* Astronomy

Title: Serendipitous Discovery of An Infrared Bow Shock Near PSR J1549-4848 with Spitzer
Authors: Z. Wang, D. L. Kaplan, P. Slane, N. Morrell, V. M. Kaspi

We report on the discovery of an infrared cometary nebula around PSR J1549-4848 in our Spitzer survey of a few middle-aged radio pulsars. Following the discovery, multi-wavelength imaging and spectroscopic observations of the nebula were carried out. We detected the nebula in Spitzer IRAC 8.0, MIPS 24 and 70 µm imaging and in Spitzer IRS 7.5--14.4 µm spectroscopic observations, and also in the WISE all-sky survey at 12 and 22 µm. These data were analysed in detail, and we find that the nebula can be described with a standard bow-shock shape, and that its spectrum contains polycyclic aromatic hydrocarbon and H_2 emission features. However, it is not certain which object drives the nebula. We analyse the field stars and conclude that none of them can be the associated object because stars with a strong wind or mass ejection that usually produce bow shocks are much brighter than the field stars. The pulsar is approximately 15\arcsec\ away from the region in which the associated object is supposed to be located. In order to resolve the discrepancy, we suggest that a highly collimated wind could be emitted from the pulsar and produce the bow shock. X-ray imaging to detect the interaction of the wind with the ambient medium and high-spatial resolution radio imaging to determine the proper motion of the pulsar should be carried out, which will help verify the association of the pulsar with the bow shock nebula.

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