- Email: [email protected]
The Swift γ-ray burst mission
New Astronomy Reviews 48 (2004) 431–435 www.elsevier.com/locate/newastrev
The Swift c-ray burst mission N. Gehrels Goddard Space Flight Center, Mail Code 661, Greenbelt, MD 20771, USA on behalf of the Swift team
Abstract Swift is a first-of-its-kind multiwavelength transient observatory for GRB astronomy. It has the optimum capabilities for the next breakthroughs in determining the origin of GRBs and their afterglows, as well as using bursts to probe the early Universe. Swift will also perform the first sensitive hard X-ray survey of the sky. The mission is being developed by an international collaboration and consists of three instruments, the Burst Alert Telescope (BAT), the XRay Telescope (XRT), and the Ultraviolet and Optical Telescope (UVOT). The BAT, a wide-field c-ray detector, will detect >100 GRBs per year with a sensitivity five times that of BATSE. The sensitive narrow-field XRT and UVOT will be autonomously slewed to the burst location in 20–75 s to determine 0.3–5.000 positions and perform optical, UV, and X-ray spectrophotometry. Strong education/public outreach and follow-up programs will help to engage the public and astronomical community. The Swift launch is planned for 2004. Ó 2004 Elsevier B.V. All rights reserved.
1. Introduction The discovery by BeppoSAX and ground observers (Costa et al., 1997; Van Paradijs et al., 1997; Frail et al., 1997) of afterglow from GRBs has shown that they are cosmological, involving the most powerful explosions known. These explosions are thought to create super-relativistic blast-waves resulting in afterglow that fades from c-rays to radio. However, important information on the afterglow is lost by the 8 h or longer delay between the initial burst and follow-up observations. Swift is a multiwavelength observatory that exploits the afterglow characteristics of GRBs to make a comprehensive study of hundreds of bursts. E-mail address: [email protected] (N. Gehrels).
It will determine the origin of GRBs, tell us how the blast wave interacts with its surroundings, and identify classes of bursts. Swift will also investigate how GRBs can be used to study the early Universe.
2. Swift instruments The Swift instrumentation was carefully chosen for GRB discovery. It incorporates a wide-field GRB detector and two sensitive narrow-field telescopes (Fig. 1). 2.1. Burst Alert Telescope The Burst Alert Telescope (BAT) covers the 15– 150 keV energy band and will detect >100 bursts
1387-6473/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.newar.2003.12.055
432
N. Gehrels / New Astronomy Reviews 48 (2004) 431–435 Table 2 XRT parameters Energy range Telescope Effective area Field of view Detection elements Telescope PSF Sensitivity
0.2–10 keV JET-X Wolter 1 110 cm3 @ 1.5 keV 23.6 23.60 600 600 pixels 1800 HPD @ 1.5 keV 2 1014 erg cm2 s1
Table 3 UVOT parameters
Fig. 1. The Swift satellite.
