HST image of the bow-shock nebula around
RX J1856.5-3754 (van Kerkwick & Kulkarni 2001)
The Soft/Hard light curve shift
Crosscorrelation of the
bands (0.3-0.7) and (2-4) keV:
dj = 80° ± 20° at F35 = 0.60
dj = 130°
± 20° at F35 = 0.02
dj = 160°
± 20° at F35 = 0.17
dj = 340°
± 20° at F35 = 0.26
Hard/soft phase
shift expected if soft photons result from reprocessing of hard X-rays in the
inner part of the accretion disk.
If a non-tilted disk intercepts and reprocesses the NS beam, directed and reflected components will be shifted by dj = 180°.
Æ dj ~250°
observed in the past during the main-on was associated with evidence of a tilt angle.
dj derived from EPIC data is very different
from past main-on observations.
Also, it changes dramatically in the other
two states.
Æ First observation of a
substantial, continuous change in the tilt of the disk !