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13th of November 2023
New insights on 30 Dor B revealed by multi-wavelength observations
by Chen et al.
The supernova remnant (SNR) 30 Dor B is associated with the H II region ionized by a nearby OB association, however the complex interstellar environment has made it difficult to study the physical structure of this SNR. Chen et al. have used deep Chandra X-ray observations to find that 30 Dor B hosts three zones with very different X-ray surface brightnesses and nebular kinematics that are characteristic of SNRs in different interstellar environments and/or evolutionary stages.

Observations made over two decades ago with the ATCA at wavelengths of 3.5 and 6 cm indicated a radio spectral index of −0.19 in the central pulsar wind nebula (PWN), named PWN N157B. A more recent ASKAP 888 MHz map of 30 Dor B shows counterparts to all X-ray emission features except the faint halo. The ASKAP 888 MHz map also peaks within the PWN. In addition, it shows an extended component. As the radio emission from 30 Dor B contains both a nonthermal (synchrotron radiation) component from the SNR and a thermal (bremsstrahlung radiation) component from the photoionized gas, the team compare the radio map to the X-ray image to assess the nature of the radio emission.

The image above shows the Chandra X-ray image in the 0.5–7.0 keV band overplotted with the ASKAP 888 MHz radio contours. The main part of the radio emission has many correspondences with the X-ray image: (1) both radio and X-ray images exhibit prominent emission from the PWN; (2) both exhibit a bright spot to the southeast of the pulsar wind nebula; and (3) the radio image shows a shell structure similar to the X-ray shell with similar surface brightness variations. The most obvious differences between the radio and X-ray images are: (1) radio emission is not detected in the faint X-ray halo region; (2) the diffuse radio emission patches to the southeast and to the southwest of the main part have no counterparts in X-rays and most likely originate from diffuse photoionized gas, instead of shocked gas associated with the 30 Dor B SNR. Chen et al. conclude that the bright central region of 30 Dor B and the X-ray shell requires two separate SN events, and the faint diffuse X-ray halo perhaps other older SN events.

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