VLT/NACO observations of the high-magnetic field radio pulsar PSR J1119-6127^*

¹ University College London, Mullard Space Science Laboratory, Holmbury St. Mary, Dorking, Surrey, RH5 6NT, UK e-mail: rm2@mssl.ucl.ac.uk
² JILA and Department of Astrophysical and Planetary Sciences, University of Colorado, 440 UCB, Boulder, 80309, USA
³ SRON Netherlands Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
⁴ University of Sydney, School of Physics A29, NSW 2006, Australia
⁵ INAF Astronomical Observatory of Rome, via di Frascati 33, 00040 Monte Porzio, Italy
⁶ Istitituto di Astrofisica Spaziale, via Bassini 15, 20133 Milan, Italy
⁷ European Southern Observatory, Alonso de Cordova 3107, Vitacura, Santiago, Casilla 19001 Santiago 19, Chile

Received: 16 March 2007
Accepted: 13 June 2007

Abstract

Context.Recent radio observations have unveiled the existence of a number of radio pulsars with spin-down derived magnetic fields in the magnetar range. However, their observational properties appear to be more similar to those of the classical radio pulsars than to the magnetars's ones.

Aims. To shed light on this puzzle we first have to determine whether the spin-down derived magnetic field values for these radio pulsars are indeed representative of the actual neutron star magnetic field or if they are polluted, e.g. by the effects of a torque from a fallback disk.

Methods.To investigate this possibility, we have performed deep IR (J, H, K_s bands) observations of one of these high magnetic field radio pulsars (PSR J1119–6127) with the ESO VLT to search for IR emission which can be associated with a disk.

Results.No IR emission is detected from the pulsar position down to J ~ 24, 23 and K_s ~ 22.

Conclusions.By comparing our flux upper limits with the predictions of fallback disk models, we have found that we can only exclude the presence of a disk with accretion rate 3  10¹⁶ g s^-1. This lower limit cannot rule out the presence of a substantial disk torque on the pulsar, which would then lead to overestimate the value of the magnetic field inferred from P and . We have also compared the upper limit on the IR luminosity of PSR J1119–6127 with the IR luminosities of rotation-powered pulsars and magnetars. We found that, while magnetars are intrinsically more efficient IR emitters than rotation-powered pulsars, possibly because of their higher magnetic field, the relatively low IR emission efficiency of PSR J1119–6127 suggests that it is more similar to the latters than to the former.