Welcome to the summer 2006 issue of the Swift newsletter. Its been an eventful season! We had a wonderful gathering of the GRB community this summer in Venice organized by the Swift Italian lead, Guido Chincarini and colleagues. On the secluded island of San Servolo we spent a week looking at and discussing the GRB results from Swift and other observatories. Up to now we have studied individual bursts, but we now have enough data from Swift to start drawing conclusions about the ensemble of GRBs and we got a surprise. When the distances to the 150 GRBs Swift has detected in the past 1.5 years are plotted (as shown in the accompanying plot by Jay Norris), the surprising result is how far away they are: on average, their light has been traveling to us for 10.8 billion light years. To put that in perspective, the big bang is thought to have occurred 13.7 billion years ago, so the typical Swift GRB was produced in the early epochs of the universe. Previous, less sensitive, GRB missions had put the average light travel time at 8.5 billion light years. Swift Newsletter Why are the bursts so far away on average? One reason is that long-duration GRBs are produced by the explosions of massive stars where their cores collapse to black holes. Such stars are spread throughout the universe, and therefore have a naturally large average distance. But there may be more to it: GRBs are very rare among stellar explosions, and it is beginning to appear that a key requirement to make a GRB is a low amount of heavy elements (heavier than helium) in the exploding star when compared to the Sun. We expect this of early stars in the universe, before heavier elements were created in other stellar explosions. e heavy element abundance aects many characteristics of the star, and can play a large role in whether it explodes as a GRB or not. We are very excited to see how this plays out as more GRBs are detected by Swift and more theoretical study given to the results. Issue 5 August. 2006 Plot by Jay Norris click to enlarge National Aeronautics and Space Administration Welcome Message from PI Neil Gehrels Swift Guest Investigator Program Opens Up for Non-GRB Science By: Padi Boyd, GSFC e deadline for science proposals for Swifts third year of guest investigations was July 28. New for Cycle 3, scientists can now propose to point the Swift telescopes at non-GRB cosmic sources in the sky. is is called a target of opportunity (TOO) observation: when an object does something interesting (like explodes, or has an outburst), then Swift will take the opportunity to point at it. Such events include new supernovae, outbursts of known sources, new black hole and neutron star transients in our own Galaxy, and ares seen in distant active galaxies---just the type of eeting events for which Swifts rapid response and multiwavelength capabilities are perfect! NASA received 87 proposals for Swift Cycle 3, and 33 of these are for TOOs. e ideas presented in the proposal run the gamut from the relatively nearby novae in our galaxy to distant blazars far beyond the Milky Way. In between, scientists want to use Swifts instruments to look at pulsars in binary star systems, the X-ray binary Cyg X1 (the black hole poster child of our Galaxy), study whether supernovae are standard candles (that is, can be used to measure distances) in the ultraviolet, and support observations of newly detected transients seen by other orbiting spacecraft such as INTEGRAL, RXTE, and the soon-to-be-launched GLAST. In October, an international panel of scientists will meet to discuss the merits of all proposals submitted and choose among them. is will shape the science program for Swifts third year. We wish all proposers the best of luck, and we look forward to a bright future. Guest Investigators will make sure Swift continues to make important contributions to many areas of astrophysics and work with other satellites to provide multiwavelength views that would not be possible otherwise.
Swift Sees a Dierent Kind of Explosion By: Kim Page and Michael Bode, University of Leicester On 12th February 2006, the recurrent nova RS Ophiuchi went into outburst for the rst time in 21 years. It is one of only a few novae which erupt every few decades, rather than on timescales of thousands of years as do classical novae. e RS Oph system consists of a white dwarf (thought to be near the upper mass limit for such a star) and a red giant, in a 456-day orbit around each othersuch a system is called a binary. e white dwarf accretes matter from the outer layers of the red giant until there is sucient hydrogen on its surface to explode like a runaway nuclear bomb. anks to the rapid turnaround of the Swift Target of Opportunity system, we obtained X-ray observations of RS Oph far more rapidly and frequently than has ever been the case for previous outbursts of such systems: observations started after only three days and have continued ever since. All three instruments onboard Swift have observed (and detected) RS Oph. For the UVOT, the grisms had to be used the source was far too bright for the lters! In addition, when the BAT data were examined, we found that the source was detected during the outburst itself (see gure) the rst time this has been accomplished for any nova. For the rst few days, the X-ray emission brightened rapidly, then began to fade. is emission is thought to be from shock waves generated as ejecta from the nova, traveling at several thousand km per second, slam into the stellar wind from the red giant at a large distance from the stars themselves. A paper is now in press with the Astrophysical Journal about this aspect of the nova, where RS Oph acts like a dramatically sped-up supernova remnant. About a month after the outburst the character of the emission changed dramatically and seemed to be coming from the central binary itself. Work is now in progress to fully understand this new phase. 2 Swift in the News by Lynn Cominsky, SSU E/PO 3/31/06 Exploding star within a star X-ray observations by Swift of the outburst from RS Ophiuchi were reported at the Na tional Astronomy Meeting in the UK. RS Oph is a binary system containing a white dwarf orbiting around a red giant star. For more information see newsletter article or the UK Swift sit e ( http://www.swift.ac.uk/ RSOph.shtml ). 