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Swift Newsletter
Issue 11/November 2009
Swift Year in Review - PI Neil Gehrels
Hello, friends of
Swift. Our mission
has now been in orbit
for 5 years, with the
anniversary on 20
November 2009. It
sometimes boggles to
mind to think of the
satellite orbiting above
us, reorienting from
target to target every
few minutes day-in,
day-out. We will celebrate the 5-year milestone
with a science workshop at Penn State.
For this anniversary newsletter, I would like to
tell you about a couple of neat scientific findings
from the mission, both of which have taken 5 years
to happen. The first is a “blast-from-the-past” very
distant gamma-ray burst and the second is a survey
of the gamma-ray sky being performed by the BAT
instrument on Swift.
The world astronomical community is still abuzz
about the Swift detection of the most distant object
in the universe last April. It was gamma-ray burst
GRB 090423. Check out Nial Tanvir’s article in this
newsletter for more about this burst and the
exciting chase to observe
it. Scientific articles about
it have just appeared this
month in the prestigious
Nature journal.
We have been
waiting for years
for such a distant
burst and were
finally rewarded.
The BAT sky survey is
something you don’t hear much
about, but it is producing discoveries left and right.
Prior to Swift, there were whole missions proposed
to do such a survey, which we are now doing as a biproduct
of Swift’s gamma-ray burst chasing. Here is
how it works. BAT monitors a large portion of the sky (about 1/6) all the time to look for GRBs.
They occur about twice per week and last only
a few tens of 
seconds each. BAT’s detection
of GRBs is what makes Swift tick, but it only
takes 0.01% of the instrument’s time. The rest
of the time, BAT is surveying the gamma-ray
sky at a sensitivity level never before achieved.
(BAT operates in the low energy portion of the
gamma-ray band, between X-rays and gammarays,
so it is sometimes called a “hard X-ray”
survey.) To date, BAT has detected nearly a
thousand sources. Most of them are massive
black holes at the centers of galaxies, many of
which are surrounded by thick clouds of gas
and dust. Gamma rays are the most penetrating
radiation and zip right through the clouds. BAT
is giving the first complete census of massive
black holes in our local universe. This is the
opposite kind of science from GRBs. Instead
of a flash and bang, it is a slow process of adding
data over months and years. Now, five years
into the mission the results are starting to flow
from the BAT survey.
There is another new development for Swift.
We are now performing many observations
in coordination with the newly-launched
Fermi Gamma-ray Space Telescope.
More on this exciting new pairing of
gamma ray
missions
in the next
newsletter.
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Mission Director Report
By John Nousek, Penn State, Swift Mission Director
Here at the Mission Operations Center (MOC),
we are eagerly awaiting the Fifth Anniversary
milestone of the Swift launch on November 20,
2009. Swift was designed to have a minimum
mission life of two years with a design goal of
five years. I’m happy to report that the observatory
and all its instruments continue to operate
smoothly, really as well or better than they operated
at launch.
This excellent behavior is a combination of the
sound original design and improvements made in
ground operations and on-board flight software.
At the observatory level Swift is carrying out observations approximately
98% of the useable time (i.e. time when the satellite is
outside the South Atlantic Anomaly). We have had only two
episodes where Swift was off-line due to anomalies. One, resulting
from a small instability in one of the gyro units, has
been corrected by a software approach which combines
data from all three gyros,  resulting in accuracy in pointing
which is higher now than the original design. The
other, resulting most likely from a cosmic ray hit in the
electronics of the solid state recorder, was repaired by a
software reset of the recorder.
We have made improvements to the ground operations
which allow us to be much more responsive
to Target of Opportunity (ToO) requests, resulting
in a great increase in Swift science beyond
GRBs. We now typically receive about 2 ToO requests
per day with 2-3 observations per request.
We also continue to improve our ground software
which checks the planned science target list,
catching the very rare situations in which Swift
would be inaccurate in pointing, or forced to violate
the pointing constraints. This improved software
reduces the few times (out of about 150,000
maneuvers) when the on-board software produces
undesirable results.
Each of the instruments has also made significant
improvements in performance. The BAT now
captures data during the times of slewing, and via
ground-processing is able to detect GRBs during
the slews (albeit delayed slightly by the relay and
processing time). The BAT also causes GRB triggers for events slightly below the normal threshold, followed by
short snap shots by the XRT. If the XRT detects an afterglow the
information is reported to the GCN, but for the false positives we
do not continue observations. The XRT uses the UVOT image
to improve knowledge of the XRT positions from 4.5 arcseconds
to 2.2 arcseconds. Software and voltage settings now allow the
XRT to operate about 5 degrees warmer than the original values.
