ner_tags: O O O O O O O O B-Tag O O O O O O O B-Telescope O O O O O O O O O O O O O O O O O O O O O O O O O B-CelestialObject I-CelestialObject O O O O B-Telescope O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-CelestialObject I-CelestialObject O O B-Observatory B-Telescope O O O O O O O B-Formula I-Formula I-Formula O O O B-Citation I-Citation I-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O O O O O B-Wavelength O O O O O O O B-Telescope O O O O O O O O O B-Telescope O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Formula I-Formula I-Formula O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Formula I-Formula I-Formula I-Formula I-Formula O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation I-Citation I-Citation O O B-Telescope B-Instrument O O O B-CelestialObject I-CelestialObject O O O O O O B-Telescope O O O O O O O O B-Telescope O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Telescope O O O O O O O O O O O O O O O O O O O O B-Telescope O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Observatory B-Telescope O O O O O O O O B-Telescope O O O O O O O O B-CelestialObject I-CelestialObject O O O O O O O O O O O O O B-Telescope O B-Telescope O O O O O O O O O O O O O O O O O O O O O O O O O O O
tokens: 115 ks with 25 ks on-source exposure. 4.1 <italic>INTEGRAL</italic> context Previous studies of this source with INTEGRAL have revealed a long (30 d), eccentric (e ∼ 0.3–0.4) orbit and shown detections in more than 60 per cent of neutron star periastron passages. SAX J1818.6−1703 was not detected by INTEGRAL in an observation carried out between 2013 March 12 and 2013 March 13 during Revolution 1271, at a time that corresponds to an orbital phase of 0.804–0.862. During this region of a long eccentric orbit, the stellar wind, through which the neutron star passes, is not expected to be sufficiently dense or structured so as to produce detectable emission from accretion. A bright flare from SAX J1818.6−1703 detected by Swift /BAT on 2013 March 17 (corresponding to phase, φ = 0.970) was reported by Romano et al. ( 2014 ). During this flare the source reached a peak flux of 146 mCrab (15–50 keV), clearly showing that the source exhibited enhanced X-ray emission a few days prior to the XMM observation reported here. The source was also detected by INTEGRAL during Revolution 1274 at a significance of ∼13σ. A more detailed analysis of this revolution shows that the source was first observed between UTC 11:10:03 and UTC 20:44:48 on 2013 March 20, corresponding to orbital phases φ = 0.086–0.099, with a total source exposure of 7.5 ks. During this observation, the source was detected with an average count rate of 2.17 ± 0.22 counts s −1 (18–60 keV) or ∼10 mCrab. The source was subsequently observed between UTC 09:00:11 and UTC 20:13:27 on 2013 March 22, corresponding to orbital phases φ = 0.150 – 0.165, again with a total source exposure of 7.5 ks. The average count rate in this observation was 1.27 ± 0.22 counts s −1 (18–60 keV). In order to compare these fluxes to previous periastron passages, we performed the recurrence analysis of Bird et al. ( 2008 ) using an INTEGRAL /IBIS light curve of SAX J1818.6−1703 from the first 1000 revolutions of INTEGRAL . We calculated the mean flux detected by INTEGRAL during a 4-day period centred on periastron and from this, we find that during the first observation of Revolution 1274, the source is brighter than 80 per cent of periastron passages observed by INTEGRAL . The flux detected between UTC 09:00:11 and UTC 20:13:27 on 2013 March 22 is consistent with fluxes observed by INTEGRAL during the majority of periastron passages. However, it is different from the distribution of apastron flux measurements and still represents a significant detection of the source. When considering both the Swift /BAT bright flare on 2013 March 17 and the INTEGRAL observations during Revolution 1274, it is clear that SAX J1818.6−1703 was in an atypically active state during the periastron passage covered by the INTEGRAl and XMM observations presented in this work. 4.2 Source distance Knowledge of the source distance is critical in order to calculate associated luminosities and hence disentangle the accretion processes