45 research outputs found
Neutron Star Astronomy in the era of the European Extremely Large Telescope
About 25 isolated neutron stars (INSs) are now detected in the optical
domain, mainly thanks to the HST and to VLT-class telescopes. The European
Extremely Large Telescope (E-ELT) will yield ~100 new identifications, many of
which from the follow-up of SKA, IXO, and Fermi observations. Moreover, the
E-ELT will allow to carry out, on a much larger sample, INS observations which
still challenge VLT-class telescopes, enabling studies on the structure and
composition of the NS interior, of its atmosphere and magnetosphere, as well as
to search for debris discs. In this contribution, I outline future perspectives
for NS optical astronomy with the E-ELT.Comment: 4 pages, to be published in Proceedings of the Conference
"ASTROphysics of Neutron Stars 2010", a conference in honor of M. Ali Alpar,
held in Cesme (Izmir) August 2-6 201
HST Proper Motion confirms the optical identification of the nearby pulsar PSR 1929+10
We report on the proper motion measurement of the proposed optical
counterpart of the X-ray/radio pulsar PSR 1929+10. Using images obtained with
the HST/STIS (average epoch 2001.73) we computed a yearly displacement of +97
+/- 1 mas yr^{-1} in RA and +46 +/- 1 mas yr^{-1} in Dec since the epoch
(1994.52) of the original HST/FOC detection. Both the magnitude and direction
of the optical proper motion components are found to be fully consistent with
the most recent VLBA radio measurements. This result provides an unambiguous
confirmation of the pulsar optical identification. In addition, we have used
the combined STIS/FOC datasets to derive information on the pulsar spectrum,
which seems characterized by a power law component, apparently unrelated to the
X-ray emission.Comment: 12 pages, 3 figures, submitted to ApJ Letter
Evidence for vacuum birefringence from the first optical-polarimetry measurement of the isolated neutron star RX J1856.5-3754
The "Magnificent Seven" (M7) are a group of radio-quiet Isolated Neutron
Stars (INSs) discovered in the soft X-rays through their purely thermal surface
emission. Owing to the large inferred magnetic fields ( G),
radiation from these sources is expected to be substantially polarised,
independently on the mechanism actually responsible for the thermal emission. A
large observed polarisation degree is, however, expected only if
quantum-electrodynamics (QED) polarisation effects are present in the
magnetised vacuum around the star. The detection of a strongly linearly
polarised signal would therefore provide the first observational evidence of
QED effects in the strong-field regime. While polarisation measurements in the
soft X-rays are not feasible yet, optical polarisation measurements are within
reach also for quite faint targets, like the M7 which have optical counterparts
with magnitudes --. Here, we report on the measurement of
optical linear polarisation for the prototype, and brightest member, of the
class, RX\, J1856.53754 (), the first ever for one of the M7,
obtained with the Very Large Telescope. We measured a polarisation degree
and a polarisation position angle
\mathrm{P.A.}=145\fdg39\pm9\fdg44, computed east of the North Celestial
Meridian. The that we derive is large enough to support the
presence of vacuum birefringence, as predicted by QED.Comment: 9 pages, 7 figures, accepted for publication on MNRA
The two tails of PSR J2055+2539 as seen by Chandra: analysis of the nebular morphology and pulsar proper motion
We analyzed two Chandra observations of PSR J2055+2539 (for a total
integration time of 130 ks) in order to measure its proper motion and
study its two elongated nebular features. We did not detect the proper motion,
setting an upper limit of 240 mas yr (3 level), that translates
into an upper limit on the transverse velocity of 700 km s, for an
assumed distance of 600 pc. A deep H observation did not reveal the
bow-shock associated with a classical pulsar wind nebula, thus precluding an
indirect measurement of the proper motion direction. We determined the main
axes of the two nebulae, which are separated by an angle of 160.8, using a new approach based on the Rolling Hough Transformation
(RHT). We analyzed the shape of the first 8' (out of the 12' seen by
XMM-Newton) of the brighter, extremely collimated one. Based on a combination
of our results from a standard analysis and a nebular modeling obtained from
the RHT, we find that the brightest nebula is curved on an arcmin-scale, with a
thickness ranging from " to " and a possible (single or
multiple) helicoidal pattern. We could not constrain the shape of the fainter
nebula. We discuss our results in the context of other known similar features,
with particular emphasis on the Lighthouse nebula (associated with PSR
J11016101). We speculate that a peculiar geometry of the powering pulsar may
play an important role in the formation of such features.Comment: 12 pages, 9 figures, 1 table; accepted by Astronomy & Astrophysic