A Catalog of Diffuse X-ray-Emitting Features within 20 pc of Sgr A*: Twenty Pulsar Wind Nebulae?

TL;DR

This paper catalogs 34 diffuse X-ray features near Sgr A* in the Galactic center, identifying 20 new features, and suggests many are pulsar wind nebulae or related to black hole activity, based on spectral and size analysis.

Contribution

It provides the first comprehensive catalog of diffuse X-ray features near Sgr A*, including 20 previously unreported structures, and proposes their nature based on spectral and morphological evidence.

Findings

20 new diffuse X-ray features identified near Sgr A*

Most features are consistent with pulsar wind nebulae

One feature likely represents a jet from the supermassive black hole

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 7 that are associated with a complex of molecular clouds that exhibits fluorescent line emission, 4 that are superimposed on the supernova remnant Sgr A East, 2 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. Based on the weakness of iron emission in their spectra, we propose that most of them are non-thermal. 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, 2-8 keV), and spectra (power laws with Gamma=1-3) are consistent with those of pulsar wind nebulae. Based on 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 one 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<la10^31 erg/s. These radio limits do not strongly constrain their natures, which underscores the need for further multi- wavelength studies of this unprecedented sample of Galactic X-ray emitting structures.