EDP Sciences
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Volume 429, Number 1, January I 2005
Page(s) 257 - 265
Section Stellar structure and evolution
DOI http://dx.doi.org/10.1051/0004-6361:20048019

A&A 429, 257-265 (2005)
DOI: 10.1051/0004-6361:20048019

The proper motion of the isolated neutron star RX J1605.3+3249

C. Motch1, K. Sekiguchi2, F. Haberl3, V. E. Zavlin1, 3, A. Schwope4 and M. W. Pakull1

1  Observatoire Astronomique, UMR 7550 CNRS, 11 rue de l'Université, 67000 Strasbourg, France
    e-mail: motch@newb6.u-strasbg.fr
2  Subaru Telescope, National Astronomical Observatory of Japan, 650 North A'ohoku Place, Hilo, HI 96720, USA
3  Max-Planck-Institut für extraterrestrische Physik, 85740 Garching bei München, Germany
4  Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany

(Received 4 April 2004 / Accepted 6 August 2004 )

We obtained deep optical imaging of the thermally emitting X-ray bright and radio-quiet isolated neutron star RX J1605.3+3249 with the Subaru telescope in 1999 and 2003. Together with archival HST images acquired in 2001 these data reveal a proper motion of $\mu = 144.5\pm13.2$ mas/yr. This implies a relatively high spatial velocity and indicates that the star is unlikely to be re-heated by accretion of matter from the interstellar medium. Assuming that RX J1605.3+3249 is a young (10 5-106 yr) cooling neutron star, its apparent trajectory is consistent with a birth in the nearby Sco OB2 OB association at a location close to that derived for RX J1856.5-3754 and perhaps also to that of RX J0720.4-3125 . This suggests that the X-ray bright part of ROSAT-discovered isolated neutron stars is dominated by the production of the Sco OB2 complex which is the closest OB association and a part of the Gould belt. The B and R magnitudes of the faint optical counterpart did not vary from 1999 to 2003 at $B = 27.22\pm0.10$. Its B-R colour index of $+0.32\pm0.17$ is significantly redder than that of other isolated neutron stars and the optical flux lies a factor 11.5 above the extrapolation of the X-ray blackbody-like spectrum. The red optical colour reveals the presence of an additional emitting component in the optical regime over the main neutron star thermal emission. We also discovered a small elongated H ${\alpha}$ nebula approximately centered on the neutron star and aligned with the direction of motion. The width of the nebula is unresolved and smaller than ~0.4´´ for a length of about 1´´. The shape of the Balmer emitting nebula around RX J1605.3+3249 is very different from those seen close to other neutron stars and should be confirmed by follow-up observations. We shortly discuss the possible mechanisms which could give rise to such a geometry.

Key words: stars: pulsars: individual: RX J51605.3+3249 -- stars: neutron

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© ESO 2004