Multi-wavelength Observations of 3FGL J2039.6-5618: A Candidate Redback Millisecond Pulsar

Journal
Date Issued
2015
Author(s)
Salvetti, D.
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•
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Delvaux, C.
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Pallanca, C.
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Belfiore, A.
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Breeveld, A. A.
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Greiner, J.
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Becker, W.
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Pizzocaro, D.
DOI
Description
The research leading to these results has received funding from the European Commission Seventh Framework Programme (FP7/2007-2013) under grant agreement n. 267251. This work was supported by the ASI-INAF contract I/004/11/0, art.22 L.240/2010 for the project “Studio di sorgenti di alta energia con Swift .” C.D. acknowledges support through EXTraS, funded from the European Union's Seventh Framework Programme for research, technological development, and demonstration under grant agreement no 607452. Part of the funding for GROND (both hardware as well as personnel) was generously granted from the Leibniz-Prize to Prof. G. Hasinger (DFG grant HA 1850/28-1). Note added in proof. After our manuscript was submitted, we became aware of an independent analysis of our XMM-Newton and GROND data carried out by Romani (2015) soon after they became public, which is in line with our results. Facilities: XMM-Newton , Max Planck: 2.2m (GROND) , Swift , Suzaku , VISTA .
Abstract
We present multi-wavelength observations of the unassociated γ-ray source 3FGL J2039.6-5618 detected by the Fermi Large Area Telescope. The source γ-ray properties suggest that it is a pulsar, most likely a millisecond pulsar, for which neither radio nor γ-ray pulsations have been detected. We observed 3FGL J2039.6-5618 with XMM-Newton and discovered several candidate X-ray counterparts within/close to the γ-ray error box. The brightest of these X-ray sources is variable with a period of 0.2245 ± 0.0081 days. Its X-ray spectrum can be described by a power law with photon index ΓX = 1.36 ± 0.09, and hydrogen column density NH < 4 × 1020 cm-2, which gives an unabsorbed 0.3-10 keV X-ray flux of 1.02 × 10-13 erg cm-2 s-1. Observations with the Gamma-Ray Burst Optical/Near-Infrared Detector discovered an optical counterpart to this X-ray source, with a time-averaged magnitude g′ ̃ 19.5. The counterpart features a flux modulation with a period of 0.22748 ± 0.00043 days that coincides, within the errors, with that of the X-ray source, confirming the association based on the positional coincidence. We interpret the observed X-ray/optical periodicity as the orbital period of a close binary system where one of the two members is a neutron star. The light curve profile of the companion star, which has two asymmetric peaks, suggests that the optical emission comes from two regions with different temperatures on its tidally distorted surface. Based upon its X-ray and optical properties, we consider this source as the most likely X-ray counterpart to 3FGL J2039.6-5618, which we propose to be a new redback system.
Volume
814
Issue
2
Start page
88
Uri
Url
Issn Identifier
0004-637X
Ads BibCode
2015ApJ...814...88S
Rights
open.access
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