IGR J17480-2446: a new class of accreting binaries?

¹ INAF – Osservatorio Astrofisico di Catania, via S.Sofia 78, 95123 Catania, Italy
e-mail: abo@oact.inaf.it
² INFN, Sezione di Catania, via S.Sofia 72, 95123 Catania, Italy
³ A.F.Ioffe Institute of Physics and Technology and Isaac Newton Institute of Chile, Branch in St. Petersburg, 194021 St. Petersburg, Russia

Received: 3 July 2014
Accepted: 7 December 2014

Abstract

Context. The recent discovery of long-period, low magnetic field pulsars in low-mass X-ray binaries (LMXBs) represents a challenge for the standard evolutionary scenario. These pulsars have a magnetic field strength comparable to that of millisecond pulsars (~10⁸−10⁹ G), but their period is at least an order of magnitude longer.

Aims. We discuss the origin of this new class of pulsars within the standard picture of LMXBs formation and apply our results to the case of IGR J17480-2446.

Methods. The magnetothermal evolution of the binary system is studied numerically by taking into account the effect of different accretion rates during the Roche-lobe overflow in the framework of the minimal cooling scenario.

Results. We show that, in addition to standard millisecond pulsars, long-period low magnetic field pulsars should also be expected as a possible outcome of the binary evolution, depending on the strength of the accretion rate during the Roche-lobe overflow. In particular, we argue that IGR J17480-2446 belongs to this new class of objects.