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We report on the analysis of new X-ray data obtained with XMM-Newton andChandra from two ROSAT-discovered X-ray dim isolated neutron stars. RXJ0806.4-4123 was observed with XMM-Newton in April 2003, 2.5 years after thefirst observation. The EPIC-pn data confirm that this object is an X-ray pulsarwith 11.371 s neutron star spin period. The X-ray spectrum is consistent withabsorbed black-body emission with a temperature kT = 96 eV and NH = 4x10^19cm^-2 without significant changes between the two observations. Four XMM-Newtonobservations of RX J0420.0-5022 between December 2002 and July 2003 did notconfirm the 22.7 s pulsations originally indicated in ROSAT data, but clearlyreveal a 3.453 s period. A fit to the X-ray spectrum using an absorbedblack-body model yields kT = 45 eV, the lowest value found from the small groupof XDINs and NH = 1.0x10^20 cm^-2. Including a broad absorption line improvesthe quality of the spectral fits considerably for both objects and may indicatethe presence of absorption features similar to those reported from RBS1223, RXJ1605.3+3249 and RX J0720.4-3125. For both targets we derive accurate X-raypositions from the Chandra data and present an optical counterpart candidatefor RX J0420.0-5022 with B = 26.6+/-0.3 mag from VLT imaging.Comment: 11 pages, 7 figures, accepted for publication in A&

The isolated neutron star X-ray pulsars RX J0420.0–5022 and RX J0806.4–4123: New X-ray and optical observations