Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userResolving the soft X-ray ultra fast outflow in PDS 456
113
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Past X-ray observations of the nearby luminous quasar PDS 456 (at $z=0.184$) have revealed a wide angle accretion disk wind (Nardini et al. 2015), with an outflow velocity of $sim-0.25c$, as observed through observations of its blue-shifted iron K-shell absorption line profile. Here we present three new XMM-Newton observations of PDS 456; one in September 2018 where the quasar was bright and featureless, and two in September 2019, 22 days apart, occurring when the quasar was five times fainter and where strong blue-shifted lines from the wind were present. During the second September 2019 observation, three broad ($sigma=3000$ km s$^{-1}$) absorption lines were resolved in the high resolution RGS spectrum, which are identified with blue-shifted OVIII Ly$alpha$, NeIX He$alpha$ and NeX Ly$alpha$. The outflow velocity of this soft X-ray absorber was found to be $v/c=-0.258pm0.003$, fully consistent with iron K absorber with $v/c=-0.261pm0.007$. The ionization parameter and column density of the soft X-ray component ($logxi=3.4$, $N_{rm H}=2times10^{21}$ cm$^{-2}$) outflow was lower by about two orders of magnitude, when compared to the high ionization wind at iron K ($logxi=5$, $N_{rm H}=7times10^{23}$ cm$^{-2}$). Substantial variability was seen in the soft X-ray absorber between the 2019 observations, declining from $N_{rm H}=10^{23}$ cm$^{-2}$ to $N_{rm H}=10^{21}$ cm$^{-2}$ over 20 days, while the iron K component was remarkably stable. We conclude that the soft X-ray wind may originate from an inhomogeneous wind streamline passing across the line of sight and which due to its lower ionization, is located further from the black hole, on parsec scales, than the innermost disk wind.
rate research
Read More
We present an improved model for excess variance spectra describing ultra-fast outflows and successfully apply it to the luminous (L ~ 10^47 erg/s) low-redshift (z = 0.184) quasar PDS 456. The model is able to account well for the broadening of the spike-like features of these outflows in the excess variance spectrum of PDS 456, by considering two effects: a correlation between the outflow velocity and the logarithmic X-ray flux and intrinsic Doppler broadening with v_int = 10^4 km/s. The models were generated by calculating the fractional excess variance of count spectra from a Monte Carlo simulation. We find evidence that the outflow in PDS 456 is structured, i.e., that there exist two or more layers with outflow velocities 0.27-0.30 c, 0.41-0.49 c, and 0.15-0.20 c for a possible third layer, which agrees well with the literature. We discuss the prospects of generally applicable models for excess variance spectra for detecting ultra-fast outflows and investigating their structure. We provide an estimate for the strength of the correlation between the outflow velocity and the logarithmic X-ray flux and investigate its validity.
Simultaneous XMM-Newton, NuSTAR and HST observations, performed in March 2017, of the nearby ($z=0.184$) luminous quasar PDS 456 are presented. PDS 456 had a low X-ray flux compared to past observations, where the first of the two new XMM-Newton observations occurred during a pronounced dip in the X-ray lightcurve. The broad-band X-ray spectrum is highly absorbed, attenuated by a soft X-ray absorber of column density $N_{rm H}=6times10^{22}$ cm$^{-2}$. An increase in obscuration occurs during the dip, which may be due to an X-ray eclipse. In addition, the persistent, fast Fe K outflow is present, with velocity components of $-0.25c$ and $-0.4c$. The soft absorber is less ionized ($logxi=3$) compared to the iron K outflow ($logxi=5$) and is outflowing with a velocity of approximately $-0.2c$. A soft X-ray excess is present below 1 keV against the highly absorbed continuum and can be attributed to the re-emission from a wide angle wind. The complex X-ray absorption present in PDS 456 suggests that the wind is inhomogeneous, whereby the soft X-ray absorber originates from denser clumps or filaments which may form further out along the outflow. In contrast to the X-ray observations, the simultaneous UV spectrum of PDS 456 is largely unabsorbed, where only a very weak broad absorption trough is present bluewards of Ly$alpha$, compared to a past observation in 2000 when the trough was significantly stronger. The relative weakness of the UV absorption may be due to the soft X-ray absorber being too highly ionized and almost transparent in the UV band.
