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Register a new userA Search for the Optical Counterpart of PSR B1951+32 in the Supernova Remnant CTB 80
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Using time-resolved two-dimensional aperture photometry we have put upper limits on the pulsed emission from two proposed optical counterparts for PSR B1951+32. Our pulsed upper limits of m_{vpulsed}>23.3, m_{bpulsed}>24.4$, for the first candidate and m_{vpulsed}>23.6$, m_{bpulsed}>24.3 for the second, make it unlikely that either of these is, in fact, the pulsar. We discuss three further candidates, but also reject these on the basis of timing results. A search of a 5.5arcs x 5.5arcs area centred close to these stars failed to find any significant pulsations at the reported pulsar period.
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We present a radio polarization study of the supernova remnant CTB 80 based on images at 1420 MHz from the Canadian Galactic plane survey, at 2695 MHz from the Effelsberg survey of the Galactic plane, and at 4800 MHz from the Sino-German 6cm polarization survey of the Galactic plane. We obtained a rotation measure (RM) map using polarization angles at 2695 MHz and 4800 MHz as the polarization percentages are similar at these two frequencies. RM exhibits a transition from positive values to negative values along one of the shells hosting the pulsar PSR B1951+32 and its pulsar wind nebula. The reason for the change of sign remains unclear. We identified a partial shell structure, which is bright in polarized intensity but weak in total intensity. This structure could be part of CTB 80 or part of a new supernova remnant unrelated to CTB 80.
We investigated the kinematics of the pulsar wind nebula (PWN) associated with PSR B1951+32 in the old supernova remnant CTB 80 using the Fabry-Perot interferometer of the 6m Special Astrophysical Observatory telescope. In addition to the previously known expansion of the system of bright filaments with a velocity of 100-200km/s, we detected weak high-velocity features in the H-alpha line at least up to velocities of 400-450km/s. We analyzed the morphology of the PWN in the H-alpha, [SII], and [OIII] lines using HST data and discuss its nature. The shape of the central filamentary shell, which is determined by the emission in the [OIII] line and in the radio continuum, is shown to be consistent with the bow-shock model for a significant (about 60 degrees) inclination of the pulsars velocity vector to the plane of the sky. In this case, the space velocity of the pulsar is twice higher than its tangential velocity, i.e., it reaches ~500 km/s, and PSR B1951+32 is the first pulsar whose line-of-sight velocity (of about 400 km/s) has been estimated from the PWN observations. The shell-like H-alpha-structures outside the bow shock front in the east and the west may be associated with both the pulsars jets and the pulsar-wind breakthrough due to the layered structure of the extended CTB 80 shell.
The radio pulsar B1951+32 and the supernova remnant CTB 80 provide a rich laboratory for the study of neutron stars and supernova remnants. Here, we present ground-based optical and near-infrared observations of them, along with X-ray observations with Chandra and a re-analysis of archival data obtained with the Hubble Space Telescope. The X-ray observations reveal a cometary pulsar wind nebula which appears to be confined by a bow shock produced by high-velocity motion of the pulsar, making PSR B1951+32 a rare pulsar exhibiting both an H alpha bow shock and a shocked X-ray pulsar wind nebula. The distribution of H alpha and radio continuum emission is indicative of a contact discontinuity of the shocked pulsar winds and shocked ambient medium at ~0.05 pc. On the other hand, the optical synchrotron knot of PSR B1951+32 likely has a flat spectrum in the optical and near-infrared wavebands, and our astrometry is consistent with only one of the two reported optical counterpart candidates for the pulsar.
CTB 80 (G69.0+2.7) is a relatively old (50--80 kyr) supernova remnant (SNR) with a complex radio morphology showing three extended radio arms and a radio and X-ray nebula near the location of the pulsar PSR B1951+32. We report on a study of the GeV emission in the region of CTB 80 with emph{Fermi}-LAT data. An extended source with a size of 1.3$^circ$, matching the size of the infrared shell associated to the SNR, was discovered. The GeV emission, detected up to an energy of $sim 20$ GeV, is more significant at the location of the northern radio arm where previous observations imply that the SNR shock is interacting with ambient material. Both hadronic and leptonic scenarios can reproduce the multiwavelength data reasonably well. The hadronic cosmic ray energy density required is considerably larger than the local Galactic value and the gamma-ray leptonic emission is mainly due to bremsstrahlung interactions. We conclude that GeV particles are still trapped or accelerated by the SNR producing the observed high-energy emission when interacting with ambient material.
PSR B1951+32 is a gamma-ray pulsar detected by the Energetic Gamma Ray Experiment Telescope (EGRET) and identified with the 39.5 ms radio pulsar in the supernova remnant CTB 80. The EGRET data shows no evidence for a spectral turnover. Here we report on the first observations of PSR B1951+32 beyond 30 GeV. The observations were carried out with the 10m gamma-ray telescope at the Whipple Observatory on Mt. Hopkins, Arizona. In 8.1 hours of observation we find no evidence for steady or periodic emission from PSR B1951+32 above ~260 GeV. FLux upper limits are derived and compared with model extrapolations from lower energies and the predictions of emission models.
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