Letter to the Editor

Discovery of an optical bow-shock around pulsar B0740-28^*

¹ European Southern Observatory, Casilla 19001, Santiago 19, Chile, e-mail: hjones@eso.org
² Observatorio Cerro Calán, Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago, Chile
³ Stichting ASTRON, 7990 Dwingeloo, The Netherlands e-mail: stappers@astron.nl
⁴ Sterrenkundig Instituut “Anton Pannekoek”, 1098 SJ Amsterdam, The Netherlands
⁵ Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge MA 02138, USA

Corresponding author: D. H. Jones, hjones@eso.org

Received: 6 February 2002
Accepted: 24 April 2002

Abstract

We report the discovery of a faint Hα pulsar wind nebula (PWN) powered by the radio pulsar B0740-28. The characteristic bow-shock morphology of the PWN implies a direction of motion consistent with the previously measured velocity vector for the pulsar. The PWN has a flux density more than an order of magnitude lower than for the PWNe seen around other pulsars, but, for a distance 2 kpc, it is consistent with propagation through a medium of atomic density  cm^-3, and neutral fraction of 1%. The morphology of the PWN in the area close to the pulsar is distinct from that in downstream regions, as is also seen for the PWN powered by PSR B2224+65. In particular, the PWN associated with PSR B0740–28 appears to close at its rear, suggesting that the pulsar has recently passed through a transition from low density to high density ambient gas. The faintness of this source underscores that deep searches are needed to find further examples of optical pulsar nebulae.