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Issue A&A
Volume 458, Number 1, October IV 2006
Page(s) 245 - 257
Section Stellar structure and evolution
DOI 10.1051/0004-6361:20065247



A&A 458, 245-257 (2006)
DOI: 10.1051/0004-6361:20065247

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

N. La Palombara1, R. P. Mignani2, E. Hatziminaoglou3, M. Schirmer4, G. F. Bignami5, 6 and P. Caraveo1

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 $\gamma$-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 $\gamma$-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 $f_{\rm X}/f_{\rm opt}$. Therefore, the systematic X-ray and optical coverage of low-latitude unidentified $\gamma$-ray sources aiming at high $f_{\rm X}/f_{\rm opt}$ 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 $\gamma$-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 $f_{\rm X}/f_{\rm opt}\ge 100$, which we consider promising INS candidates.


Key words: stars: neutron -- gamma-rays: observations -- X-rays: general



© ESO 2006


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