23 research outputs found
The Vela Pulsar in the Near-Infrared
We report on the first detection of the Vela pulsar in the near-infrared with
the VLT/ISAAC in the Js and H bands. The pulsar magnitudes are Js=22.71 +/-
0.10 and H=22.04 +/- 0.16. We compare our results with the available
multiwavelength data and show that the dereddened phase-averaged optical
spectrum of the pulsar can be fitted with a power law F_nu propto
nu^(-alpha_nu) with alpha_nu = 0.12 +/- 0.05, assuming the color excess
E(B-V)=0.055 +/-0.005 based on recent spectral fits of the emission of the Vela
pulsar and its supernova remnant in X-rays. The negative slope of the pulsar
spectrum is different from the positive slope observed over a wide optical
range in the young Crab pulsar spectrum. The near-infrared part of the Vela
spectrum appears to have the same slope as the phase-averaged spectrum in the
high energy X-ray tail, obtained in the 2-10 keV range with the RXTE. Both of
these spectra can be fitted with a single power law suggesting their common
origin. Because the phase-averaged RXTE spectrum in this range is dominated by
the second X-ray peak of the pulsar light curve, coinciding with the second
main peak of its optical pulse profile, we suggest that this optical peak can
be redder than the first one. We also detect two faint extended structures in
the 1.5''-3.1'' vicinity of the pulsar, projected on and aligned with the
south-east jet and the inner arc of the pulsar wind nebula, detected in X-rays
with Chandra. We discuss their possible association with the nebula.Comment: 12 pages, 8 figures, accepted for publication in A&A, the associated
near-infrared images in the fits format are available at
http://www.ioffe.ru/astro/NSG/obs/vela-ir
Subaru optical observations of the old pulsar PSR B0950+08
We report the B band optical observations of an old (17.5 Myr) radiopulsar
PSR B0950+08 obtained with the Suprime-Cam at the Subaru telescope. We detected
a faint object, B=27.07(16). Within our astrometrical accuracy it coincides
with the radio position of the pulsar and with the object detected earlier by
Pavlov et al. (1996) in UV with the HST/FOC/F130LP. The positional coincidence
and spectral properties of the object suggest that it is the optical
counterpart of PSR B0950+08. Its flux in the B band is two times higher than
one would expect from the suggested earlier Rayleigh-Jeans interpretation of
the only available HST observations in the adjacent F130LP band. Based on the B
and F130LP photometry of the suggested counterpart and on the available X-ray
data we argue in favour of nonthermal origin of the broad-band optical spectrum
of PSR B0950+08, as it is observed for the optical emission of the younger,
middle-aged pulsars PSR B0656+14 and Geminga. At the same time, the optical
efficiency of PSR B0950+08, estimated from its spin-down power and the detected
optical flux, is by several orders of magnitude higher than for these pulsars,
and comparable with that for the much younger and more energetic Crab pulsar.
We cannot exclude the presence of a compact, about 1'', faint pulsar nebula
around PSR B0950+08, elongated perpendicular to the vector of its proper
motion, unless it is not a projection of a faint extended object on the pulsar
position.Comment: 8 pages, LaTeX, aa.cls style, 5 PS figures, submitted to A&A. Image
is available in FITS format at
http://www.ioffe.rssi.ru/astro/NSG/obs/0950-subar
Deep BVR Imaging of the Field of the Millisecond Pulsar PSR J0030+0451 with the VLT
We report on deep BVR-imaging of the field of the nearby millisecond pulsar
PSR J0030+0451 obtained with the ESO/VLT/FORS2. We do not detect any optical
counterpart down to B>27.3, V>27.0 and R>27.0 in the immediate vicinity of the
radio pulsar position. The closest detected sources are offset by >3'', and
they are excluded as counterpart candidates by our astrometry. Using our upper
limits in the optical, and including recent XMM-Newton X-ray data we show that
any nonthermal power-law spectral component of neutron star magnetospheric
origin, as suggested by the interpretation of X-ray data, must be suppressed by
at least a factor of ~500 in the optical range. This either rules out the
