GRO J1744-28: an intermediate B-field pulsar in a low-mass X-ray binary
Date Issued
2015
Author(s)
•
Di Salvo, T.
•
Iaria, R.
•
García, J. A.
•
•
•
Riggio, A.
•
Burderi, L.
•
Bozzo, E.
•
Dauser, T.
•
Matranga, M.
•
Galiano, C. G.
•
Robba, N. R.
Description
We are especially grateful to N. Schartel who made possible this ToO observation through the Director Discretionary Time and all the XMM–Newton team who performed and supported this observation. The High-Energy Astrophysics Group of Palermo acknowledges support from the Fondo Finalizzato alla Ricerca (FFR) 2012/13, project no. 2012-ATE-0390, founded by the University of Palermo. AR gratefully acknowledges the Sardinia Regional Government for the financial support (P. O. R. Sardegna F.S.E. Operational Programme of the Autonomous Region of Sardinia, European Social Fund 2007–2013 – Axis IV Human Resources, Objective l.3, Line of Activity l.3.1).
Abstract
The bursting pulsar, GRO J1744-28, went again in outburst after ̃18 yr of quiescence in 2014 mid-January. We studied the broad-band, persistent, X-ray spectrum using X-ray data from a XMM-Newton observation, performed almost at the peak of the outburst, and from a close INTEGRAL observation, performed 3 d later, thus covering the 1.3-70.0 keV band. The spectrum shows a complex continuum shape that cannot be modelled with standard high-mass X-ray pulsar models, nor by two-components models. We observe broad-band and peaked residuals from 4 to 15 keV, and we propose a self-consistent interpretation of these residuals, assuming they are produced by cyclotron absorption features and by a moderately smeared, highly ionized, reflection component. We identify the cyclotron fundamental at ̃4.7 keV, with hints for two possible harmonics at ̃10.4 and ̃15.8 keV. The position of the cyclotron fundamental allows an estimate for the pulsar magnetic field of (5.27 ± 0.06) × 1011 G, if the feature is produced at its surface. From the dynamical and relativistic smearing of the disc reflected component, we obtain a lower limit estimate for the truncated accretion disc inner radius (≳100 Rg) and for the inclination angle (18°-48°). We also detect the presence of a softer thermal component that we associate with the emission from an accretion disc truncated at a distance from the pulsar of 50-115 Rg. From these estimates, we derive the magnetospheric radius for disc accretion to be ̃0.2 times the classical Alfvén radius for radial accretion.
Volume
449
Issue
4
Start page
4288
Issn Identifier
0035-8711
Ads BibCode
2015MNRAS.449.4288D
Rights
open.access
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