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G. Chartas

Publications and source records attributed to G. Chartas.

At least 37 records · Page 2Linked to original sources
arXiv2016

XMM-Newton reveals a Seyfert-like X-ray spectrum in the z=3.6 QSO B1422+231

Matter flows in the central regions of quasars during their active phases are probably responsible for the properties of the super-massive black holes and that of the bulges of host galaxies. To understand how this mechanism works, we need to characterize the geometry and the physical state of the accreting matter at cosmological redshifts. The few high quality X-ray spectra of distant QSO have been collected by adding sparse pointings of single objects obtained during X-ray monitoring campaigns. This could have introduced spurious spectral features due to source variability. Here we present a single epoch, high-quality X-ray spectrum of the z=3.62 quasar B1422+231 whose flux is enhanced by gravitationally lensing (F$_{2-10 keV}\sim$10$^{-12}$erg s$^{-1}$ cm$^{-2}$). The X-ray spectrum of B1422+231 is found to be very similar to the one of a typical nearby Seyfert galaxy. Neutral absorption is detected (N$_{H}\sim$5$\times$10$^{21}$ cm$^{-2}$ at the redshift of the source) while a strong absorption edge is measured at E$\sim$7.5 keV with an optical depth of $τ\sim$0.14. We also find hints of the FeK$α$ line in emission at E$\sim$6.4 keV line (EW$\lesssim$70 eV) and a hump is detected in the E$\sim$15-20 keV energy band (rest-frame) suggesting the presence of a reflection component. In this scenario, the primary emission of B1422+231 is most probably dominated by the thermal Comptonization of UV seed photons in a corona with kT$\sim$40 keV and the reflection component has a relative direct-to-reflect normalization r$\sim$1. These findings confirm that gravitational lensing is effective to obtain good quality X-ray spectral information of quasar at high-z, moreover they support the idea that the same general picture characterizing active galactic nuclei in the nearby Universe is valid also at high redshift.

astro-ph.GA↗
arXiv2016

The Wide-Angle Outflow of the Lensed z = 1.51 AGN HS 0810+2554

We present results from X-ray observations of the gravitationally lensed z = 1.51 AGN HS 0810+2554 performed with the Chandra X-ray Observatory and XMM-Newton. Blueshifted absorption lines are detected in both observations at rest-frame energies ranging between ~1-12 keV at > 99% confidence. The inferred velocities of the outflowing components range between ~0.1c and ~0.4c. A strong emission line at ~6.8 keV accompanied by a significant absorption line at ~7.8 keV is also detected in the Chandra observation. The presence of these lines is a characteristic feature of a P-Cygni profile supporting the presence of an expanding outflowing highly ionized iron absorber in this quasar. Modeling of the P-Cygni profile constrains the covering factor of the wind to be > 0.6, assuming disk shielding. A disk-reflection component is detected in the XMM-Newton observation accompanied by blueshifted absorption lines. The XMM-Newton observation constrains the inclination angle to be < 45 degrees at 90% confidence, assuming the hard excess is due to blurred reflection from the accretion disk. The detection of an ultrafast and wide-angle wind in an AGN with intrinsic narrow absorption lines (NALs) would suggest that quasar winds may couple efficiently with the intergalactic medium and provide significant feedback if ubiquitous in all NAL and BAL quasars. We estimate the mass-outflow rate of the absorbers to lie in the range of 1.5 and 3.4 Msolar/yr for the two observations. We find the fraction of kinetic to electromagnetic luminosity released by HS 0810+2554 is large (epsilon = 9 (-6,+8)) suggesting that magnetic driving is likely a significant contributor to the acceleration of this outflow.

