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Why did a black hole blast star stuff into space at a quarter of light-speed on June 3, 2009? Here is what happened

January 10, 2012 3 comments

On June 3, 2009, in an X-ray binary star system far, far away. . .


We know the what of the extraordinary event that occurred in May 2009 around a distant black hole; we just don’t know the why of it, although the possibilities are pretty amazing.

At the 2012 American Astronomical Society (AAS) meeting in Austin, Texas, Gregory Sivakoff of the University of Alberta in Canada reported some astounding observations he and his colleagues accomplished using a globe-spanning array of radio telescopes and two NASA satellites.

The whole episode was a cosmic stroke of luck: The light from an event that happened some 28,000 years ago reached Earth just days before the global collaboration was scheduled to open for business. Goddard astrophysics writer Francis Reddy explains the details of the science today in a web feature story and animation.

Let’s start with the what: On or about June 3, 2009, enormous blobs of hot electrically charged matter were ejected from a black hole at about a quarter of the speed of light — roughly 75 million meters per second.

Next, the where: These black-hole “bullets,” as Reddy calls them in his web feature, were ejected from a binary star system. Called H1743–322, the  system lies about 28,000 light-years from Earth. NASA’s HEAO-1 satellite discovered it in 1977

In H1743–322, a black hole and a star orbit each other at close quarters, every few days. They are close enough that the black hole’s massive gravity draws a steady stream of material off its companion’s wispy surface. The hot electrically charged gas swirls around the edge of the black hole, forming a whirlpool-like “accretion disc.” As the gas accelerates to high speed, it radiates X-rays that satellites at Earth can detect.

“Some of the infalling matter becomes re-directed out of the accretion disk as dual, oppositely directed jets,” Reddy writes. “Most of the time, the jets consist of a steady flow of particles. Occasionally, though, they morph into more powerful outflows that hurl massive gas blobs at significant fractions of the speed of light.”

Years ago, Sivakoff’s colleague James Miller-Jones, currently based at the International Center for Radio Astronomy Research at Curtin University in Perth, Australia, conceived of a plan to mount a “multiwavelength campaign” to study the periodic outbursts that astronomers observe from X-ray binaries like H1743–322. They got their chance on May 22, 2009.

On that date, renewed activity around the black hole triggered the Burst Alert Telescope on NASA’s Swift satellite. Miller-Jones, Sivakoff, and the other members of the international team of observers were able to marshal three radio telescopes: the Very Long Baseline Array, the Very Large Array, and the Australia Telescope Compact Array. The team also drew on data from NASA’s Rossi X-ray Timing Explorer (RXTE) satellite (which was just switched off this week, by the way, after 16 years of meritorious service).

Using information from the telescopes and satellites, the scientists were able to reconstruct the events leading up to and following the ejection of black-hole bullets from the binary system. Sivakoff reported those findings today at the AAS meeting.

Now, finally, what about the “how” of this outburst? That’s not very clear yet.

In similar black hole binaries, Miller-Jones says, astronomers have measured ejections traveling 92 percent of the speed of light!  What process can shoot giant blobs of stuff out of the accretion zone of a black hole at such incredible speeds?

Sivakoff sketches out one possible explanation: Imagine knots of mass in the accretion disc, swirling around, getting closer and closer to the black hole. The disc is looped by powerful magnetic fields, which twist and tangle together as the disc rotates. When magnetic flux lines cross and connect, it could release enough energy to boost the black-hole bullets up and out of the disk.

“I think of a fairly stiff rope that is firmly to attached to the accretion disc,” Sivakoff explains. “As the disc spins, the rope is wound up, forming a sort of helix. Of course, there’s not one but many such ropes in an accretion disc. If two of those ropes touch — what astronomers call magnetic reconnection — lots of energy can be released. I like to envision ‘crossing the streams,’ a la Ghost Busters. This energy can accelerate particles, launching the bullet.”

There is another scenario, Miller-Jones says. Some scientists have proposed that what actually happens is that the inner edge of the accretion disc constricts, edging closer to the black hole’s “event horizon,” beyond which matter cannot escape. The magnetic and gravitational forces at this border region are extremely intense.

The forces could unleash a surge of material into the black hole’s paired jets, with a wavelike shock front ahead of it. “This causes particle acceleration,” Miller-Jones says, “and hence bright radio emission at this shock front.” So the bullets may actually be sudden surges in the jets, not discrete blobs.

