In This Issue:
Swift Year in Review - PI Neil Gehrels
I have been looking forward to tell you about a profound change that is happening with Swift. The observing program is evolving toward a broader range of science topics. This is dramatically illustrated in Figure 1 showing observing time fraction. The fraction of time spent observing gamma-ray bursts (GRBs) has declined since 2006 while more time is spent observing non-GRB Targets of Opportunity (TOO) and Planned Targets.
There are several reasons for the evolving observing program. Swift is still NASA's GRB satellite and that is the primary science. However, we are now being more selective on which GRBs to observe. The satellite continues to respond to every burst that the burst alert telescope (BAT) detects, but x-ray telescope (XRT) and ultraviolet/optical telescope (UVOT) afterglow observations are now terminated earlier for some GRBs. Nowadays, we only follow the most scientifically interesting bursts and ones that are not near the sun on the sky. Sunward bursts are not good for our friends with ground-based telescopes since they are not visible much at night. By dropping the sunward bursts, we are able to keep the satellite more oriented toward the night sky which means a higher fraction of new bursts away from the sun. It is counter-intuitive, but spending less time on GRBs actually gives us better ones on average. Less is sometimes more!
Figure 1: TOOs are "targets of opportunity" which are astronomical sources we point the observatory to on a rapid turn-around basis at community request. Planned Targets are sources that the Swift team and community submit for observations when the observatory is not busy with GRBs and TOOs. Down time is when the instruments are not taking data while Swift is orbiting through high radiation zones or when we are taking calibration data.
The other big reason for the evolving program is that researchers in non-GRB areas of science are discovering Swift's capabilities. They are flocking to our gates at ever increasing numbers as can be seen in Figure 2.
The rate at which TOOs are being requested is increasing dramatically. Scientists send us requests on the Web to observe new or varying objects in the sky, based on data they have from other telescopes or sometimes from our own BAT. We then send a command up to Swift to re-point XRT and UVOT in that direction - just like for a GRB, but with ground command. When a request comes in, I review it for approval and then the Penn State Mission Operations Center (MOC) generates and sends the command. The MOC scientists have gotten very proficient at doing this quickly, sometimes in just a few minutes. Swift now has by far the highest TOO rate of any astronomical satellite. On average we perform one or more TOOs every day, 7 days a week.
The Swift TOOs are a boon for science and great excitement for the team. Here is brief list of discoveries coming from the TOO program:
It is fun looking through the list of more than 700 Swift TOOs to pick out the gems above. There are pages of interesting findings that could be listed. We look forward to the next 700 TOOs!
Figure 2: The increase in the rate of TOO observations performed by Swift is seen in this plot.
By John Nousek, Penn State, Swift Mission DirectorHere at the Mission Operations Center (MOC) we have just celebrated the fourth anniversary of the launch of Swift. The observatory is operating at peak efficiency, and we believe that the performance is even better that it was at launch, due to small improvements to the flight software.
The observatory points at targets more accurately with our latest 'three-gyro' attitude control (instituted in October, 2007). We also respond more often to Targets of Opportunity and modifying GRB observations to maximize science by using a highly flexible Automated Target re-planning which enables the team to make changes anytime, day or night, without travelling to the MOC.
The burst alert telescope (BAT) has increased its science yield by making experiments with lower thresholds to detect faint GRBs, and to search for GRBs via ground processing of data collected during slews. The x-ray telescope (XRT) has improved its GRB localization by utilizing the ultraviolet/optical telescope (UVOT) as a super-accurate star tracker, and has reduced the detector background by raising voltages on the CCD chip. The UVOT has refined the GRB observing parameters to enable observations at very early times using the grisms, which included tuning the safety circuit parameters to protect the instrument while still allowing sensitive grism observations of bright sources.
In the year ahead we are working with the Swift spacecraft manufacturer, General Dynamics, to introduce an observatory flight software patch to let us return to a 'two-gyro' mode of operation, but with precise alignments to keep or improve on the current pointing accuracy. We are also planning on a flight software change to the star tracker software to eliminate a bug which has been resulting in occasional attitude safeholds. (Note that even with the bug, we have been averaging better than 99% 'up' time - defined as time when we are actively able to use the observing time to detect GRBs.)
We have received funding to continue Swift operations for another two years and a budget plan for two years beyond that.
We believe that the observatory is in excellent condition to carry out the exciting work of discovery - from GRBs to supernovae, to cataclysmic variables, to Active Galactic Nuclei - with unique capabilities for rapid response, multiple duration monitoring, and high energy transient discovery!
