The localization of gamma-ray bursts (GRBs) has provided the key to unlocking the cosmological nature of these events. With perhaps a few exceptions, all GRBs with a measured redshift have revealed cosmological distances and many associations have been made with individual host galaxies. Spectral characteristics and decay curves of the burst afterglows across the electromagnetic spectrum are consistent with model predictions of synchrotron emission emitted by particles accelerated to relativistic energies by shock waves. These, in turn, are suspected to result from the impact of relativistic particles with the interstellar medium, where the particles have an origin in the collapse of massive stars or the merger of compact objects.
Swift, due for launch in May 2004, will makes the next leap forward after the BeppoSAX and HETE-II missions. A wide angle, hard X-ray/g ray Burst Alert Telescope (BAT) will detect approximately 100 bursts per year and locate them to within 4 arcmin on the sky. An on-board ``figure-of-merit'' algorithm will decide to slew pointed X-ray, optical and UV sensitive detectors (XRT, UVOT) to the burst. Initial pointed observations and on-board analysis will determine X-ray positions to 5 arcsec. This position, an optical finding chart and an X-ray spectrum will be distributed via the GCN within minutes of the original burst.
The great advantage of the Swift mission is the on-board suite of multi-frequency, imaging, timing and spectroscopic pointed detectors. While the rapid dissemination of pointing positions to ground based observers is vital, another major drive behind the mission is that the rich and dense multi-wavelength data sets obtained from the Swift instruments during the first few hours of the afterglow phase will result in a new and unique view of GRB environments and the surrounding and inter-galactic media.
My current involvement with
Swift is as a member of the Swift Science Team that
drives the primary science directions of the mission and as the
designer of the UVOT data reduction software, data formats and
calibration products.
The Swift mission
holds great potential for undergraduate and graduate training and
post-graduate studies. Gamma-ray bursts are a relatively untapped but
rapidly blossoming field, which is related to stellar formation and
death, black hole birth, neutron star coalescence, large-scale
structure and early nucleosynthesis. Multiple classes of burst
progenitors probably exist. Swift will allow a statistical
approach to classification, based on luminosity, temperature,
redshift, variability and time lags within the burst and
afterglow. Distances to bursts can be determined approximately by
determining which filter contains the Lyman break, or more robustly
with discrete atomic lines and edges using UVOT grism and XRT spectral
data. Redshifts pushing z ~ 10 are predicted using the
instrument sensitivities. Imaging resolution is ~ 1 arcsec enabling
analysis of host galaxy properties and a search for lensing
events. Time-variability allows a picture of the unresolved outflow
structure to be built. Internal and external shocks are predicted,
signatures of supernova are expected in many afterglows, filling
factors can be estimated and time-lag properties can determine size
scales.
A number of pointed
observations that showcase Swift’s hardware are also budgeted
for during the first three years of operation, including supernovae,
classical novae, dwarf novae outbursts, polars, X-ray transients,
galactic black holes, active galactic nuclei and soft gamma-ray
repeaters. Furthermore the prospects of serendipitous science during
the mission are fantastic. In performing many revisits to burst fields
for up to several months after the event, Swift uniquely supplies high
quality X-ray and UV observations of field sources over a wide range
of timescales from milli-seconds to months. We can expect the
serendipitous discovery and high quality, simultaneous,
multi-wavelength monitoring of coronal sources, star forming regions,
cataclysmic variables, X-ray binaries, novae, supernovae, dark bursts,
galactic nuclei and clusters.
All data obtained by
Swift are immediately public. Burst positions, finding charts
and X-ray positions will be available to the community within 30
minutes of a detection in order to allow rapid follow-up by
ground-based telescope facilities. “First-run” analysis-quality
satellite data will be available within 2 hours of the burst and
complete burst sequences will be fully available no later than 1 week
after the event.
The mission requirement for
rapid response and delivery of an unambiguous burst location means
that the position of the source must be screened in real-time, i.e.
within 30 minutes of the burst, in order to avoid
misidentifications. The Swift Science Team will be setting up
“Burst Advocates” to perform screening duties in shifts. The advocate
will be responsible for communications between the operations center
and the afterglow hunters stationed on telescopes around the world as
the event occurs. The Advocate will be actively involved in all
aspects of observational research for a given burst. The opportunity
will be there for trained University personnel to sign up to the
Advocate rotation.
The Swift archive
will prove to be a gold mine for university research and teaching in
the coming years.