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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: 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 #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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Night owls: meet the duo of amateur astronomers in Japan who discovered the star that delivered a "shocking surprise" to NASA's Fermi Gamma-ray Space Telescope

August 12, 2010 12 comments
Click to read Japan Times article about Nishiyama & Kabashima

Click to read Japan Times article about Nishiyama & Kabashima

On March 11, 2010, the evening skies were clear over the town of Miyaki in Saga Prefecture on the island of Kyūshū, Japan. Two elderly stargazers, though comfortably retired from their jobs, were just getting to work in their Miyaki Argenteus Observatory.

All night, Koichi Nishiyama, 72, snapped pictures of the sky through the barrel of a 16-inch-wide reflecting telescope. His observing partner, Fujio Kabashima, 70, used computer software to compare the images with shots of the same patches of sky taken on previous nights.

In the pre-dawn hours, Nishiyama and Kabashima finally nabbed themselves a nova — the sudden, short-lived, and dramatic brightening of a formerly inconspicuous star. This particular star, V407 Cyg, lies about 9,000 light-years from Earth in the constellation Cygnus the Swan. Nishiyama and Kabashima determined that V407 Cyg had flared to 10 times its former brightness.

The amateurs reported the observation to astronomer Hiroyuki Maehara at Kyoto University, who notified his colleagues around the world so they could organize follow-up observations. Three other Japanese observers — Tadashi Kojima, Kazuo Sakaniwa and Akihiko Tago — reported the same nova the next day, March 11.

PR buttonOn March 11, NASA’s Fermi Gamma-ray Space Telescope started picking up gamma rays streaming from a new source in Cygnus, which turned out to be V407 Cyg. This was totally unexpected and out of character for a nova. It’s the topic of a major press release from Goddard today and the subject of an electronic publication in the journal Science. (Actually, Nishiyama and Kabashima are co-authors on the Science paper.)

Fermi's Large Area Telescope saw no sign of a nova in 19 days of data prior to March 10 (left), but the eruption is obvious in data from the following 19 days (right). The images show the rate of gamma rays with energies greater than 100 million electron volts (100 MeV); brighter colors indicate higher rates. Credit: NASA/DOE/Fermi LAT Collaboration

Fermi's Large Area Telescope saw no sign of a nova in 19 days of data prior to March 10 (left), but the eruption is obvious in data from the following 19 days (right). The images show the rate of gamma rays with energies greater than 100 million electron volts (100 MeV); brighter colors indicate higher rates. Credit: NASA/DOE/Fermi LAT Collaboration


Sky lovers
The Fermi discovery is a perfect moment to celebrate hard-working amateur observers around the world like Nishiyama and Kabashima. These folks make significant and valuable contributions to astronomy every day.

So let’s give these sleepless gentlemen from Saga Prefecture their nova-nabbing props, and in their own words. Special thanks to Hiromitsu Takahashi of Hiroshima University for relaying my questions by email to Nishiyama and Kabashima and translating their responses.

gogblog: To date, how many novae and or other objects you have spotted and reported officially?

Nishiyama & Kabashima: “We started observations on August 1st 2007. Up to now, we have discovered 53 novae and one supernova (SN2009ls, on November 26, 2009). Of the novae, 13 are galactic and 40 extragalactic.”

Just a quick pause for the science literacy cause: “Galactic” refers to novae in our Milky Way Galaxy. “Extragalactic” means it happened in other galaxies.

And let’s be clear about another thing: Spotting 53 novae in three years is an extraordinary achievement for any human observer. In 2008, they discovered five in a single year, tying the record set in 1991 by Australian Paul Camilleri. In March 2008, the pair received a special award for their achievements from the Astronomical Society of Japan.

What better person to put it in perspective than astronomy author Stephen James O’Meara, one of the most celebrated amateur observers in the business.

“Nova hunters are a dedicated group of amateur astronomers who demonstrate infinite patience,” Steve says. “What does seem to stand out about Nishiyama and Kabashima’s success is its magnitude. Most nova hunters spend years searching before they find one. Bill Liller (in Chile), for instance, has been searching in earnest, I believe, since the mid-1980s. Yet Nishiyama and Kabashima have nearly tied him in galactic nova discoveries in only three years time! That’s almost unheard of. It means that either their observing conditions are exceptional or that they are exceptionally fortunate when they do have clear skies to nab most of the few novae that occur briefly in the Northern skies each year.”

Japanese amateur astronomers discovered Nova Cygni 2010 in an image taken on March 10 (4:08 a.m. Japan Standard Time, March 11). The erupting star (circled) was 10 times brighter than in an image taken several days earlier. Credit: K. Nishiyama and F. Kabashima/H. Maehara, Kyoto Univ.

Japanese amateur astronomers discovered Nova Cygni 2010 in an image taken on March 10 (4:08 a.m. Japan Standard Time, March 11). The erupting star (in center of circles) was 10 times brighter than in an image taken several days earlier. Credit: K. Nishiyama and F. Kabashima/H. Maehara, Kyoto Univ.


And it’s not like Nishiyama and Kabashima don’t have any competition. . .

gogblog: How many other amateur observers in Japan are doing this kind of work?

Nishiyama & Kabashima: “There are about 50 amateurs searching for supernovae in Japan. Among them, the number of the people who have really discovered them (and are still observing actively) is about 10. In the case of novae, because the observation requires relatively simple equipment, many more people are searching. However, the number of the discoverers is similar to that of the supernovae (about 10).”

gogblog: Is there friendly competition between the observers to be the first to discover new objects?

Nishiyama & Kabashima: “Yes. We think all the observers are not only rivals but also friends. Actually, we send/receive emails very frequently with some of them — for example, Hideo Nishimura in Kakekawa city, Shizuoka prefecture, who has discovered the same number of galactic novae as us. Also, Koichi Itagaki in Yamagata city, Yamagata prefecture, who is one of the leading discoverers of supernovae.”



Despite getting through many nights on just three hours of sleep, Nishiyama and Kabashima appear to have inexhaustible enthusiasm for nova hunting. This is not really surprising, considering that the word “amateur” is French for “lover of,” ultimately derived from the Latin for “lover.”

gogblog: After discovering so many objects, what motivates you to continue? What holds your interest about this work?

Nishiyama & Kabashima: “Following our discoveries, many researchers take the spectra and study them. Some of them contact us to ask for more information or to give feedback, such as confirmation of the brightening. Therefore, we understand our activities are helpful for the research of astronomy and astrophysics. It’s our motivation. We really hope that our discoveries are useful for the research. We try to observe the sky every night with little sleep if the weather is fine.”

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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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