Chandra monitoring of the candidate anomalous X-ray pulsar AX J1845.0-0258 |
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Authors: | Cindy R Tam Victoria M Kaspi Bryan M Gaensler Eric V Gotthelf |
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Institution: | (1) Department of Physics, Rutherford Physics Building, McGill University, 3600 University Street, Montreal, QC, H3A 2T8, Canada;(2) Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA;(3) Present address: School of Physics, University of Sydney, Sydney, NSW, 2006, Australia;(4) Columbia Astrophysics Laboratory, Columbia University, 550 West 120th Street, New York, NY 10027-6601, USA |
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Abstract: | The population of clearly identified anomalous X-ray pulsars has recently grown to seven, however, one candidate anomalous
X-ray pulsar (AXP) still eludes re-confirmation. Here, we present a set of seven Chandra ACIS-S observations of the transient
pulsar AX J1845.0-0258, obtained during 2003. Our observations reveal a faint X-ray point source within the ASCA error circle
of AX J1845.0-0258’s discovery, which we designate CXOU J184454.6-025653 and tentatively identify as the quiescent AXP. Its
spectrum is well described by an absorbed single-component blackbody (kT∼2.0 keV) or power law (Γ∼1.0) that is steady in flux on timescales of at least months, but fainter than AX J1845.0-0258 was during its 1993 period
of X-ray enhancement by at least a factor of 13. Compared to the outburst spectrum of AX J1845.0-0258, CXOU J184454.6-025653
is considerably harder: if truly the counterpart, then its spectral behavior is contrary to that seen in the established transient
AXP XTE J1810-197, which softened from kT∼0.67 keV to ∼0.18 keV in quiescence. This unexpected result prompts us to examine the possibility that we have observed an
unrelated source, and we discuss the implications for AXPs, and magnetars in general.
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Keywords: | Pulsar AXP Neutron star Magnetar AX J1845 0-0258 |
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