But these explanations are just informed speculation at the moment. Additional multi-telescope observations could eventually provide enough clues to untangle the extreme physics that power black-hole bullets.

The team can only hope their recent stroke of luck holds out. Sivakoff says that the H1743–322  system conveniently started to flare up in late May 2009 — just as the team was preparing for the official opening of their observing window.

“Technically our observing was supposed to start in June 2009,” Sivakoff says. “But when this outburst went off a few days before our window was supposed to open up, we actually got permission to start observing earlier.”

So the discovery was the team’s inaugural run. “This was quite a trial by fire,” Sivakoff says.


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OH AND DID I MENTION? All opinions and opinionlike objects in this blog are mine alone and NOT those of NASA or Goddard Space Flight Center. And while we’re at it, links to websites posted on this blog do not imply endorsement of those websites by NASA.


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Coincidentally, about those exploding stars. . .

October 24, 2011 Leave a comment

An exploding star can release a massive amount of energy, an event called a gamma ray burst, as shown in this National Science Foundation illustration. But it's hard sometimes to tell the different between a statistical blip in data from the real thing.

An exploding star can release a massive amount of energy, an event called a gamma ray burst, as shown in this National Science Foundation illustration. But it's hard sometimes to tell the difference between a statistical blip in data from the real thing.


Phil Evans, an X-ray astronomer in England and frequent guest blogger for Geeked On Goddard, sends us this report on the fascinating nature of coincidence in science.


I have the power to make stars explode!

No, seriously. True, I can’t draw my sword and turn miraculously into a muscle-bound hero, like He-Man, nor can I turn my pet cat (Tinkabell) into Battle Cat, He-Man’s ferocious feline familiar.

But I really can make explosions at the other end of the universe. Skeptical? Here is the proof:

Last year, NASA’s Swift satellite (data from which I use in my work) was going through a bit of a lean observing period, with no gamma ray bursts (GRBs) detected for some time. GRBs are vast releases of energy from collapsing or collidign stars.

So, just as my duty week began at the University of Leicester, I tweeted, “Wake up universe!”

In the next 24 hours, Swift snagged four GRBs. Coincidence?

The only other time that we have had that many bursts in one day was the day celebrated science fiction author Arthur C. Clarke died? Coincidence?

Well, actually — yes. The thing is that coincidences happen all of the time.

A couple of years ago on her BBC Radio show, Sarah Kennedy asked people to send in their “coincidence” stories. Countless people mailed in about times they’d gone around the world on holiday, and met someone from three streets away. The response was continually, “Wow! Isn’t that amazing?” when what the was program actually demonstrating was that these “unlikely” events actually happen regularly.

In fact, when people respond to these stories by saying, “Small world,” they’ve got it totally wrong! It’s because it’s a big world that these things happen. Imagine something that only affects 1 in a million people. Pretty unlikely? Well, it will affect something like 300 Americans, and 60 Brits!

image of possible gamma ray burst

Image of possible gamma ray burst, or statistical blip? (click to make me big)

Coincidences happen. And this can be a real pain for astronomers. I’ve got some data, there’s a cluster of pixels close together. Is it a faint source, or just a coincidence that some background light has clustered? (See image at right.) This spectrum shows a blip. Is it a real feature, or just noise?

Fortunately, using statistics we can at least quantify how likely things are. Typically in astronomy we would only claim we’d found a source, for example, if there was less than a 0.3% chance that it was just a “lucky” fluctuation in the background. Even this happens, well, 0.3% of the time!

For Swift, we have to be even more conservative. When the Burst Alert Telescope (BAT) thinks it’s found a GRB, there has to be only a 0.0000000000008% chance that it’s just a fluctuation in the background [for us to interpret the observation as “probably real.” This threshold was carefully determined to minimize the number of false alarms, without losing real (possible) GRBs.]

Despite this, we do get a few false alarms every year, because of the number of times and ways the BAT looks for GRBs. We tried a “subthreshold” test a couple of years ago, where we triggered on things which were more likely to be spurious, that is, there was a 0.00000000006% chance of them being a random change in the background. We expected, and got, about 2 false alarms a day.

