The first satellite dedicated to detecting
Gamma-Ray Bursts and following up their afterglows autonomously, Swift has
revolutionised research in this area. Some highlights are described below and more details are
available from "Gamma-Ray Bursts in
the Swift Era", a review by Gehrels, Ramirez-Ruiz & Fox (2009). There is also a BBC webpage about GRBs in general.
- High-redshift GRBs
Swift-discovered GRBs 050904, 080913, 090423 and 090429B have each held the position as the
most distant burst discovered, with redshift values of 6.3, 6.7, 8.2 and ~9.2
respectively; GRB 090429B is the most distant star measured in the
Universe so far!
- The "Naked-Eye" Burst
GRB 080319B was extraordinarily bright, breaking the luminosity records. It
reached a peak optical magnitude of 5.3, meaning that it would have been
visble to the naked eye from a dark location, despite being at a redshift of
0.937 (corresponding to 7.5 billion light years away - more than halfway
across the visible Universe!); the γ-ray and X-ray fluxes
were extremely high, too. One possible explanation is that there could have
been a 2-component jet.
See Racusin et
al. (2008) for details.
Magnetars are neutron stars with extreme magnetic fields. When these fields
decay, γ- and X-ray radiation can be emitted.
It is thought that some magnetars may be related to Gamma-Ray Bursts, being
formed before the final collapse of the system, leading to an unusal plateau
and steep decay in the X-ray light-curve. See, for example, Rowlinson et
al. (2010), Lyons
et al. (2010) and Troja et al. (2007).
GRB 070110 (Troja et al. 2007) has an interesting abrupt drop-off in the X-ray light-curve, which could be related to the spin-down of a magnetar.
- Long GRBs with no accompanying supernovae
The progenitor model for long GRBs is the death of a massive star and the connection between long GRBs and core-collapse supernovae has been known
since 1998, when GRB 980425 and SN 1998bw were identified with each other;
this was further confirmed through observations of GRB 030329. Long GRBs closer
than a redshift of z ~ 0.2 are therefore expected to show evidence of a
supernova in the optical band. However, GRBs 060505 and 060614
did not show associated supernovae, down to a luminosity at least a factor of 100
lower than that of SN 1998bw. There are many papers on these objects,
et al. (2006), Della
Valle et al. (2006), Fynbo et
al. (2006), Mangano et
al. (2007) and Ofek et al. (2007)
- Thermal spectral components
- Arcsecond localisation of a short GRB
GRB 050509B was the first short (40 ms) burst to be promptly localised by the Swift-X-ray
Telescope. A large elliptical galaxy was found within the error circle, at a
redshift of 0.225. Ellipticals have low star-formation rates, meaning that
such a host galaxy is consistent with the hypothesis that short GRBs are the
result of merging neutron stars. See Gehrels et
al. (2005) for more details. See also Barthelmy et
al. (2005) for further discussion.
- Complex X-ray afterglow light-curves
Prior to the launch of Swift, observations of GRB afterglows did not tend to
begin until many hours, if not days, after the trigger. Swift's autonomous
slewing capabilities allows for observations with the narrow-field onboard
instruments to begin typically 60-100 seconds after the trigger. Such a rapid
follow-up revealed X-ray light-curves much more complex than the slow,
unbroken decay previously expected, with an initial steep decline followed by
a flat so-called "plateau" phase before a "normal" decay. See Tagliaferri et
al. (2005), Nousek et
al. (2006), Zhang et
al. (2006), Evans et
al. (2007) and Evans et al. (2010) for further information.
In addition, many X-ray light-curves show flares superimposed on the decay,
sometimes very large, occurring out to late times, which are thought to be
related to central engine activity (i.e., collisions within faster and slower
material within the ejected jet). Burrows et
al. (2005) describes the first bright X-ray flares detected.