VLT/FORS2 observations of the optical counterpart of the isolated neutron star RBS 1774

Details VLT/FORS2 observations of the optical counterpart of the isolated neutron star RBS 1774 VLT/FORS2 observations of the optical counterpart of the isolated neutron star RBS 1774

2011-03-21

arxiv.org/abs/1103.4099v1

Astronomy and Astrophysics

Astrophysics

High Energy Astrophysical Phenomena

8 pages, 8 postscript figures, accepted for publication in Astronomy & Astrophysics

Scientific paper

X-ray observations performed with ROSAT led to the discovery of a group (seven to date) of X-ray dim and radio-silent middle-aged isolated neutron stars (a.k.a. XDINSs), which are characterised by pure blackbody spectra (kT~40-100 eV), long X-ray pulsations (P=3-12 s), and appear to be endowed with relatively high magnetic fields, (B~10d13-14 G). RBS 1774 is one of the few XDINSs with a candidate optical counterpart, which we discovered with the VLT. We performed deep observations of RBS 1774 in the R band with the VLT to disentangle a non-thermal power-law spectrum from a Rayleigh-Jeans, whose contributions are expected to be very much different in the red part of the spectrum. We did not detect the RBS 1774 candidate counterpart down to a 3 sigma limiting magnitude of R~27. The constraint on its colour, (B-R)<0.6, rules out that it is a background object, positionally coincident with the X-ray source. Our R-band upper limit is consistent with the extrapolation of the B-band flux (assuming a 3 sigma uncertainty) for a set of power-laws F_nu ~nu^alpha with spectral indeces alpha<0.07. If the optical spectrum of RBS 1774 were non-thermal, its power-law slope would be very much unlike those of all isolated neutron stars with non-thermal optical emission, suggesting that it is most likely thermal. For instance, a Rayleigh-Jeans with temperature T_O = 11 eV, for an optically emitting radius r_O=15 km and a source distance d=150 pc, would be consistent with the optical measurements. The implied low distance is compatible with the 0.04 X-ray pulsed fraction if either the star spin axis is nearly aligned with the magnetic axis or with the line of sight, or it is slightly misaligned with respect to both the magnetic axis and the line of sight by 5-10 degrees

Affiliated with

Also associated with

No associations

Rating

VLT/FORS2 observations of the optical counterpart of the isolated neutron star RBS 1774 does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.

If you have personal experience with VLT/FORS2 observations of the optical counterpart of the isolated neutron star RBS 1774, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and VLT/FORS2 observations of the optical counterpart of the isolated neutron star RBS 1774 will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFWR-SCP-O-323984