Overall, I’d say we get maybe 5 false alarms a year — but about 100 real GRBs. And the false alarms we usually identify within 20 minutes or so, so they take very little of our time.

So, next time someone tells you something unusual that’s happened, and asks if it could be coincidence, the best answer is probably, “Yes!”

Check out Phil’s twitter feed: @swift_phil

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OH AND DID I MENTION? All opinions and opinionlike objects in this blog are mine alone and NOT those of NASA or Goddard Space Flight Center. And while we’re at it, links to websites posted on this blog do not imply endorsement of those websites by NASA.

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Swift Detects Most Distant Object In The Universe! AGAIN!

May 25, 2011 2 comments

Now where have we heard THAT news before? For aficionados of NASA’s Swift satellite, or even space science and astronomy in general, this headline probably rings a few bells. Like this one for example, announced on April 28, 2009:

New Gamma-Ray Burst Smashes Cosmic Distance Record

But what many of you may not be aware of is that, within 24 hours of the April 28 headline, Swift detected yet another gamma-ray burst (the death-throes of a massive star), which was even more distant. Why didn’t you know? Well, because we didn’t either!

image of GRB 090429b
A Gemini Observatory color image of the afterglow of GRB 090429B, a candidate for the most distant object in the universe. This “izH” image has been constructed from three images taken at the Gemini Observatory North telescope through different optical and infrared filters. The red color results from the absence of all optical light, which has been absorbed by hydrogen gas in the distant universe. Without that absorption, the afterglow color would be bluer than any of the galaxies and stars seen here. (Credit: Credit: Gemini Observatory/AURA/NASA/ Levan, Tanvir, Cucchiara, Fox)

The explosion, termed GRB 090429B, was detected on April 29, 2009, by Swift. Nino Cucchiara and his then-PhD supervisor Derek Fox, along with collaborators including Nial Tanvir and Andrew Levan from the UK, observed the GRB with the 8-meter Gemini telescope in Hawai’i, and found that it was red. Very red.

Now this can mean two things: either it’s a really long way away, or it went off in a really dusty galaxy. So Nino and collaborators asked the Gemini operators to take a spectrum of the source, which would provide a measurement of the object’s distance.

Unfortunately, even on Hawai’i, astronomers are at the mercy of the weather. And just as Gemini prepared to take the spectrum, the weather turned and observing was impossible. By the next observing opportunity, the GRB was too faint to take a usable spectrum.

Fortunately, that’s not the end of the story, but it made the job much harder. Now, after two years of hard graft, and observations with Gemini and with the Hubble Space Telescope, Nino and collaborators have released their findings. And the cosmic record holder has fallen!

Well, probably. Their result shows, based on analysis of the images, that there is a 99.3 percent likelihood that this object was more distant that GRB 090423 — the object being trumpeted just before this star exploded. The precise distance is not known because of the lack of spectrum, but there is a 98.9 percent chance that is lies further away than a galaxy discovered in 2010 — 13.07 billion light years away — which surpassed April 2009’s GRB 090423 as the most distant known object. Whether it is the farthest object ever seen is not entirely clear: a galaxy detected in 2011 may lie a little further away…. or may actually not be a distant object at all.

Either way, this new result is another triumph for GRB science, for Swift and the optical and infrared facilities like Gemini, and above all for the hard-working determination of the scientists studying these enigmatic phenomena.

Follow Phil Evans on twitter: @swift_phil

Has-been: In 2008, GRB 080319b had it's 15 minutes of fame as the farthest known object in the universe.

A gamma-ray burst is a tremendous release of energy triggered by the collapse of a massive star.

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OH AND DID I MENTION? All opinions and opinionlike objects in this blog are mine alone and NOT those of NASA or Goddard Space Flight Center. And while we’re at it, links to websites posted on this blog do not imply endorsement of those websites by NASA.


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Phil Evans' Swift Universe: It's official — NASA's Swift satellite reveals a galaxy eating a star!

April 20, 2011 1 comment

Here is another guest post from Swift X-ray astronomer Phil Evans, “our man in the Midlands.” This time it’s an update about the galaxy that ate a star. — gogblog


Hungry? Fancy a snack? How about eating a star?

That, it seems, is what happened at lunchtime (in the UK) on March 28th. Here is an image of the burst from the Swift X-ray Telescope:


swift_grb_image_600

The Swift satellite detected what was at first thought to be a long Gamma Ray Burst (GRB), much like the 90-odd we detect every year although a bit on the long side. But then it “went off” again.

