M ar 2 00 5 A Radio Study of the Mouse , G 359 . 23 – 0 . 82

The recent detection of a young pulsar powering " the Mouse " , G359.23–0.82, as well as detailed imaging of surrounding nebular X-ray emission, have motivated us to investigate the structural details and polarization characteristics of the radio emission from this axisymmetric source with a supersonic bow shock. Using polarization data at 3.6 and 6cm, we find that the magnetic field wraps around the bow shock structure near the apex of the system, but downnstream runs parallel to the inferred direction of the pulsar's motion. The rotation measure (RM) distribution of the Mouse also suggests that the low degree of polarization combined with a high RM ahead of the pulsar result from internal plasma within the bowshock region. In addition, using sub-arcsecond radio image of the Mouse, we identify modulations in the brightness distribution of the Mouse that may be associated with the un-shocked pulsar wind behind the pulsar. Lastly, we discuss the relationship between the Mouse and its neighboring shell-type supernova remnant G359.1–0.5 and argue that these two sources could potentially have the same origin. 1 Background G359.23–0.82 (" the Mouse "), with its long axisymmetric nonthermal nebula extending for 12 arcminutes, was first discovered as part of a Very Large Array (VLA) radio continuum survey of the Galactic center at 20cm (Yusef-Zadeh and Bally 1987). A bow-shock structure was noted along the eastern edge of the nebula (Yusef-Zadeh and Bally 1989). In addition, radio continuum data show linearly polarized emission from the full extent of the nebula and the spectral index distribution between 2, 6 and 20cm remains flat at the head of the nebula but steepens in the direction away from the head of the Mouse (Yusef-Zadeh and Bally 1989). The detection of X-ray emission from this source and the identification of a young radio pulsar G359.23–0.82 at the head of the nebula resulted in a breakthrough in our understanding of what powers this More recently, Chandra observations show detailed structural and spectral characteristics of this bow-shock pulsar wind nebula (PWN) associated with the Mouse (Gaensler et al. 2004). Modeling of the X-ray emission suggests a high space velocity ≈600 km s −1 in a relatively warm phase of the ISM in order to explain the cometary morphology of this source. The region where the Mouse is found contains a number of other nonthermal radio continuum sources. Figure 1 shows a large-scale 20cm view of this region …