New modes also help XRT offset the effects of the micrometeorite
damage to the XRT CCD.
The UVOT has developed and changed software and modes to
allow more frequent use of the grism on GRB response, and the
white-light filter, thus giving a more sensitive detection limit to
the GRBs, and if the GRB afterglow is sufficiently bright, a low resolution spectrum. The UVOT also developed new data products
(called the GeNIE image) which allows the UVOT team to
rapidly set more sensitive limits on afterglow brightness when no
bright object is near the XRT position.
As we move to the future more improvements lie ahead. We
are conducting a study to increase the automation of science
planning. The effect of this will be to reduce the time
required for creating new schedules. We are working on
software to incorporate the effect of radiation on the CCD
in the XRT. We are working to add the capability of using ground stations at Santiago, Chile; MILA, Florida; and
Wallops Island, Virginia. With added stations we will be
able to more fully exploit the BAT’s ability to sense GRBs
during slews and do single photon data analysis. We will also
implement spacecraft software changes to avoid the occasional
(~6 times per year) events when a software bug in the
star tracker gives an erroneous position.
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Swift in the News
By Logan Z. Hill (SSU E/PO)
2/10/09 - NASA's Swift, Fermi Probe Fireworks
from a Flaring Gamma-ray Star
The soft-gamma-ray repeater, SGR J1550-5418
has been producing unpredictable X-ray and
gamma-ray flares that Swift and Fermi have observed.
Sometimes producing more than a hundred
flares within twenty minutes, this neutron
star has long been known for its radio and X-ray
emissions, but with eruptions on October 3,
2008 and January 22, 2009, viewed by Swift and
Fermi, it has been reclassified as a soft-gammaray
repeater, one of only six known.
To read more:
Click Here
2/20/09 - NASA's Swift Spies Comet Lulin
Using Swift’s Ultraviolet/Optical Telescope
(UVOT) and X-Ray Telescope (XRT), on the
28th of January, Comet Lulin was observed
to have a hydroxyl cloud over 200,000 miles
long. The data Swift gained from observing the
comet have helped to add further details to its
make-up and structure, especially the tail where
solar radiation separates the hydroxyl ion into
oxygen and hydrogen creating a region of X-ray
emission. To read more: Click Here.
4/3/09 - Swift’s Comet Tally Highlighted in
Observatory Webcast
As part of the 100 Hours of Astronomy project,
the European Southern Observatory’s webcast
included a montage of Swift’s comet observations.
Comet images used included 73P/Schwassmann-Wachmann 3, Lulin (see above), and
8P/Tuttle. Read more:
here.
4/28/09 - New Gamma-ray Burst Smashes
Cosmic Distance Record
On April 23 2009, at 3:55 am EDT (7:55
GMT), Swift observed a gamma-ray burst
which lasted ten seconds and had only an Xray
afterglow. The burst was determined to have
originated 13.035 billion light-years away, at a
redshift of 8.2, making it the most distant burst
ever recorded. See Nial Tanvir’s article, “A light
from the end of the dark age: GRB 090423.”
Read more: here.
5/15/09 - Swift Mission team wins the Maria and
Eric Muhlmann Award for 2009
The Board of Directors of the Astronomical Society of
the Pacific has awarded the Swift Mission team with the
Maria and Eric Muhlmann Award. The award is given
for “recent significant observational results made possible
by innovative advances in astronomical instrumentation,
software or observational infrastructure.” Swift
was recognized for “the innovative way in which the
satellite’s trio of instrumentation works in concert to
discover gamma-ray bursts and their afterglow, combining
gamma-ray, X-ray, ultraviolet and optical data.” The
award was received by Swift team member Dr. Edward
Fenimore of Los Alamos National Laboratory.
Credit: NASA/Sonoma State University/Aurore Simonnet
6/8/09 - Keck Study Sheds New Light on 'Dark' Gamma-ray
Bursts
Using the 10-meter Keck I telescope, Joshua Bloom’s international
team found that for eleven of fourteen dark bursts
observed by Swift, there was a distant faint quiescent galaxy
which suggests that there is dust obscuring the visible light of
the bursts even though the galaxies do not appear to be dusty
themselves.
Read more: Click here.
