Radio study of two pulsar wind nebulae powered by PSR B1706−44 and the Vela Pulsar

Abstract

Pulsar wind nebulae (PWNe) are very energetic galactic objects. The pulsar wind carries away the majority of the pulsar spin down power and accelerates particles to relativistic speeds. To help understand related high energy physics in PWNe, I analyzed the PWN powered by PSR B1706−44 and that powered by the Vela pulsar with radio observations.

I performed a radio study of the PWN powered by PSR B1706−44 at 3, 6, 13, and 21cm using observations taken with the Australia Telescope Compact Array (ATCA). The nebula shows an overall arc-like morphology at 3 and 6cm, and the “arc” resembles a double-lobe at 6cm. The inner PWN is faint in radio but bright in X-rays, and the radio emission only brightens beyond that. The radio PWN morphology is interpreted using a thick torus model with Doppler boosting effect in this study. The PWN morphological differences between 3 and 6 cm images are explained by introducing a spectral gradient, and the model suggests a bulk flow speed of ∼0.2c in the radio PWN, which is much lower than that (∼0.7c) in the X-ray PWN. The radio PWN shows a highly ordered toroidal B-field, with an equipartition strength of ∼10μG. 13 and 21cm radio images show that the surrounding supernova remnant (SNR)G343.1−2.3 has a semi-circular rim and an east-west ridge. The ridge has a radio spectrum, which is comparable to that of the PWN but significantly flatter than that of the SNR rim. In addition, our polarization maps reveal that the intrinsic B-field in the ridge generally aligns with the pulsar motion direction and the ridge never extends beyond the SNR rim. All these suggest that the ridge could be a tail of the PWN.

I also studied the radio Vela PWN with ATCA observations at 3, 6, and 21 cm. The overall PWN wraps around the Vela pulsar from the northwest, with two lobes northeast (NE) and southwest (SW) of the pulsar and fainter emission northwest of it. An X-ray radio anti-correlation is also found in this PWN: the radio emission is dim in the X-ray PWN and only becomes bright beyond the X-ray structures. The thick torus model with the Doppler boosting effect, which has a ≤0.2c bulk flow speed, can better explain the features of Vela PWN. Compared with 0.44c in the X-ray tori, it implies a deceleration as the flow goes out. The polarization images also show a toroidal B-field with an equipartition B-field strength is 39 μG. The radio spectra of the overall PWN, the NE lobe, and the SW lobe have similar spectral indices of −0.3.