Target-of-Opportunity Chandra Observations of Anomalous X-ray Pulsars
Victoria Kaspi (McGill University) , P. M. Woods (Dynetics), F. P. Gavriil (NASA/GSFC), R. Dib (McGill), C. Tam (McGill)
Since Cycle 4, we have led a Chandra Target-of-Opportunity program to observe Anomalous X-ray Pulsars (AXPs), a small class of isolated neutron stars thought to be magnetars, in outburst. Under this program, we have obtained a total of seven ToO observations of three different AXPs (three of CXOU J164710.2-455216, three of 1E 1048.1-5937 and one of 4U 0142+61), in order to study their rotational, spectral and pulsed fraction evolutions during times of instability. We describe here what we have learned from these observations. In particular we report on a tight, quantitative correlation between flux and pulsed fraction in 1E 1048.1-5937; the first measurement of a period derivative (hence magnetic field) in CXOU J164710.2-455216, thus confirming its AXP nature; as well unique pulse profile evolution, both in the short- and long-terms, in 4U 0142+61. These Chandra observations support the magnetar model for these sources, and put tight constraints on a variety of the outstanding physical questions remaining about magnetars.