XMM-Newton and ESO observations of the two unidentified γ-ray sources 3EG J0616-3310 and 3EG J1249-8330

¹ INAF – IASF Milano, Via E. Bassini 15, 20133 Milano, Italy e-mail: nicola@iasf-milano.inaf.it
² Mullard Space Science Laboratory, University College London, Holmbury St Mary, Dorking, Surrey RH5 6NT, UK
³ Instituto de Astrofisica de Canarias, Via Lactea, 38200 La Laguna-Tenerife, Spain
⁴ Isaac Newton Group of Telescopes, Edificio Mayantigo, Calle Alvarez Abreu 68, 38700 Santa Cruz de la Palma, Spain
⁵ Centre d'Étude Spatiale des Rayonnements (CESR), CNRS–UPS, 9 Avenue du colonel Roche, 31028 Toulouse, France
⁶ Università di Pavia, Dipartimento di Fisica Teorica e Nucleare, via Ugo Bassi 6, 27100 Pavia, Italy

Received: 22 March 2006
Accepted: 29 June 2006

Abstract

The limited angular resolution of γ-ray telescopes prevents a direct identification of the majority of sources detected so far. This is particularly true for the low latitude, probably galactic, ones only 10% of which has been identified. Most counterparts of the identified low-latitude γ-ray sources are Isolated Neutron Stars (INS), both radio-loud and radio-quiet (Geminga-like) objects, which are characterised by an extremely high value of the X-ray-to-optical flux ratio . Therefore, the systematic X-ray and optical coverage of low-latitude unidentified γ-ray sources aiming at high sources seems one of the most promising ways to spot INS candidate counterparts. Since low latitude sources are heavily affected by the interstellar absorption at both X-ray and optical wavelengths, we have focussed on two middle-latitude, probably galactic, GRO/EGRET sources: 3EG  J0616-3310 and 3EG J1249-8330. These two sources, which could belong to a local galactic population, have been selected owing to their relatively good positional accuracy, spectral shape and lack of candidate extragalactic radio counterparts. Here we report on X-ray observations of the two γ-ray error boxes performed with XMM-Newton and on their optical follow-up carried on with the Wide Field Imager at the ESO/MPG 2.2 m telescope. Less than half of the ~300 sources detected by the X-ray coverage have no optical counterparts. Among those, we have selected few interesting sources with , which we consider promising INS candidates.