GRBs don’t do that. As it happens, I had just left to play football (alright, soccer if you insist) so I missed this second outburst, and I should point out that, although as your friendly blogger I’m telling this tale, it’s not my tale and I can’t claim any of the credit (alas!).

In fact, the first indication to me that this was a special event came that evening when, as I was replacing the grease filter in my cooker, my mobile phone rang. After degreasing myself enough to answer it I found that Dave Burrows, head of the Swift X-ray telescope team, asking if I could double-check some of the automatic results my code produces, because this object appeared to be weird.

(By the way, my twitter followers @swift_phil were among the first to learn that Swift had found something exciting and new!)

Weird it was. Gamma Ray Bursts get fainter over time. This didn’t, and hasn’t. Swift triggered on outbursts from it 4 times in 48 hours, and in the X-rays it remains bright today. (Back on April 7, NASA issued a press release about the event by science writer Francis Reddy.)

So what is it? Many astronomers have trained their telescopes on it in the past few weeks, taking data and reporting it quickly. Andrew Levan from Warwick University (UK) and collaborators used the Gemini telescope and found that the object was about 5 billion light years away! Further observations with infra-red and radio telescopes showed it to be right at the centre of it’s host galaxy.

Although only three weeks have passed since the event, papers are already appearing online. The consensus which is forming suggests that what Swift saw was a star straying too close to the super-massive black hole at the centre of its galaxy. The unfortunate star was torn apart and the pieces are now being gobbled up by the hungry black hole!

We’ve seen evidence for these events before — after the event — but Swift has captured yet another first: actually catching the black-hole perpetrating its massacre red-handed!

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OH AND DID I MENTION? All opinions and opinionlike objects in this blog are mine alone and NOT those of NASA or Goddard Space Flight Center. And while we’re at it, links to websites posted on this blog do not imply endorsement of those websites by NASA.

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Phil Evans' Swift Universe: Contemplating the inconstancy of the Crab

January 12, 2011 Leave a comment

New results from NASA space observatories have revealed something surprising about the Crab Nebula: This famous supernova remnant — long considered a veritable “old faithful” of X-ray sources for the constancy of it energy output — appears to be dimming over time. We asked Phil Evans, gogblog’s on-call X-ray scientist and a member of the NASA Swift Observatory science team, to tell us why the inconstancy of the Crab is so important to astronomers.

image of crab nebulaThe Crab Nebula has a prestigious history. It formed when a star exploded in a supernova, and was first observed and recorded by Chinese observers in 1054 AD. The glow of the supernova was so bright, people could see it during the day for more than 3 weeks!

The material which was blown off the star has been expanding since then in a complex structure with leg-like filaments that earned it its name. It’s also a very bright source of X-rays, and — particularly usefully — its brightness and spectrum don’t change; so astronomers can (and do) use it to calibrate their X-ray instruments. In fact, “a Crab” is an internationally recognized unit of measurement.

The problem is, these new results suggest that the Crab is not constant after all, according to a press release issued today by NASA’s Goddard Space Flight Center. The measurements taken over the last few years by the Fermi, Swift, RXTE and INTEGRAL satellites show that the Crab actually varies by a few percent every year. This is not too disastrous right now: It’s pretty hard to calibrate high-energy instruments to an accuracy of 1 percent or so, and the definition of “a Crab” as a unit of measurement has a fixed definition. But as technology advances, we will probably find that the Crab is no longer the ideal calibration source.

This type of finding, by the way, is not unusual. It is often the case that an object described as the “protoype” of its class turns out to be atypical! Indeed the star Vega, long used as a standard in optical astronomy, was recently found not to be standard. The exciting thing about all of this is it shows us how much we still have to learn. The Crab is among the brightest X-ray sources in the sky, and yet it is able to jump out and surprise us.

In a related point under the same press release, recently published work from the NASA’s Fermi Gamma-ray Space Telescope and the Italian Space Agency’s AGILE satellite have found large gamma-ray flares from the Crab Nebula. Investigation is ongoing, but this may indicate a really strong electric field. As study coauthor Stefan Funk said, “The strength of the gamma-ray flares shows us they were emitted by the highest-energy particles we can associate with any discrete astrophysical object,” which in themselves present plenty of challenges.

