Deciphering the accretion structure in Vela X-1

Deciphering the accretion structure in Vela X-1 Victoria Grinberg MIT Kavli Institute for Astrophysics and Space Research N. Hell, M.A. Nowak, D. Huenemoerder, N.S. Schulz, M. Kühnel, J. Wilms, F. Fürst, K. Pottschmidt, J. García, P. Kretschmar Chandra Workshop 215: The Universe in High-resolution X-ray Spectra August 19, 215 Victoria Grinberg August 19, 215 1

Vela X-1 B.5 Iab supergiant line-driven CAK winds possible presence of clumps in the wind 283 s pulsar eclipsing 9 d orbit binary separation: 53.4 R neutron star embedded in companion wind Victoria Grinberg August 19, 215 2

Variability along the orbit changing baseline absorption best accessed with all sky monitors, e.g., MAXI, averaging over many orbits: Doroshenko et al. 213 Victoria Grinberg August 19, 215 3

Wind and accretion structure accretion wake focussing of the wind through gravity photoionization wake shocks on interface between CAK-wind and ionized plasma around neutron star Fig. from Kaper et all, 1994 absorption highly variable with orbital phase φ orb Victoria Grinberg August 19, 215 4

High resolution spectra along the orbit Watanabe et al. 26 Watanabe et al. 26 high & low ionization stages seen at φ orb.5 simultaneous presence of hot and cold gas Victoria Grinberg August 19, 215 5

Short-term variability Suzaku at φ orb =.17 36: Odaka et al. 213 highly variable absorption atop orbital variability time scales as short as 1 2 ks also seen in XMM (Martinez-Nunez et al. 214) and EXOSAT (Haberl et al. 199) BUT: Chandra-HETG observations always been analyzed as a whole! Victoria Grinberg August 19, 215 6

Short term variability in Chandra observations countrate [cps] 3 2 1 4.5 3 kev 3 1 kev hardness 3 2 1 3 1 kev/.5 3 kev 6 8 1 12 hours since MJD 51945 14 ObsID 1928, Feb 11 21 Victoria Grinberg August 19, 215 7

Short term variability in Chandra observations countrate [cps] 3 2 1 4.5 3 kev 3 1 kev hardness 3 2 1 3 1 kev/.5 3 kev 6 8 1 12 hours since MJD 51945 14 ObsID 1928, Feb 11 21 clearly defined periods of enhanced hardness Victoria Grinberg August 19, 215 7

Hardness-resolved spectra Photons cm 2 s 1 kev 1 2 1 7 5 4 3 2 1.5 1.2.12.1.8.6.4.2 2 4 6 Energy [kev] 8 1 the 2.5 1 kev continuum: cannot be described with same N h, but different power laws can be described with same power law, but different N h Victoria Grinberg August 19, 215 8

Hardness-resolved spectra Photons cm 2 s 1 kev 1.3.2.1 Energy [kev] 9 8 7 6 5 4 3 1.5 2 2.5 3 3.5 4 4.5 Photons cm 2 s 1 kev 1.6.4.2 4.5 2.5 5 5.5 Energy [kev] 2 6 6.5 1.8 7 7.5 1.6 Marked: detection in composite spectrum (Goldstein et al. 24) Victoria Grinberg August 19, 215 9

Hardness-resolved spectra Photons cm 2 s 1 kev 1.3.2.1 9 8 1.5 7 6 2 5 2.5 Energy [kev] 4 3 3 3.5 4 4.5 Photons cm 2 s 1 kev 1.6.4.2 4.5 2.5 5 5.5 Energy [kev] 2 Si XIII Lyα 6 6.5 1.8 Si XII triplett 7 7.5 1.6 Marked: detection in composite spectrum (Goldstein et al. 24) Victoria Grinberg August 19, 215 9

Hardness-resolved spectra Photons cm 2 s 1 kev 1.2.1 1.6 8 8.5 1.4 Energy [kev] 9 9.5 1 1.2 1.5 11 Photons cm 2 s 1 kev 1.1.5 11 1.1 11.5 12 Energy [kev] 1 12.5 13 13.5.9 14 Marked: detection in composite spectrum (Goldstein et al. 24) Victoria Grinberg August 19, 215 9

Hardness-resolved spectra Photons cm 2 s 1 kev 1.2.1 1.6 8 Energy [kev] 1.4 8.5 Mg XI triplett 9 9.5 1 1.2 Ne X Lyβ 1.5 11 Photons cm 2 s 1 kev 1.1.5 11 1.1 11.5 12 Energy [kev] 1 12.5 13 13.5.9 14 Marked: detection in composite spectrum (Goldstein et al. 24) Victoria Grinberg August 19, 215 9

