Discovery of ABSORPTION LINES in Low Mass X-ray Binaries:

MXB 1659-298 and GX13+1

L. Sidoli (IASF, Milano)A.N. Parmar

T. OosterbroekD. Lumb & C. Erd

(ESA/ESTEC, Noordwijk,The Netherlands)

Summary of the XMM observations

● MXB 1659-298 (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 1659-298 EPIC lightcurve

MXB1659-298 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 XXV Fe XXVI

MXB 1659-298

MXB 1659-298

Orbital Dependence of the IRON Absorption Lines

MXB1659-298 RGS Spectrum

MXB1659-298 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

GX13+1 PN Spectrum

Summary of the GX13+1 features

● Absorption line @ 4.1 keV (EW~7 eV) likely due to CaXX

● Absorption lines @ 6.7 & 7 keV (EWs ~ 20 & 50 eV respectively) produced by Fe XXV Kalpha and Fe XXVI Kalpha absorption

● Absorption lines @ 7.8 & 8.3 keV (EW ~ 30 & 40 eV respectively), probably due to Fe XXV Kbeta and Fe XXVI Kbeta absorption

● Fe xxv edge @ 8.83 keV

● Fe xxvi edge @ 9.28 keV

● Fe broad emission line @ 6.3 keV

CONCLUSIONS

● MXB 1659-298:– 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