The Crab nebula: exciting and enigmatic? Yes! Constant and well understood? No! A fantastic natural laboratory? You bet.

— Phil Evans

Follow Phil on Twitter to get updates on his life and work in X-ray astronomy.
@Swift_Phil

chart of declining crab nebula x-ray output

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OH AND DID I MENTION? All opinions and opinionlike objects in this blog are mine alone and NOT those of NASA or Goddard Space Flight Center. And while we’re at it, links to websites posted on this blog do not imply endorsement of those websites by NASA.


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Phil Evans Swift Universe: how nature's strongest magnets power some of nature's brightest blasts

November 4, 2010 Leave a comment

A magnetar formed inside a collapsing massive star

A magnetar formed inside a collapsing massive star

Today “Swift Universe” guest blogger Phil Evans brings us some breaking news from the Gamma Ray Bursts 2010 conference in Annapolis, Maryland.

You’re all familiar with magnets. Well, two of my colleagues at the University of Leicester — Professor Paul O’Brien and his graduate students Antonia Rowlinson and Nicola Lyons — have announced evidence that some gamma-ray bursts (GRBs) are powered by stars called magnetars — super-strong magnets in space, if you like.

The idea is that, when the GRB goes off, the core of the dying star may not collapse straight to a black hole but instead could live for a couple of minutes as a rapidly rotating, magnetic neutron star called a magnetar. The magnetic field acts like a brake slowing the magnetar down and pumping its energy into the GRB, until after a few minutes the star has slowed down and collapses into a black hole.

Using data from the Swift satellite, my colleagues found that some GRBs show a period of constant brightness and then suddenly get really faint: just as the magnetar model predicts.

“So what?” you may ask. Well, GRBs are pretty much unique tools to study the early universe, and it’s the deaths of massive stars, some of which die as GRBs, which gives the universe the chemicals that you are I are made from. Getting a handle on the processes by which a star dies, and how it gives off its energy, is fundamental to using GRBs to study these matters. Showing that some GRBs are powered by magnetars is a big step forward.

One note of caution though: this isn’t “the” answer. While it seems to be the only explanation for some GRBS, in this same conference scientists from Berkeley university have shown using data from the Fermi satellite that the brightest GRBs can’t be powered by magnetars, but need a black hole right from the word go. Life’s never straightforward… but it’s often interesting!

Follow Phil as a Swift scientist on Twitter:  @Swift_Phil

Ron Cowen at Science News published a detailed write-up on the research.

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OH AND DID I MENTION? All opinions and opinionlike objects in this blog are mine alone and NOT those of NASA or Goddard Space Flight Center. And while we’re at it, links to websites posted on this blog do not imply endorsement of those websites by NASA.

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Our man in England: Guest blogger Phil Evans explains why you should care about a new X-ray nova in the Milky Way spotted by NASA's Swift observatory and a gizmo on the International Space Station

October 26, 2010 3 comments

before and after images of new x ray source in centaurusABOVE: The X-ray nova MAXI J1409-619 before (October 12) and after (October 17) it dramatically brightened.


What’s new in cosmic X-rays? This is: Astronomers in Japan, using an X-ray detector on the International Space Station, and scientists at Penn State University, using NASA’s Swift space observatory, have just discovered a new X-ray nova hiding inside our Milky Way galaxy in the constellation Centaurus.

Ho, hum, another day, another X-ray nova. I’m not an expert in cosmic thingies that emit X-rays, but I know someone who is: Phil Evans, gogblog’s on-tap X-ray astronomer. He’s a post-doctoral research assistant in the X-ray and Observational Astronomy group at the University of Leicester, and has previously appeared on the blog. I asked him to explain why this discovery is interesting. You can also read the Penn State press release for lots of details.

Gogblog:  Ok, Phil, so what’s the big deal about this X-ray nova?

Phil Evans: This may be a new Supergiant Fast X-ray Transients, or SFXT. It’s a class of object which INTEGRAL discovered, through their outbursts — Swift has since shown — are actually not so fast or transient at all!

These systems contain a giant star and a compact object such as a neutron star or black hole. Their orbit is rather eccentric — more an oval than a circle. The outbursts here occur because the giant star has a strong wind, blowing its outer layers off. As the stars pass close to each other, the compact object slams into this wind and a shock front forms ahead of it, heating the material up so that it emits X-rays.