Guest Investigator Program Success
By Stefan Immler (NASA/GSFC)
In January 2009, a panel of scientists will meet to discuss the merits of all submitted proposals and choose those that are recommended for funding and observing time. The accepted targets will shape the science program for Swift's sixth year of operation. Cycle 5 observations and funding will commence on or around April 1, 2009, and will last approximately 12 months.The Swift GI program will continue to solicit proposals in GRB and non-GRB research in Cycle 6. In response to requests by the community, we expect that a larger number of monitoring programs will be accepted during Cycle 6. Notice of Intent for Cycle 6 proposals will be due September 16, 2009 and the deadline for submitting Cycle 6 proposals is October 28, 2009.
The Naked-Eye Gamma-Ray Burst
By Judith Racusin (Penn State)
Gamma-ray bursts (GRBs), one of the most extreme astrophysical phenomena ever observed, result from a stellar explosion due the collapse of a massive star to a black hole or neutron star in which material is ejected at nearly the speed of light in narrow jets. The shells of material crash into each other and the surrounding environment producing an initial burst of gamma-rays followed by a fading multi-wavelength afterglow.
These rare stellar deaths briefly outshine their entire host galaxies and have been seen from enormous distances that are comparable to the most distance quasars. Despite these extreme conditions, the optical counterparts are usually faint, fade quickly, and are often obscured by dust and gas in their host galaxies. Astronomers never imagined there would be a GRB that was visible to the unaided eye for even a brief moment, and certainly not at a distance of nearly halfway across the Universe.
That all changed on March 19, 2008 when NASA's Swift satellite discovered one of the brightest GRBs ever seen in the 40-year history of the field accompanied by the brightest optical and X-ray counterparts ever observed. With the help of a little luck, the extreme brightness of the transient, and the preparedness of the follow-up community, robotic telescopes observed GRB 080319B starting from minutes before the time of the explosion and a well-coordinated campaign followed for weeks afterwards.
As reported in a recent paper in the journal Nature (Racusin, et al., 2008, Nature, 455, 183), the combinations of these gamma-ray, X-ray, ultraviolet, optical, infrared, millimeter and radio observations are the best broadband dataset ever obtained.
Swift in the News
By Logan Z. Hill (SSU E/PO)
9/10/08 - "Naked-Eye" Gamma-Ray Burst Was Aimed Squarely At Earth GRB 080319B, the March 19th, naked-eye observable, 7.5 billion light year distant, awe-inspiring gamma-ray burst was determined to be aimed directly at Earth. A paper published in Nature by Judith Racusin and 92 coauthors calculated the material shot from the object towards Earth travelled at 99.99995 percent the speed of light. To read more visit the Official GSFC Press Release.
9/19/08 - Swift Catches Farthest Gamma-Ray BurstGRB 080913, the most distant gamma-ray burst so far, was detected by Swift on the 13th of September. The estimated distance of the burst is 12.8 billion light-years (redshift of 6.7), and is located in the constellation Eridanus. GRB 080913 beats the previous distance record holder by approximately 70 million light-years. For more information visit the Official GSFC Press Release.
9/29/08 - A Day in the Life of Swift Scientists
Brady Haran has made a film Day in the Life: Astrophysicists for the East Midlands STEM Partnership.
It follows two scientists, Rhaana Starling and Phil Evans, and their use of Swift to study gamma-ray bursts. The video is hosted on YouTube here: http://www.youtube.com/watch?v=8icydzuxd84
All Swift related news and images can be found here.
As is common with an observational science, better observations don't necessarily confirm our theories, but rather force us to ask new questions. With the detailed optical and gamma-ray observations during the burst itself, we learned that these components must have come from the same physical region, but different radiation mechanisms. Therefore, the gamma-rays couldn't be produced by the typical synchrotron mechanism attributed to other bursts.
As the shock wave swept up the surrounding material, the afterglow faded at different rates between the X-ray and optical, both of which appeared rather different than the usual pattern. Rather than the usual one sudden decrease in flux that indicates the slowing of the ejecta and the edge of the jet, we saw two.
By assembling all of the observational pieces of the puzzle, we concluded that the emission from GRB 080319B was concentrated into a very narrow jet with an opening angle of 0.4 degrees, that just happened to pointed right at us, surrounded by a wider slower jet of material with an opening angle of 8 degrees.
The small probability of this occurrence explains both the unusual observational properties and the rarity of naked-eye GRBs. This suggests that if all GRBs have this two-component jet structure, then we usually only observe the wide jet. The implications on GRB energy outputs, geometry, and physics are far reaching.
