The Magnetar XTE J1810−197: Variations in Torque, Radio Flux Density, and Pulse Profile Morphology

F. Camilo (1) , Ismaël Cognard (2) , S.M. Ransom (3) , J.P. Halpern (1) , J. Reynolds (4) , N. Zimmerman (1) , E.V. Gotthelf (1) , D.J. Helfand (1) , P. Demorest (5) , Gilles Theureau (2) , D.C. Backer (5)

1 CAL - Columbia Astrophysics Laboratory
2 LPCE - Laboratoire de physique et chimie de l'environnement
3 NRAO - National Radio Astronomy Observatory [Charlottesville]
4 ATNF - Australia Telescope National Facility
5 Department of Astronomy [Berkeley]

We report on 9 months of observations of the radio-emitting anomalous X-ray pulsar XTE J1810 - 197 starting in 2006 May using the Nanc, ay, Parkes, Green Bank Telescope, and VLA telescopes mainly at a frequency of 1.4 GHz. The torque experienced by the neutron star during this period, as inferred from a measurement of its rotational frequency derivative, decreased by 60%, although not in a steady manner. We have also observed very large ongoing fluctuations in flux density and pulse shape. Superimposed on these, a general diminution of flux density and a broadening of the pulse profile components occurred nearly contemporaneously with a decrease in torque of about 10% that took place in late 2006 July over an interval of 2 weeks. After a slight increase in average flux density, since 2006 October the flux density has continued to decline and the pulse profiles, while still varying, appear more uniform. In addition, a simultaneous observation of the pulsar with the Chandra X-ray Observatory and the Green Bank Telescope allows us to show how the X-ray and radio profiles are aligned. We discuss briefly the implications of these results for the magnetospheric currents in this remarkable object.

Mots clés: pulsars : individual (XTE J1810-197); stars : neutron

Domaines: Astrophysique stellaire et solaire [astro-ph.SR]

F. Camilo, Ismaël Cognard, S.M. Ransom, J.P. Halpern, J. Reynolds, et al.. The Magnetar XTE J1810−197: Variations in Torque, Radio Flux Density, and Pulse Profile Morphology. The Astrophysical Journal, 2007, 663 (1), pp.497-504. ⟨10.1086/518226⟩. ⟨insu-02778358⟩