4/4/06 An unusual burst in distant Uni verse. Swift detected a burst on August 1, 2005 that made the news at the National Astron omy Meeting in the UK. GRB 050801 was unusual in that Swift observed a bright after glow with steady emission both in X-ray and optical wavelengths that lasted for 250 sec onds after the end of the prompt gamma-ray emission, and occurred before the afterglow began its typical decline in brightness. Scien tists have suggested that the end product of this GRB could have been a magnetar, rather than a black hole. 5/12/06 X-rays Fly as Cracking Comet Streaks Across the Sky. Scientists using NASAs Swift satellite have detected X-rays from a comet that is now passing the Earth and rapidly disintegrat ing on what could be its nal orbit around the sun. e press releas e ( http://swift.gsfc. nasa.gov/docs/swift/news/2006/06-35.html ) is on the NASA Goddard Space Flight Cen ter website, and the image is on the NASA sit e (http://www.nasa.gov/mission_pages/swift/ main/index.html). For links to all of these press releases and im ages, see: http://swift.gsfc.nasa.gov/docs/swift/news/
by email that they have won the GRB lottery, and then they can download a certicate with their name, the name and location of the burst, which satellite saw the burst, and when the burst was detected. As a prize, they can also order an educational product from the SSU group, an ability usually reserved for teachers and scientists. e Lottery page itself has lots of charming graphics, including an animated Swift that follows your cursor and a GRB that runs away when you try to point to it. e site comes with complete instructions, and also has a tutorial about GRBs which includes a history of how GRBs were rst discovered, and the science behind these violent and exciting explosions in deep space. e GRB Lottery By: Phil Plait and Tim Graves, SSU E/PO Observing gamma-ray bursts is frustrating. ey may only last for a few seconds before fading into obscuri ty, making them very hard to detect. Worse, they ap pear in random parts of the sky, meaning they might pop o during local daytime, or below the horizon. Its an astronomers nightmare. But it can also be an educators dream. Why not take the random time and placement of the next GRB and turn it into a game for students? at way, the very thing that makes GRB astronomy dicult for scientist becomes an exciting way to engage students about the highest of high-energy events. ats ex actly what the SSU E/PO group did by creating the Gamma-Ray Burst Lottery: http://swift.sonoma.edu/grb_lotto / When students enter the game, they pick a spot on the map where they think the next GRB will ap pear. ey can then enter a screen name and a rea son why they chose that spot -creativity is encour aged! When the next GRB is detected, the location is checked against all the students guesses. e student with the closest guess wins the game! eyre notied Swift is ideal for following such an event, since we could obtain X-ray and UV/optical data simultaneously, and, at peak brightness, we were observing RS Oph during every orbit of the day! Observations are planned until the end of October at least; RS Oph will then not be visible to Swift until early next year. 3 Swifts Burst Alert Telescopes X-ray view of the region around RS Oph about two days before (left) and two days after (right) the outburst. e nova is clearly visible in the later image.
Amateur Corner By: Phil Plait, SSU E/PO GRBs are becoming a favorite target for amateur as tronomers who love the thrill of the chase. One such skywatcher is Michael Koppelman, who lives near Minneapolis, Minnesota. By day hes a part owner of Clockwork.net, a company that develops websites and applications he created an automated skychart plotter for the American Association of Variable Star Observers (AAVSO), for example but by night hes an avid astronomer. Koppelman built his Starhouse Observatory on a friends farm in 2000, after getting tired of lugging around his telescope. He became hooked on digital imaging and it didnt take long before he started look ing for GRBs. I thought hunting GRBs was a very cool thing for amateurs to do and so I signed up for the [GRB alert] email list. But they always seem to go o when Im at home or at work. But persistence pays o. ere came a night in April of 2006 when the stars aligned for him. Finally, the dome was open, I was observing, and the alert came in. e GRB was like 11 degrees above the horizon, literally in the trees, but I was on the thing within about ve minutes. I didnt see it at rst but later pro cessing brought it out. He sent the data to the AAVSO, and they issued an email circular about i t (http://gcn.gsfc.nasa.gov/ gcn3/4977.gcn3) : Koppelman had denitely detected GRB 060418A, which turned out to be at whopping distance of more than 9 billion light years away. He was amazed at this result. When I rst calculated the distance, I did it naively, and I got that it was far ther away than possible. Like a kazillion light years away! I had to fold in relatively and cosmology to get the right number. Michael Koppelman standing outside his Starhouse observatory. 4 Koppelman has information about his observatory and the work he does on his websit e (http://www.lolife. com/astronomy/starhouse/Home.html) He also keeps a blog there, where he wrote about bagging his rst GRB. He hopes it isnt his last, though. e next time Im in the right place at the right time I want to capitalize on it better. Id like to show people a three hour time series of itno one has anything like that. Im poised, Im ready. Every time I go out, I think, come on, lets get a GRB! In the meantime, hes working on getting his under graduate degree in astronomy; hes only one course credit away. And between GRBs, he uses his observa tory to observe suspected variable stars. His attitude is one every astronomeramateur or professional shares. A lot of run-of-the-mill stu comes up, but a lot of interesting objects show up, too. Its fun to unravel the puzzle of stars.