Chichuan Jin

Durham University, Durham, England, United Kingdom

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Publications (8)20.84 Total impact

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    Chris Done · Chichuan Jin
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    ABSTRACT: We show the broadband spectral energy distribution of the extreme Narrow Line Seyfert 1 (NLS1) 1H0707-495. This is the most convincing example of an extreme spin black hole as determined from both its iron K$\alpha$ line profile, extreme variability and the new reverberation lag techniques. We compare this with another NLS1, PG 1244+026, which has much less obvious signs of high spin. This has a small and not very broad iron line, no deep variability dips, and longer reverberation lags. We show that these two very different objects have similar H$\beta$ line width and optical luminosity, hence have similar masses and mass accretion rates. The only remaining free parameters which can determine their very different X-ray spectra and variability are black hole spin, and inclination angle. We show that the optical/UV emission from the outer disc strongly implies that both these objects are highly super-Eddington (assuming that the H$\beta$ FWHM mass is reliable), and lose substantial energy via advection and/or a wind. The accretion flow cannot then be a flat disc, and inclination angle with respect to its vertical structure (which may also be variable due to time dependent clumps in a wind) is the most likely origin for the different properties seen in simple and complex NLS1. This geometry is quite different to the clean view of a flat disc which is assumed for the spin measurements, so it is possible that even 1H0707-495 has low spin. If so, this re-opens the simplest and hence very attractive possibility that high black hole spin is a necessary and sufficient condition to trigger highly relativistic (bulk Lorentz factor $\sim$10) jets.
    Preview · Article · Jun 2015
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    Chichuan Jin · Chris Done · Matthew Middleton · Martin Ward
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    ABSTRACT: We explore the origin of the strong soft X-ray excess in narrow-line Seyfert 1 galaxies using spectral-timing information from a 120 ks XMM–Newton observation of PG 1244+026. Spectral fitting alone cannot distinguish between a true additional soft X-ray continuum component and strongly relativistically smeared reflection, but both models also require a separate soft blackbody component. This is most likely intrinsic emission from the disc extending into the lowest energy X-ray bandpass. The rms spectra on short time-scales (200–5000 s) contain both (non-disc) soft excess and power-law emission. However, the spectrum of the variability on these time-scales correlated with the 4–10 keV light curve contains only the power law. Together these show that there is fast variability of the soft excess which is independent of the 4–10 keV variability. This is inconsistent with a single reflection component making the soft X-ray excess as this necessarily produces correlated variability in the 4–10 keV bandpass. Instead, the rms and covariance spectra are consistent with an additional cool Comptonization component which does not contribute to the spectrum above 2 keV.
    Preview · Article · Sep 2013 · Monthly Notices of the Royal Astronomical Society
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    Chichuan Jin · Martin Ward · Chris Done
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    ABSTRACT: In this third paper in a series of three, we present a detailed study of the broad-band spectral energy distribution (SED) of active galactic nuclei (AGNs) based on a nearby unobscured type 1 AGN sample. We perform a systematic cross-correlation study of several key parameters, i.e. Γ2-10 keV, L2-10 keV, Lbol/LEdd = λEdd, Lbol/L2-10 keV = κ2-10 keV, , FWHMHβ, MBH, αox, αX and αUV. The well-defined spectral properties of the sample enable us to improve existing relations and to identify new correlations among these parameters. We confirm a break region around FWHMHβ ≃ 4000 km s−1 in the Γ2-10 keV versus FWHMHβ correlation and log(MBH) ≃ 8.0 in the Γ2-10 keV versus MBH correlation, where these correlations appear to change form. Beyond the break point, the intrinsic Γ2-10 keV index is dispersed around 1.8. Several new correlations are also reported in this paper, e.g. strong correlations in κ5100 versus λEdd, κ5100 versus κ2-10 keV and κ2-10 keV versus MBH. The principal component analysis (PCA) is performed on the correlation matrix of the above parameters. This shows that the three physical parameters, i.e. black hole mass, mass accretion rate and Eddington ratio, drive the majority of the correlations. This is consistent with PCA results found from previous optical spectral studies. For each key parameter, we split the AGNs into three subsamples, binned based on increasing value of that parameter. We co-add the model SEDs for each object in the subsample to see how the SED changes with that