (GRBs) has declined
since 2006 while more time is spent observing non-GRB
Targets of Opportunity (TOO) and Planned Targets.
There are several reasons for the evolving observing
program. Swift is still NASA's GRB satellite and that is the
primary science. However, we are now being more selective on
which GRBs to observe. The satellite continues to respond to
every burst that the burst alert telescope (BAT) detects,
but x-ray telescope (XRT) and ultraviolet/optical telescope
(UVOT) afterglow observations are now terminated earlier for
some GRBs. Nowadays, we only follow the most scientifically
interesting bursts and ones that are not near the sun on the
sky. Sunward bursts are not good for our friends with
ground-based telescopes since they are not visible much at
night. By dropping the sunward bursts, we are able to keep
the satellite more oriented toward the night sky which means
a higher fraction of new bursts away from the sun. It is
counter-intuitive, but spending less time on GRBs actually
gives us better ones on average. Less is sometimes more!
Figure 1:
TOOs are "targets of opportunity" which are astronomical sources we point the observatory to on a rapid turn-around basis at community request. Planned Targets are sources that the Swift team and community submit for observations when the observatory is not busy with GRBs and TOOs. Down time is when the instruments are not taking data while Swift is orbiting through high radiation zones or when we are taking calibration data.
The other big reason for the evolving program is
that researchers in non-GRB areas of science are
discovering Swift's capabilities. They are flocking to
our gates at ever increasing numbers as can be seen in Figure 2.
The rate at which TOOs are being requested is
increasing dramatically. Scientists send us requests
on the Web to observe new or varying objects in the
sky, based on data they have from other telescopes or
sometimes from our own BAT. We then send a command up
to Swift to re-point XRT and UVOT in that direction -
just like for a GRB, but with ground command. When a
request comes in, I review it for approval and then
the Penn State Mission Operations Center (MOC)
generates and sends the command. The MOC scientists
have gotten very proficient at doing this quickly,
sometimes in just a few minutes. Swift now has by far
the highest TOO rate of any astronomical satellite. On
average we perform one or more TOOs every day, 7 days
a week.
The Swift TOOs are a boon for science and great
excitement for the team. Here is brief list of
discoveries coming from the TOO program:
- The first observation of an X-ray flash coming from
the surface of a supernova star just prior to its
explosion (SN 2008D described by Alicia Soderberg in the
June 2008 newsletter.)
- Nova events such as RS Ophiuchi with flash nuclear
explosions taking place on the surface of a white
dwarf star.
- Bright flares coming from distant quasars such as
3C 454.3, observed in coordination with the Fermi and
AGILE satellites.
- X-ray emission from comets approaching the sun
such as Comet Tuttle in January 2008.
- Highly variable X-ray and optical light coming
from black holes such as GX 339-4 in the central
region of our galaxy.
It is fun looking through the list of more than 700
Swift TOOs to pick out the gems above. There are pages of
interesting findings that could be listed. We look
forward to the next 700 TOOs!
Figure 2: The increase in the rate
of TOO observations performed by Swift is seen in this
plot.
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Mission Director Report
By John Nousek, Penn State, Swift Mission Director
Here at the Mission Operations Center (MOC) we have just
celebrated the fourth anniversary of the launch of Swift. The
observatory is operating at peak efficiency, and we believe that
the performance is even better that it was at launch, due to small
improvements to the flight software.
The observatory points at targets more accurately with our
latest 'three-gyro' attitude control (instituted in October,
2007). We also respond more often to Targets of Opportunity and
modifying GRB observations to maximize science by using a highly
flexible Automated Target re-planning which enables the team to
make changes anytime, day or night, without travelling to the MOC.
The burst alert telescope (BAT) has increased its science yield
by making experiments with lower thresholds to detect faint GRBs,
and to search for GRBs via ground processing of data collected
during slews. The x-ray telescope (XRT) has improved its GRB
localization by utilizing the ultraviolet/optical telescope (UVOT)
as a super-accurate star tracker, and has reduced the detector
background by raising voltages on the CCD chip. The UVOT has
refined the GRB observing parameters to enable observations at
very early times using the grisms, which included tuning the
safety circuit parameters to protect the instrument while still
allowing sensitive grism observations of bright sources.
In the year ahead we are working with the Swift spacecraft
manufacturer, General Dynamics, to introduce an observatory flight
software patch to let us return to a 'two-gyro' mode of operation,
but with precise alignments to keep or improve on the current
pointing accuracy. We are also planning on a flight software
change to the star tracker software to eliminate a bug which has
been resulting in occasional attitude safeholds. (Note that even
with the bug, we have been averaging better than 99% 'up' time -
defined as time when we are actively able to use the observing
time to detect GRBs.)
We have received funding to continue Swift operations for
another two years and a budget plan for two years beyond that.
We believe that the observatory is in excellent condition to
carry out the exciting work of discovery - from GRBs to
supernovae, to cataclysmic variables, to Active Galactic Nuclei -
with unique capabilities for rapid response, multiple duration
monitoring, and high energy transient discovery!
