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

Abstract

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.

Identification of two new HMXBs in the LMC: an ∼2013 s pulsar and a probable SFXT

“…This is also consistent with the quasiperiodic flaring activity observed in other galactic SFXT (e.g. IGR J11215-5952 & IGR J16418-4532: Sidoli et al 2017bSidoli et al , 2012.…”

“…For HMXB systems observed at low luminosities this soft excess can have two different origins. It can be due to the NS hot spot (CASE I) and can therefore be modelled by a black-body component with typical size of 1 km radius (La Palombara & Mereghetti 2006;Bartlett et al 2013;Vasilopoulos et al 2013;Sidoli et al 2017b). Alternatively, it can be associated with X-ray absorption from the clumpy wind of a supergiant star (CASE II).…”

Supergiant Fast X-ray Transients - A short review

“…Supergiant Fast X-ray Transients -A short review Lara Sidoli [27] 2.7 [28] 9.5436 [23] 0.63 [23] -285 ± 10 [23] IGR J11215-5952 B0.5Ia [29], [30], [31] >7 [31] 164.6 ,[32, 21, 33] >0.8 [31] 187 [34,15] -IGR J16328-4726 O8Iafpe [35], [36], [37] 7.2 [38] 10.068 [39], [40] ---IGR J16418-4532 OB Sg ∼13 [41] 3.753 [42] -1212 [43] 14.6842 [44], [45] IGR J16465-4507 O9.5Ia [46] 9.5 [47] 30.243 [48], [49] -228 [50] -IGR J16479-4514 O8.5I, O9.5Iab [51], [52] 4.9, 2.8 [51], [52] 3.3194 [53], [22] --11.880 [44], [45] XTE J1739-302…”

“…1 shows the comparison between long-term X-ray INTEGRAL light curve of an SFXT and Vela X-1, the prototype of persistent HMXBs.Since their discovery, more than a decade ago, a huge observational effort has involved both long-term, X-ray monitoring investigations (summarized by [6] using RXT E, by [7] and [8] using INTEGRAL, by [9] and [10] using Swift) and deep, very sensitive, X-ray pointings (by Chandra, e.g. [11], and XMM-Newton, starting from the pioneering observations discussed by [12], to the more recent works by [13], [14], [15], ending with the latest published paper on SFXTs with XMM-Newton [16]).These X-ray observations led to the characterization of the SFXT properties, as follows:1. low duty cycle ( < ∼ 5%) in bright X-ray flares (at L X > ∼ 10 36 erg s −1 ) 2. high dynamic range (ratio between maximum and minimum X-ray luminosity) > ∼ 100 3. low time-averaged luminosity L X < ∼ 10 34 erg s −1Within the above limits, a variety of behaviours is present among the members of the class.…”

“…Since their discovery, more than a decade ago, a huge observational effort has involved both long-term, X-ray monitoring investigations (summarized by [6] using RXT E, by [7] and [8] using INTEGRAL, by [9] and [10] using Swift) and deep, very sensitive, X-ray pointings (by Chandra, e.g. [11], and XMM-Newton, starting from the pioneering observations discussed by [12], to the more recent works by [13], [14], [15], ending with the latest published paper on SFXTs with XMM-Newton [16]).…”