What Swift has shown for many of these sources is that actually they emit X-rays outside of outburst as well. For — most of, maybe all of — the rest of the orbit, where the compact object is not shocking the giant star’s wind, it’s actually sucking it up. This wind falls onto the compact object and as it slams into the surface of the compact object it gets heated up and also gives off X-rays, albeit at a much lower rate than in outburst.

Gogblog: Two teams observed this thing, right? First scientists in Japan, who then alerted the Swift observatory to follow up.

Phil Evans: Yes. And this is a great example of why international collaboration is so important. The sky is so big that to spot something like this — a sudden bright outburst in soft X-rays— is almost impossible unless you have some device which looks at a large part of the sky, something like the MAXI instrument, which sits on the ISS and scans the whole sky as the station orbit the Earth. But then, working out what the object is and locating it accurately is impossible unless you have some device that can continue to look at the source for some time and with higher resolution: something like Swift.

Thanks to a collaboration between these two instruments, within hours of the MAXI discovery Dr. Jamie Kennea, a Penn State scientist who leads the MAXI-Swift transient team, had triggered Swift observations of the source. Swift was built to respond rapidly to phenomena it discovers for itself, but it’s pretty cool that it can also respond so fast to phenomena one of its cousins finds.



Learn more about Swift:


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OH AND DID I MENTION? All opinions and opinionlike objects in this blog are mine alone and NOT those of NASA or Goddard Space Flight Center. And while we’re at it, links to websites posted on this blog do not imply endorsement of those websites by NASA.

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Phil Evans' Swift Universe #1: a blinding X-ray GRB, the "nonsense and half-truths" of the science news cycle, and the thrill of prising open Nature's secrets

September 1, 2010 Leave a comment

*** gogblog is happy to announce a new guest blogger: Phil Evans. He’s an X-ray astronomer in England who taps into NASA’s Swift satellite for data. Swift is managed, as a project, from Goddard Space Flight Center, but it was developed by scientists in the United States, the United Kingdom, and Italy. Phil works at the University of Leicester in England’s East Midlands.

In an earlier post, I told the story of how Phil discovered a blindingly bright (in X-rays) gamma-ray burst. In “Swift Universe,” Phil will give us a backstage peek at the life of an X-ray astronomer and Swiftophile. Here’s his first post, where he gives you the low-down on Swift and his role in the mission.

Flash! X-rayss from this collapsing star temporarily dazzled NASA's Swift satellite

Flash! X-rays from this collapsing star temporarily dazzled NASA's Swift satellite

Welcome to the first Swift Universe blog, where you’ll get a (hopefully) insightful and (if you’re lucky) entertaining update on what’s going on in the universe, at least as far a member of the Swift satellite team is concerned.

Swift is a satellite which was launched in 2004 to study gamma ray bursts. These are thought to be the most powerful explosions in the universe. A typical gamma-ray burst, or GRB, gives off in 10 seconds as much energy as you would need to run your microwave for around 400,000,000,000,000,000,000,000,000,000,000,000 years, which is 30 million million million million times the age of the universe. Don’t try it; the bill will be horrendous.

I work in the UK branch of the Swift team, at the University of Leicester. I am part of the XRT team (that’s the X-Ray Telescope on Swift) and also part of the UK Swift Science Data Centre. My day to day work involves looking at the X-ray data from Swift and producing web-based tools to help scientists use these data.

Just recently I was involved in one of Swift’s discoveries: finding the brightest X-ray flash from outside our own galaxy ever seen. Not only was it exciting as a scientist, but it proved to be a very educational experience for me, as I was for the first time involved in writing a press release.

Although I’ve been tweeting in my role as a Swift scientist for some months now, I’ve never had to write more than 168 characters announcing something work-related to the public, and it was quite surprising how tough it was. All my natural instincts were to start blabbering on about pile-up, exclusion regions, correction factors, and ergs per second — most of which probably means nothing to most people.

Fortunately, press officers at NASA and Penn State University — and your own Geeked on Goddard blogger — were on hand, and they knew (as I now do) that “this was so bright it dazzled our telescope” conveys the “wow” factor much better than just floating numbers around does! It was a very good experience for me, and a reminder of how important it is for scientist to learn to communicate with the public. (See the Penn State press release about the X-ray GRB.)

click me to see the cartoon!

click to see the cartoon!

