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Catching Gamma Ray Bursts on the Fly

Catching Gamma-Ray Bursts on the Fly Duty Calls, Swift Responds:

Gamma-ray bursts are the most powerful ex- Swift is the first mission to focus on study- plosions in the Universe other than the Big ing the burst afterglow, a phenomenon Bang. They occur several times discovered in 1997. Within sec- per day, yet scientists still have onds after detecting a gamma-ray only patchy details about what burst, Swift will relay an accurate causes them. Each burst likely burst position to scores of orbit- signals the birth of a new black ing and ground-based observato- hole -- perhaps either through ries so that they can observe the a massive star explosion or a afterglow before it fades. The fantastic merger between neu- message goes out literally via e- tron stars or black holes. mail and cell phones to scientists and amateur astronomers. Swift Now there’s a satellite designed is also in contact with ground- to capture and analyze these based robotic telescopes waiting bursts, some of which last only for Swift’s commands. for a few milliseconds. NASA’s Swift mission is a three-tele- Artist’s Illustration of Swift Swift itself will focus its X-ray and scope space observatory. One UV/optical telescopes on the af- of the telescopes will detect gamma- terglow within about a minute. This ray bursts; the other two will scru- enables Swift to determine distances tinize the afterglow of the burst. for most of the bursts that it detects Swift is a unique multi-wavelength and provide detailed multi-wave- mission. Its three telescopes span length light curves for the duration the gamma-ray, X-ray, ultraviolet of the afterglow. Time is of the es- and optical light bands, a swath of sence. Many bursts last about 10 sec- the spectrum over a million times onds; the longest last about a minute. wider than what the Hubble Space Once they are gone, the afterglows Telescope detects. are hard to find. And the afterglows, Hubble Image of GRB like a crime scene, contain all the evi- 990123 dence about the burst. Scientists have yet to collect will enable find an afterglow of a short burst (less than 2 scientists to test the- seconds). Maybe there is no afterglow; may- ories and, for the be we’re just not fast enough. Swift will lead first time, perform to the detection of short-burst afterglows, if multi-wavelength they exist, and determine whether they are observations of the intrinsically different from longer bursts. very short bursts, which have eluded Swift Electronics Testing ground-based ob- servers. We may find that different kinds of bursts are Neutron Star Merger caused by different Illustration origins, such as merg- ers of orbiting neutrons stars or gigantic stel- lar explosions known as hypernovae.

Astronomy and Physics Lessons: Understanding gamma-ray bursts will reveal new insights about the Universe. Most bursts originate at cosmological distances, Importance of Afterglow which means they ignited billions Measurements: of light years away when the Uni- verse was much younger. They act Distances determined from gamma-ray burst like beacons shining through every- afterglows have enabled scientists to under- thing along their paths, including stand that these bursts originate very far away the gas between and within galaxies from us. In fact, the bursts may be located along the line of sight. in the most distant galaxies we can observe. The power they produce each second is truly Some bursts may be from the first extreme, about 1050 – 1051 ergs, compared generation of stars. If so, we can be- to the Sun’s 4 x1033 ergs. Each gamma-ray gin to map out early star formation, burst is like a billion billion suns. which has not yet been done. Also, if gamma-ray bursts truly signal the Many models have been proposed to explain birth of a black hole, scientists can gamma-ray bursts and their afterglows. at last measure the black hole for- What remains bewildering is the sheer mation rate in the Universe. diversity of the bursts. Some last for only a few milliseconds. Others last upwards of a Gamma-ray bursts are laboratories minute. Some produce afterglows. Some are for extreme physics. The explo- dominated by X-ray photons (light particles). sions create blast waves that accel- Some show traces of iron atoms, a sign of erate matter to nearly the speed of a star explosion. light. Such conditions cannot be Scientists indeed reproduced on Earth, but scientists joke that if you’ve can watch and learn from afar. seen one gamma- ray burst, you’ve Swift Instrumentation: seen one gamma- ray burst. The main instrument onboard Swift is the Burst Alert Telescope (BAT). The large sample of The BAT has a wide field of view bursts that Swift will and will detect and locate about two gamma ray bursts per week, Hypernova Illustration relaying a 1- to 4-arcminute posi- UVOT Swift is one of five satellites tion to the ground in about 20 that relays gamma-ray burst seconds. As it is relaying this in- activity to the GCN. The GCN formation, Swift is turning so that distributes Swift information its other two instruments -- X-ray via e-mail to scientists and of- Telescope (XRT) and the UltraVi- ten to robotic telescopes di- olet/Optical Telescope (UVOT) rectly. The robotic telescopes -- have a direct view of the after- are dedicated to the gamma- glow... and maybe even part of the ray burst hunt and, because burst itself! The XRT and UVOT they react immediately to an will determine the position of the alert, offer the opportunity to burst to within arcseconds and catch an image of the burst also measure the distance to the while it is occurring. The GCN source. is also a repository of current burst information, a place where science After the burst fades or is out of view, the teams post what they have learned BAT will resume its “other job” of per- about the burst, usually several times forming a sensitive all-sky survey in high- a day for the biggest and most excit- er-energy (hard) X rays at the 15-150 keV en- ing bursts. Relying on this GCN information, ergy level. This will be at least 20 times more scientists at major observatories -- such as sensitive than previous measurements and the Keck Observatory in Hawaii, the Hubble should uncover more Space Telescope and the Spitzer Space Tele- than 400 supermas- scope -- will often turn these world-class in- sive black holes that struments to study the regions surrounding are obscured at lower the gamma-ray burst in the hours and days energies. after an event.