By Kevin McLin (SSU NASA E/PO)
A single night's break in the Northern California clouds during the first week of December was all it took for GORT, the 14-inch robotic telescope run by the SSU E/PO Group, to catch its first GRB. On December 3rd, Swift detected and localized a GRB in the far northern sky, at about +63 degrees. News of the burst was automatically sent out via the GRB Coordinates Network (GCN) to observatories throughout the world, as well as to the Skynet server at the University of North Carolina. At that moment, Skynet was controlling GORT. Though the burst was midway up from the northeastern horizon as seen from Sonoma, and the sun was a mere 13 degrees from rising, Skynet directed GORT to slew and begin observing. In the brief minutes before the twilight became too bright, GORT captured five images, the earliest ones obtained from the ground for this gamma-ray burst.
Skynet has standard software it runs for a GRB alert. As directed by the script, GORT made a series of R and I images. The first, in I, started only 125 seconds after the trigger. It was 40 seconds in duration, as were the next two. The remaining images were each 80 seconds long, and the last one was started 586 seconds after the trigger. The GRB blazed forth in all five images.
The images were downloaded several hours later by K. McLin (Sonoma State) and K. Ivarson (UNC), and independent photometric analysis was done at each location. The GRB was bright, about 12th magnitude in both R and I during the entire approximately 10 minutes of observations. Unfortunately, twilight prevented continued observations, so a more complete light curve was not obtainable for the afterglow. A Circular has been posted to the GCN. It is GCN 8617.
The ability to make automated observations was a critical part of the detection of this afterglow. As is typically the case, no one was at the observatory for these observations. Skynet, an automated observing system, was developed at UNC to perform precisely this kind of observation. It currently directs telescopes in Chile and North America. The SSU group has been working in partnership for the past several years with the UNC group, putting GORT under the direction of Skynet most clear nights. Generally the telescopes are used for routine monitoring of AGN (Active Galactic Nuclei, or quasars), variable stars, and the like. However, in the event of a GRB alert, Skynet determines which of its client telescopes is able to observe the event, and it then interrupts whatever they are doing and directs them to the burst. On December 3, GORT was the only telescope able to view the burst, as the other Skynet telescopes were all several hours farther east, and thus in daylight. The next-earliest observations from the ground were obtained in early evening twilight from Slovakia, but those had to wait 90 minutes, and by that time the burst had faded below R ~ 15.
While the day-to-day job of GORT is to monitor AGN and provide access to a telescope for undergraduates and high school students throughout the United States, we have been waiting to capture a GRB for a long time. In the past, GRB that would have been visible were too faint, or we were shut for maintenance or clouded out. Finally getting one of these feels great, and we look forward to catching many more.
By Swift Educator Ambassador Janet Moore (Challenger Learning Center of Central Illinois)
A powerful stellar explosion detected March 19 by NASA's Swift satellite has shattered the record for the most distant object that could be seen with the naked eye. I am passionate about engaging students in scientific investigations that are led by "what if" questions. When students start to ask themselves, "What if I do this?" or "What will happen if I try that instead?" that is when real scientific inquiry starts. When students start to wonder and ask questions, they take their education into their own hands and they begin to capture the essence of scientific exploration. NASA's Swift materials are perfect for helping teachers create an environment of exploration in the classroom.
Recently, I presented at a National Science Teachers Association conference in Cincinnati, Ohio. Nearly 150 teachers crowded into a room with seating for about 80. The session began with a time for play. There were about 40 different stations set up around the room and in the adjacent hallway. Each station had a common toy or object and some instructions. The teachers were instructed to visit as many stations as possible, follow the directions at each station, and make observations. Some flew toy airplanes; others rode skateboards; still others observed rocks sitting on the table. All used Newton's Laws of Motion in their play.
When playtime was over, I facilitated a discussion of exactly how Newton's Laws of Motion governed the events at each station, encouraging the teachers not to let their students off easy with "simple explanations." Letting go of an inflated balloon and watching it fly around the room is not just a demonstration of Newton's Third Law of Motion. It is a complex and intricate demonstration of all of Newton's Laws working together to take the balloon on that path through the air. Sometimes, it does an injustice to our students to oversimplify.
I ended the session by explaining the Swift mission and the role of Newton's Laws of Motion in Swift's success. I encouraged the teachers to use the thrill of NASA exploration to infuse excitement into their classrooms. The teachers in the overflowing crowd were excited and grateful for the session and the Newton's Laws posters provided by Swift. One teacher in particular praised the session, saying "All high school teachers could learn from this session."
I have been a NASA Educator Ambassador since October 2003. Since then, I have taught thousands of teachers about the Swift mission.