astro-ph.HE↗
arXiv2015

Gravitational Lensing Size Scales for Quasars

We review results from our monitoring observations of several lensed quasars performed in the optical, UV, and X-ray bands. Modeling of the multi-wavelength light curves provides constraints on the extent of the optical, UV, and X-ray emission regions. One of the important results of our analysis is that the optical sizes as inferred from the microlensing analysis are significantly larger than those predicted by the theoretical-thin-disk estimate. In a few cases we also constrain the slope of the size-wavelength relation. Our size constraints of the soft and hard X-ray emission regions of quasars indicate that in some objects of our sample the hard X-ray emission region is more compact than the soft and in others the soft emission region is smaller. This difference may be the result of the relative strengths of the disk-reflected (harder and extended) versus corona-direct (softer and compact) components in the quasars of our sample. Finally, we present the analysis of several strong microlensing events where we detect an evolution of the relativistic Fe line profile as the magnification caustic traverses the accretion disk. These caustic crossings are used to provide constraints on the innermost stable circular orbit (ISCO) radius and the accretion disk inclination angle of the black hole in quasar RX J1131-1231.

astro-ph.HE↗
arXiv2015

A Consistent Picture Emerges: A Compact X-ray Continuum Emission Region in the Gravitationally Lensed Quasar SDSS J0924+0219

We analyze the optical, UV, and X-ray microlensing variability of the lensed quasar SDSS J0924+0219 using six epochs of Chandra data in two energy bands (spanning 0.4-8.0 keV, or 1-20 keV in the quasar rest frame), 10 epochs of F275W (rest-frame 1089A) Hubble Space Telescope data, and high-cadence R-band (rest-frame 2770A) monitoring spanning eleven years. Our joint analysis provides robust constraints on the extent of the X-ray continuum emission region and the projected area of the accretion disk. The best-fit half-light radius of the soft X-ray continuum emission region is between 5x10^13 and 10^15 cm, and we find an upper limit of 10^15 cm for the hard X-rays. The best-fit soft-band size is about 13 times smaller than the optical size, and roughly 7 GM_BH/c^2 for a 2.8x10^8 M_sol black hole, similar to the results for other systems. We find that the UV emitting region falls in between the optical and X-ray emitting regions at 10^14 cm < r_1/2,UV < 3x10^15 cm. Finally, the optical size is significantly larger, by 1.5*sigma, than the theoretical thin-disk estimate based on the observed, magnification-corrected I-band flux, suggesting a shallower temperature profile than expected for a standard disk.

astro-ph.GA↗
arXiv2014

Magnified Views of the Ultrafast Outflow of the z = 1.51 AGN HS 0810+2554

We present results from an observation of the gravitationally lensed z=1.51 narrow absorption line AGN HS 0810+2554 performed with the Chandra X-ray Observatory. The factor of ~100 lensing magnification of HS 0810+2554 makes this source exceptionally bright. Absorption lines are detected at rest-frame energies of ~ 7.7 keV and ~11.0 keV at >97% significance. By interpreting these lines to arise from highly ionized iron the implied outflow velocities of the X-ray absorbing gas corresponding to these lines are 0.13c and 0.41c, respectively. The presence of these relativistic outflows and the absence of any significant low-energy X-ray absorption suggest that a shielding gas is not required for the generation of the relativistic X-ray absorbing winds in HS 0810+2554. UV spectroscopic observations with VLT/UVES indicate that the UV absorbing material is outflowing at v_UV ~0.065c. Our analysis indicates that the fraction of the total bolometric energy released by HS 0810+2554 into the IGM in the form of kinetic energy is epsilon_k = 1.0(-0.6,+0.8). An efficiency of greater than unity implies that magnetic driving is likely a significant contributor to the acceleration of this X-ray absorbing wind. We also estimate the mass-outflow rate of the strongest absorption component to be Mdot_abs=1.1(-0.7,+0.9) M_solar yr^-1. Assuming that the energetic outflow detected in the NAL AGN HS 0810+2554 is a common property of most AGN it would suggest that the X-ray absorbing wind may have a larger opening angle than previously thought. This has important consequences for estimating the feedback contribution of X-ray absorbing winds to the surrounding IGM.

