Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userProbing the nature and origin of dust in the reddened quasar IC 4329A with global modelling from X-ray to infrared
116
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Cosmic dust is a key tracer of structure formation and evolution in the universe. In active galactic nuclei (AGN) the origin and role of dust are uncertain. Here, we have studied dust in the X-ray bright and reddened type-1 quasar IC 4329A, which exhibits an ionised AGN wind. We incorporated high-resolution X-ray and mid-IR spectroscopy, combined with broad-band continuum modelling, to investigate the properties of dust in this AGN. We used new Chandra HETGS observations taken in June 2017, as well as archival data from XMM-Newton, Swift, HST, Spitzer, IRAS, and Herschel for our IR-optical-UV-X-ray modelling. Two distinct components of dust in IC 4329A are found. One component is in the interstellar medium (ISM) of the host galaxy, and the other is a nuclear component in the AGN torus and its associated wind. The emitting dust in the torus is evident in mid-IR emission (9.7 and 18 micron features), while dust in the wind is present through both reddening and X-ray absorption (O, Si, and Fe edge features). The gas depletion factors into dust for O, Si, and Fe are measured. We derive an intrinsic reddening E(B-V) ~ 1.0, which is most consistent with a grey (flat) extinction law. The AGN wind consists of three ionisation components. From analysis of long-term changes in the wind, we determine limits on the location of the wind components. The two lowest ionisation components are likely carriers of dust from the AGN torus. We find that the dust in the nuclear component of IC 4329A is different from dust in the Milky Way. The dust grains in the AGN torus and wind are likely larger than the standard Galactic dust, and are in a porous composite form (containing amorphous silicate with iron and oxygen). This can be a consequence of grain coagulation in the dense nuclear environment of the AGN.
rate research
Read More
We present the X-ray broadband power spectral density function (PSD) of the X-ray-luminous Seyfert IC 4329a, constructed from light curves obtained via Rossi X-ray Timing Explorer monitoring and an XMM-Newton observation. Modeling the 3-10 keV PSD using a broken power-law PSD shape, a break in power-law slope is significantly detected at a temporal frequency of 2.5(+2.5,-1.7) * 10^-6 Hz, which corresponds to a PSD break time scale T_b of 4.6(+10.1,-2.3) days. Using the relation between T_b, black hole mass M_BH, and bolometric luminosity as quantified by McHardy and coworkers, we infer a black hole mass estimate of M_BH = 1.3(+1.0,-0.3) * 10^8 solar masses and an accretion rate relative to Eddington of 0.21(+0.06,-0.10) for this source. Our estimate of M_BH is consistent with other estimates, including that derived by the relation between M_BH and stellar velocity dispersion. We also present PSDs for the 10-20 and 20-40 keV bands; they lack sufficient temporal frequency coverage to reveal a significant break, but are consistent with the same PSD shape and break frequency as in the 3-10 keV band.
We have obtained a deep, simultaneous observation of the bright, nearby Seyfert galaxy IC 4329A with Suzaku and NuSTAR. Through a detailed spectral analysis, we are able to robustly separate the continuum, absorption and distant reflection components in the spectrum. The absorbing column is found to be modest at $N_H = 6 times 10^{21}$ cm$^2$, and does not introduce any significant curvature in the Fe K band. We are able to place a strong constraint on the presence of a broadened Fe K{alpha} line: $E = 6.46^{+0.08}_{-0.07}$ keV rest frame with ${sigma} = 0.33^{+0.08}_{-0.07}$ keV and $EW = 34^{+8}_{-7}$ eV, though we are not able to constrain any of the parameters of a relativistic reflection model. These results highlight the range in broad Fe K{alpha} line strengths observed in nearby, bright AGN (roughly an order of magnitude), and imply a corresponding range in the physical properties of the inner accretion disk in these sources. We have also updated our previously reported measurement of the high-energy cutoff of the hard X-ray emission using both observatories rather than just NuSTAR alone: $E_{cut} = 186 pm 14$ keV. This high-energy cutoff acts as a proxy for the temperature of the coronal electron plasma, enabling us to further separate this parameter from the optical depth of the plasma and to update our results for these parameters as well. We derive $kT = 50^{+6}_{-3}$ keV with ${tau} = 2.34^{+0.16}_{-0.11}$ using a spherical geometry, $kT = 61 pm 1$ keV with ${tau} = 0.68 pm 0.02$ for a slab geometry, with both having an equivalent goodness-of-fit.
Over the past two decades, the most commonly adopted explanation for high and hard X-ray emission in resolved quasar jets has been inverse Compton upscattering of the Cosmic Microwave Background (IC/CMB), which requires jets which remain highly relativistic on 10-1000 kpc scales. In more recent years various lines of observational evidence, including gamma-ray upper limits, have disfavored this explanation in favor of a synchrotron origin. While the IC/CMB model generally predicts a high level of gamma-ray emission, it has never been detected. Here we report the detection of a low-state Fermi/LAT gamma-ray spectrum associated with two jetted AGN which is consistent with the predictions of the IC/CMB model for their X-ray emission. We have used archival multiwavelength observations to make precise predictions for the expected minimum flux in the GeV band, assuming that the X-ray emission from the kpc-scale jet is entirely due to the IC/CMB process. In both sources -- OJ 287 and PKS 1510-089 -- the minimum-detected gamma-ray flux level agrees with predictions. Both sources exhibit extreme superluminal proper motions relative to their jet power, which argues for the well-aligned jets required by the IC/CMB model. In the case of PKS~1510-089, it cannot be ruled out that the minimum gamma-ray flux level is due to a low state of the variable core which only matches the IC/CMB prediction by chance. Continued long-term monitoring with the Fermi/LAT could settle this issue by detecting a plateau signature in the recombined light-curve which would clearly signal the presence of a non-variable emission component.
The X-ray regime is a largely underused resource for constraining interstellar dust grain models and improving our understanding of the physical processes that dictate how grains evolve over their lifetimes. This is mostly due to current detectors relatively low sensitivity and high background, limiting the targets to the brightest sources. The improved sensitivity of the next generation of X-ray detectors will allow studies of much fainter sources, at much higher angular resolution, expanding our sampled sightlines in both quality and quantity.
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.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