Included in this Swift science network are Support on the over 30 follow-up teams spread out across the Ground and in the southern and northern hemispheres. The Sky: teams cast a wide net to ensure that no burst detected by Swift will go unstudied because Swift is connected to of daylight, clouds or viewing angle. The the Gamma-ray Burst GCN is a resource available to schools, sci- Coordinates Network ence museums and anyone with an Internet (GCN), a largely auto- connection. mated system to relay burst information in real-time to scientists around the world.

XRT

BAT

Swift Follow Up Team Observatories and Facilities: Swift Mission AEOS Telescope (Hawaii) ARAGO Telescope (Antarctica) ARC Telescope (New Mexico) Lifetime 2 years minimum Brera Observatory (Italy) Height 5.64 m ESO (La Silla, Paranal, VLT) Mass 1470 kg ESA’s INTEGRAL mission Power 1040 Watts Fast Alert MachinE (Italy) Launch vehicle Delta 7320 Faulkes Telescope Project (Hawaii and Australia) Orbital inclination 21 degrees Galileo National Telescope (La Palma) GRB Position Accuracy 0.3-5 arcsec Hobby-Eberly Telescope (Texas) Repointing Time 20-75 seconds Isaac Newton Telescopes (La Palma) KAIT (California) W. M. Keck Observatory (Hawaii) Lead Institutions Involved Large Binocular Telescope (Arizona) Area of Support LIGO (Louisiana and Washington) NASA Goddard Space Flight Center, USA Liverpool Telescope (La Palma) - BAT instrument, Project Management McDonald Observatory (Texas) Penn State University, USA Milagro Gamma-ray Observatory (New Mexico) - XRT, UVOT, Operations NASA (IRTF, Hubble & Spitzer Space Telescopes) University of Leicester, UK NOAO (CTIO, KPNO) - X-ray Telescope and Detectors Nordic Optic Telescope (La Palma) Okayama Observatory (Japan) Mullard Space Science Lab, UK - UVOT Assembly Rapid Eye Mount Telescope (Chile) ROTSE-III (New Mexico) Brera Observatory (OAB), Italy SARA Observatory (Arizona) - X-ray mirrors for the XRT South African Large Telescope Italian Space Agency, Italy Super-LOTIS (Arizona) - Ground Station Support TAOS Telescope (Taiwan) Los Alamos National Laboratory, USA TAROT Telescope (France) - BAT Instrument Flight Software Tenerife Observatory U.S. Naval Observatory (Arizona) General Dynamics C4 Systems, USA Spectrum Astro Space Systems VERITAS Observatory (Arizona) - Spacecraft Vendor WASP Telescope (La Palma) Sonoma State University, USA WIYN Observatory (Arizona) - Education and Public Outreach Wyoming Infrared Observatory