astro-ph.HE↗
arXiv2013

A Mini X-Ray Survey of Sub-DLAs; Searching for AGNs Formed in Protogalaxies

A significant fraction of the sub-damped Lyman-alpha (sub-DLA) absorption systems in quasar spectra appear to be metal-rich, many with even super-solar element abundances. This raises the question whether some sub-DLAs may harbor active galactic nuclei (AGN) since supersolar metallicities are observed in AGN. Here we investigate this question based on a mini-survey of 21 quasars known to contain sub-DLAs in their spectra. The X-ray observations were performed with the Chandra X-ray Observatory. In cases of no detection we estimated upper limits of the X-ray luminosities of possible AGNs at the redshifts of the sub-DLAs. In six cases we find possible X-ray emission within ~ 1 arcsec of the background quasar consistent with the presence of a nearby X-ray source. If these nearby X-ray sources are at the redshifts of the sub-DLAs, their estimated 0.2-10 keV luminosities range between 0.8 x 10^{44}h^{-2} and 4.2 x 10^{44}h^{-2} erg s^{-1}, thus ruling out a normal late-type galaxy origin, and suggesting that the emission originates in a galactic nucleus near the center of a protogalaxy. The projected distances of these possible nearby X-ray sources from the background quasars lie in the range of 3-7 h^{-1} kpc, consistent with our hypothesis that they represent AGNs centered on the sub-DLAs. Deeper follow-up X-ray and optical observations are required to confirm the marginal detections of X-rays from these sub-DLA galaxies.

astro-ph.CO↗
arXiv2013

The Structure of the X-ray and Optical Emitting Regions of the Lensed Quasar Q 2237+0305

We use gravitational microlensing to determine the size of the X-ray and optical emission regions of the quadruple lens system Q 2237+0305. The optical half-light radius, log(R_{1/2,V}/cm)=16.41\pm0.18 (at lambda_{rest}=2018 Å), is significantly larger than the observed soft, log(R_{1/2,soft}/cm)=15.76^{+0.41}_{-0.34} (1.1-3.5 keV in the rest frame), and hard, log(R_{1/2,hard}/cm)=15.46^{+0.34}_{-0.29} (3.5-21.5 keV in the rest frame), band X-ray emission. There is a weak evidence that the hard component is more compact than the soft, with log(R_{1/2,soft}/R_{1/2,hard}) \sim 0.30^{+0.53}_{-0.45}. This wavelength-dependent structure agrees with recent results found in other lens systems using microlensing techniques, and favors geometries in which the corona is concentrated near the inner edge of the accretion disk. While the available measurements are limited, the size of the X-ray emission region appears to be roughly proportional to the mass of the central black hole.

astro-ph.CO↗
arXiv2012

HS 1700+6416: the first high redshift non lensed NAL-QSO showing variable high velocity outflows

We present a detailed analysis of the X-ray emission of HS 1700+6416, a high redshift (z=2.7348), luminous quasar, classified as a Narrow Absorption Line (NAL) quasar on the basis of its SDSS spectrum. The source has been observed 9 times by Chandra and once by XMM from 2000 to 2007. Long term variability is clearly detected, between the observations, in the 2-10 keV flux varying by a factor of three (~3-9x10^-14 erg s^-1 cm^-2) and in the amount of neutral absorption (Nh < 10^22 cm^-2 in 2000 and 2002 and Nh=4.4+-1.2x10^22 cm^-2 in 2007). Most interestingly, one broad absorption feature is clearly detected at 10.3+-0.7 keV (rest frame) in the 2000 Chandra observation, while two similar features, at 8.9+-0.4 and at 12.5+-0.7 keV, are visible when the 8 contiguous Chandra observations of 2007 are stacked together. In the XMM observation of 2002, strongly affected by background flares, there is a hint for a similar feature at 8.0+-0.3 keV. We interpreted these features as absorption lines from a high velocity, highly ionized (i.e. Fe XXV, FeXXVI) outflowing gas. In this scenario, the outflow velocities inferred are in the range v=0.12-0.59c. To reproduce the observed features, the gas must have high column density (Nh>3x10^23 cm^-2), high ionization parameter (log(xi)>3.3 erg cm s^-1) and a large range of velocities (Delta V~10^4 km s^-1). This Absorption Line QSO is the fourth high-z quasar displaying X-ray signatures of variable, high velocity outflows, and among these, is the only one non-lensed. A rough estimate of the minimum kinetic energy carried by the wind of up to 18% L(bol), based on a biconical geometry of the wind, implies that the amount of energy injected in the outflow environment is large enough to produce effective mechanical feedback.