per year (Table 1). It has a CdZnTe (CZT) detector array with an area of 5200 cm2 and a coded aperture mask covering 1.4 sr of the sky. The mask is positioned one meter away from the detectors and will provide positions of 1–40 accuracy. The large detector area and sophisticated triggering system will allow BAT to detect bursts of all durations to a sensitivity two to five times better than BATSE depending on the burst position in the BAT field of view. The instrument development is led by Goddard Space Flight Center with the imaging flight software written at Los Alamos National Laboratory. 2.2. X-Ray Telescope The X-Ray Telescope (XRT) will locate bursts to 500 accuracy using flight-spare optics from the JET-X instrument on the Spectrum X (Table 2). The mirror has a 1800 half-power diameter at 1.5 keV. The detector is a 600 square pixel CCD from the XMM/EPIC, giving a FOV of 24 arcsec square Table 1 BAT parameters Energy range Detecting area Detector operation Field of view Detector element size Telescope PSF
15–150 keV 5200 cm2 Photon counting 1.4 sr (half-coded) 4 4 2 mm3 170
Wavelength range Telescope Aperture Detector Detector operation Field of view Detection elements Telescope PSF Sensitivity
170–600 nm Modified Ritchey–Chretien 30 cm diameter Intensified CCD Photon counting 17 170 2048 2048 pixels 0.900 @ 350 nm B ¼ 24 in white light in 1000 s
in an energy range 0.2–10.0 keV. The instrument is being developed by Penn State University, University of Leicester, and Osservatorio Astronomico di Brera (Table 2). 2.3. UV–Optical Telescope The UV–Optical Telescope (UVOT) is a 30-cm diameter modified Ritchey–Cretien equipped with an image intensified CCD covering 170–600 nm (Table 3). It has a FOV 17 arcmin square and is based closely on the design of the XMM Optical Monitor (OM). The UVOT is able to reach mB ¼ 24 in 1000 s (open filter). A filter wheel provides six colors, two grisms and a four times magnifier. The optical point spread function of the telescope is 0.900 allowing for excellent astrometry. By registering the field against foreground stars, the UVOT will provide <0.300 positions. The instrument is being developed by Penn State University and Mullard Space Science Laboratory.
3. Swift mission The strategy of the Swift mission (Table 4) is to slew to each new GRB and follow the afterglows
N. Gehrels / New Astronomy Reviews 48 (2004) 431–435 Table 4 Swift mission characteristics Autonomous slew decision capability Fast slew – 50° in <75 s Low earth orbit, 22° inclination Launch vehicle: Delta 7320 with 3 m fairing Mass: 1500 kg Power: 1000 W
as long as it is visible. To observe the earliest phase of the afterglow, new BAT positions will trigger an autonomous spacecraft slew followed by a programmed sequence of observations with the XRT and UVOT. The initial GRB position is normally determined by the BAT, but positions can also be uploaded from other satellites through a real-time TDRSS uplink. Either case will trigger the spacecraft software to plan and execute an autonomous slew. All calculations of slew path and pointing constraints will be done on-board. Each of the three Swift instruments rapidly produces alert messages after a GRB is detected. To ensure prompt delivery, these messages are sent through a real-time TDRSS downlink to the ground, and routed immediately to the GRB Coordinates Network (GCN) (Barthelmy et al., 1998) for delivery to the community. When Swift is not engaged in prompt observations of the most recent bursts, it will follow a schedule uploaded from the ground each working day and as needed. This schedule will provide for long term follow-up of GRB afterglows and other science. The PSU Mission Operational Center (MOC) will be capable of generating a new schedule in <2 h.
4. Swift science Recent GRB discoveries have shown that Xray, optical, and radio afterglows exist, continuing for days after the bursts, but fading quickly (t1 to t2 is typical). Better data on faster time scales for many more bursts is needed. The Swift mission provides the capability to answer the following four key science questions: What are the progenitors of GRBs? How does the blast-wave evolve
433
and interact with its surroundings? Are there different classes of bursts? What can GRBs tell us about the early Universe? 