Abstract for Proposal 086127
Hunting for transitional millisecond pulsars with XMM-Newton and NuStar
The XMM discovery of a ms pulsar swinging between an accretion-powered
(X- ray) and a rotation-powered (radio) pulsar state demonstrated that
transitions between the two states can be observed over timescales
of a few weeks. We propose an XMM/NuStar ToO observation of 60 ks
aimed at studying the accretion state of transitional ms pulsars,
detecting X-ray accretion powered pulsations, and characterizing its
variability over three decades in energy. Candidates are restricted to
black widows and redbacks, systems in an evolutionary phase that allows
state transitions. Enlarging the number of systems in this transitional
phase is crucial to test binary evolution theories, and to study the
disk-field interaction over a large range of mass accretion rates.
Details on Observing Strategy and Trigger Criteria
A 60 ks XMM/NuSTAR observation will be triggered by a transient with
flux > 0.1 mCrab (5E-12 erg/cm2/s; 0.5-10 keV) and/or flux > 0.5 mCrab
(4E-12 erg/cm2/s; 20- 40 keV), whose position is compatible with one of
the target listed, or with an unidentified Fermi/LAT gamma-ray source
of the Galactic disk (target #42). Reaction in <~ 5 days will ensure
the best scientific return. Triggers of bright events such as outbursts
will be provided by X-ray transients monitoring programs performed by
ISGRI/INTEGRAL, BAT/Swift and GSC/MAXI. Already accepted monitoring
programs in optical bands (Galileo at La Palma, OAdM at Montsec, REM
at La Silla, PI: Papitto) will be also used to detect a transition to
a fainter accretion state.