Abstract for Proposal 092368
Fast multi-wavelength variability from LMXBs
Correlated fast multi-wavelength variability is a powerful tool for
studying the physics of accretion and ejection in X-ray binaries. Using
simultaneous X-ray and near-IR data we have secured the first detection
of sub-second IR variability from a jet (including quasi-periodic
oscillations) in a BH LMXB, allowing us to estimate the jet speed and
size. Further data showed that significant jet variability is also
present in NS LMXBs, opening a new window in the study of jets. Here,
we propose to monitor the evolution of an outburst of both systems with
XMM, simultaneously with ground-based optical, infrared facilities,
across different spectral states. Thus, we propose to perform up to 20
short XMM observations (7 ks each) to cover the different stages of the
outburst in both systems.
Details on Observing Strategy and Trigger Criteria
For both systems the condition is that the X-ray flux > ~1E-11 erg
sec-1 cm-2 (low hard state for LMXBs) IR magnitude <15 (typical value for
jet-dominated emission) For BH LMXBs the triggering probability is 30%.
Regarding NS LMXBs, along with a rate of ~1 new system outburst/year,
a handful of persistent sources offer the possibility to perform the
requested observations. Among the several persistent NS LMXBs, the most
notorious examples of sources showing this behaviour of 1 month timescale
are 4U 1728-34, 4U 1636-53,4U1705-44. Despite their persistent nature,
their irregular outburst duration requires also triggered observations:
we will activate the monitoring as soon as one NS LMXB is in its hard
state (as clearly visible from Siwft-BAT and MAXI monitoring data)
during an XMM visibility window. Given their individual time evolution,
we estimate a 100% chance that this happens for at least one of them.
N.B, for NS LMXBs priority will be still given to a transient NS LMXB
(which again have 30% probability of being triggered). Thus, a persistent
source will be observed ONLY IF a new transient is NOT in outburst.