Public seminar of PhD Candidate:- Radio observation of the pulsar wind nebulae powered by PSR B1706-44 and vela pulsar
Pulsar wind nebulae(PWNe) are among the most energetic galactic objects discovered. The pulsar wind carries away majority of the pulsar spin down power and flow into the nebula. Particles can be accelerated to relativistic speeds and generate synchrotron radiations. To help understand the related high energy processes in PWNe, the speaker analyzed the PWN synchrotron emission in radio bands to study information of relativistic particle distribution and dynamics and the magnetic fields in the PWNe.
頻道：Zoom ID: 912-1420-2327
He performed a radio study of the PWN powered by PSR B1706−44 at 3, 6, 13, and 21 cm using observations taken with the Australia Telescope Compact Array(ATCA). The nebula shows an overall arc-like morphology at 3 and 6 cm, 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 speaker interpreted radio PWN morphology at 3 cm using a thick torus model with Doppler boosting effect and found a bulk flow speed of ~0.2c. The radio PWN shows a highly ordered toroidal B-field, with an equipartition strength of ~10μG. 13 and 21 cm 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 comparable to that of the PWN and is significantly flatter than that of the SNR rim. In addition, his team’s polarization maps reveal that the intrinsic B-field in the ridge generally aligns with 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.
The speaker 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. An X-ray radio anticorrelation 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 Vela PWN in radio can be interpreted using the thick torus model with Doppler boosting effect, which has a 0.3c bulk flow speed. 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 39μG. The radio spectra of the overall PWN, the NE lobe, and the SW lobe have similar spectral indices of −0.3. The X-ray “tail” of the Vela PWN coincides with the SW radio lobe, but the X-ray and radio spectra in this region do not intersect, implying different particle populations in this region.