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Swift Newsletter
Issue 7/April 2007
Welcome Message from PI Neil Gehrels
Welcome to the spring 2007 issue of the Swift newsletter. We had
wonderful news in January that the Swift team was awarded the
Bruno Rossi Prize of the American Astronomical Society (AAS).
The prize is sponsored by the High Energy Astrophysics Division of
the AAS and was announced at the AAS meeting in Seattle. The
citation states that the award is for gamma-ray burst discoveries
of the mission, particularly calling out the breakthrough in
our understanding of short bursts and the afterglows of bursts.
While the Rossi prizes looks back at the accomplishments of
the past two years, the team is busy analyzing today's
data and planning ahead to the future. As one important
step in the future planning is a workshop that will be held
at Penn State on May 1-2 (a time of typically beautiful weather
in mid-Pennsylvania). The one and only topic of the public
workshop is to gather input from the astronomical community
about how best to use Swift's capabilities over the coming
years to advance our understanding of the universe.
The meeting will focus not only on gamma-ray burst science,
but also on non-burst opportunities. You may not be aware,
but about 1/3 of the Swift observing time is used for non-GRB
observations when bursts are not visible. A large and growing
percentage of non-GRB time is spent on "Target of Opportunity"
(ToO) observations based on urgent requests that come in via the
internet. Here is an example: Suppose an astronomer has
access to data in the optical band from a black
hole or neutron star system in our Galaxy and sees that
the source is brightening dramatically. This kind of event
happens frequently
in our variable universe. She or he then fills out a form on
the Swift web site requesting a Swift ToO observation of the source.
Depending on the urgency, the web site initiates cell phone alerts
to the duty scientist, the operations engineer at Penn State,
and to me. We then quickly arrange a repointing of the satellite
to observe the outburst. The fastest response to date has been
~30 minutes between alert and Swift data taking. The rate of
such requests has been ramping up and is now at about
one every other day.
I'm getting off track describing this exciting aspect of
Swift operations ... the point is that we will discuss
GRB and non-GRB science at the Penn State workshop and gather
community opinions on what topics should be emphasized the
most in the future. I predict we will continue to spend most
of the Swift observing time on GRBs, but we may make small changes
in the balance and will definitely tune the kinds and methods
of GRB and non-GRB observations. It occurred to me just
this week how precious this time is, with Swift fully operational
and powerful telescopes all over the world and in space participating
in Swift science. Optimizing the use of Swift observing time is
a priority. I will report to you on the outcome of the May
workshop in the next newsletter.
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GRBeaming
By: Dirk Grupe, Penn State University
Gamma-ray bursts (GRBs) are the most energetic transient objects
in the Universe. Within seconds, they release more energy than
our Sun does in its entire 10 billion year lifetime. As we
know today, GRBs are explosions of very massive stars, in
many ways similar to a normal supernova. However, their
total energy seems to be a hundred or a thousand times larger
than that of a typical supernova, and this energy is released
over the course of less than a minute, while a normal supernova
lasts for weeks. How can this be?
Theorists found a solution for this problem by having the emission
from the GRB concentrated in a well-collimated light beam,
what's called a "jet". Like looking down the beam of a
flashlight, we are looking down the jet of a GRB
when we observe it. This solves the energy problem of a GRB:
if we assume the total energy of the GRB is emitted in every
direction (more like a lantern than a flashlight), then it
has to be extremely powerful, far more than we can understand.
But if the energy is concentrated into a narrow beam, the total
power emitted can be far, far less and still account for
our observations.
The crucial issue here is the opening angle of that
jet – the angle that describes how the jet spreads
out over distance. The smaller the opening angle –
the narrower the jet is – the smaller the total amount
of energy is needed to explain the measured flux from the source. Going
back to our previous example, we would need 2000 Watts of
power from a lantern – which emits in all directions – to equal
the amount of light we'd see from a flashlight powered by
only 4 Watts, assuming the flashlight beam has an opening angle
of a modest 5 degrees.
The same applies for GRBs. Because the light we see is like a
light beam from a flashlight, the total energy needed is much
less than what is expected if the emission is isotropic.
One crucial confirmation of the jet theory is the occurrence
of what's called the "jet break". As the jet plows through the
dust and gas between stars, it loses energy. It gives off
X-rays as it does so, and after some time – usually a few days –
the amount of X-rays detected drops suddenly.
The jet break depends on the opening angle of the jet
and the amount of energy in the burst itself, and has been
seen in almost all the GRBs in which X-rays have been detected.
GRB 060729 was a burst detected by the Swift Burst
Alert Telescope on July 29th, 2006, and it seems to
challenge this standard theory of GRBs and jets. Swift
was still able to detect the X-ray afterglow of this
burst even four months after the explosion, the current record for an
afterglow follow-up by Swift. During that time no
sign of a transition to a more rapid decay in the X-ray
flux was detected: no jet break was seen for at least
125 days after the burst.
This length of time indicates that the opening angle of the jet
has to be at least 28 degrees, far wider than ever seen before.
