Variability of the X-ray obscuring wind in Mrk 335 with XMM-Newton/RGS

Abstract

Transient X-ray obscuration in Seyfert 1 galaxies is thought to arise from clumpy accretion-disk winds near the broad-line region (BLR), but the wind structure and its short-timescale variability are difficult to measure because high-resolution spectra are often suppressed during deep low states. We analyse a coordinated XMM-Newton/NuSTAR campaign on Mrk 335 in June 2021, complemented by long-term Swift monitoring, which captured the source in an intermediate-flux state that preserves strong RGS absorption features. We first model the broadband spectral energy distribution to determine the ionising continuum and then perform self-consistent photoionisation modelling of the RGS spectra. The stacked RGS spectrum requires three photoionised absorbers with time-averaged log xi approx 3.63, 3.10, and 2.01 and outflow velocities |v_out| approx 5820, 3210, and 2140 km/s. Their properties are broadly consistent with the three-phase obscurer reported in the 2009 intermediate state, indicating recurring multi-phase obscuration over decade timescales. Using five consecutive RGS observations, we track the wind evolution on day timescales and find strong variability in column density and ionisation in all phases, together with smaller but coherent changes in outflow velocity. During a flare, the low-ionisation phase shows an extreme drop in N_H, and the subsequent epoch exhibits an increase in outflow velocity in all phases, consistent with rapid restructuring and possible radiative acceleration in a clumpy wind. The high-ionisation phase responds most directly to changes in the ionising luminosity, while the lowest-ionisation phase shows at most a delayed response. Order-of-magnitude constraints place the obscurer at BLR scales (approx 10^3-10^5 R_g), and simple continuity arguments suggest kinetic power that can reach the percent level of L_bol for plausible estimates of geometry and clumpiness.

Figures (10)

• Figure 1: EPIC-pn and NuSTAR spectra of Mrk 335 obtained during the 2021 campaign. Open symbols show the EPIC-pn data ($0.3$--$10$ keV), while filled symbols indicate the simultaneous NuSTAR observations ($3$--$50$ keV). The coloured datasets correspond to the five 2021 campaign epochs, using the same colour scheme adopted for the light curves in Fig. \ref{['fig:pn_nu_lc']}. For comparison, we also show one of the lowest-flux EPIC-pn spectra ever observed (2019) and one of the highest-flux spectra (2006), just before the onset of the obscuration phase in Mrk 335.
• Figure 2: Multiwavelength light curves of Mrk 335. Top panel: Long-term Swift/XRT monitoring up to May 2025. The vertical dashed line marks the epoch of the joint XMM- Newton and NuSTAR campaign. We indicate the approximate high-, mid- and low- flux states with the color palette yellow, red and brown. Second panel: XMM- Newton/EPIC-pn light curves in the $0.3$--$10\ \mathrm{keV}$ band for the five observed epochs. The Swift/XRT points are overplotted after rescaling with WebPIMMS to match the EPIC-pn count rate. Third panel: NuSTAR FPMA light curve in the $3$--$78\ \mathrm{keV}$ band. Fourth panel: Optical/UV light curve from the OM UVW1 filter, shown in units of $10^{-14}\ \mathrm{erg\ cm^{-2}\ s^{-1}\ \AA^{-1}}$. Bottom panel: Hardness ratio defined as $HR=(H-S)/(H+S)$, where $S$ and $H$ are the XMM- Newton/EPIC-pn count rates in the 0.3--2 keV and 2--10 keV bands, respectively.
• Figure 3: Spectral energy distribution (SED) modelling of Mrk 335. Top: Time-averaged SED modeling with the best-fit model components overplotted (see text for a description of each component), together with the multiwavelength data used in the modelling: XMM/EPIC-pn (orange), NuSTAR (gray), Swift/UVOT (magenta), XMM/OM (purple), and XMM/RGS (cyan). The intrinsic SED (all absorption removed) is shown as a solid black line, while the absorbed (observed) SED is shown as a dashed black line. For visual clarity, the model curves are displayed at an arbitrary energy resolution. Bottom: Best-fit SED models for the individual XMM/NuSTAR epochs in June 2021.
• Figure 4: Segments of the stacked RGS spectrum of Mrk 335 (net exposure of 440 ks), shown in the rest frame of the source. The magenta line represents the best-fit photoionisation model. Prominent absorption and emission features are marked with blue and red labels, respectively, while Galactic absorption lines at $z=0$ are indicated in black. The absorption features are systematically blueshifted, tracing ionised outflows. Narrow and broad emission lines (e.g. O7, O8, C6) are also detected. For display purposes, the RGS1 and RGS2 spectra have been combined in this figure; they were fitted simultaneously in the analysis.
• Figure 5: Left panel: Transmission spectrum of Mrk 335, obtained by dividing the observed RGS spectrum by the intrinsic continuum model. The plot zooms in on two key regions: the Fe UTA (15.5--16.5 Å) and the O8 Ly$\alpha$ line ($\sim$18.7 Å). The low-$\xi$ wind component provides the dominant contribution to the Fe UTA, while all three ionisation components are required, in different proportions, to reproduce the O8 absorption profile. Right panel: Zoom-in on the O8 Ly$\alpha$ absorption line, shown in velocity space with respect to the rest-frame wavelength of 18.97 Å. The black data points and magenta line represent the transmitted RGS spectrum and best-fit model, respectively, while the coloured curves show the transmission of the individual photoionised wind components. The low-, mid-, and high-$\xi$ winds are shown in blue, green, and orange, respectively. Vertical dashed lines mark the best-fit outflow velocities: $v_{\rm out}=-2100$ km s$^{-1}$ (low-$\xi$), $v_{\rm out}=-3135$ km s$^{-1}$ (mid-$\xi$), and $v_{\rm out}=-5900$ km s$^{-1}$ (high-$\xi$). The figure highlights that the O8 absorption is shaped by the superposition of all three wind components, each contributing with different velocities and strengths.