ABOVE: 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.
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.
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.
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.
On 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
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 (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.”
_____________________________________________________________________________________________________ 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.