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Guest Investigator Program Success
By Stefan Immler (NASA/GSFC)
The deadline for submitting science proposals for the Swift
Cycle 5 Guest Investigator (GI) program was October 15. NASA
received 154 proposals, requesting a total observing time of
16 Ms and $4.4M in funds for 1,123 targets. About 67% of all
proposals are non gamma-ray burst (non-GRB) proposals and
26% of all proposals are target of opportunity (TOO)
proposals.In January 2009, a panel of scientists will
meet to discuss the merits of all submitted proposals and
choose those that are recommended for funding and observing
time. The accepted targets will shape the science program
for Swift's sixth year of operation. Cycle 5 observations
and funding will commence on or around April 1, 2009, and
will last approximately 12 months.
The Swift GI program will continue to solicit proposals in
GRB and non-GRB research in Cycle 6. In response to requests
by the community, we expect that a larger number of
monitoring programs will be accepted during Cycle 6.
Notice of Intent for Cycle 6 proposals will be due
September 16, 2009 and the deadline for submitting Cycle 6
proposals is October 28, 2009.
The Naked-Eye Gamma-Ray Burst
By Judith Racusin (Penn State)
Gamma-ray bursts (GRBs), one of the most extreme
astrophysical phenomena ever observed, result from a stellar
explosion due the collapse of a massive star to a black hole
or neutron star in which material is ejected at nearly the
speed of light in narrow jets. The shells of material crash
into each other and the surrounding environment producing an
initial burst of gamma-rays followed by a fading
multi-wavelength afterglow.
These rare stellar deaths briefly outshine their entire
host galaxies and have been seen from enormous distances
that are comparable to the most distance quasars. Despite
these extreme conditions, the optical counterparts are
usually faint, fade quickly, and are often obscured by dust
and gas in their host galaxies. Astronomers never imagined
there would be a GRB that was visible to the unaided eye for
even a brief moment, and certainly not at a distance of
nearly halfway across the Universe.
That all changed on March 19, 2008 when NASA's Swift
satellite discovered one of the brightest GRBs ever seen in
the 40-year history of the field accompanied by the
brightest optical and X-ray counterparts ever observed.
With the help of a little luck, the extreme brightness of
the transient, and the preparedness of the follow-up
community, robotic telescopes observed GRB 080319B starting
from minutes before the time of the explosion and a
well-coordinated campaign followed for weeks afterwards.
As reported in a recent paper in the journal Nature (Racusin,
et al., 2008, Nature, 455, 183), the combinations of these
gamma-ray, X-ray, ultraviolet, optical, infrared, millimeter
and radio observations are the best broadband dataset ever
obtained.
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Swift in the News
By Logan Z. Hill (SSU E/PO)
9/10/08 - "Naked-Eye" Gamma-Ray Burst Was Aimed Squarely At Earth
GRB 080319B, the March 19th, naked-eye observable,
7.5 billion light year distant, awe-inspiring gamma-ray burst was determined
to be aimed directly at Earth. A paper published in Nature by Judith Racusin
and 92 coauthors calculated the material shot from the object towards Earth
travelled at 99.99995 percent the speed of light. To read more visit the
Official GSFC Press Release.
9/19/08 - Swift Catches Farthest Gamma-Ray Burst
GRB 080913, the most distant gamma-ray burst so
far, was detected by Swift on the 13th of September. The estimated distance
of the burst is 12.8 billion light-years (redshift of 6.7), and is located
in the constellation Eridanus. GRB 080913 beats the previous distance record
holder by approximately 70 million light-years. For more information visit
the
Official GSFC Press Release.
9/29/08 - A Day in the Life of Swift Scientists
Brady Haran
has made a film Day in the Life: Astrophysicists for the
East Midlands STEM
Partnership. It follows two scientists, Rhaana Starling and Phil
Evans, and their use of Swift to study gamma-ray bursts. The video is
hosted on YouTube here:
http://www.youtube.com/watch?v=8icydzuxd84
All Swift related news and images can be found
here.
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As is common with an observational science, better observations
don't necessarily confirm our theories, but rather force us
to ask new questions. With the detailed optical and
gamma-ray observations during the burst itself, we learned
that these components must have come from the same physical
region, but different radiation mechanisms. Therefore, the
gamma-rays couldn't be produced by the typical synchrotron
mechanism attributed to other bursts.
The extremely luminous afterglow of GRB 080319B was imaged by Swift's X-ray Telescope (left) and Optical/Ultraviolet Telescope (right).
As the shock wave swept up the surrounding material, the
afterglow faded at different rates between the X-ray and
optical, both of which appeared rather different than the
usual pattern. Rather than the usual one sudden decrease in
flux that indicates the slowing of the ejecta and the edge
of the jet, we saw two.
By assembling all of the observational pieces of the
puzzle, we concluded that the emission from GRB 080319B was
concentrated into a very narrow jet with an opening angle of
0.4 degrees, that just happened to pointed right at us,
surrounded by a wider slower jet of material with an opening
angle of 8 degrees.
The small probability of this occurrence explains both
the unusual observational properties and the rarity of
naked-eye GRBs. This suggests that if all GRBs have this
two-component jet structure, then we usually only observe
the wide jet. The implications on GRB energy outputs,
geometry, and physics are far reaching.