4.1. GRB progenitors To determine the origin of GRBs, three parameters are needed: the total energy released, the nature of the host galaxy (if one exists), and the location within the host galaxy. The Swift mission is optimized to measure all three of these for hundreds of bursts. Obtaining the energetics requires a reliable redshift measurement. Ideally this should be done independently for both the afterglow and any host galaxy to check that there has not been a chance coincidence (Hogg and Fruchter, 1999). The UV grisms and filters of Swift can make redshift determinations by searching for the Ly-a cutoff in the UV and eliminate the 1:3 < z < 2:5 deadband of current observations during the early phase of the afterglow. In addition, time varying optical, UV and X-ray lines and edges are expected within the first hour following a burst from the illumination of the immediate (100 pc) environment by the initial event (Perna and Loeb, 1998; Meszaros and Rees, 1998). The rapid response of Swift will enable a search for predicted X-ray lines and again provide a direct redshift. The UVOT will obtain <0.300 positions by using background stars to register the field, providing a unique host galaxy ID and allowing later comparison with HST fields to determine the position within the galaxy. There will probably be events where no optical afterglow is detected because of dust extinction surrounding the site of the GRB. The position from the XRT will then be crucial. By obtaining 5.000 positions, the XRT will enable unique identification of candidate host galaxies down to mR 26. 4.2. Blast-wave interactions Afterglow is thought to be produced by the interaction of an ultra-relativistic blast-wave with the interstellar or intergalactic medium. The blastwave model (Meszar os and Rees, 1993) predicts a
434
N. Gehrels / New Astronomy Reviews 48 (2004) 431–435
series of stages as the wave slows. A key prediction is a break in the spectrum that moves from the gamma to optical band, and is responsible for the power law decay of the source flux. This break moves through the X-ray band in a few seconds, but takes up to 1000 s to reach the optical. Thus observations within the first 1000 s in the optical and UV are crucial to see this early phase. While it now seems likely that all the GRBs have X-ray afterglow, not all have bright optical afterglow (at least after several hours). This may be due to optical extinction, but it is also possible that in some cases the optical (and X-ray) afterglow is present but decays much more rapidly and is a function of the density of the local environment (Piran, 1998). Prompt high-quality X-ray, UV and optical observations over the first minutes to hours of the afterglow (inaccessible without Swift) are crucial to resolve this question. Star forming regions are embedded in large columns of neutral gas and dust. The presence of extinction can be readily determined by multiband photometry in the optical and IR. The simultaneous detection of high X-ray absorption, coupled with photometric EðB V Þ measurements with Swift, will determine whether dust and gas are present. 4.3. Classes of GRBs While some evidence of sub-classes has been obtained (e.g., bimodal duration distribution, possible correlation of hardness and log N log P shape, short bursts having V =Vmax consistent with a Euclidean distribution), it is not clear if these are real differences or, rather, the result of the distribution function of GRB properties such as beaming angle, density of the local medium, or initial energy injection. Swift data will determine locations, redshifts, and afterglow properties of the different classes and thus allow physical understanding. If there are classes of GRBs that are the signal of conventional supernova explosions (Bloom et al., 1999; Woosley et al., 1999), the UVOT will provide unique and unprecedented coverage of the optical and UV light curve during the early stage.
4.4. Bursts as astrophysical tools Since GRBs are the most luminous objects in the Universe, they provide a unique opportunity to probe the IGM and the ISM of the host galaxies via measurement of absorption along the line of sight (Lamb and Reichart, 2000). Depending on evolution, GRBs might originate from redshifts up to 15 and have a median redshift >2, larger than that of any other observable population. By rapidly providing both accurate positions and optical brightness, Swift will enable the immediate followup of those GRBs bright enough for high resolution optical absorption line spectroscopy at redshifts large enough to study the reionization of the IGM (Miralda-Escude, 1998). This information on the high-z Ly-a forest will be unique because there are currently no known bright (m < 17) galaxies or quasars at z > 7.
5. Ground system and data analysis A layered data analysis approach will be used to achieve rapid dissemination of Swift results and data to the community. The most urgently needed results, namely GRB positions, are produced on the spacecraft. Quicklook results, including optical finding charts and multiwavelength light curves, are produced in the Penn State Mission OperaTable 5 Swift mission responsibilities and institutions Responsibility
Institution
Mission management XRT UVOT BAT Ground system Mission operations Data centers EPO GRB follow-up coordination
GSFC PSU, LU, OAB PSU, MSSL GSFC, LANL GSFC PSU GSFC, ASI, LU SSU, PSU, GSFC UCB
GSFC, Goddard Space Flight Center; LU, Leicester University; MSSL, Mullard Space Science Laboratory; ASI, Italian Space Agency; UCB, University of California, Berkele; PSU, Penn State University; OAB, Osservatorio Astronomico di Brera; LANL, Los Alomos National Laboratory and SSU, Sonoma State University.
