Diffuse Hot Gas under X-ray Absorption line Spectroscopy

1. Diffuse Hot Gas under X-ray Absorption line Spectroscopy Daniel Wang and Yangsen Yao (UMass) in collaboration with Taotao Fang (Berkeley), Wei Cui (Purdue), Fabrizio Nicastro (CfA), & Rupert Croft (Carnegie Mellon)

2. Sd Sc Sb Sa Starburst Why interesting?

3. Why absorption lines? • Add the velocity and/or depth • Measure the column density, thus the mass • Direct line diagnostics • Independent of cool gas absorption

4. AGN X-ray binary No detection Lines of sight

5. Instrument Properties FWHM ~ 5x102 km/s

6. Absorption line model I()=Ic() exp[-()] ()NHfafi(T)flu(,0,b) b=(2kT/mi+2)1/2 b =100 km/s is actually used!

7. OVII OVIII Ne IX Ne VIII OVI Ne IX Ionization fraction Assuming CIE and solar abundances

8. PKS 2155 3C 273 Mkn 421 LETG/ACIS

9. LMC X-3

10. Results from extragalactic sources

11. Galactic source selection and observations • LMXBs with |b| > 2 • S/N > 7 per bin at ~0.6 keV • Excluding sources with intrinsic emission/absorption features • Ten LMXBs with 17 observations (6 with the LETG)

12. Ne IX absorption lines in LMXB spectra Mean T ~ 106.3+/-0.2 K nH~3.4(-1.4,+1.7)x10-3 cm-3

13. Exponential distribution models Sphere model nH = 6.1(-3.0,+3.6)x10-2 cm-3 exp[-R/2.7(-0.4,+0.8) kpc] ~3 x 10-3 cm-3 at the Sun NH~6.1 x1019 cm-2 MH~7.5(2.5-16)x108 Msun Disk model nH = 5.0(-1.8,+2.6)x10-3 cm-3 exp[-|z|/1.1(-0.5,+0.7) kpc] NH~1.6 x1019 cm-2

14. Comparisons with other measurements • OVI absorption (e.g., Savage et al. 2003) • Comparable to the scale height and velocity dispersion of OVI-absorbing gas • The predicted NOVI is ~1/4 of the observed (assuming CIE and cosmic abundances) • X-ray emission • dI/d=4.8(+-0.8) ph/(s cm2 sr) in OVII triple, averaged over a large field (McCammon et al. 2002) • Marginally consistent with the expected from our inferred exponential distribution, assuming T = 106.3+-0.2 K • Correlation with diffuse ¾-keV band intensity

15. Comparison Cont. • Pulsar dispersion measures (e.g., Gomez et al. 2001) • Ne=6x1019cm-2 (Galactic only) • Ne=2x1020cm-2 (including MC pulsars) • lower limit to the metal abundance of hot gas NH/Ne ~ 0.06 – 0.3 solar • Excluding the HII contribution, the abundance is likely to be solar. • Or a substantial fraction of the pulsar DM is due to hot gas.

16. Summary A systematic analysis of Chandra grating spectra of XBs and AGNs to study the OVII, OVIII, and Ne IX absorption, accounting for line saturation and multiple line detections • No evidence for significant X-ray absorption beyond the LMC (probably ~< 1019 cm-2, assuming the solar abundance) • X-ray absorption primarily around the Galactic disk within a few kpc • Vertical scale height ~1-2 kpc, similar to the values for OVI absorbers and free electrons from pulsar dispersion measures • Metal abundance probably ~ solar • Total absorbing gas mass ~ (0.2-1.6)x109 Msun • Mean temperature ~ 106.3+-0.2 K, density ~ 3 x 10-3 cm-3 • Predicts ~0.4 x10-8 cm-2 of OVI, ~¼ of the observed.

17. Chandra grating observations

18. High Energy Transmission Grating Spectrometer

19. AGN X-ray binary No detection Lines of sight