9 research outputs found
Spectral evolution and polarization of variable structures in the pulsar wind nebula of PSR B0540-69.3
We present high spatial resolution optical imaging and polarization
observations of the PSR B0540-69.3 and its highly dynamical pulsar wind nebula
(PWN) performed with HST, and compare them with X-ray data obtained with the
Chandra X-ray Observatory. We have studied the bright region southwest of the
pulsar where a bright "blob" is seen in 1999. We show that it may be a result
of local energy deposition around 1999, and that the emission from this then
faded away. Polarization data from 2007 show that the polarization properties
show dramatic spatial variations at the 1999 blob position arguing for a local
process. Several other positions along the pulsar-"blob" orientation show
similar changes in polarization, indicating previous recent local energy
depositions. In X-rays, the spectrum steepens away from the "blob" position,
faster orthogonal to the pulsar-"blob" direction than along this axis of
orientation. This could indicate that the pulsar-"blob" orientation is an axis
along where energy in the PWN is mainly injected, and that this is then
mediated to the filaments in the PWN by shocks. We highlight this by
constructing an [S II]-to-[O III]-ratio map. We argue, through modeling, that
the high [S II]/[O III] ratio is not due to time-dependent photoionization
caused by possible rapid Xray emission variations in the "blob" region. We have
also created a multiwavelength energy spectrum for the "blob" position showing
that one can, to within 2sigma, connect the optical and X-ray emission by a
single power law. We obtain best power-law fits for the X-ray spectrum if we
include "extra" oxygen, in addition to the oxygen column density in the
interstellar gas of the Large Magellanic Cloud and the Milky Way. This oxygen
is most naturally explained by the oxygen-rich ejecta of the supernova remnant.
The oxygen needed likely places the progenitor mass in the 20 - 25 Msun range.Comment: Accepted by MNRAS on December 6th 2010, 18 pages, 15 figures. The
article with full resolution figures is available here
ftp://ftp.astro.su.se/pub/peter/papers/pwn0540_2010_corrected.pd
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
Six Years of Chandra Observations of Supernova Remnants
We present a review of the first six years of Chandra X-ray Observatory
observations of supernova remnants. From the official "first-light" observation
of Cassiopeia A that revealed for the first time the compact remnant of the
explosion, to the recent million-second spectrally-resolved observation that
revealed new details of the stellar composition and dynamics of the original
explosion, Chandra observations have provided new insights into the supernova
phenomenon. We present an admittedly biased overview of six years of these
observations, highlighting new discoveries made possible by Chandra's unique
capabilities.Comment: 82 pages, 28 figures, for the book Astrophysics Update
The young pulsar PSR B0540-69.3 and its synchrotron nebula in the optical and X-rays
The young PSR B0540-69 (B0540) in the LMC is the only pulsar (except the Crab pulsar) for which a near-UV spectrum has been obtained. However, the absolute flux and spectral index of previously published HST/FOS data are significantly higher than suggested by broadband groundbased UBVRI photometry. Using our ESO/VLT/FORS1 spectral observations and HST/WFPC2 archival images we show that the old HST and new VLT spectral data are >50% contaminated by the Pulsar Wind Nebula (PWN) and that this is the reason for the above mentioned difference. We find that the broadband HST spectrum for the range 3300-8000 A is clearly non- thermal and has a negative spectral index of 1.07(+0.20/-0.19). This is dif- ferent from the almost flat spectrum of the Crab pulsar. The PWN of B0540 shows a clear asymmetry of the surface brightness distribution along the major axis of the PWN torus-like structure with respect to the pulsar position, also seen in Chandra X-ray images. This can be linked to the asymmetry of the surrounding SN ejecta. We find no significant spectral index variation over the PWN. Using HST archival images we estimate the proper motion of B0540 to be 4.9+/-2.3 mas/yr, i.e. a transverse velocity of 1190+/-560 km/s along the southern jet of the PWN. This can make PSR B0540 the third pulsar with a proper motion aligned with the jet axis of its PWN, which poses constraints on pulsar kick models. We discuss the interstellar absorption toward B0540 including the contributions from the Milky Way, LMC and the supernova ejecta, and compare unabsorbed multi- wavelength spectra of B0540 and the Crab pulsar, and their PWNs. Compared with the Crab, B0540 and its PWN show a significant depression in the optical range
Dynamical influence of gravity waves generated by the Vestfjella Mountains in Antarctica: radar observations, fine-scale modelling and kinetic energy budget analysis
Gravity waves generated by the Vestfjella Mountains (in western Droning Maud Land, Antarctica, southwest of the Finnish/Swedish Aboa/Wasa station) have been observed with the Moveable atmospheric radar for Antarctica (MARA) during the SWEDish Antarctic Research Programme (SWEDARP) in December 2007/January 2008. These radar observations are compared with a 2-month Weather Research Forecast (WRF) model experiment operated at 2 km horizontal resolution. A control simulation without orography is also operated in order to separate unambiguously the contribution of the mountain waves on the simulated atmospheric flow. This contribution is then quantified with a kinetic energy budget analysis computed in the two simulations. The results of this study confirm that mountain waves reaching lower-stratospheric heights break through convective overturning and generate inertia gravity waves with a smaller vertical wavelength, in association with a brief depletion of kinetic energy through frictional dissipation and negative vertical advection. The kinetic energy budget also shows that gravity waves have a strong influence on the other terms of the budget, i.e. horizontal advection and horizontal work of pressure forces, so evaluating the influence of gravity waves on the mean-flow with the vertical advection term alone is not sufficient, at least in this case. We finally obtain that gravity waves generated by the Vestfjella Mountains reaching lower stratospheric heights generally deplete (create) kinetic energy in the lower troposphere (upper troposphere–lower stratosphere), in contradiction with the usual decelerating effect attributed to gravity waves on the zonal circulation in the upper troposphere–lower stratosphere