N. Gehrels / New Astronomy Reviews 48 (2004) 431–435
tions Center (MOC) in near real-time and distributed using the GCN. Definitive standard products, including spectra, multi-band light curves, and images, will be made into production FITS files. All the Swift data will be processed at the Swift data center at Goddard and will be made available to the general public through the HEASARC in the US and data centers in the UK and Italy. The end result will be easy access for the entire community to a broad range of timely information on GRBs. 6. Organization Swift is the result of an international collaboration. The responsibilities of the various institutions are listed in Table 5.
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References Barthelmy, S. et al., 1998. In: Meegan, C., Preece, R., Koshut, T. (Eds.), Gamma-Ray Bursts: 4th Huntsville Symposium. AIP Conference Proceedings, vol. 428. American Institute of Physics, New York, p. 139. Bloom, J.S. et al., 1999. Nature 401, 453. Costa, E. et al., 1997. Nature 387, 783. Frail, D.A. et al., 1997. Nature 389, 261. Hogg, D.W., Fruchter, A.S., 1999. ApJ 520, 54. Lamb, D.Q., Reichart, D.E., 2000. ApJ 536, 1. Meszar os, P., Rees, M., 1993. ApJL 418, L59. Meszaros, P., Rees, M.J., 1998. ApJL 502, 105. Miralda-Escude, J., 1998. ApJ 501, 15. Perna, R., Loeb, A., 1998. ApJ 501, 467. Piran, T., 1998. Gamma-ray bursts – the second revolution. In: Sato, H., Sugiyama, N. (Eds.), Black Holes and High Energy Astrophysics. Universal Academy Press, p. 21. Van Paradijs, J. et al., 1997. Nature 386, 686. Woosley, S.E., Eastman, R.G., Schmidt, B.P., 1999. ApJ 516, 788.
The Swift c-ray burst mission N. Gehrels Goddard Space Flight Center, Mail Code 661, Greenbelt, MD 20771, USA on behalf of the Swift team
Abstract Swift is a first-of-its-kind multiwavelength transient observatory for GRB astronomy. It has the optimum capabilities for the next breakthroughs in determining the origin of GRBs and their afterglows, as well as using bursts to probe the early Universe. Swift will also perform the first sensitive hard X-ray survey of the sky. The mission is being developed by an international collaboration and consists of three instruments, the Burst Alert Telescope (BAT), the XRay Telescope (XRT), and the Ultraviolet and Optical Telescope (UVOT). The BAT, a wide-field c-ray detector, will detect >100 GRBs per year with a sensitivity five times that of BATSE. The sensitive narrow-field XRT and UVOT will be autonomously slewed to the burst location in 20–75 s to determine 0.3–5.000 positions and perform optical, UV, and X-ray spectrophotometry. Strong education/public outreach and follow-up programs will help to engage the public and astronomical community. The Swift launch is planned for 2004. Ó 2004 Elsevier B.V. All rights reserved.
1. Introduction The discovery by BeppoSAX and ground observers (Costa et al., 1997; Van Paradijs et al., 1997; Frail et al., 1997) of afterglow from GRBs has shown that they are cosmological, involving the most powerful explosions known. These explosions are thought to create super-relativistic blast-waves resulting in afterglow that fades from c-rays to radio. However, important information on the afterglow is lost by the 8 h or longer delay between the initial burst and follow-up observations. Swift is a multiwavelength observatory that exploits the afterglow characteristics of GRBs to make a comprehensive study of hundreds of bursts. E-mail address: [email protected] (N. Gehrels).
It will determine the origin of GRBs, tell us how the blast wave interacts with its surroundings, and identify classes of bursts. Swift will also investigate how GRBs can be used to study the early Universe.
