5 Thermonuclear X-ray Bursts
221
than 50 sources, led to a much greater capacity for broad-scale investigation into
the burst phenomenology [53]. Much of these investigations have focussed on the
burst oscillation phenomenon, as described in Sect. 5.5. The RXTE burst sample, as
with earlier compilations (e.g. [28]) from other instruments, revealed a much more
complex picture for unstable burning than predicted by theory.
An example is the study of photospheric radius-expansion bursts, which are
thought to reach the local Eddington luminosity, and have been used as “standard
candles” to determine the distance to bursting sources [184]. Observations of
bursts from globular cluster systems, which have an independently determined
distance, allowed empirical measurement of the peak PRE burst luminosity, which
is somewhat in excess of theoretical predictions for pure He fuel [109]. Such studies
also showed that in some systems there are substantial variations in the peak flux of
PRE bursts from the same source. In 4U 1636−536, a small subset of PRE bursts
reach a peak flux a factor of 1.7 lower than the majority of events, explained as a
variation in the electron scattering dominated opacity between pure He and mixed
H/He at solar composition. This result, obtained for a sample of PRE bursts much
larger than in any other source, further suggests that typical PRE bursts reach the
Eddington flux for material devoid of hydrogen, even in systems accreting a mix of
H and He [52]. In other systems, the typically 5–10% variation in the peak fluxes
may be attributed to interactions with the accretion disk [51]. Eddington-limited
bursts remain the primary source of information on the distances to burst sources,
but more work is required to reduce the effect of systematic contributions to the
peak flux distribution.
Independently of the studies that accompanied the catalogue data itself, the
provision of an index (i.e. burst times and observation IDs) into an otherwise
undifferentiated collection of burst observations enabled other researchers to perform their own analyses on the burst sample, further increasing its impact. The
RXTE sample has been extended with further observations through to the end of
the mission in 2012 January, and now totals more than 2000 bursts. These data
will be incorporated into a new, and more comprehensive sample of bursts, the
Multi-INstrument Burst ARchive (MINBAR 3 ). Together with burst observations of
the BeppoSAX/WFCs [28], and INTEGRAL/JEM-X, MINBAR contains over 7000
bursts.
5.2 X-ray Burst Ignition
In Sect. 5.1.1.2 we explained burst ignition as due to runaway thermonuclear
burning. Here we discuss the other fundamental processes that facilitate the ignition
of different types of bursts, including the so-called short recurrence time bursts, as
well as the role of the latitude of the ignition location.
3 http://burst.sci.monash.edu/minbar.
221
than 50 sources, led to a much greater capacity for broad-scale investigation into
the burst phenomenology [53]. Much of these investigations have focussed on the
burst oscillation phenomenon, as described in Sect. 5.5. The RXTE burst sample, as
with earlier compilations (e.g. [28]) from other instruments, revealed a much more
complex picture for unstable burning than predicted by theory.
An example is the study of photospheric radius-expansion bursts, which are
thought to reach the local Eddington luminosity, and have been used as “standard
candles” to determine the distance to bursting sources [184]. Observations of
bursts from globular cluster systems, which have an independently determined
distance, allowed empirical measurement of the peak PRE burst luminosity, which
is somewhat in excess of theoretical predictions for pure He fuel [109]. Such studies
also showed that in some systems there are substantial variations in the peak flux of
PRE bursts from the same source. In 4U 1636−536, a small subset of PRE bursts
reach a peak flux a factor of 1.7 lower than the majority of events, explained as a
variation in the electron scattering dominated opacity between pure He and mixed
H/He at solar composition. This result, obtained for a sample of PRE bursts much
larger than in any other source, further suggests that typical PRE bursts reach the
Eddington flux for material devoid of hydrogen, even in systems accreting a mix of
H and He [52]. In other systems, the typically 5–10% variation in the peak fluxes
may be attributed to interactions with the accretion disk [51]. Eddington-limited
bursts remain the primary source of information on the distances to burst sources,
but more work is required to reduce the effect of systematic contributions to the
peak flux distribution.
Independently of the studies that accompanied the catalogue data itself, the
provision of an index (i.e. burst times and observation IDs) into an otherwise
undifferentiated collection of burst observations enabled other researchers to perform their own analyses on the burst sample, further increasing its impact. The
RXTE sample has been extended with further observations through to the end of
the mission in 2012 January, and now totals more than 2000 bursts. These data
will be incorporated into a new, and more comprehensive sample of bursts, the
Multi-INstrument Burst ARchive (MINBAR 3 ). Together with burst observations of
the BeppoSAX/WFCs [28], and INTEGRAL/JEM-X, MINBAR contains over 7000
bursts.
5.2 X-ray Burst Ignition
In Sect. 5.1.1.2 we explained burst ignition as due to runaway thermonuclear
burning. Here we discuss the other fundamental processes that facilitate the ignition
of different types of bursts, including the so-called short recurrence time bursts, as
well as the role of the latitude of the ignition location.
3 http://burst.sci.monash.edu/minbar.