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Distances to Anomalous X-ray Pulsars using Red Clump Stars

Martin Durant·Marten H. van Kerkwijk
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Abstract

We identify `red clump stars' - core helium-burning giants - among 2MASS stars and use them to measure the run of reddening with distance in the direction of each of the Galactic Anomalous X-ray Pulsars (AXP). We combine this with extinction estimates from X-ray spectroscopy to infer distances and find that the locations of all AXP are consistent with being in Galactic spiral arms. We also find that the 2-10 keV luminosities implied by our distances are remarkably similar for all AXPs, being all around 1.3e35 erg s-1. Furthermore, using our distances to estimate effective black-body emitting radii, we find that the radii are tightly anti-correlated with pulsed fraction, and somewhat less tightly anti-correlated with black-body temperature. We find no obvious relationship of any property with the dipole magnetic field strength inferred from the spin-down rate.

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Martin Durant, Marten H. van Kerkwijk. 2006-06-01. Distances to Anomalous X-ray Pulsars using Red Clump Stars. https://doi.org/10.1086/506380

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