nonthermal interpretation or suggests a dramatic spectral break in the
0.003-0.1 keV range of the power-law spectrum. Such a situation has never been
observed in the optical/X-ray spectral region of ordinary pulsars, and the
origin of such a break is unclear. An alternative interpretation with a purely
thermal X-ray spectrum is consistent with our optical upper limits. In this
case the X-ray emission is dominated by hot polar caps of the pulsar.Comment: 6 pages, LaTeX aa.cls style, 5 EPS figures. Accepted for publication
in Astronomy and Astrophysic
Detection of Giant Radio Pulses from the Pulsar PSR B0656+14
Giant pulses (GPs) have been detected from the pulsar PSR B0656+14. A pulse
that is more intense than the average pulse by a factor of 120 is encountered
approximately once in 3000 observed periods of the pulsar. The peak flux
density of the strongest pulse, 120 Jy, is a factor of 630 higher than that of
the average pulse. The GP energy exceeds the energy of the average pulse by up
to a factor of 110, which is comparable to that for other known pulsars with
GPs, including the Crab pulsar and the millisecond pulsar PSR B1937+21. The
giant pulses are a factor of 6 narrower than the average pulse and are
clustered at the head of the average pulse. PSR B0656+14 along with PSR
B0031-07, PSR B1112+50, and PSR J1752+2359 belong to a group of pulsars that
differ from previously known ones in which GPs have been detected without any
extremely strong magnetic field on the light cylinder.Comment: 10 pages, 3 figures, 1 table; originally published in Russian in
Pis'ma Astron. Zh., 2006, v.32, 650; translated by George Rudnitskii; the
English version will be appear in Astronomy Letter
X-Ray Observations of the supernova remnant G21.5-0.9
We present the analysis of archival X-ray observations of the supernova
remnant (SNR) G21.5-0.9. Based on its morphology and spectral properties,
G21.5-0.9 has been classified as a Crab-like SNR. In their early analysis of
the CHANDRA calibration data, Slane et al. (2000) discovered a
low-surface-brightness, extended emission. They interpreted this component as
the blast wave formed in the supernova (SN) explosion. In this paper, we
present the CHANDRA analysis using a total exposure of ~150 ksec. We also
include ROSAT and ASCA observations. Our analysis indicates that the extended
emission is non-thermal -- a result in agreement with XMM observations. The
entire remnant of radius ~ 2'.5 is best fitted with a power law model with a
photon index steepening away from the center. The total unabsorbed flux in the
0.5-10 keV is 1.1E-10 erg/cm2/s with an 85% contribution from the 40" radius
inner core. Timing analysis of the High-Resolution Camera (HRC) data failed to
detect any pulsations. We put a 16% upper limit on the pulsed fraction. We
derive the physical parameters of the putative pulsar and compare them with
those of other plerions (such as the Crab and 3C 58). G21.5-0.9 remains the
only plerion whose size in X-rays is bigger than in the radio. Deep radio
observations will address this puzzle.Comment: 23 pages including 11 figures and 3 tables; accepted by ApJ June 22,
2001; to appear in Oct 20, 2001 issue of Ap
Optical spectroscopy of the radio pulsar PSR B0656+14
We have obtained the spectrum of a middle-aged PSR B0656+14 in the 4300-9000
AA range with the ESO/VLT/FORS2. Preliminary results show that at 4600-7000 AA
the spectrum is almost featureless and flat with a spectral index $\alpha_nu ~
-0.2 that undergoes a change to a positive value at longer wavelengths.
Combining with available multiwavelength data suggests two wide, red and blue,
flux depressions whose frequency ratio is about 2 and which could be the 1st
and 2nd harmonics of electron/positron cyclotron absorption formed at magnetic
fields ~10^8G in upper magnetosphere of the pulsar.Comment: 4 pages, 4 figures, To appear in Astrophysics and Space Science,
Proceedings of "Isolated Neutron Stars: from the Interior to the Surface",
eds. D. Page, R. Turolla and S. Zan
The near-infrared detection of PSR B0540-69 and its nebula
The ~1700 year old PSR B0540-69 in the LMC is considered the twin of the Crab
pulsar because of its similar spin parameters, magnetic field, and energetics.