2. Swift instruments The Swift instrumentation was carefully chosen for GRB discovery. It incorporates a wide-field GRB detector and two sensitive narrow-field telescopes (Fig. 1). 2.1. Burst Alert Telescope The Burst Alert Telescope (BAT) covers the 15– 150 keV energy band and will detect >100 bursts
1387-6473/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.newar.2003.12.055
432
N. Gehrels / New Astronomy Reviews 48 (2004) 431–435 Table 2 XRT parameters Energy range Telescope Effective area Field of view Detection elements Telescope PSF Sensitivity
0.2–10 keV JET-X Wolter 1 110 cm3 @ 1.5 keV 23.6 23.60 600 600 pixels 1800 HPD @ 1.5 keV 2 1014 erg cm2 s1
Table 3 UVOT parameters
Fig. 1. The Swift satellite.
per year (Table 1). It has a CdZnTe (CZT) detector array with an area of 5200 cm2 and a coded aperture mask covering 1.4 sr of the sky. The mask is positioned one meter away from the detectors and will provide positions of 1–40 accuracy. The large detector area and sophisticated triggering system will allow BAT to detect bursts of all durations to a sensitivity two to five times better than BATSE depending on the burst position in the BAT field of view. The instrument development is led by Goddard Space Flight Center with the imaging flight software written at Los Alamos National Laboratory. 2.2. X-Ray Telescope The X-Ray Telescope (XRT) will locate bursts to 500 accuracy using flight-spare optics from the JET-X instrument on the Spectrum X (Table 2). The mirror has a 1800 half-power diameter at 1.5 keV. The detector is a 600 square pixel CCD from the XMM/EPIC, giving a FOV of 24 arcsec square Table 1 BAT parameters Energy range Detecting area Detector operation Field of view Detector element size Telescope PSF
15–150 keV 5200 cm2 Photon counting 1.4 sr (half-coded) 4 4 2 mm3 170
Wavelength range Telescope Aperture Detector Detector operation Field of view Detection elements Telescope PSF Sensitivity
170–600 nm Modified Ritchey–Chretien 30 cm diameter Intensified CCD Photon counting 17 170 2048 2048 pixels 0.900 @ 350 nm B ¼ 24 in white light in 1000 s
in an energy range 0.2–10.0 keV. The instrument is being developed by Penn State University, University of Leicester, and Osservatorio Astronomico di Brera (Table 2). 2.3. UV–Optical Telescope The UV–Optical Telescope (UVOT) is a 30-cm diameter modified Ritchey–Cretien equipped with an image intensified CCD covering 170–600 nm (Table 3). It has a FOV 17 arcmin square and is based closely on the design of the XMM Optical Monitor (OM). The UVOT is able to reach mB ¼ 24 in 1000 s (open filter). A filter wheel provides six colors, two grisms and a four times magnifier. The optical point spread function of the telescope is 0.900 allowing for excellent astrometry. By registering the field against foreground stars, the UVOT will provide <0.300 positions. The instrument is being developed by Penn State University and Mullard Space Science Laboratory.
3. Swift mission The strategy of the Swift mission (Table 4) is to slew to each new GRB and follow the afterglows
N. Gehrels / New Astronomy Reviews 48 (2004) 431–435 Table 4 Swift mission characteristics Autonomous slew decision capability Fast slew – 50° in <75 s Low earth orbit, 22° inclination Launch vehicle: Delta 7320 with 3 m fairing Mass: 1500 kg Power: 1000 W
as long as it is visible. To observe the earliest phase of the afterglow, new BAT positions will trigger an autonomous spacecraft slew followed by a programmed sequence of observations with the XRT and UVOT. The initial GRB position is normally determined by the BAT, but positions can also be uploaded from other satellites through a real-time TDRSS uplink. Either case will trigger the spacecraft software to plan and execute an autonomous slew. All calculations of slew path and pointing constraints will be done on-board. Each of the three Swift instruments rapidly produces alert messages after a GRB is detected. To ensure prompt delivery, these messages are sent through a real-time TDRSS downlink to the ground, and routed immediately to the GRB Coordinates Network (GCN) (Barthelmy et al., 1998) for delivery to the community. When Swift is not engaged in prompt observations of the most recent bursts, it will follow a schedule uploaded from the ground each working day and as needed. This schedule will provide for long term follow-up of GRB afterglows and other science. The PSU Mission Operational Center (MOC) will be capable of generating a new schedule in <2 h.