I am reminded of an excellent PhD Comic item lampooning “The Science News Cycle.” The jokes are a bit of an exaggeration, but not always so far from the truth!

And I think in the age of the Internet, where nonsense and half-truths can spread so quickly, it’s increasingly important for scientists to communicate properly. Take all of the climate change skepticism that exists at the moment for example. Why is it that so many people who are not trained scientists and without having conducted extensive research, tend not believe the scientists who really are experts?


“. . . in the age of the Internet, where nonsense and half-truths can spread so quickly, it’s increasingly important for scientists to communicate properly.”


I don’t know the answer, but if scientists were as good at communicating their research as skeptics and conspiracy theorists are at communicating their doubts, perhaps this situation would not exist.

Like a lot of us, you might be wondering WHY that GRB was so bright in X-rays, especially as it was at other wavelengths a fairly typical burst. Right now, we still don’t know.

I suppose you could call this the “unsexy” part of the science, although this can be where the real excitement comes and you just can’t see it. In public we show the thrill of the discovery, and eventually the satisfaction of writing a paper explaining it. (This effort will be led by Tilan Ukwatta at Goddard Space Flight Center, who was the duty scientist with overall responsibility for this GRB).

But in between comes the real work and (for us) the real fun. It’s the subtle cut and thrust duel with the universe as we try to prise open its secrets, exploiting the details of our data, battling with their limits and finding out how it all fits into the bigger picture. It probably doesn’t make for exciting reading as we go along (“Within 3-sigma we’re consistent with the k=2 closures, assuming…..”) but when you consider the vastness of the universe, plugging away at its mysteries is a real privilege, and the reason we’re in this business.

My own current theory probably won’t make it into the scientific paper: this year the University of Leicester celebrates 50 years of performing space science research. Although the GRB went off before the celebratory conference, thanks to my holiday we didn’t make this discovery until the conference has started. So the cause is obvious: the universe was saying “Happy Birthday” to Space Science at the University of Leicester!

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OH AND DID I MENTION? All opinions and opinionlike objects in this blog are mine alone and NOT those of NASA or Goddard Space Flight Center. And while we’re at it, links to websites posted on this blog do not imply endorsement of those websites by NASA.

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And then the universe said 'Hah!' NASA's Swift satellite can't believe its eyes when it spots the brightest X-ray glow from a gamma ray burst outside our galaxy

July 14, 2010 14 comments

Credit: NASA/Swift/Mary Pat Hrybyk-Keith and John JonesThree weeks ago, a distant point in space in another galaxy released a blast of X-rays so bright even the satellite that saw it first didn’t believe its eyes. Then Phil Evans came home from vacation and got very, very lucky.

“One of the things I personally like most about doing research,” he says, “is when you discover something brand new — even if it’s ‘just’ the brightest X-ray object that we think we’ve ever seen — there’s a moment when there is only one person in the universe who knows about this. And sometimes you get to be that one person.”

It went down this way: On June 21, NASA’s orbiting Swift observatory was on sentry duty for Earth’s astronomers, watching the universe for Gamma ray bursts. A GRB went off on June 21, later catalogued GRB 100621A. (GRBs are violent eruptions of energy from the explosion of a massive star turning into a black hole.)

Gamma ray bursts announce their appearance as, well, a burst of gamma rays. Since gammas are the most energetic form of electromagnetic radiation, GRBs are the most powerful beacons in the universe.

When Swift detects a burst, it radios the coordinates to Earth. Astronomers and robotic observatories scramble to aim their instruments at the GRB. Swift also slews its instruments, such as the X-Ray Telescope (XRT), to the target.

Swift's X-Ray Telescope captured this image of GRB 100621A

Swift's X-Ray Telescope captured this image of GRB 100621A

Ideally, astronomers want to observe both the immediate or “prompt” emissions and, as time passes, the fading afterglow of X-rays, ultraviolet light, and (rarely) visible light.

Swift beams to Earth a record of when it detected each photon, and then software on the ground turns this into a “light curve” — literally a record of how the GRB’s brightness changes over time in various wavelengths.

