Spectral variation in the supergiant fast X-ray transient SAX J1818.6−1703 observed by<i>XMM–Newton</i>and<i>INTEGRAL</i>

Boon, C. M.; Bird, A. J.; Hill, A. B.; Sidoli, L.; Sguera, V.; Goossens, Marcel; Fiocchi, M.; McBride, V. A.; Drave, S. P.

doi:10.1093/mnras/stv2975

Cited by 14 publications

(12 citation statements)

References 56 publications

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“…While previous observations of the source have already revealed a high absorbing column density of (7.5−10)×10 22 cm −2 (Tomsick (2009), D'Aì et al (2011), the absorption detected between the flares in observation one is still about a factor of two higher than any previously measured in this source. Absorbing column densities of this level have previously been seen in other SFXTs such as IGR J18410−0535 (Bozzo et al 2011) and SAX J1818.6−1703 (Boon et al 2016). The former measured an increase in N H from 3 − 20 × 10 22 cm −2 with a further increase to a value of ∼ 50×10 22 cm −2 towards the end of the observation.…”

Section: Continuum Emission and Absorption Columnsupporting

confidence: 68%

XMM–Newton andINTEGRALanalysis of the Supergiant Fast X-ray Transient IGR J17354−3255

Goossens

Bird

Hill

et al. 2018

Monthly Notices of the Royal Astronomical Society

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We present the results of combined INTEGRAL and XMM-Newton observations of the supergiant fast X-ray transient (SFXT) IGR J17354−3255. Three XMM-Newton observations of lengths 33.4 ks, 32.5 ks and 21.9 ks were undertaken, the first an initial pointing to identify the correct source in the field of view and the latter two performed around periastron. Simultaneous INTEGRAL observations across ∼ 66% of the orbital cycle were analysed but the source was neither detected by IBIS/ISGRI nor by JEM-X. The XMM-Newton light curves display a range of moderately bright X-ray activity but there are no particularly strong flares or outbursts in any of the three observations. We show that the spectral shape measured by XMM-Newton can be fitted by a consistent model throughout the observation, suggesting that the observed flux variations are driven by obscuration from a wind of varying density rather than changes in accretion mode. The simultaneous INTEGRAL data rule out simple extrapolation of the simple powerlaw model beyond the XMM-Newton energy range.

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Section: Continuum Emission and Absorption Columnsupporting

confidence: 68%

XMM–Newton andINTEGRALanalysis of the Supergiant Fast X-ray Transient IGR J17354−3255

Goossens

Bird

Hill

et al. 2018

Monthly Notices of the Royal Astronomical Society

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“…SAX J1818.6-1703, Boon et al 2016), would be produced when the shell, after a collapse, is replenished by new wind capture, so the flares repeat on a regular timescale, as long as the mass accretion into the magnetosphere is allowed. The energy normally released in an SFXT bright flare (∼10 39 erg) is in agreement with estimated mass of the hot shell (Shakura et al 2014), that is also consistent with the accreted mass we have derived here from the luminosity of the flares in IGR J11215-5952 (∼10 19 g) Our XMM-Newton and NuSTAR observations of IGR J11215-5952 allowed us also to observe, for the first time in this source, X-ray flares repeating every ∼2-2.5 ks, a property that in the settling accretion scenario is explained in a natural way.…”