4. Swift science Recent GRB discoveries have shown that Xray, optical, and radio afterglows exist, continuing for days after the bursts, but fading quickly (t1 to t2 is typical). Better data on faster time scales for many more bursts is needed. The Swift mission provides the capability to answer the following four key science questions: What are the progenitors of GRBs? How does the blast-wave evolve
433
and interact with its surroundings? Are there different classes of bursts? What can GRBs tell us about the early Universe? 4.1. GRB progenitors To determine the origin of GRBs, three parameters are needed: the total energy released, the nature of the host galaxy (if one exists), and the location within the host galaxy. The Swift mission is optimized to measure all three of these for hundreds of bursts. Obtaining the energetics requires a reliable redshift measurement. Ideally this should be done independently for both the afterglow and any host galaxy to check that there has not been a chance coincidence (Hogg and Fruchter, 1999). The UV grisms and filters of Swift can make redshift determinations by searching for the Ly-a cutoff in the UV and eliminate the 1:3 < z < 2:5 deadband of current observations during the early phase of the afterglow. In addition, time varying optical, UV and X-ray lines and edges are expected within the first hour following a burst from the illumination of the immediate (100 pc) environment by the initial event (Perna and Loeb, 1998; Meszaros and Rees, 1998). The rapid response of Swift will enable a search for predicted X-ray lines and again provide a direct redshift. The UVOT will obtain <0.300 positions by using background stars to register the field, providing a unique host galaxy ID and allowing later comparison with HST fields to determine the position within the galaxy. There will probably be events where no optical afterglow is detected because of dust extinction surrounding the site of the GRB. The position from the XRT will then be crucial. By obtaining 5.000 positions, the XRT will enable unique identification of candidate host galaxies down to mR 26. 4.2. Blast-wave interactions Afterglow is thought to be produced by the interaction of an ultra-relativistic blast-wave with the interstellar or intergalactic medium. The blastwave model (Meszar os and Rees, 1993) predicts a
434
N. Gehrels / New Astronomy Reviews 48 (2004) 431–435
series of stages as the wave slows. A key prediction is a break in the spectrum that moves from the gamma to optical band, and is responsible for the power law decay of the source flux. This break moves through the X-ray band in a few seconds, but takes up to 1000 s to reach the optical. Thus observations within the first 1000 s in the optical and UV are crucial to see this early phase. While it now seems likely that all the GRBs have X-ray afterglow, not all have bright optical afterglow (at least after several hours). This may be due to optical extinction, but it is also possible that in some cases the optical (and X-ray) afterglow is present but decays much more rapidly and is a function of the density of the local environment (Piran, 1998). Prompt high-quality X-ray, UV and optical observations over the first minutes to hours of the afterglow (inaccessible without Swift) are crucial to resolve this question. Star forming regions are embedded in large columns of neutral gas and dust. The presence of extinction can be readily determined by multiband photometry in the optical and IR. The simultaneous detection of high X-ray absorption, coupled with photometric EðB V Þ measurements with Swift, will determine whether dust and gas are present. 4.3. Classes of GRBs While some evidence of sub-classes has been obtained (e.g., bimodal duration distribution, possible correlation of hardness and log N log P shape, short bursts having V =Vmax consistent with a Euclidean distribution), it is not clear if these are real differences or, rather, the result of the distribution function of GRB properties such as beaming angle, density of the local medium, or initial energy injection. Swift data will determine locations, redshifts, and afterglow properties of the different classes and thus allow physical understanding. If there are classes of GRBs that are the signal of conventional supernova explosions (Bloom et al., 1999; Woosley et al., 1999), the UVOT will provide unique and unprecedented coverage of the optical and UV light curve during the early stage.
