Swift Follow-up Observations

Swift will observe hundreds of GRBs per year, producing positions, light curves, and, in most cases, redshift distances. Under our data distribution policy of Everything to Everyone, Immediately, any observer using any instrument can make follow-up observations based on the data as soon as it is ready (within seconds of the GRB for arc-minute positions, minutes for arc-second positions, hours for redshifts). Members of the Swift follow-up team have access to the following instruments, but more observatories are always welcome:

Follow-Up Teams

1m, 1.3m USNO 3.5m ARC 9m SALT AEOS

ARAGO (TAROT-2) CTIO EOS ESO

FAME Faulkes Galileo HET

HST INTEGRAL IRTF KAIT (0.8m auto)

Keck KPNO La Silla LBT

LIGO Liverpool Telescope McDonald Milagro

Newton Telescopes NOT La Palma (2.5m) Okayama Observatory Paranal

REM ROTSE SAAO SARA Kitt Peak

SIRTF Super-LOTIS TAOS TAROT

Tenerife VERITAS VLT WASP

WIRO WIYN

The types of follow-up observations made will typically depend on the questions of interest, and on the properties of the GRB measured by Swift. Swift will produce so many GRB measurements that most will not be followed up from the ground, due to the lack of available observing time. After the first few dozen intensively studied GRBs, observing plans probably will concentrate on bursts with specific properties to answer specific questions. Population studies will probably be based on the uniform measurements of positions, spectra, light curves, and distances that Swift provides.

Hubble Deep Field Image, with XRT and UVOT position accuracy shown
Comparison of Hubble deep field image with UVOT and XRT position. See text.

Spatial distribution of counterparts. See text.

The UVOT will precisely locate GRBs to sub-arcsecond accuracy. Leisurely follow-up studies, based on existing surveys or on observations scheduled some time later, can use these positions to determine the relationship between GRBs and affiliated galaxies. Even at the limits of the Hubble Deep Field, the UVOT positions will be able to locate where in the structure of a host galaxy a GRB arises. The predictions of different GRB models can then be distinguished. For example, hypernovae (very massive brief-lived collapsing stars) will be found mostly in star-forming regions, while neutron star binaries are expected to be produced with high velocities and to last long enough to get far from their galaxy of birth before coalescing. Both of these scenarios may produce GRBs, and if short GRBs are found at large distances from galaxies while long bursts are found in spiral arms, then that could indicate that these different classes of GRBs come from these two different mechanisms.

VLA observation of 970508 (Frail et al. 1997).

Radio observations are thought to measure the interaction of the GRB fireball with the surrounding material. This can tell us about the environment of the GRB and (if the surrounding material was originally blown out as wind from the GRB progenitor) the evolution of the source in the stages before it became a GRB. The presence of interstellar scintillation in the radio signal provides a measurement of the source size, which tells how the fireball expands in its late (non-relativistic) phases.

Data plot of 4 lyman-alpha forest. See text.
Swift notifies observers of high-redshift GRBs with bright afterglows, which provide the best back lights to illuminate Z > 4 Ly-α forest. From Songalia & Cowlie, (1996)

When Swift detects a bright optical afterglow with a large redshift, this provides an opportunity to study the 'Lyman alpha forest'. This is the set of absorption lines that are produced when light from distant objects passes through clouds of neutral gas on its way to Earth. The redshift and thickness of each individual cloud can be measured by examining the absorption lines it cuts out of the source's continuum spectrum. GRB afterglows provide bright, if temporary, back lights to illuminate the forest, allowing more detailed measurements than dim distant quasars. These measurements of primordial gas clouds are valuable clues to the structure and evolution of the Universe.

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This page was last modified on Monday, 26-Jul-2004 11:18:13 EDT.