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GORT Catches GRB 081203A
By Kevin McLin (SSU NASA E/PO)
A single night's break in the Northern California clouds during the first
week of December was all it took for GORT, the 14-inch robotic telescope run by
the SSU E/PO Group, to catch its first GRB. On December 3rd, Swift detected and
localized a GRB in the far northern sky, at about +63 degrees. News of the burst
was automatically sent out via the GRB Coordinates Network (GCN) to
observatories throughout the world, as well as to the Skynet server at the
University of North Carolina. At that moment, Skynet was controlling GORT.
Though the burst was midway up from the northeastern horizon as seen from
Sonoma, and the sun was a mere 13 degrees from rising, Skynet directed GORT to
slew and begin observing. In the brief minutes before the twilight became too
bright, GORT captured five images, the earliest ones obtained from the ground
for this gamma-ray burst.
SSU E/PO's 14-inch robotic telescope.Skynet has standard software it runs for a GRB alert. As directed by the
script, GORT made a series of R and I images. The first, in I, started only 125
seconds after the trigger. It was 40 seconds in duration, as were the next two.
The remaining images were each 80 seconds long, and the last one was started 586
seconds after the trigger. The GRB blazed forth in all five images.
The images were downloaded several hours later by K. McLin (Sonoma State) and
K. Ivarson (UNC), and independent photometric analysis was done at each
location. The GRB was bright, about 12th magnitude in both R and I during the
entire approximately 10 minutes of observations. Unfortunately, twilight
prevented continued observations, so a more complete light curve was not
obtainable for the afterglow. A Circular has been posted to the GCN. It is GCN
8617.
The ability to make automated observations was a critical part of the
detection of this afterglow. As is typically the case, no one was at the
observatory for these observations. Skynet, an automated observing system, was
developed at UNC to perform precisely this kind of observation. It currently
directs telescopes in Chile and North America. The SSU group has been working in
partnership for the past several years with the UNC group, putting GORT under
the direction of Skynet most clear nights. Generally the telescopes are used for
routine monitoring of AGN (Active Galactic Nuclei, or quasars), variable stars,
and the like. However, in the event of a GRB alert, Skynet determines which of
its client telescopes is able to observe the event, and it then interrupts
whatever they are doing and directs them to the burst. On December 3, GORT was
the only telescope able to view the burst, as the other Skynet telescopes were
all several hours farther east, and thus in daylight. The next-earliest
observations from the ground were obtained in early evening twilight from
Slovakia, but those had to wait 90 minutes, and by that time the burst had faded
below R ~ 15.
GORT image showing GRB 081203A
While the day-to-day job of GORT is to monitor AGN and provide access to a
telescope for undergraduates and high school students throughout the United
States, we have been waiting to capture a GRB for a long time. In the past, GRB
that would have been visible were too faint, or we were shut for maintenance or
clouded out. Finally getting one of these feels great, and we look forward to
catching many more.
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Presenting at the National Science Teachers
Association
By Swift Educator Ambassador Janet Moore (Challenger Learning Center of
Central Illinois)
A powerful stellar explosion detected March 19 by NASA's Swift satellite has shattered the record for the most distant object that could be seen with the naked eye. I
am passionate about engaging students in scientific investigations that are led
by "what if" questions. When students start to ask themselves, "What if I do
this?" or "What will happen if I try that instead?" that is when real scientific
inquiry starts. When students start to wonder and ask questions, they take their
education into their own hands and they begin to capture the essence of
scientific exploration. NASA's Swift materials are perfect for helping teachers
create an environment of exploration in the classroom.
Recently, I presented at a National Science Teachers Association conference
in Cincinnati, Ohio. Nearly 150 teachers crowded into a room with seating for
about 80. The session began with a time for play. There were about 40 different
stations set up around the room and in the adjacent hallway. Each station had a
common toy or object and some instructions. The teachers were instructed to
visit as many stations as possible, follow the directions at each station, and
make observations. Some flew toy airplanes; others rode skateboards; still
others observed rocks sitting on the table. All used Newton's Laws of Motion in
their play.
When playtime was over, I facilitated a discussion of exactly how Newton's
Laws of Motion governed the events at each station, encouraging the teachers not
to let their students off easy with "simple explanations." Letting go of an
inflated balloon and watching it fly around the room is not just a demonstration
of Newton's Third Law of Motion. It is a complex and intricate demonstration of
all of Newton's Laws working together to take the balloon on that path through
the air. Sometimes, it does an injustice to our students to oversimplify.
I ended the session by explaining the Swift mission and the role of Newton's
Laws of Motion in Swift's success. I encouraged the teachers to use the thrill
of NASA exploration to infuse excitement into their classrooms. The teachers in
the overflowing crowd were excited and grateful for the session and the Newton's
Laws posters provided by Swift. One teacher in particular praised the session,
saying "All high school teachers could learn from this session."
I have been a NASA Educator Ambassador since October 2003. Since then, I have
taught thousands of teachers about the Swift mission.
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