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Register a new userChandra Monitoring of the Candidate Anomalous X-ray Pulsar AX J1845.0-0258
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C. R. Tam
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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 J1845.0-0258s 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 (Gamma~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 behaviour 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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We present the results of Chandra X-ray Observatory observations of the transient anomalous X-ray pulsar (AXP) candidate AX J1845.0-0258 in apparent quiescence. Within the sources error circle, we find a point source and possible counterpart, which we designate CXOU J184454.6-025653. No coherent pulsations are detected, and no extended emission is seen. The sources spectrum is equally well described by a blackbody model of temperature kT~2.0 keV or a power law model with photon index Gamma~1.0. This is considerably harder than was seen for AX J1845.0-0258 during its period of brightening in 1993 (kT~0.6 keV) despite being at least ~13 times fainter. This behavior is opposite to that observed in the case of the established transient AXP, XTE J1810-197. We therefore explore the possibility that CXOU J184454.6-025653 is an unrelated source, and that AX J1845.0-0258 remains undetected since 1993, with flux 260-430 times fainter than at that epoch. If so, this would represent an unprecedented range of variability in AXPs.
We report on Very Large Array observations in the direction of the recently-discovered slow X-ray pulsar AX J1845-0258. In the resulting images, we find a 5-arcmin shell of radio emission; the shell is linearly polarized with a non-thermal spectral index. We class this source as a previously unidentified, young (< 8000 yr), supernova remnant (SNR), G29.6+0.1, which we propose is physically associated with AX J1845-0258. The young age of G29.6+0.1 is then consistent with the interpretation that anomalous X-ray pulsars (AXPs) are isolated, highly magnetized neutron stars (magnetars). Three of the six known AXPs can now be associated with SNRs; we conclude that AXPs are young (~<10 000 yr) objects, and that they are produced in at least 5% of core-collapse supernovae.
Pulsations from the high mass X-ray binary AXJ1910.7+0917 were discovered during Chandra observations performed in 2011 (Israel et al. 2016). We report here more details on this discovery and discuss the source nature. The period of the X-ray signal is P=36200+/-110s, with a pulsed fraction, PF, of 63+/-4%. Given the association with a massive B-type companion star, we ascribe this long periodicity to the rotation of the neutron star, making AXJ1910.7+0917 the slowest known X-ray pulsar. We report also on the spectroscopy of XMM-Newton observations that serendipitously covered the source field, resulting in an highly absorbed (column density almost reaching 1e23cm-2), power law X-ray spectrum. The X-ray flux is variable on a timescale of years, spanning a dynamic range >60. The very long neutron star spin period can be explained within a quasi-spherical settling accretion model, that applies to low luminosity, wind-fed, X-ray pulsars.
We present X-ray imaging, timing, and phase resolved spectroscopy of the anomalous X-ray pulsar 1E 2259+58.6 using the Chandra X-ray Observatory. The spectrum is well described by a power law plus blackbody model with power law index = 3.6(1), kT_BB = 0.412(6) keV, and N_H=0.93(3) x 10^{22} cm^{-2}; we find no evidence for spectral features (0.5-7.0 keV). We derive a new, precise X-ray position for the source and determine its spin period, P=6.978977(24) s. Time resolved X-ray spectra show no significant variation as a function of pulse phase. We have detected excess emission beyond 4 arcsec from the central source extending to beyond 100 arcsec, due to the supernova remnant and possibly dust scattering from the interstellar medium.
We report on a 25 ks observation of the 8.7 s anomalous X-ray pulsar 4U~0142+61 with the High Energy Transmission Grating Spectrometer (HETGS) on the Chandra X-ray Observatory. The continuum spectrum is consistent with previous measurements and is well fit by an absorbed power-law + blackbody with photon index Gamma=3.3+/-0.4 and kT=0.418+/-0.013 keV. No evidence was found for emission or absorption lines, with an upper limit of ~50 eV on the equivalent width of broad features in the 2.5-13 A (0.95-5.0 keV) range and an upper limit of ~10 eV on the equivalent width of narrow features in the 4.1-17.7 A (0.7-3.0 keV) range. If the source is a magnetar, then the absence of a proton cyclotron line strongly constrains magnetar atmosphere models and hence the magnetic field strength of the neutron star. We find no strong features that are indicative of cyclotron absorption for magnetic field strengths of (1.9-9.8)x10^{14} G. This is still consistent with the dipole field strength of B=1.3x10^{14} G (at the polar cap) estimated from the pulsars spindown.
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