HST optical polarimetry of the Vela pulsar & nebula

Polarisation measurements of pulsars offer an unique insight into the geometry of the emission regions in the neutron star magnetosphere. Therefore, they provide observational constraints on the different models proposed for the pulsar emission mechanisms. Optical polarisation data of the Vela pulsar was obtained from the {\em Hubble Space Telescope} ({\em HST}) archive. The data, obtained in two filters (F606W; central wavelength = 590.70 nm, and F550M; central wavelength = 558.15 nm), consists of a series of observations of the pulsar taken with the {\em HST}/Advanced Camera for Surveys (ACS) and covers a time span of 5 days. This data have been used to carry out the first high-spatial resolution and multi-epoch study of the polarisation of the pulsar. We produced polarisation vector maps of the region surrounding the pulsar and measured the degree of linear polarisation (P.D.) and the position angle (P.A.) of the pulsar's integrated pulse beam. %This yielded We obtained $\rm P.D.=8.1\%\pm0.7\%$ and \rm P.A.=146.3\degr\pm2.4\degr, averaged over the time span covered by these observations. These results not only confirm those originally obtained by \citeauthor{Wagner00} and \citeauthor{Mignani07}, both using the Very Large Telescope (VLT), but are of greater precision. Furthermore, we confirm that the P.A. of the pulsar polarisation vector is aligned with the direction of the pulsar proper-motion. The pulsar wind nebula (PWN) is undetected in polarised light as is the case in unpolarised light, down to a flux limit of 26.8 magnitudes arcsec$^{-2}$.Comment: 11 pages accepted for publication in MNRAS. arXiv admin note: text overlap with arXiv:1305.682

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

Is the Fuzziness of GRB970228 constant?

In view of the data gathered in September 1997, we review the flux values collected so far for the "fuzziness" seen in the optical counterpart of GRB970228. Comparison between the ground based data collected in March and the data of September 1997 suggests a fading of the fuzz. Given the diversity of the data in hand, the magnitude of the effect and its significance are not easy to quantify. Only new images, both from the ground and with the Space Telescope, directly comparable to the old ones could settle this problem.Comment: 6 pages, Latex, 6 postscript figures, 1 postscript table Proceedings of the 4th Huntsville Gammma-Ray Burst Symposiu