Meanwhile, back at the lab…
OK, enough about Swift; back to Phil. He’s is a post-doctoral research assistant in the X-ray and Observational Astronomy group at the University of Leicester in England, and part of the Swift team. He wrote the software that converts the photo detections from Swift into light curves.

So he got home from holiday on June 29. The next morning, he examined the light curves that his software had created while he was in the Lake District in North West England, camping with his wife and two young sons.

And he saw something very puzzling: For one event, GRB 100621A, the record of its earliest X-ray emission was missing. He’d also received an email from another astronomer who had also noticed the gap.

Swift beauty 1 202“I looked at this and thought that’s odd, I’ll have to come back to it. I was looking at it and thinking, this is very strange.”

By noon, he had the data gap plugged. It took him a few more hours to check it, and to appreciate what had actually happened. The next day he announced it to the rest of the Swift community around the globe.

It turned out that GRB 100621A had been so bright early on, it had temporarily blinded Swift’s detectors. At the center of the image, which is the brightest part of the image, X-rays streamed in at a peak rate of 143,000 per second — well, for 0.2 seconds, anyway! But the X-ray camera literally could not count that fast. It was like a lone soccer goalkeeper being fired at by a dozen World Cup strikers.

Correct me if I’m wrong
Phil’s light-curve-making software has a way of dealing with this situation. It counts the X-ray photons streaming in around the edges of the image, where it’s not so bright and intense. Then it multiplies that by a correction factor to estimate how bright it must be in the glaring center of the image.

This correction was used in the famous “naked eye” GRB 080319B of 2008, which was so bright you could have seen it without a telescope, briefly, in a dark location on Earth. The correction: 32 times.

Correction for the June 21 GRB: 168!

Phil designed the software so that if the correction factor exceeds a certain expected threshold, the software just doesn’t report the data to astronomers on the ground. In a sense, Swift didn’t believe its own eyes.

“When it did the correction, it saw the size of it and said, no, that’s got to be nonsense, there’s got to be some sort of mistake,” Phil explains. “It just said, ‘This can’t be real. I’m not publishing this to the world because I’m going to look like an idiot.”

Or to put it more politely, Phil’s software refuses to report what it determines to be bad data. But it wasn’t bad; it was spot-on correct.

Swift beauty 2 202A new (X-ray) world record

“I didn’t totally register at first how bright it is, and then I mentioned it to a few people, and they went ‘What!’ And then we started to get a better feel for the fact that this was something to put in your record books.”

What kind of record are we talking about?

When the system was designed, astronomers weren’t expecting to see anything as bright as what Swift saw on June 21. The next brightest such object in X-rays was 2008’s naked-eye GRB 080319B.

This GRB was seven times fainter but twice as far away as the June 21 event. But move the new record holder to the same distance, and it would still be 1.5 times as bright as GRB 080319B.

Both of these events happened outside our Milky Way Galaxy. For example, the June 21 GRB happened 5 billion light years away, which means the light from it left about the time our solar system formed. There are brighter X-ray sources in our own galaxy, but that’s like comparing your next-door neighbor’s porch light to the blinking aircraft beacon atop a radio tower 10 miles away.

Relative to Swift, the latest GRB is a clear record-breaker. It is definitely the brightest thing, GRB or otherwise, Swift’s X-ray eye has ever seen.

And that is, perhaps, the most striking thing about this whole episode: the way in which this latest GRB has confounded expectations.

Barbara Kennedy said it best recently on a teleconference with Phil and a couple of other scientists, including Dave Burrows of Penn State University (PSU), the lead scientist for Swift’s X-ray telescope. Barbara is a press officer for PSU, which has issued a release about the event.

We — the scientists, Barbara, and a couple other media people who cover Swift — were discussing what approach to use to explain this GRB to the public. Biggest? Brightest? First?

I thought Barbara nailed it when she said:  “The best scientists in the world thought ‘We’ll never see anything that bright, so we don’t have to design the software to handle it.’ And then the universe said ‘Hah! Look what I can throw at you!'”

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Phil_40Follow Phil Evans in his role as a Swift Scientist on Twitter: @Swift_Phil, where news of this discovery was first announced!]

See Barbara Kennedy’s press release on the X-ray GRB on the PSU website.

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OH AND DID I MENTION? All opinions and opinionlike objects in this blog are mine alone and NOT those of NASA or Goddard Space Flight Center.


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