4.4. Bursts as astrophysical tools Since GRBs are the most luminous objects in the Universe, they provide a unique opportunity to probe the IGM and the ISM of the host galaxies via measurement of absorption along the line of sight (Lamb and Reichart, 2000). Depending on evolution, GRBs might originate from redshifts up to 15 and have a median redshift >2, larger than that of any other observable population. By rapidly providing both accurate positions and optical brightness, Swift will enable the immediate followup of those GRBs bright enough for high resolution optical absorption line spectroscopy at redshifts large enough to study the reionization of the IGM (Miralda-Escude, 1998). This information on the high-z Ly-a forest will be unique because there are currently no known bright (m < 17) galaxies or quasars at z > 7.
5. Ground system and data analysis A layered data analysis approach will be used to achieve rapid dissemination of Swift results and data to the community. The most urgently needed results, namely GRB positions, are produced on the spacecraft. Quicklook results, including optical finding charts and multiwavelength light curves, are produced in the Penn State Mission OperaTable 5 Swift mission responsibilities and institutions Responsibility
Institution
Mission management XRT UVOT BAT Ground system Mission operations Data centers EPO GRB follow-up coordination
GSFC PSU, LU, OAB PSU, MSSL GSFC, LANL GSFC PSU GSFC, ASI, LU SSU, PSU, GSFC UCB
GSFC, Goddard Space Flight Center; LU, Leicester University; MSSL, Mullard Space Science Laboratory; ASI, Italian Space Agency; UCB, University of California, Berkele; PSU, Penn State University; OAB, Osservatorio Astronomico di Brera; LANL, Los Alomos National Laboratory and SSU, Sonoma State University.
N. Gehrels / New Astronomy Reviews 48 (2004) 431–435
tions Center (MOC) in near real-time and distributed using the GCN. Definitive standard products, including spectra, multi-band light curves, and images, will be made into production FITS files. All the Swift data will be processed at the Swift data center at Goddard and will be made available to the general public through the HEASARC in the US and data centers in the UK and Italy. The end result will be easy access for the entire community to a broad range of timely information on GRBs. 6. Organization Swift is the result of an international collaboration. The responsibilities of the various institutions are listed in Table 5.
435
References Barthelmy, S. et al., 1998. In: Meegan, C., Preece, R., Koshut, T. (Eds.), Gamma-Ray Bursts: 4th Huntsville Symposium. AIP Conference Proceedings, vol. 428. American Institute of Physics, New York, p. 139. Bloom, J.S. et al., 1999. Nature 401, 453. Costa, E. et al., 1997. Nature 387, 783. Frail, D.A. et al., 1997. Nature 389, 261. Hogg, D.W., Fruchter, A.S., 1999. ApJ 520, 54. Lamb, D.Q., Reichart, D.E., 2000. ApJ 536, 1. Meszar os, P., Rees, M., 1993. ApJL 418, L59. Meszaros, P., Rees, M.J., 1998. ApJL 502, 105. Miralda-Escude, J., 1998. ApJ 501, 15. Perna, R., Loeb, A., 1998. ApJ 501, 467. Piran, T., 1998. Gamma-ray bursts – the second revolution. In: Sato, H., Sugiyama, N. (Eds.), Black Holes and High Energy Astrophysics. Universal Academy Press, p. 21. Van Paradijs, J. et al., 1997. Nature 386, 686. Woosley, S.E., Eastman, R.G., Schmidt, B.P., 1999. ApJ 516, 788.