743 research outputs found
The Optical Spectrum of the Vela Pulsar
Our knowledge of the optical spectra of Isolated Neutron Stars (INSs) is
limited by their intrinsic faintness. Among the fourteen optically identified
INSs, medium resolution spectra have been obtained only for a handful of
objects. No spectrum has been published yet for the Vela pulsar (PSR B0833-45),
the third brightest (V=23.6) INS with an optical counterpart. Optical
multi-band photometry underlines a flat continuum.In this work we present the
first optical spectroscopy observations of the Vela pulsar, performed in the
4000-11000 A spectral range.Our observations have been performed at the ESO VLT
using the FORS2 instrument. The spectrum of the Vela pulsar is characterized by
a flat power-law (alpha = -0.04 +/- 0.04), which compares well with the values
obtained from broad-band photometry. This confirms, once more, that the optical
emission of Vela is entirely of magnetospheric origin. The comparison between
the optical spectral indeces of rotation-powered INSs does not show evidence
for a spectral evolution suggesting that, as in the X-rays, the INS aging does
not affect the spectral properties of the magnetospheric emission. At the same
time, the optical spectral indeces are found to be nearly always flatter then
the X-rays ones, clearly suggesting a general spectral turnover at lower
energies.Comment: 7 pages, 8 figures, accepted for publication in A&
HST and VLT observations of the neutron star 1E 1207.4-5209
1E 1207.4-5209, the peculiar Central Compact object in the G296.5+10.0
supernova remnant, has been proposed to be an "anti-magnetar" - a young neutron
star born with a weak dipole field. Accretion, possibly of supernova fallback
material, has also been invoked to explain a large surface temperature
anisotropy as well as the generation of peculiar cyclotron absorption features
superimposed to its thermal spectrum. Interestingly enough, a faint
optical/infrared source was proposed as a possible counterpart to 1E
1207.4-5209, but later questioned, based on coarse positional coincidence.
Considering the large offset of 1E 1207.4-5209 with respect to the center of
its host supernova remnant, the source should move at ~70 mas/yr. Thus, we
tested the association by measuring the proper motion of the proposed optical
counterpart. Using HST observations spanning 3.75 years, we computed a 3 sigma
upper limit of 7 mas/yr. Absolute astrometry on the same HST data set also
places the optical source significantly off the 99% confidence Chandra
position. This allows us to safely rule out the association. Using the HST data
set, coupled to ground-based observations collected at the ESO/VLT, we set the
deepest limits ever obtained to the optical/infrared emission from 1E
1207.4-5209. By combining such limits to the constraints derived from X-ray
timing, we rule out accretion as the source of the thermal anisotropy of the
neutron star.Comment: 8 pages, 3 figures. Accepted for publication in Astronomy &
Astrophysic
The first deep X-ray and optical observations of the closest isolated radio pulsar
With a distance of 170 pc, PSR J2144-3933 is the closest isolated radio
pulsar currently known. It is also the slowest and least energetic radio
pulsar; indeed, its radio emission is difficult to account for with standard
pulsar models, since its position in the P-Pdot diagram is far beyond typical
"death lines". Here we present the first deep X-ray and optical observations of
PSR J2144-3933, performed in 2009 with XMM-Newton and the VLT, from which we
can set one of the most robust upper limits on the surface temperature of a
neutron star. We have also explored the possibility of measuring the neutron
star mass from the gravitational lensing effect on a background optical source.Comment: 4 pages, 3 figures; to appear in the Proceedings of the Pulsar
Conference 2010, Chia, Sardinia (Italy), 10-15 October 201
A Search for the Optical/Infrared Counterpart of the Anomalous X-ray Pulsar 1E 1841-045
We have carried out a search for the optical and infrared counterpart of the
Anomalous X-ray Pulsar 1E 1841-045, which is located at the center of the
supernova remnant Kes73. We present the first deep optical and infrared images
of the field of 1E 1841-045, as well as optical spectroscopy results that