9/16/09 - Swift Makes Best-ever Ultraviolet Portrait of Andromeda Galaxy
While waiting for gamma-ray bursts to observe, Swift used its UVOT to take over 300 images of M31, the Andromeda
Galaxy, with three ultraviolet filters. The brilliant portrait took a total of 24 hours of exposure time and images amounting to
85 GB of storage. Read more: here.
Credit: NASA/Swift/Stefan Immler (GSFC) and Erin Grand (UMCP)
A light from the end of the dark age:
By Nial Tanvir (University of Leicester)
Many of us who are involved in making followup observations of Swift
GRBs (not to mention their partners and families!) have learned to live
with frequent mobile phone alerts at all hours of the day and night.
One of the main reasons we do it is in the hope that occasionally something
rather special will come along. On 23 April this year we were
rewarded with a very special burst indeed.
The trick to finding high redshift GRBs is to search for afterglows
which appear bright and blue in the infrared, but invisible in the visible,
as it were. This is the unmistakable signature of the Lyman-alpha
break wiping out the flux throughout the optical region.
As ever, though, ground observers have to contend with the vagaries of
the weather, and on occasions technical difficulties. In the case of GRB
090423, high winds at Mauna Kea made observations difficult, with
UKIRT being forced to close immediately after taking the first image in
which we identified an infrared afterglow of the burst. Thankfully, the
coordinated efforts of telescopes around the world, in particular Gemini,
VLT and the TNG, ensured that in this case further high-quality
infrared photometry and spectroscopy of the afterglow were obtained,
showing the burst to have originated at a record-breaking z=8.2. This
translates to a light travel time of 13.0 billion years compared to the
13.7 billion year age of the universe – the gamma rays were traveling to
us since near the beginning of time!
It has long been recognised that GRBs have the potential to be detected
at very high redshifts, at distances where other objects are too
GRB 090423. The image is a composite of data from Swift's UV/Optical and X-Ray telescopes.Credit: NASA/Swift Stefan Immler faint and
too rare to be seen, or if seen, too hard to obtain redshifts for. The problem
is, GRBs are rare – in four and a half years of searching, the highest
redshift GRB found by Swift was 080913 at z=6.7. At the time,
this was the second highest spectroscopic redshift
known for any object, which illustrated the promise,
but also the difficulty of searching for early GRBs.
The great attraction of gamma-ray bursts is not only that we can
see them at great distances, but also that when we do, they can
be used to study the earliest generations of stars, and their effect
on the Universe. Their existence tells us that massive stars were
forming at that time, and pinpoints the location of their host
galaxies. Their afterglow spectra allow us to study the progress
of reionization and chemical enrichment enrichment, giving
clues to the properties of even earlier stars.
So, what have we learned from GRB 090423? Perhaps the most
important lesson is that GRBs really were being produced 700
million years after the Big Bang, giving considerable confidence
that we will be able to use them as beacons in the era of reionization.
This is tremendously important since galaxies are expected
to be very faint at these distances, and even JWST and the
new generation of extremely large ground-based telescopes will
struggle to study them in any detail.
Regretably, on this occasion, the afterglow fell well short of
the staggering intrinsic brightness we have seen in GRBs such
as 080319B. Furthermore, the first spectroscopic observations
were not possible for many hours, which limited the information
which could be obtained. However, deep searches may yet
reveal the host galaxy of GRB 090423, and in coming years the
discovery and followup of further extremely high redshift GRBs
may make them the most important tools we have for investigating
the earliest collapsed structures in the Universe.
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From Earth To The Universe (FETTU)
By Logan Z. Hill (SSU NASA E/PO)
For the International Year of Astronomy (IYA), Swift E/PO teamed
up with other San Francisco Bay Area E/PO groups in order to put
on the FETTU traveling exhibit. Fourteen six-foot by three-foot
banners on seven stands have made their way around the SF/Oakland
area sparking excitement and wonder among all ages.
The spectacular objects included in the exhibit are Antares, Andromeda
Galaxy, and Milky Way. Each image includes descriptive
text and its distance from Earth (where applicable) in both English
and Spanish.
Venues have included Sonoma State’s Seawolf Day, Oakland
Aviation Museum, San Ramon Art & Wind Festival,
and the Annual Meeting of the Astronomical Society
of the Pacific. The next scheduled event is the Exploration
Station at the American Geophysical Union,
San Francisco on December 12 – 13, 2009.
This exhibit is a smaller version of the original FETTU exhibit
sponsored by the IAU which is being displayed all over the world
for the IYA. In addition, the Bay Area missions also sponsored a
larger exhibit at the California Academy of Sciences which is now
currently at the San Jose Tech Museum. You can visit the FETTU
home page here: http://www.fromearthtotheuniverse.org/index.php
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