Abstract for Proposal 086437
Observations of the outbursts of very-faint X-ray transients with XMM-Newton
We propose a 35 ks XMM-Newton observation during the outburst of
a very-faint X-ray transient. These peculiar X-ray binaries are
underluminous by orders of magnitudes compared to the well-studied
classical (bright) X-ray transient population. Some of them have been
identify as accreting neutron stars, whereas only one black hole has
been conclusively identified so far. However, the nature of the vast
majority remains unclear. This XMM-Newton observation will allow us
to carry out a detailed spectral analysis of a very faint transient (<
10 performed so far) in order to (i) shed light on the nature of this
growing population, (ii) the cause for their sub-luminous behaviour and
(iii) progress in our understanding of the geometry and accretion physics
at low accretion rates.
Details on Observing Strategy and Trigger Criteria
We trigger this proposal once a currently known or new transient LMXB
that has a peak outburst luminosity of only E34-E36 erg/s (2- 10 keV),
i.e. classifies as a very-faint X-ray transient, is reported active
(e.g. as seen by all-sky monitors such as Swift/BAT, MAXI, INTEGRAL,
or ASTROSAT). We require a suitable target to have NH<5E22 cm-2 so that
its X- ray spectrum can be accurately characterised.