Detection of an X‐Ray Pulsar Wind Nebula and Tail in SNR N157B

Abstract

We report Chandra X-ray observations of the supernova remnant N157B in the Large Magellanic Cloud, which are presented together with an archival HST optical image and a radio continuum map for comparison. This remnant contains the recently discovered 16 ms X-ray pulsar PSR J0537-6910, the most rapidly rotating young pulsar known. Using phase-resolved Chandra imaging, we pinpoint the location of the pulsar to 5 h 37 m 47. s 36, −69 • 10 ′ 20. ′′ 4 (J2000) with an uncertainty of < ∼ 1 ′′ . PSR J0537-6910 is not detected in any other wavelength band. The Xray observations resolve three distinct features: the pulsar itself, a surrounding compact wind nebula which is strongly elongated (dimension ∼ 0.6 pc ×1.7 pc), and a feature of large-scale ( > ∼ 5 pc long) diffuse emission trailing from the pulsar. This latter comet tail-shaped feature coexists with enhanced radio emission and is oriented nearly perpendicular to the major axis of the pulsar wind nebula.We propose the following scenario to explain these features. The bright, compact nebula is likely powered by a toroidal pulsar wind of relativistic particles which is partially confined by the ram-pressure from the supersonic motion of the pulsar. The particles, after being forced out from the compact nebula (the head of the "comet"), are eventually dumped into a bubble (the tail), which is primarily responsible for the extended diffuse X-ray and radio emission. The ram-pressure confinement also allows a natural explanation for the observed X-ray luminosity of the compact nebula and for the unusually small X-ray to spin-down luminosity ratio of ∼ 0.2%, compared to similarly energetic pulsars. We estimate the pulsar wind Lorentz factor of N157B as ∼ 4 × 10 6 (with an uncertainty of a factor ∼ 2), consistent with that inferred from the modeling of the Crab Nebula.

The X-ray emission of the Crab-like pulsar PSR J0537–6910

“…2: it is characterized by a narrow single peak with a duty cycle of 0.28 at zero level. Fitting the peak with a gaussian, a value of 0.11±0.07 is obtained for the FWHM, compatible with the value obtained with ROSAT [5] and Chandra data [6] …”

“…The light curve is characterized by a narrow pulse shape with a full width duty cycle of about 10% [6,5]. The 2-10 keV pulsed spectrum has been modeled with a simple power law: RXTE+ASCA measured a spectral index of 1.6±0.4 and a 2-10 flux of (6.7±0.6)×10 [4].…”

ChandraACIS Spectroscopy of N157B: A Young Composite Supernova Remnant in a Superbubble

“…This morphology is reminiscent of those associated with trailing plerions in SNRs G327.1À1.1 (Sun et al 1999), W44 ( Frail et al 1996), and IC 443 (Olbert et al 2001;Gaensler et al 2006), as well as the PWN around PSR B1757À24 near SNR G5.4À1.2 (the Duck X-ray Nebula; Kaspi et al 2001). Using a Chandra HRC observation with high angular and timing resolutions, Wang et al (2001) were able to pinpoint (to arcsecond precision) the location of PSR J0537À6910, which is still undetected in any other wavelength band (e.g., Mignani et al 2005;Crawford et al 2005). The nebula was shown to consist primarily of a $0:6 pc ; 1:7 pc compact barlike feature around the pulsar and a tail k5 pc long.…”

Pulsar-Wind Nebulae

“…These maps are expected to provide manifestation of synchrotron burn-off (X-ray spectra should become softer farther away from the pulsar) which depends on the strength of magnetic field and bulk flow speed (Kennel and Coroniti 1984b;Wang et al 2001;Reynolds 2009) but they may also contain signatures of spatially distributed (in-situ) particle acceleration or rapid particle diffusion. These spectral maps demonstrate that the pulsar spectra measured just downstream of the termination shock can differ substantially.…”