Section: Discussionmentioning

confidence: 99%

XMM-Newton and NuSTAR Simultaneous X-Ray Observations of IGR J11215-5952

Sidoli

Tiengo

Paizis

et al. 2017

ApJ

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We report the results of an XMM-Newton and NuSTAR coordinated observation of the Supergiant Fast Xray Transient (SFXT) IGR J11215-5952, performed on February 14, 2016, during the expected peak of its brief outburst, which repeats every ∼165 days. Timing and spectral analysis were performed simultaneously in the energy band 0.4-78 keV. A spin period of 187.0 (±0.4) s was measured, consistent with previous observations performed in 2007. The X-ray intensity shows a large variability (more than one order of magnitude) on timescales longer than the spin period, with several luminous X-ray flares which repeat every 2-2.5 ks, some of which simultaneously observed by both satellites. The broad-band (0.4-78 keV) time-averaged spectrum was well deconvolved with a double-component model (a blackbody plus a power-law with a high energy cutoff) together with a weak iron line in emission at 6.4 keV (equivalent width, EW, of 40±10 eV). Alternatively, a partial covering model also resulted in an adequate description of the data. The source time-averaged X-ray luminosity was 10 36 erg s −1 (0.1-100 keV; assuming 7 kpc). We discuss the results of these observations in the framework of the different models proposed to explain SFXTs, supporting a quasi-spherical settling accretion regime, although alternative possibilities (e.g. centrifugal barrier) cannot be ruled out.

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“…A first analysis of these data was reported by Boon et al (2016). During our re-analysis of the data, we noticed that the observation was affected by a high background during the last 8.3 ks and thus we discarded these data for the spectral analysis.…”

Section: Sax J18186-1703 231 Observation Id 0693900101mentioning

confidence: 99%

The accretion environment of supergiant fast X-ray transients probed withXMM-Newton

Bozzo

Bernardini²,

Ferrigno

et al. 2017

A&A

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Context. Supergiant fast X-ray transients are a peculiar class of supergiant X-ray binaries characterized by a remarkable variability in the X-ray domain, widely ascribed to the accretion from a clumpy stellar wind. Aims. In this paper we performed a systematic and homogeneous analysis of the sufficiently bright X-ray flares observed with XMMNewton from the supergiant fast X-ray transients to probe spectral variations on timescales as short as a few hundred of seconds. Our ultimate goal is to investigate if SFXT flares and outbursts are triggered by the presence of clumps and eventually reveal whether strongly or mildly dense clumps are required. Methods. For all sources, we employ a technique developed by our group already exploited in a number of our previous papers, making use of an adaptive rebinned hardness ratio to optimally select the time intervals for the spectral extraction. A total of twelve observations performed in the direction of five SFXTs are reported, providing the largest sample of events available so far. Results. Using the original results reported here and those obtained with our technique from the analysis of two previously published XMM-Newton observations of IGR J17544-2619 and IGR J18410-0535, we show that both strongly and mildly dense clumps can trigger these events. In the former case, the local absorption column density may increase by a factor of ≫3, while in the latter case, the increase is only by a factor ∼2-3 (or lower). An increase in the absorption column density is generally recorded during the rise of the flares/outbursts, while a drop follows when the source achieves the peak flux. In a few cases, a re-increase of the absorption column density after the flare is also detected, and we discovered one absorption event related to the passage of an unaccreted clump in front of the compact object. Overall, there seems to be no obvious correlation between the dynamic ranges in the X-ray fluxes and absorption column densities in supergiant fast X-ray transients, with an indication that lower densities are recorded at the highest fluxes. Conclusions. The spectral variations measured in all sources are in agreement with the idea that the flares/outbursts are triggered by the presence of dense structures in the wind interacting with the X-rays from the compact object (leading to photoionization). The lack of correlation between the dynamic ranges in the X-ray fluxes and absorption column densities can be explained by the presence of accretion inhibition mechanism(s). Based on the knowledge acquired so far on the SFXTs, we propose a classification of the flares/outbursts from these sources to drive future observational investigations. We suggest that the difference between the classes of flares/outbursts is related to the fact that the mechanism(s) inhibiting accretion can be overcome more easily in some sources compared to others. We also investigate the possibility that different stellar wind structures, rather than clumps, could provide the means to temporarily overcome the...

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Spectral variation in the supergiant fast X-ray transient SAX J1818.6−1703 observed byXMM–NewtonandINTEGRAL

Cited by 14 publications

References 56 publications

XMM–Newton andINTEGRALanalysis of the Supergiant Fast X-ray Transient IGR J17354−3255

XMM–Newton andINTEGRALanalysis of the Supergiant Fast X-ray Transient IGR J17354−3255

XMM-Newton and NuSTAR Simultaneous X-Ray Observations of IGR J11215-5952

The accretion environment of supergiant fast X-ray transients probed withXMM-Newton

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