Because the opening angle is so wide this burst requires an
enormous energy reservoir. One possible solution to this
dilemma is that there is a continuous energy injection
from a central magnetar, a neutron star with a very powerful
magnetic field. This magnetic field works like an electromagnetic
brake, taking the energy from the rotation of the magnetar (and
hence slowing it down) and injecting it into the initial
blast wave, keeping it going for far longer than usual.
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Artist's illustration of the evolution of GRB060729
(click for bigger version).
From left to right:
1) The core of a massive star in a distant galaxy collapses, ending
its life – though there is little effect visible at the surface.
Deep inside, twin beams of matter and energy begin to blast their way
outward.
2) Within seconds, the beams have eaten their way
outof the starm and observers at Earth see it as a gamma-ray burst,
GRB 060729A.
3) The outer envelope explodes outward, causing a supernova.
4) Deep at the heart of this event, the core has shrunk into a
fantastically dense magnetar, a neutron star possessing a magnetic field
trillions or even quadrillions of times stronger than Earth's.
The magnetar could be what powers the long glow of X-rays
seen by Earthbound scientists.
Illustrations by Aurore Simonnet.
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The results of the Swift observations of GRB 060729 will be
published by Penn State's astronomer Dirk Grupe as the lead
author in the June 20th, 2007 edition of the Astrophysical Journal.
Further observations of the X-ray afterglow by NASA's Chandra
X-ray satellite are also planned to extend the observations of this
extraordinary X-ray afterglow beyond any GRB afterglow that has
ever been detected.
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Swift in the News
1/16/07 - Top High-Energy Astronomy Prize Awarded for Swift Discoveries -
The Bruno Rossi Prize, the top honor given by the High
Energy Astrophysics Division of the American Astronomical Society,
was awarded to Neil Gehrels and the Swift team "for major advances
in the scientific understanding of gamma-ray bursts. These include
ground-breaking observations to determine precise location of
short gamma-ray bursts, and the discovery of enormously
bright X-ray flares in the early afterglows."
+More
2/7/07 - Magnetic Explosions in the Distant Universe -
A new theory to explain the high-energy gamma-ray emissions from
collapsing stars has been put forward by Pawan Kumar from the
University of Texas, and appeared in the Monthly Notices of the
Royal Astronomical Society.
+More
3/8/07 - Gamma-Ray Birth Cries Suggest Massive Magnetic Engines -
Studies of two peculiar gamma-ray bursts: GRB060729 and GRB070110 have
led to conjectures that magnetic engines are behind unusually
long-lived x-ray afterglows.
+More (Goddard Space Flight Center)
+More (Penn State University)
3/15/07 - Robotic Telescope unravels mystery of cosmic blasts -
Scientists from Liverpool John Moores University and colleagues
in the UK, Italy, France and Slovenia used the world's largest
robotic telescope, the Liverpool Telescope on the island of La Palma,
and its novel new polarimeter, RINGO, to perform the earliest-ever
measurement (203 seconds) of the optical polarization following detection
of a burst by NASA's Swift satellite. The article by Carole Mundell
et al. appeared online in Science magazine.
+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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E/PO Update - MySpace and Cafe Press
By: Phil Plait, SSU E/PO
In the E/PO world, a lot of time is spent on the E
– Education – and forget about the PO – Public
Outreach. For Swift, communicating with the public (which includes
students outside the classroom) is never far from our minds. It allows us to
be less formal, more fun, and experiment with outlets we might not
otherwise employ.
On the web, one of the best ways to communicate with people is through
social networking sites — places where people can gather virtually
to chat, read bulletin boards, and find out what's new with their friends.
The premier site for this is, of course, MySpace, so we decided to create
MySpace pages for all the satellites we support: XMM-Newton, GLAST,
and of course Swift (and SNAP, too, though that's still
in the mission concept stage).
MySpace pages are actually an excellent venue for E/PO. We have information
about the satellites there, and can keep people up-to-date on news through
the inline blog. But that's not to say this has to be stuffy. Tongue firmly
planted in cheek, we created these pages as if the satellites are alive, and
post accordingly.
XMM-Newton
is the oldest (having launched in 1999) so is the most mature.
Swift
is next, and is tolerant though often miffed at its little brother
GLAST, which
is jealous that Swift is already in orbit.
SNAP is
the youngest — it's not even built yet!
On MySpace, people (and satellites) can collect "friends", who
can read the blog and exchange comments and messages. Currently, Swift
has 53 friends, which isn't too bad for something that's not even
technically alive. We encourage everyone on the team (and especially younger
family members) to take a look and sign up! It's a fun way to keep current
on Swift's progress.
Also, for people who want to show off their affiliation on the team, we have
opened
an online store with Swift swag on CafePress.
You can buy Swift hats, shirts,
mugs, even an apron, a teddy bear, and Swift US Mail stamps!
We make no profit off of sales, and prices are reasonable (T-shirts run
about $15US). The advantage of this process is that CafePress makes
each item individually, so that you make your order and it's sent out
right away; we don't have to collect many orders and do them all at once.
Another advantage is that we can easily create a new product. If you
want a different logo, a different image, or a different product,
just let us know! We'll see what we can do.
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If you have a question about Swift, please contact us via the Feedback form.
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