A UNIFIED TIMING AND SPECTRAL MODEL FOR THE ANOMALOUS X-RAY PULSARS XTE J1810-197 AND CXOU J164710.2-455216

Journal Article · Sun Oct 10 04:00:00 EDT 2010 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/722/1/788· OSTI ID:21464662

Albano, A; Turolla, R; Nobili, L ^[1]; Israel, G L; Stella, L ^[2]; Zane, S ^[3]

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1. Department of Physics, University of Padova, Via Marzolo 8, I-35131 Padova (Italy)
2. INAF-Astronomical Observatory of Rome, via Frascati 33, I-00040, Monte Porzio Catone (Italy)
3. Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey, RH5 6NT (United Kingdom)

Anomalous X-ray pulsars (AXPs) and soft gamma repeaters (SGRs) are two small classes of X-ray sources strongly suspected to host a magnetar, i.e., an ultra-magnetized neutron star with B {approx} 10{sup 14}-10{sup 15} G. Many SGRs/AXPs are known to be variable, and recently the existence of genuinely 'transient' magnetars was discovered. Here, we present a comprehensive study of the pulse profile and spectral evolution of the two transient AXPs (TAXPs) XTE J1810-197 and CXOU J164710.2-455216. Our analysis was carried out in the framework of the twisted magnetosphere model for magnetar emission. Starting from three-dimensional Monte Carlo simulations of the emerging spectrum, we produced a large database of synthetic pulse profiles which was fitted to observed light curves in different spectral bands and at different epochs. This allowed us to derive the physical parameters of the model and their evolution with time, together with the geometry of the two sources, i.e., the inclination of the line of sight and the magnetic axis with respect to the rotation axis. We then fitted the (phase-averaged) spectra of the two TAXPs at different epochs using a model similar to that used to calculate the pulse profiles (ntzang in XSPEC) freezing all parameters to the values obtained from the timing analysis and leaving only the normalization free to vary. This provided acceptable fits to XMM-Newton data in all the observations we analyzed. Our results support a picture in which a limited portion of the star surface close to one of the magnetic poles is heated at the outburst onset. The subsequent evolution is driven both by the cooling/varying size of the heated cap and by a progressive untwisting of the magnetosphere.

• OSTI ID: 21464662
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 722; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
BARYONS
CALCULATION METHODS
COMPUTERIZED SIMULATION
COSMIC RADIO SOURCES
COSMIC RAY SOURCES
COSMIC X-RAY SOURCES
ELEMENTARY PARTICLES
EVOLUTION
FERMIONS
HADRONS
INCLINATION
MAGNETIC FIELDS
MONTE CARLO METHOD
NEUTRON STARS
NEUTRONS
NUCLEONS
PULSARS
PULSES
SIMULATION
STAR EVOLUTION
STARS