The Mouse that Soared: High‐Resolution X‐Ray Imaging of the Pulsar‐powered Bow Shock G359.23−0.82

Abstract

We present an observation with the Chandra X-ray Observatory of the unusual radio source G359.23-0.82 ("the Mouse"), along with updated radio timing data from the Parkes radio telescope on the coincident young pulsar J1747-2958. We find that G359.23-0.82 is a very luminous X-ray source (L X [0.5 − 8.0 keV] = 5 × 10 34 ergs s −1 for a distance of 5 kpc), whose morphology consists of a bright head coincident with PSR J1747-2958, plus a 45 ′′ -long narrow tail whose power-law spectrum steepens with distance from the pulsar. We thus confirm that G359.23-0.82 is a bow-shock pulsar wind nebula powered by PSR J1747-2958; the nebular stand-off distance implies that the pulsar is moving with a Mach number of ∼ 60, suggesting a space velocity ≈ 600 km s −1 through gas of density ≈ 0.3 cm −3 . We combine the theory of ion-dominated pulsar winds with hydrodynamic simulations of pulsar bow shocks to show that a bright elongated X-ray and radio feature extending 10 ′′ behind the pulsar represents the surface of the wind termination shock. The X-ray and radio "trails" seen in other pulsar bow shocks may similarly represent the surface of the termination shock, rather than particles in the postshock flow as is usually argued. The tail of the Mouse contains two components: a relatively broad region seen only at radio wavelengths, and a narrow region seen in both radio and X-rays. We propose that the former represents material flowing from the wind shock ahead of the pulsar's motion, while the latter corresponds to more weakly magnetized material streaming from the backward termination shock. This study represents the first consistent attempt to apply our understanding of "Crab-like" nebulae to the growing group of bow shocks around high-velocity pulsars.

The Tale of the Two Tails of the Oldish PSR J2055+2539

“…In order to produce a population of high-energy particles, a highly energetic pulsar is required (Ė greater than ∼10 34 ; see, e.g., Kargaltsev & Pavlov 2008b). For classical synchrotron nebulae, we expect a relatively bright diffuse emission surrounding the pulsar, where the emission from the wind termination shock is brightest, as observed in all the other known cases (see, e.g., Gaensler et al 2004;McGowan et al 2006;Kargaltsev & Pavlov 2008b). The brightness is only slightly dependent on the ISMdensity ( n ISM 1 2 µ );thus, we expect a relatively uniform brightness profile.…”

Mass loading of bow shock pulsar wind nebulae

“…The thin-layer approximation is conceptually analogous to a 1-D model as it neglects the thickness of the nebula, while all quantities depend only on the distance from the apex. Despite the above-mentioned simplifications, these models provide a good description of the head region of the nebulae in terms of shape, hydrogen penetration length scale, and Hα luminosity, as was later confirmed by more accurate 2-D axisymmetric simulations, both in the hydrodynamic (HD) regime (Bucciantini 2002a;Gaensler et al 2004) and in the relativistic magnetohydrodynamic (MHD) regime (Bucciantini et al 2005). Using a 3-D model, Vigelius et al (2007) was able to extend the study of these systems by also taking into account either a nonuniform ambient medium, or the anisotropy of the pulsar wind energy flux.…”

“…Noticeably, an opposite situation has been observed for the Mouse nebula (J1747-2958), where radio polarimetry shows a poloidal magnetic field structure along the tail (Gaensler et al 2004). In this case X-ray and radio emission are both peaked in the head of the nebula and decrease smoothly along the tail.…”

“…The effect of mass loading for the Mouse nebula is probably negligible, in fact the Hα emission is not detected, and this is probably due to its exceptional luminosity able to photo-ionise the ISM around it. The Xray luminosity measured by Chandra is LX = 5 · 10 34 erg s −1 for a distance of 5 kpc (Gaensler et al 2004), while the pulsar spin down luminosity is Lw = 2.5 × 10 36 erg s −1 , giving an X-ray efficiency ηx = 0.02. Gaensler et al (2004) also measured the photon index as 1.8 < ΓX < 2.5, and provide an estimate of the ISM density of ≈ 0.3 cm −3 .…”

“…The Xray luminosity measured by Chandra is LX = 5 · 10 34 erg s −1 for a distance of 5 kpc (Gaensler et al 2004), while the pulsar spin down luminosity is Lw = 2.5 × 10 36 erg s −1 , giving an X-ray efficiency ηx = 0.02. Gaensler et al (2004) also measured the photon index as 1.8 < ΓX < 2.5, and provide an estimate of the ISM density of ≈ 0.3 cm −3 . Using these values we can estimate the upper limit for the X-ray efficiency from Eq.…”