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Astron. Astrophys. 361, 85-91 (2000)

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7. Association with other sources of high-energy emission

In Fig. 11, the WFC- and MECS-determined positions of SAX J2239.3+6116 are shown, as well as those of three other possibly related X-ray sources. It appears likely that SAX J2239.3+6116 is the same source as the one seen in the early seventies with Uhuru (4U 2238+60, Forman et al. 1978), OSO-7 (1M 2233+595, Markert et al. 1979), and Ariel-V (3A 2237+608, Warwick et al. 1981). 4U 2238+60 was detected at a level of [FORMULA] erg cm-2 s-1 (2-10 keV, statistical error only) which is about 4 times lower than the peak of the March 1997 outburst. This is not really surprising because neither measurement encompassed the whole outburst. The Ariel source (Warwick et al. 1981) is classified as an irregular variable source during the 1974-1980 operational period with a measured peak flux of [FORMULA] erg cm-2 s-1 (2-10 keV) which is also of the same order of magnitude as SAX J2239.3+6116 and 4U 2238+60.

[FIGURE] Fig. 11. Map of relevant high-energy sources. The large error circle to the right is that of 3EG J2227+6122, the two straight lines refer to the fast transient AT 2238+584, the dashed quadrilateral to 3A 2237+608, the solid quadrilateral to 4U 2238+60, the two small circles to the WFC error box (large) and NFI error box (small) of SAX J2239.3+6116.

There are two other interesting sources which have error boxes that are close to that of SAX J2239.3+6116 but are formally inconsistent. The first one is the fast transient AT 2238+584 which was seen in July 1975 with the sky-survey instrument on Ariel V (Pye & McHardy 1983). The outburst was not covered completely. The maximum measured flux was [FORMULA] erg cm-2 s-1 (2-10 keV) which is 5 times as bright as for SAX J2239.3+6116. The e-folding decay time of AT 2238+584 was 0.78 d. The other inconsistent source is 3EG J2227+6122 which is one of the unidentified EGRET sources (Hartman et al. 1999). We mention this because SAX J2239.3+6116 is the bright X-ray source closest to 3EG J2227+6122 and because SAX J2239.3+6116 has quite a hard spectrum in the X-ray range. Nevertheless, the distance between the centroids of both sources is 87´ while the 95% confidence error region of 3EG J2227+6122 is three times smaller (28´).

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© European Southern Observatory (ESO) 2000

Online publication: September 5, 2000