exclude the brightest objects in the error circle as possible counterparts. A
few of the more reddened objects in this region can be considered as
particularly interesting candidates, in consideration of the distance and
absorption expected from the association with Kes73. The strong interstellar
absorption in the direction of the source does not allow to completely exclude
the presence of main sequence massive companions.Comment: 8 pages, latex, 6 figures, Submitted to Mon. Not. R. Astron. So
VLT Suzaku observations of the Fermi pulsar PSR J1028-5819
We used optical images taken with the Very Large Telescope (VLT) in the B and
V bands to search for the optical counterpart of PSR J1028-5819 or constrain
its optical brightness. At the same time, we used an archival Suzaku
observation to confirm the preliminary identification of the pulsar's X-ray
counterpart obtained by Swift. Due to the large uncertainty on the pulsar's
radio position and the presence of a bright (V = 13.2) early F-type star at <
4", we could not detect its counterpart down to flux limits of B~25.4 and V
~25.3, the deepest obtained so far for PSR J1028-5819. From the Suzaku
observations, we found that the X-ray spectrum of the pulsar's candidate
counterpart is best-fit by a power-law with spectral index 1.7 +/- 0.2 and an
absorption column density NH < 10^21 cm-2, which would support the proposed
X-ray identification. Moreover, we found possible evidence for the presence of
diffuse emission around the pulsar. If real, and associated with a pulsar wind
nebula (PWN), its surface brightness and angular extent would be compatible
with the expectations for a ~100 kyr old pulsar at the PSR J1028-5819 distance.Comment: 10 pages, 9 figures, submitted to Astronomy and Astrophysic
A Comment on "A note on polarized light from Magnetars: QED effects and axion-like particles" by L.M. Capparelli, L. Maiani and A.D. Polosa
The recent detection of a large polarization degree in the optical emission
of an isolated neutron star led to the suggestion that this has been the first
evidence of vacuum polarization in a strong magnetic field, an effect predicted
by quantum electrodynamics but never observed before. This claim was challanged
in a paper by Capparelli, Maiani & Polosa (2017), according to whom a much
higher polarization degree would be necessary to positively identify vacuum
polarization. Here we show that their conclusions are biased by several
inadequate assumptions and have no impact on the original claim.Comment: 10 pages, 2 figure
VLT observations of the Central Compact Object in the Vela Jr. supernova remnant
X-ray observations have unveiled the existence of enigmatic point-like
sources at the center of young (a few kyrs) supernova remnants. These sources,
known as Central Compact Objects (CCOs), are thought to be neutron stars
produced by the supernova explosion, although their X-ray phenomenology makes
them markedly different from all the other young neutron stars discovered so
far.The aim of this work is to search for the optical/IR counterpart of the
Vela Junior CCO and to understand the nature of the associated Halpha nebula
discovered by Pellizzoni et al. (2002).}{We have used deep optical (R band) and
IR (J,H,Ks bands) observations recently performed by our group with the ESO VLT
to obtain the first deep, high resolution images of the field with the goal of
resolving the nebula structure and pinpointing a point-like source possibly
associated with the neutron star.Our R-band image shows that both the nebula's
flux and its structure are very similar to the Halpha ones, suggesting that the
nebula spectrum is dominated by pure Halpha line emission. However, the nebula
is not detected in our IR observations, whick makes it impossible to to
constrain its spectrum. A faint point-like object (J>22.6, H~21.6, Ks ~ 21.4)
compatible with the neutron star's Chandra X-ray position is detected in our IR
images (H and Ks) but not in the optical one (R > 25.6), where it is buried by
the nebula background. The nebula is most likely a bow-shock produced by the
neutron star motion through the ISM or, alternatively, a photo-ionization
nebula powered by UV radiation from a hot neutron star.Comment: 8 pages, 4 figures, A&Aaccepte
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