9 Summary and Conclusions

To summarize, we observed the optically bright quasar PG1211+143 with the Chandra -HETGS  for a total of 433ks in 2015 April as part of a program that simultaneously took HST-COS and VLA observations. In this paper we have used the HETGS X-ray spectra averaged over 390ks, when the source was at low brightness. We have utilized XSTAR photoionization modeling to probe the physical conditions in the ionized absorbers of this quasar. We have compared the results of this analysis to the findings from the HST-COS study (Kriss et al., 2018). The key findings from both our Chandra and HST analysis are:

1. The combined 1st-order Chandra -MEG and -HEG gratings spectra shows that the hard X-ray spectrum of PG1211+143 is well described by a simple power law above $\sim 1$keV in the rest frame, and a soft excess below $\sim 1$keV. We use a phenomenological model consisting of an absorbed Comptonized accretion disk to characterize the shape of the soft X-ray continuum.

2. We also have identified three emission lines in the hard X-ray spectrum, which are consistent with the K-shell, He-like and H-like iron lines at 6.41keV (FeK$\alpha$), 6.67keV (FeHe$\alpha$), and 6.96keV (FeLy$\alpha$)/7.05keV (FeK$\beta$) in the rest frame, respectively. We did not detect any clearly identifiable blue-shifted Fe absorption lines, in contrast with the XMM-Newton  observations (Pounds et al., 2003). This could be due to the low signal-to-noise ratio of the HEG spectra at high energy.

3. We discovered absorption lines from H-like and He-like ions of Ne, Mg, and Si; their observed wavelengths are consistent with an outflow velocity of $-$17300 kms$^{-1}$ ( $z_{\rm out}\sim -0.0561$) relative to systemic. Their ionic column densities and turbulent velocities are not the same for all ionic species, which are related to blending and/or contamination from other atomic transition lines, as well as insufficient counts.

4. The absorption lines have been modeled using the photoionization XSTAR grid constrained by the ionizing SED constructed using the simultaneous VLA radio, HST-COS UV, and Chandra X-ray HETGS data, as well as by archival HST-FOS UV and infrared measurements. The absorption lines from H-like and He-like ions of Ne, Mg, and Si were best fitted with a highly ionized warm absorber with ionization parameter of $\log \xi = 2.87$ ergs$^{-1}$cm, column density of $\log N_{\rm H} = 21.47$ cm$^{-2}$, and an outflow velocity of $-$17300 kms$^{-1}$ ( $z_{\rm out}\sim -0.0561$). This velocity is in reasonable agreement with the component at $\sim -0.06c$ ( $-18\,000~\rm km\,s^{-1}$) measured in the XMM-Newton observations, albeit with dissimilar physical conditions ( $\log \xi = 3.4$ ergs$^{-1}$cm, $\log N_{\rm H} = 22.0$-$23.3$ cm$^{-2}$; Reeves et al., 2018; Pounds et al., 2016a). Moreover, we did not identify any additional spectral features associated with higher velocity components (e.g., the $\sim -0.129c$ [ $-38\,700~\rm km\,s^{-1}$], $\log \xi = 4$ ergs$^{-1}$cm, and $\log N_{\rm H} = 23.57$ cm$^{-2}$ absorber measured by Pounds et al. 2016a), which are due to extremely low signal-to-noise ratio over those energy band.

5. We have detected a broad blueshifted Ly$\alpha$ absorption line that has a similar outflow velocity ( $v_{\rm out} = -16\,980 \pm 10~\rm km~s^{-1}$, $z_{\rm out} = -0.0551$) as the X-ray absorber, and could be its likely counterpart (Kriss et al., 2018). The apparent optical depth of the Ly$\alpha$ absorption line profile yields an HI column density of $\log N_{\text{H\,{\sc i}}} \gtrsim 14.5$ cm$^{-2}$ (assuming $C_f = 1$). The ionization parameter ( $\log \xi = 2.87$) of our best-fit X-ray absorber corresponds to the HI ionization fraction of $2.99\times 10^{-8}$. From our best-fit total hydrogen column density ( $\log N_{\rm H} = 21.47$ cm$^{-2}$), we obtain $\log N_{\text{H\,{\sc i}}} = 13.95_{ }^{+0.26}$ cm$^{-2}$, which is roughly consistent with the empirical HI column density of the Ly$\alpha$ line.

6. While inconclusive, our VLA observations hint at a possible tantalizing scenario for VLBI observations to test, in which the shock driven by the jet/lobe system responsible for the radio emission may be connected to the X-ray and UV-detected bulk outflows.

Our Chandra -HETGS and HST-COS  observations of PG1211+143 are the first evidence for the same ultra-fast outflow occuring in both X-ray and UV spectra. Crucial to this discovery were spectrometers with velocity resolutions well-matched to the width of the absorption lines. Verifying these results, searching for the additional absorption systems suggested by the XMM-Newton spectra, and studying the variations of these absorbers with X-ray flux and/or spectral shape will either require significantly longer Chandra -HETGS spectra, or a high resolution X-ray spectrometer with significantly higher effective area. For the latter possibility, the Arcus mission, recently accepted for Phase A study, would provide 2-3$\times$ the HEG resolution and $>20\times$ the HEG +MEG effective area at energies $\approx0.2$-1keV (Smith et al., 2016), and would allow us to perform a systematic study of the ultra-fast outflows in PG1211+143 .