1 Introduction

X-ray observations of active galactic nuclei (AGNs) reveal blueshifted absorption features, which have been interpreted as outflows of photoionized gas along the line of sight (Halpern, 1984). Soft X-ray absorption lines are commonly referred to as warm absorbers (WAs), while those ionized absorbers with a velocity higher than 10000 kms$^{-1}$ are defined as ultra-fast outflows (UFOs; Tombesi et al., 2010). WAs have been observed in over half of Seyfert 1 galaxies (e.g., Reynolds & Fabian, 1995; Laha et al., 2014; George et al., 1998; Reynolds, 1997), which exhibit outflow velocities in the range of 100-500 kms$^{-1}$ (e.g., Blustin et al., 2002; McKernan et al., 2007; Kaspi et al., 2000). On the other hand, X-ray observations of iron absorption lines can indicate outflow velocities that are quite large, up to mildly relativistic values of $\sim 0.1$-$0.4c$ (e.g., Cappi, 2006; Braito et al., 2007; Pounds et al., 2003; Cappi et al., 2009). More recent studies show that UFOs are identified in a significant fraction ($\sim 30$ per cent) of radio-quiet and radio-loud AGNs (Tombesi et al., 2014; Tombesi et al., 2012; Tombesi et al., 2010; Tombesi et al., 2011). Recently, Tombesi et al. (2013) concluded that UFOs and WAs are associated with different locations of a single large-scale stratified outflow in the AGN, suggesting a unified model for accretion powered sources (Kazanas et al., 2012). However, Laha et al. (2016); Laha et al. (2014) instead suggested that UFOs and WAs may be associated with two different outflows with distinctive physical conditions and outflow velocities.

Table: Observation log of PG1211+143 

Observatory	Detector	Gratings	Seq./PID	Obs.ID	UT Start	UT End	Time (ks)
Chandra	ACIS-S	HETGS	703109	17109	2015 Apr 09, 08:22	2015 Apr 10, 14:32	104.68
Chandra	ACIS-S	HETGS	703109	17645	2015 Apr 10, 17:55	2015 Apr 11, 06:56	44.33
Chandra	ACIS-S	HETGS	703109	17646	2015 Apr 12, 02:04	2015 Apr 13, 02:15	83.65
Chandra	ACIS-S	HETGS	703109	17647	2015 Apr 13, 13:54	2015 Apr 14, 02:09	42.22
Chandra	ACIS-S	HETGS	703109	17108	2015 Apr 15, 07:13	2015 Apr 16, 03:10	68.89
Chandra	ACIS-S	HETGS	703109	17110	2015 Apr 17, 06:40	2015 Apr 18, 08:28	89.56
HST	COS	G140L	13947	LCS501010	2015 Apr 12, 15:50	2015 Apr 12, 16:28	1.90
HST	COS	G140L	13947	LCS504010	2015 Apr 14, 13:52	2015 Apr 14, 14:30	1.90
HST	COS	G140L	13947	LCS502010	2015 Apr 14, 15:37	2015 Apr 14, 16:15	1.90
HST	COS	G130M	13947	LCS502020	2015 Apr 14, 17:17	2015 Apr 14, 19:05	2.32
HST	FOS	G130H	1026	Y0IZ0304T	1991 Apr 13, 08:21	1991 Apr 13, 08:56	2.00
HST	FOS	G130H	1026	Y0IZ0305T	1991 Apr 16, 09:56	1991 Apr 16, 10:31	2.00
HST	FOS	G270H	1026	Y0IZ0404T	1991 Apr 16, 07:51	1991 Apr 16, 07:57	3.49
HST	FOS	G190H	1026	Y0IZ0406T	1991 Apr 16, 09:00	1991 Apr 16, 09:25	1.34

The optically bright quasar PG1211+143 in a nearby, luminous narrow line Seyfert 1 galaxy ( $z = 0.0809$; Rines et al., 2003; Marziani et al., 1996) is one of the AGNs with potentially mildly relativistic UFOs (Pounds & Page, 2006; Fukumura et al., 2015; Pounds et al., 2003; Pounds et al., 2016a). Over a decade ago, Pounds et al. (2003) reported absorption lines of H- and He-like ions of C, N, O, Ne, Mg, S and Fe with an outflow velocity of $\sim -24$,000 kms$^{-1}$ ( $\sim -0.08c$).¹Moreover, Reeves et al. (2005) reported the detection of redshifted H-like or He-like iron absorption lines with velocities in the range of $0.2c$-$0.4c$, which could be evidence for pure gravitational redshift by the supermassive black hole (SMBH). The presence of UFOs in PG1211+143 was challenged by Kaspi & Behar (2006); however, they were again confirmed by later works (Pounds & Reeves, 2009; Tombesi et al., 2011; Pounds & Reeves, 2007; Tombesi et al., 2010; Pounds & Page, 2006). More recently, a second high-velocity component with $\sim -0.066c$ ( $-19\,800~\rm km\,s^{-1}$) was detected, in addition to a confirmation of a previously identified higher velocity component of $\sim -0.129c$ ( $-38\,700~\rm km\,s^{-1}$) (Pounds et al., 2016a; Pounds et al., 2016b; Pounds, 2014). Hubble Space Telescope (HST ) UV observations of PG1211+143 taken with the Space Telescope Imaging Spectrograph (STIS ) had also revealed the presence of four strong absorbers at observed redshifts of $0.01649$ to $0.02586$ (implied outflow velocities of $-$15650 to $-$18400 $\rm km~s^{-1}$; Tilton et al., 2012; Tumlinson et al., 2005; Danforth & Shull, 2008; Penton et al., 2004). These authors postulated that these could be attributed to the intergalactic medium (IGM) or outflows from unseen satellite galaxies (see §6).