Its optical spectrum is fit by a power-law, ascribed to synchrotron radiation,
like for the young Crab and Vela pulsars. nIR observations, never performed for
PSR B0540-69, are crucial to determine whether the optical power-law spectrum
extends to longer wavelengths or a new break occurs, like it happens for both
the Crab and Vela pulsars in the mIR, hinting at an even more complex particle
energy and density distribution in the pulsar magnetosphere. We observed PSR
B0540-69 in the J, H, and Ks bands with the VLT to detect it, for the first
time, in the nIR and characterise its optical-to-nIR spectrum. To disentangle
the pulsar emission from that of its pulsar wind nebula (PWN), we obtained
high-spatial resolution adaptive optics images with NACO. We could clearly
identify PSR B0540-69 in our J, H, and Ks-band images and measure its flux
(J=20.14, H=19.33, Ks=18.55, with an overall error of +/- 0.1 magnitudes in
each band). The joint fit to the available optical and nIR photometry with a
power-law spectrum gives a spectral index alpha=0.70 +/-0.04. The comparison
between our NACO images and HST optical ones does not reveal any apparent
difference in the PWN morphology as a function of wavelength. The PWN
optical-to-nIR spectrum is also fit by a single power-law, with spectral index
alpha=0.56+/- 0.03, slightly flatter than the pulsar's. Using NACO at the VLT,
we obtained the first detection of PSR B0540-69 and its PWN in the nIR. Due to
the small angular scale of the PWN (~4") only the spatial resolution of the
JWST will make it possible to extend the study of the pulsar and PWN spectrum
towards the mid-IR.Comment: 11 pages, 10 figures, Accepted for publication on Astronomy and
Astrophysic
Subaru optical observations of the two middle-aged pulsars PSR B0656+14 and Geminga
We carried out a deep subarcsecond BRI imaging of the two middle-aged pulsars
to establish their properties in the optical range. Both pulsars are detected
at >10 sigma level. Geminga is for the first time reliably detected in the I
band with a magnitude of 25.10+/-0.14. We also reanalyze archival ESO/NTT and
HST broadband data and find that some published fluxes for Geminga were
estimated inaccurately. The resulting dereddened broadband spectra of both
pulsars are remarkably similar to each other and show significant flux
increases towards the far-UV and near-IR, and a wide flux excess in V-I bands.
This suggests a multicomponent structure of the optical emission. The
nonthermal power law component of the pulsar magnetospheric origin dominates in
the most part of the optical range. For PSR B0656+14 it is compatible with a
low energy extension of the power law tail seen in hard X-rays. For Geminga the
respective extension overshoots by a factor of 100 the nonthermal optical flux,
which has a less steep spectral slope than in X-rays. This implies a spectral
break at a photon energy of about 1 keV. The flux increases towards the far-UV
are compatible with contributions of the Rayleigh-Jeans parts of the blackbody
components from whole surfaces of the neutron stars dominating in soft X-rays.
The V-I excess, which is most significant for PSR B0656+14, suggests a third
spectral component of still unidentified origin. Faint, a few arcseconds in
size nebulae extended perpendicular to the proper motion directions of the
pulsars, are seen around both objects in our deepest I band images. They can be
optical counterparts of the bow-shock head of Geminga and of the tentative
pulsar wind nebula of PSR B0656+14 observed in X-rays.Comment: 15 pages, 8 figures, A&A, accepted. For higher resolution images see
http://www.ioffe.ru/astro/NSG/obs/map
Optical photometry of the PSR B0656+14 and its neighborhood
We present the results of the broad-band photometry of the nearby middle-aged
radio pulsar PSR B0656+14 and its neighborhood obtained with the 6-meter
telescope of the SAO RAS and with the Hubble Space Telescope. The broad-band
spectral flux of the pulsar decreases with increasing frequency in the
near-IR range and increases with frequency in the near-UV range. The increase
towards UV can be naturally interpreted as the Rayleigh-Jeans tail of the soft
thermal component of the X-ray spectrum emitted from the surface of the cooling
neutron star. Continuation of the power-law component, which dominates in the
high-energy tail of the X-ray spectrum, to the IR-optical-UV frequencies is
consistent with the observed fluxes. This suggests that the non-thermal pulsar
radiation may be of the same origin in a broad frequency range from IR to hard
X-rays. We also studied 4 objects detected in the pulsar's 5" neighborhood.Comment: 12 pages, 20 figures, submitted to A&A. Images are available in FITS
format at http://www.ioffe.rssi.ru/astro/NSG/obs/0656-phot.htm