A catalog of diffuse X-ray-emitting features within 20 pc of Sagittarius A*: Twenty pulsar wind nebulae?

Abstract

We present a catalog of 34 diffuse features identified in X-ray images of the Galactic center taken with the Chandra X-Ray Observatory. Several of the features have been discussed in the literature previously, including seven that are associated with a complex of molecular clouds that exhibits fluorescent line emission, four that are superimposed on the supernova remnant Sgr A East, two that are coincident with radio features that are thought to be the shell of another supernova remnant, and one that is thought to be a pulsar wind nebula only a few arcseconds in projection from Sgr A*. However, this leaves 20 features that have not been reported previously. On the basis of the weakness of the iron emission in their spectra, we propose that most of them are nonthermal. One long, narrow feature points toward Sgr A*, and so we propose that this feature is a jet of synchrotron-emitting particles ejected from the supermassive black hole. For the others, we show that their sizes (0.1-2 pc in length for D = 8 kpc), X-ray luminosities (between 10^32 and 10^34 erg s^−1; 2-8 keV), and spectra (power laws with Γ = 1-3) are consistent with those of pulsar wind nebulae. On the basis of the star formation rate at the Galactic center, we expect that ~20 pulsars have formed in the last 300 kyr and could be producing pulsar wind nebulae. Only 1 of the 19 candidate pulsar wind nebulae is securely detected in an archival radio image of the Galactic center; the remainder have upper limits corresponding to L_R ≾ 10^31 erg s^−1. These radio limits do not strongly constrain their natures, which underscores the need for further multiwavelength studies of this unprecedented sample of Galactic X-ray-emitting structures.

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