Many of these disparate results can be explained by the apparent highly variable nature of the UFO phenomenon. Long, intensive observations of AGN such as IRAS13224$-$3809 (Parker et al., 2017a; Parker et al., 2017b) and PDS456 (Matzeu et al., 2016) show UFO variability on timescales of 10,000 to 100,000 s. The character of the absorption also depends on the state of the illuminating X-ray source, with the outflowing gas often showing an ionization response (Parker et al., 2017b), or a correlation between ionization state, outflow velocity, and X-ray flux (Matzeu et al., 2017; Pinto et al., 2017). While these characteristics suggest radiative acceleration of the outflow (Matzeu et al., 2017), other authors offer a more complex vision of these observationally complex winds. Konigl & Kartje (1994) described a magnetohydrodynamical wind model as a possible explanation for the warm absorber winds observed in many AGN. Fukumura et al. (2010a) and Kazanas et al. (2012) adapted magnetohydrodynamical winds to high-velocity winds launched from the accretion disk, compatible with UFOs. These winds could have a complex structure, with velocity and ionization state dependent upon the observer's line of sight. In addition, once launched, such disk winds would be photoionized by the central X-ray source and subject to additional acceleration due to radiation pressure.

While Fukumura et al. (2010b) did attempt a theoretical demonstration that the X-ray absorption by FeXXV can co-exist with broad ultraviolet absorption by CIV, their scenario required a very low X-ray to UV luminosity ratio ( $\alpha_{ox} \sim 2$) in order to keep the UV ionization of the gas low. PG1211+143 has a fairly high X-ray to UV luminosity ratio, however, with $\alpha_{ox} = 1.47$, so although CIV absorption might not be expected, trace amounts of HI can remain, even in very highly ionized gas. Our observation is the first to detect an X-ray UFO observed simultaneously with UV broad absorption in HI Ly$\alpha$.

As an alternative to an outflowing wind producing the UFO features in PG1211+143, Gallo & Fabian (2013) presented a model in which the broad absorption is produced by blurred reflection in the X-ray illuminated atmosphere of the accretion disk. Again, in such a model, trace amounts of HI may still be present, which could give rise to similar UV absorption features.

Our main goal in this work is to identify and characterize the blueshifted X-ray absorption features of PG1211+143 based on our Chandra  observations, which are part of a program that includes simultaneous HST UV and Jansky Very Large Array (VLA) radio observations. Given the relativistic velocities of the outflows we are examining, it is important to use a full relativistic treatment for all velocities and redshifts. For clarity in understanding the nomenclature we use in this paper, we summarize the following definitions for quantities we will use: $z_{\rm rest}$ is the rest frame redshift of the host galaxy ( $z_{\rm rest}=0.0809$ for PG1211+143 ), $z_{\rm obs}$ is the observed redshift (in our reference frame) of a spectral feature, $z_{\rm out}$ is the redshift of an outflow in the frame of PG1211+143 , $v_{\rm out}$ is the velocity of an outflow in the frame of PG1211+143 , $\lambda_{\rm obs}$ is the observed wavelength of a spectral feature, $\lambda_0$ is the rest wavelength (vacuum) of a spectral feature. These quantities are related by the usual special relativistic formulations: $z_{\rm obs} = (\lambda_{\rm obs}/\lambda_0) - 1$, $z_{\rm out} = (1+z_{\rm obs})/(1+z_{\rm rest}) - 1$, $v_{\rm out} = c [(1+z_{\rm out})^2-1]/[(1+z_{\rm out})^2+1]$, and $z_{\rm out} = \sqrt{[(1+v_{\rm out}/c)/(1-v_{\rm out}/c)]} - 1$, where $c$ is the speed of light.

This paper is focused primarily on the X-ray analysis, and organized as follows. Section 2 describes the observations and data reduction. In §3 we inspect the X-ray light curve and hardness ratios in order to see whether all spectra can be co-added for analysis. In §4 we model the X-ray continuum and Fe emission lines. In §5 we describe in detail the modeling of the ionized absorber using the photoionization code XSTAR . The HST UV results are reported in a complementary paper (Kriss et al., 2018). A summary of its findings as relevant to this paper are presented in §6. Section 7 presents the results of our VLA observations. In §8, we discuss the implications of our X-ray and UV absorption features. Finally, we summarize our results in §9.