Discovery of ABSORPTION LINES in Low Mass X-ray Binaries: MXB and GX13+1 L. Sidoli (IASF, Milano) A.N. Parmar T. Oosterbroek D. Lumb & C. Erd (ESA/ESTEC, Noordwijk,The Netherlands)

Summary of the XMM observations ● MXB (Sidoli et al. 2001, A&A 379, 540) ● GX 13+1 (Sidoli et al. 2002, A&A 385, 940) ● Private data (PI: A.N. Parmar) observation performed in 2001 Feb. ● PV data (3 observations) Rev. 56 & 57 observations performed in Mar.-Apr. 2000

Two Low Mass X-ray Binaries

GX 13+1 ● Bright and persistent LMXB ● Radio & infrared counterparts ● It displays a 15% modulation with a period of ~25 days, probably orbital (but not confirmed yet) ~ 7 kpc distance ● Absorption Fe lines discovered with ASCA (Ueda et al. 2001)

MXB EPIC lightcurve

MXB Persistent Spectrum ● L (2-10 keV) = 1.6E37 erg/s 15 kpc) ● Column Density ~ 0.35 E22 cm-2 ● Fe emission line ~ 6.5 keV (EW ~ 160 eV) ● Fe absorption lines: – Fe xxv E=6.64 keV, EW= 33 eV – Fe xxvi E=6.9 keV, EW = 42 eV

Fe XXVFe XXVI MXB

Orbital Dependence of the IRON Absorption Lines

MXB RGS Spectrum

GX13+1 XMM-Newton Observation ● 3 on-axis PV observations ● MOS full frame, pile-up problems ● PN Timing Mode data have been considered ● Exposure Times = 2.5 ks (obs.0101), 2.1 ks (obs. 0901), 2.3 ks (obs. 1001) ● Continuum modeled with the ASCA model (Ueda et al. 2001): absorbed BBody + diskBB

GX13+1 PN Spectrum

Summary of the GX13+1 features ● Absorption 4.1 keV (EW~7 eV) likely due to CaXX ● Absorption 6.7 & 7 keV (EWs ~ 20 & 50 eV respectively) produced by Fe XXV Kalpha and Fe XXVI Kalpha absorption ● Absorption 7.8 & 8.3 keV (EW ~ 30 & 40 eV respectively), probably due to Fe XXV Kbeta and Fe XXVI Kbeta absorption ● Fe xxv 8.83 keV ● Fe xxvi 9.28 keV ● Fe broad emission 6.3 keV

CONCLUSIONS ● MXB : – Ovii, Ne X, Fe XXV, Fe XXVI narrow absorption lines mean highly ionized plasma & anisotropy – No orbital dependence – Absorption in persistent spectrum implies absorption NOT due to the same matter producing absorption DIPS – Flattened geometry of the absorbing matter above the accretion disk, around the central source

CONCLUSIONS 2 ● GX13+1: – Orbital period is not known yet, so the orbital dependence cannot be studied. In any case, if 25 days is the real orbital period, the XMM obs. cover only a fraction of it – No evidence for any velocity shifts in the line centroids – Narrow lines – The EWs of the Fe Kalpha lines are consistent with those measured with ASCA few years before. This means a STABLE GEOMETRY of the ABSORBING PLASMA