New Swift monitoring observations of the variable, radio-quiet quasar, PDS 456, are presented. A bright X-ray flare was captured in September 2018, the flux increasing by a factor of 4 and with a doubling time-scale of 2 days. From the light crossing argument, the coronal size is inferred to be about 30 gravitational radii for a black hole mass of $10^{9} {rm M}_{odot}$ and the total flare energy exceeds $10^{51}$ erg. A hardening of the X-ray emission accompanied the flare, with the photon index decreasing from $Gamma=2.2$ to $Gamma=1.7$ and back again. The flare is produced in the X-ray corona, the lack of any optical or UV variability being consistent with a constant accretion rate. Simultaneous XMM-Newton and NuSTAR observations were performed, $1-3$ days after the flare peak and during the decline phase. These caught PDS 456 in a bright, bare state, where no disc wind absorption features are apparent. The hard X-ray spectrum shows a high energy roll-over, with an e-folding energy of $E_{rm fold}=51^{+11}_{-8}$ keV. The deduced coronal temperature, of $kT=13$ keV, is one of the coolest measured in any AGN and PDS 456 lies well below the predicted pair annihilation line in X-ray corona. The spectral variability, becoming softer when fainter following the flare, is consistent with models of cooling X-ray coronae. Alternatively, an increase in a non-thermal component could contribute towards the hard X-ray flare spectrum.
High resolution soft X-ray spectroscopy of the prototype accretion disk wind quasar, PDS 456, is presented. Here, the XMM-Newton RGS spectra are analyzed from the large 2013-2014 XMM-Newton campaign, consisting of 5 observations of approximately 100 ks in length. During the last observation (hereafter OBS. E), the quasar is at a minimum flux level and broad absorption line profiles are revealed in the soft X-ray band, with typical velocity widths of $sigma_{rm v}sim 10,000$ km s$^{-1}$. During a period of higher flux in the 3rd and 4th observations (OBS. C and D, respectively), a very broad absorption trough is also present above 1 keV. From fitting the absorption lines with models of photoionized absorption spectra, the inferred outflow velocities lie in the range $sim 0.1-0.2c$. The absorption lines likely originate from He and H-like neon and L-shell iron at these energies. Comparison with earlier archival data of PDS 456 also reveals similar absorption structure near 1 keV in a 40 ks observation in 2001, and generally the absorption lines appear most apparent when the spectrum is more absorbed overall. The presence of the soft X-ray broad absorption lines is also independently confirmed from an analysis of the XMM-Newton EPIC spectra below 2 keV. We suggest that the soft X-ray absorption profiles could be associated with a lower ionization and possibly clumpy phase of the accretion disk wind, where the latter is known to be present in this quasar from its well studied iron K absorption profile and where the wind velocity reaches a typical value of 0.3$c$.
We present the spectral analysis of Chandra/HETGS and NuSTAR observations of the quasar PDS 456 from 2015, and XMM-Newton and NuSTAR archival data from 2013-2014, together with Chandra/HETGS data from 2003. We analyzed these three different epochs in a consistent way, looking for absorption features corresponding to highly ionized blueshifted absorption lines from H-like and He-like ions of iron (and nickel), as well as of other elements (O, Ne, Si, and S) in the soft band. We confirm the presence of a persistent ultra-fast outflow (UFO) with a velocity of v_out=-0.24 - -0.29c, previously detected. We also report the detection of an additional faster component of the UFO with a relativistic velocity of v_out=-0.48c. We implemented photoionization modeling, using XSTAR analytic model warmabs, to characterize the physical properties of the different kinematic components of the ultra-fast outflow and of the partial covering absorber detected in PDS 456. These two relativistic components of the ultra-fast outflow observed in the three epochs analyzed in this paper are powerful enough to impact the host galaxy of PDS 456 through AGN feedback.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