astro-ph.HE↗
arXiv2012

Revealing the Structure of an Accretion Disk Through Energy Dependent X-ray Microlensing

We present results from monitoring observations of the gravitationally lensed quasar RX J1131-1231 performed with the Chandra X-ray Observatory. The X-ray observations were planned with relatively long exposures that allowed a search for energy-dependent microlensing in the soft (0.2-2 keV) and hard (2-10 keV) light curves of the images of RX J1131-1231. We detect significant microlensing in the X-ray light-curves of images A and D, and energy-dependent microlensing of image D. The magnification of the soft band appears to be larger than that in the hard band by a factor of ~ 1.3 when image D becomes more magnified. This can be explained by the difference between a compact, softer-spectrum corona that is producing a more extended, harder spectrum reflection component off the disk. This is supported by the evolution of the fluorescent iron line in image D over three consecutive time-averaged phases of the light curve. In the first period, a Fe line at E = 6.36(-0.16,+0.13) keV is detected (at > 99% confidence). In the second period, two Fe lines are detected, one at E = 5.47(-0.08,+0.06) keV (detected at > 99% confidence) and another at E = 6.02(-0.07,+0.09) keV (marginally detected at > 90% confidence), and in the third period, a broadened Fe line at 6.42(-0.15,+0.19) keV is detected (at > 99% confidence). This evolution of the Fe line profile during the microlensing event is consistent with the line distortion expected when a caustic passes over the inner disk where the shape of the fluorescent Fe line is distorted by General Relativistic and Doppler effects.

astro-ph.CO↗
arXiv2011

A study of the X-rayed outflow of APM 08279+5255 through photoionization codes

We present new results from our study of the X-rayed outflow of the z = 3.91 gravitationally lensed broad absorption line (BAL) quasar APM 08279+5255. These results are based on spectral fits to all the long exposure observations of APM 08279+5255 using a new quasar-outflow model. This model is based on cloudy simulations of a near-relativistic quasar outflow. The main conclusions from our multi-epoch spectral re-analysis of Chandra, XMM-Newton and Suzaku observations of APM 08279+5255 are: 1) In every observation we confirm the presence of two strong features, one at rest-frame energies between 1-4 keV, and the other between 7-18 keV. 2) We confirm that the low-energy absorption (1-4 keV rest-frame) arises from a low-ionization absorber with logNH~23 and the high-energy absorption (7-18 keV rest-frame) arises from highly ionized (3>log xi>4; where xi is the ionization parameter) iron in a near-relativistic outflowing wind. Assuming this interpretation, we find that the velocities on the outflow could get up to ~0.7c. 3) We confirm a correlation between the maximum outflow velocity and the photon index and find possible trends between the maximum outflow velocity and the X-ray luminosity, and between the total column density and the photon index. We performed calculations of the force multipliers of material illuminated by absorbed power laws and a Mathews-Ferland SED. We found that variations of the X-ray and UV parts of the SEDs and the presence of a moderate absorbing shield will produce important changes in the strength of the radiative driving force. These results support the observed trend found between the outflow velocity and X-ray photon index in APM 08279+5255. If this result is confirmed it will imply that radiation pressure is an important mechanism in producing quasar outflows.

