  We present XMM-Newton and Chandra observations of 1E1048.1-5937, being the
first to show evidence for a significant variation in the X-ray luminosity of
this Anomalous X-ray Pulsar (AXP). While during the first XMM-Newton (2000
December) and Chandra (2001 July) observations the source had a flux consistent
with that measured on previous occasions (~5x10e-12 ergs/cmq/s), two more
recent observations found it at a considerably higher flux level of 2x10e-11
ergs/cmq/s (2002 August; Chandra) and 10e-11 ergs/cmq/s (2003 June;
XMM-Newton). All the spectra are fit by the sum of a blackbody with kT~0.6 keV
and a power law with photon index ~3. No significant changes were seen in the
spectral parameters, while the pulsed fraction in the 0.6-10 keV energy range
decreased from ~90% in 2000 to ~53% in 2003. The spectral invariance does not
support the presence of two physically distinct components in the AXP emission.
The sparse coverage of the data does not permit us to unambiguously relate the
observed variations to the two bursts seen from this source in the fall of
2001.