Fe region.34.32.3.28.26.24 Photons cm 1 1 s Å 1.22.2.18.16.14 low absorption.12.1.8.6.4.2 high absorption v 2 km/s similar strength 1.6 1.7 1.8 1.9 2 2.1 2.2 2.3 2.4 2.5 Victoria Grinberg August 19, 215 1

Si region.4.38.36 low absorption.34.32 Photons cm 1 1 s Å 1.3.28.26.24.22.2.18.16.14 Si XIV Lyα Si XIII r Si XIII f Si VIII Si VII Si II Si VI no Si lines except of Si XIII triplett have been previously detected in the composite spectra (Goldstein et al. 24) lines in the high hardness/high absorption spectrum.12.1.8 high absorption complex structure in low absorption spectrum.6.4.2 6 6.2 6.4 6.6 6.8 7 7.2 7.4 Victoria Grinberg August 19, 215 11

Si region 2 Ratio 1.5 1.5 6 6.2 6.4 6.6 6.8 7 7.2 7.4 ECS [counts/ev] 1 5 7.2 7. Si ii vi Si vii Si viii Si ix Si x Si xi 18 6.8 6.6 Si xiii f Si xii Si xiii 19 Energy [ev] EBIT measurements; see talk by N. Hell 6.4 6.2 Si xiv 2 high hardness/ high absorption v 3 km/s for high ionization lines v 1 km/s for low ionization lines Victoria Grinberg August 19, 215 12

Si region 2 Ratio 1.5 1.5 6 6.2 6.4 6.6 6.8 7 7.2 7.4 ECS [counts/ev] 1 5 7.2 7. Si ii vi Si vii Si viii Si ix Si x Si xi 18 6.8 6.6 Si xiii f Si xii Si xiii 19 Energy [ev] EBIT measurements; see talk by N. Hell 6.4 6.2 Si xiv 2 high hardness/ high absorption v 3 km/s for high ionization lines v 1 km/s for low ionization lines Victoria Grinberg August 19, 215 12

Toy geometry low hardness/absorption Victoria Grinberg August 19, 215 13

Toy geometry clumps coming into the line of sight reduced continuum, makes fluorescent lines visible but also: possible different absorption in the presence of the clumps? wind clumps or a patchy accretion wake? high hardness/absorption Victoria Grinberg August 19, 215 13

Absorption variability time scales (Blondin et al. 199) (Sundqvist et al. 212) I 2D hydro simulations consis- I wind clump timescales? tent time scales Victoria Grinberg August 19, 215 14

Even shorter timescales? countrate [cps] 3 2 1.5 3 kev 3 1 kev hardness 4 3 3 1 kev/.5 3 kev 2 1 6 8 1 12 14 hours since MJD 51945 shorter-term variability not yet accessible, but possibly crucial Victoria Grinberg August 19, 215 15

Outlook: Chandra & Astro-H Chandra-HETGS 18 ks at φ orb =.15.45 forthcoming Astro-H higher effective area, but lower energy resolution in Si-region Counts s 1 cm 2 kev 1 1 +2 1 +1 1 + 1 1 1 2 Ne IX r,i,f Ne X Lyα Ne IX Ne IX Ne X Lyβ Ne X Lyγ Mg XI r,i,f Mg XII Lyα Mg XI Si II VI Kα Si XIII r,i,f Si XIV Lyα S IV VIII Kα S XV r S XVI Lyα 1. 5. 1. 5. Ca II XII Kα Al XIII Lyα Si II-VI Kα φorb =.25 1.8 φorb =.5 Si XIII f Si XIII r 1.9 1 ks Vela X-1 @ Astro-H/SXS (1ks) Fe Kα Fe Kβ Si XIV Lyα 2 Athena? potential to resolve down to timescales of 1 s at φ orb.5 1 + 1 1 1 2 1 eclipse 2 5 1 Energy (kev) Kitamoto et al. 214; plot by M. Kühnel & N. Hell Victoria Grinberg August 19, 215 16

Summary absorption variability on short timescales influences high resolution data low charge states of Si visible during high absorption / high hardness periods variability possibly sign of clumps passing through the line of sight disentangling the different absorption stages will be crucial to understaning structure close to neutron star Victoria Grinberg August 19, 215 17