Proposal Details - 0920016
Probing the nature of the circumstellar environment around periastron in SFXTs (Drave)

Proposal Abstract

The mass transfer and accretion mechanisms in SFXTs are key questions to be answered in order to place the SFXTs in the wider context of HMXB systems. Current theories centre on mass transfer via isotropic but inhomogeneous (clumpy) winds, but some systems also show evidence of disk-like structures around the supergiant, analogous to those seen in Be/X-ray binaries. A campaign of periastron observations of 3 systems with known ephemeris is proposed using both XMM-Newton and INTEGRAL to measure the instantaneous accretion rate, emission spectrum and periodic signals generated around and on the neutron star. Now that the orbital parameters of these SFXT are well-determined, targeted continuous broad-band observations around periastron provide one with the best opportunity to use the (assumed) neutron star as a direct probe of the circumstellar wind environment.

Observation Strategy (Recommended by TAC)

Total of 206 ks in the standard 5x5 dither pattern is to be done to provide continuous coverage across the periastron ± 0.1 orbital phase regions of 3 SFXT systems (IGR J16418-4532, centered at RA, Dec = 250.450, -45.533 [l, b = 339.189, 0.500]: 65 ks; IGR J16479-4514, centered at RA, Dec = 251.996, -45.217 [l, b = 340.137, -0.117]: 58 ks; IGR J17544-2619, centered at RA, Dec = 268.607, -26.333 [l, b = 3.235, -0.338]: 83 ks). Each INTEGRAL observation is accompanied by two 10ks XMM-Newton observations within the duration of each observation (i.e., a total of 60 ks of XMM-Newton observing time).

Proposal grade: A

Data Rights (Recommended by TAC)

The TAC granted data rights for IGR J16418-4532, IGR J16479-4514 & IGR J17544-2619

Exposure Map

The exposure maps are in galactic coordinates using the Aitoff projection and units of seconds, and the colour scale is indicated at the bottom. The green lines provide the 100, 300 and 500 ksec contour.