2015/06/12 by A. Borghese, Alice Borghese, N. Rea +12
Earth and Planetary Sciences · Physics and Astronomy · #Astrophysical Phenomena and Observations #High-pressure geophysics and materials #Pulsars and Gravitational Waves Research #astro-ph.HE
paper · pdf · doi:10.48550/arxiv.1506.04206
6 pages, 4 figures; ApJ Letters accepted
arxiv created 2015/06/13 · arxiv updated 2015/06/16
We present the discovery of a strongly phase-variable absorption feature in the X-ray spectrum of the nearby, thermally-emitting, isolated neutron star RX J0720.4-3125. The absorption line was detected performing detailed phase-resolved spectroscopy in 20 XMM-Newton observations, covering the period May 2000 - September 2012. The feature has an energy of ~750eV, an equivalent width of ~30eV, and it is significantly detected for only ~20% of the pulsar rotation. The absorption feature appears to be stable over the timespan covered by the observations. Given its strong dependence on the pulsar rotational phase and its narrow width, a plausible interpretation is in terms of resonant proton cyclotron absorption/scattering in a confined magnetic structure very close to the neutron star surface. The inferred field in such a magnetic loop is Bloop ~ 2 x 1014 G, a factor of ~7 higher than the surface dipolar magnetic field.