2003/09/30 by E. V. Gotthelf, J. P. Halpern, M. Buxton +2 · 16 citations
Earth and Planetary Sciences · Physics and Astronomy · #Astrophysical Phenomena and Observations #High-pressure geophysics and materials #Pulsars and Gravitational Waves Research #astro-ph
paper · pdf · doi:10.1086/382232
published as Astrophys.J.605:368-377,2004 · 12 pages, 7 figures, AAS LaTex, uses emulateapj5.sty. Updated to include additional archival data and a new HRC observation. To appear in The Astrophysical Journal
arxiv created 2003/12/29 · openalex publication_date 2004/04/07 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/31
We report X-ray imaging, timing, and spectral studies of XTE J1810-197, a 5.54 s pulsar discovered by Ibrahim and coworkers in recent Rossi X-Ray Timing Explorer ( RXTE ) observations. In a set of short exposures with the High Resolution Camera on board the Chandra X-Ray Observatory , we detect a strongly modulated signal (55% ± 4% pulsed fraction) with the expected period located at (J2000) 18 h 09 m 51 08, -19 ° 43'51 7, with a uncertainty radius of 0 6 (90% confidence level). Spectra obtained with XMM-Newton are well fitted by a two-component model that typically describes anomalous X-ray pulsars (AXPs), an absorbed blackbody plus power law with parameters kT = 0.67 ± 0.01 keV, Γ = 3.7 ± 0.2, N H = (1.05 ± 0.05) × 10 22 cm -2 , and F X (0.5-10 keV) = 3.98 × 10 -11 ergs cm -2 s -1 . Alternatively, a two-temperature blackbody fit is just as acceptable. The location of CXOU J180951.0-194351 is consistent with a point source seen in archival Einstein , ROSAT , and ASCA images, when its flux was nearly 2 orders of magnitude fainter, and from which no pulsations are found. The spectrum changed dramatically between the "quiescent" and "active" states; the former can be modeled as a softer blackbody. Using XMM-Newton timing data, we place an upper limit of 0.03 lt-s on any orbital motion in the period range 10 minutes-8 hr. Optical and infrared images obtained on the SMARTS 1.3 m telescope at the Cerro Tololo Inter-American Observatory (CTIO) show no object in the Chandra error circle to limits V = 22.5, I = 21.3, J = 18.9, and K = 17.5. Together, these results argue that CXOU J180951.0-194351 is an isolated neutron star, one most similar to the transient AXP AX J1844.8-0256. Continuing study of XTE J1810-197 in various states of luminosity is important for understanding and possibly unifying a growing class of isolated, young neutron stars that are not powered by rotation.