astro-ph.HE↗
arXiv2009

Variable X-ray Absorption in mini-BAL QSOs

We present the results of X-ray spectral analysis of two mini-BAL QSOs, PG 1126-041 and PG 1351+640, aimed at getting insights into the physics of quasar outflows. We find strong X-ray spectral variability on timescales of years. These variations can be well reproduced by variations of physical properties as the covering factor and column density of ionized gas along the line of sight, compatible with radiatively-driven accretion disk wind models.

astro-ph.CO↗
arXiv2009

Confirmation of and Variable Energy Injection by a Near-Relativistic Outflow in APM 08279+5255

We present results from multi-epoch spectral analysis of XMM-Newton and Chandra observations of the broad absorption line (BAL) quasar APM 08279+5255. Our analysis shows significant X-ray BALs in all epochs with rest-frame energies lying in the range of ~ 6.7-18 keV. The X-ray BALs and 0.2-10 keV continuum show significant variability on timescales as short as 3.3 days (proper time) implying a source size-scale of ~ 10 r_g, where r_g is the gravitational radius. We find a large gradient in the outflow velocity of the X-ray absorbers with projected outflow velocities of up to 0.76 c. The maximum outflow velocity constrains the angle between the wind velocity and our line of sight to be less than ~ 22 degrees. We identify the following components of the outflow: (a) Highly ionized X-ray absorbing material (2.9 < logxi < 3.9) and a column density of log N_H ~ 23 outflowing at velocities of up to 0.76 c. (b) Low-ionization X-ray absorbing gas with log N_H ~ 22.8. We find that flatter spectra appear to result in lower outflow velocities. Based on our spectral analysis of observations of APM 08279+5255 over a period of 1.2 years (proper time) we estimate the mass-outflow rate and efficiency of the outflow to have varied between 16(-8,+12) M_solar yr^-1 and 64(-40,+66) M_solar yr^-1 and 0.18(-0.11,+0.15) to 1.7(-1.2+1.9), respectively. Assuming that the outflow properties of APM 08279+5255 are a common property of most quasars at similar redshifts, our results then imply that quasar winds are massive and energetic enough to influence significantly the formation of the host galaxy, provide significant metal enrichment to the interstellar medium and intergalactic medium, and are a viable mechanism for feedback at redshifts near the peak in the number density of galaxy mergers.

astro-ph.HE↗
arXiv2009

X-raying the Winds of Luminous Active Galaxies

We briefly describe some recent observational results, mainly at X-ray wavelengths, on the winds of luminous active galactic nuclei (AGNs). These winds likely play a significant role in galaxy feedback. Topics covered include (1) Relations between X-ray and UV absorption in Broad Absorption Line (BAL) and mini-BAL quasars; (2) X-ray absorption in radio-loud BAL quasars; and (3) Evidence for relativistic iron K BALs in the X-ray spectra of a few bright quasars. We also mention some key outstanding problems and prospects for future advances; e.g., with the International X-ray Observatory (IXO).

astro-ph.CO↗
arXiv2009

High Velocity Outflows in Narrow Absorption Line Quasars

The current paradigm for the AGN phenomenon is a central engine that consists of an inflow of material accreting in the form of a disk onto a supermassive black hole. Observations in the UV and optical find high velocity ionized material outflowing from the black hole. We present results from Suzaku and XMM-Newton observations of a sample of intrinsic NAL quasars with high velocity outflows. Our derived values of the intrinsic column densities of the X-ray absorbers are consistent with an outflow scenario in which NAL quasars are viewed at smaller inclination angles than BAL quasars. We find that the distributions of alpha_ox and Dalpha_ox of the NAL quasars of our sample differ significantly from those of BAL quasars and SDSS radio-quiet quasars. The NAL quasars are not significantly absorbed in the X-ray band and the positive values of Dalpha_ox suggest absorption in the UV band. The positive values of Dalpha_ox of the intrinsic NAL quasars can be explained in a geometric scenario where our lines of sight towards the compact X-ray hot coronae of NAL quasars do not traverse the absorbing wind whereas lines of sight towards their UV emitting accretion disks do intercept the outflowing absorbers.

astro-ph.CO↗
arXiv2009

The Sizes of the X-ray and Optical Emission Regions of RXJ1131-1231

We use gravitational microlensing of the four images of the z=0.658 quasar RXJ1131-1231 to measure the sizes of the optical and X-ray emission regions of the quasar. The (face-on) scale length of the optical disk at rest frame 400 nm is 1.3 10^15cm, while the half-light radius of the rest frame 0.3-17 keV X-ray emission is 2.3 10^14cm. The formal uncertainties are factors of 1.6 and 2.0, respectively. With the exception of the lower limit on the X-ray size, the results are very stable against any changes in the priors used in the analysis. Based on the Hbeta line-width, we estimate that the black hole mass is ~10^8 Msun, which corresponds to a gravitational radius of r_g~2 10^13 cm. Thus, the X-ray emission is emerging on scales of ~10r_g and the 400 nm emission on scales of ~70 r_g. A standard thin disk of this size should be significantly brighter than observed. Possible solutions are to have a flatter temperature profile or to scatter a large fraction of the optical flux on larger scales after it is emitted. While our calculations were not optimized to constrain the dark matter fraction in the lens galaxy, dark matter dominated models are favored. With well-sampled optical and X-ray light curves over a broad range of frequencies there will be no difficulty in extending our analysis to completely map the structure of the accretion disk as a function of wavelength.

astro-ph.HE↗
arXiv2009

Suzaku Observations of Near-Relativistic Outflows in the BAL Quasar APM 08279+5255

We present results from three Suzaku observations of the z=3.91 gravitationally lensed broad absorption line quasar APM 08279+5255. We detect strong and broad absorption at rest-frame energies of <2 keV (low-energy) and 7-12 keV (high-energy). The detection of these features confirms the results of previous long-exposure (80-90 ks) Chandra and XMM-Newton observations. The low and high-energy absorption is detected in both the back-illuminated (BI) and front-illuminated (FI) Suzaku XIS spectra (with an F-test significance of >99%). We interpret the low-energy absorption as arising from a low-ionization absorber with log NH~23 and the high-energy absorption as due to lines arising from highly ionized (2.75 < log xi < 4.0; where xi is the ionization parameter) iron in a near-relativistic outflowing wind. Assuming this interpretation we find that the velocities in the outflow range between 0.1c and 0.6c. We constrain the angle between the outflow direction of the X-ray absorber and our line of sight to be <36 degrees. We also detect likely variability of the absorption lines (at the >99.9% and >98% significance levels in the FI and BI spectra, respectively) with a rest-frame time scale of ~1 month. Assuming that the detected high-energy absorption features arise from Fe xxv, we estimate that the fraction of the total bolometric energy injected over the quasar's lifetime into the intergalactic medium in the form of kinetic energy to be >10%.

astro-ph.CO↗
arXiv2009

The Growth of Supermassive Black Holes Across Cosmic Time

One of the main themes in extragalactic astronomy for the next decade will be the evolution of galaxies over cosmic time. Many future observatories, including JWST, ALMA, GMT, TMT and E-ELT will intensively observe starlight over a broad redshift range, out to the dawn of the modern Universe when the first galaxies formed. It has, however, become clear that the properties and evolution of galaxies are intimately linked to the growth of their central black holes. Understanding the formation of galaxies, and their subsequent evolution, will therefore be incomplete without similarly intensive observations of the accretion light from supermassive black holes (SMBH) in galactic nuclei. To make further progress, we need to chart the formation of typical SMBH at z>6, and their subsequent growth over cosmic time, which is most effectively achieved with X-ray observations. Recent technological developments in X-ray optics and instrumentation now bring this within our grasp, enabling capabilities fully matched to those expected from flagship observatories at longer wavelengths.

astro-ph.CO↗