parameter. Most parameters, except Lbol, show similar systematic changes in the SED such that the temperature at which the disc peaks is correlated with the ratio of power in the disc versus the Comptonized components and the hard X-ray spectral index. This underlying change in SED shape shows that AGNs do exhibit intrinsically different spectral states. This is superficially similar to the SED differences in black hole binary (BHB) seen as λEdd increases, but the analogy does not hold in detail. Only objects with the highest λEdd appear to correspond to a BHB spectral state (the disc-dominated high/soft state). The AGNs with typical mass accretion rates have spectra which do not match well with any state observed in BHB. We speculate that this could be due to the presence of a powerful ultraviolet line-driven disc wind, which complicates simple mass scaling between stellar and supermassive black holes.
    Preview · Article · Sep 2012 · Monthly Notices of the Royal Astronomical Society
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    Chichuan Jin · Martin Ward · Chris Done
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    ABSTRACT: In this third paper in a series of three, we present a detailed study of the AGN broadband SED based on a nearby unobscured Type 1 AGN sample. We perform a systematic cross-correlation study of the following key parameters: $\Gamma_{2-10keV}$, $L_{2-10keV}$, $L_{bol}$, $L_{bol}/L_{Edd}$, $\kappa_{2-10keV}$, $\kappa_{5100A}$, FWHM$_{H\beta}$, M$_{BH}$, $\alpha_{ox}$, $\alpha_{X}$ and $\alpha_{UV}$, and identify various strong correlations among these parameters. The principal component analysis (PCA) is performed on the correlation matrix of the above parameters, which shows that the three physical parameters, i.e. black hole mass, mass accretion rate and Eddington ratio, drive the majority of the correlations. This is consistent with PCA results found from previous optical spectral studies. We produce various mean SEDs classified by each of the key parameters. Most parameters, except L$_{bol}$, show similar systematic changes in the mean SEDs such that the temperature at which the disc peaks is correlated with the ratio of power in the disc versus the Comptonised components and the hard X-ray spectral index. This underlying change in SED shape shows that AGN do exhibit intrinsically different spectral states. This is superficially similar to the SED differences in BHB seen as $\lambda_{Edd}$ increases, but the analogy does not hold in detail. Only objects with the highest $\lambda_{Edd}$ appear to correspond to a BHB spectral state (the disc dominated high/soft state). The AGN with typical mass accretion rates have spectra which do not match well with any state observed in BHB. We speculate that this could be due to the presence of a powerful UV line driven disc wind, which complicates simple mass scaling between stellar and supermassive black holes.
    Full-text · Article · May 2012
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    Chichuan Jin · Martin Ward · Chris Done · Jonathan Gelbord
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    ABSTRACT: We present modelling and interpretation of the continuum and emission lines for a sample of 51 unobscured type 1 active galactic nuclei (AGNs). All of these AGNs have high-quality spectra from both XMM–Newton and the Sloan Digital Sky Survey. We extend the wavelength coverage where possible by adding simultaneous ultraviolet data from the OM onboard XMM–Newton. Our sample is selected based on low reddening in the optical and low gas columns implied by their X-ray spectra, except for one case, the broad absorption line quasar PG 1004+130. They also lack clear signatures for the presence of a warm absorber. Therefore, the observed characteristics of this sample are likely to be directly related to the intrinsic properties of the central engine. To determine the intrinsic optical continuum, we subtract the Balmer continuum and all major emission lines (including Fe ii). We also consider possible effects of contamination from the host galaxy. The resulting continuum is then used to derive the properties of the underlying accretion disc. We constrain the black hole masses from spectral fits of the Balmer emission lines and determine the best-fitting value from the modelling of broad-band spectral energy distributions (SEDs). In addition to the disc component, many of these SEDs also exhibit a strong soft X-ray excess, plus a power law extending to higher X-ray energies. We fit these SEDs by applying a new broad-band SED model which comprises accretion disc emission, low-temperature optically-thick Comptonization and a hard X-ray tail by introducing the concept of a corona radius. We find that in order to fit the data, the model often requires an additional long-wavelength optical continuum component, whose origin is discussed in this paper. We also find that the photorecombination edge of the Balmer continuum shifts and broadens beyond the standard limit of 3646 Å, implying an electron number density which is far higher than that in the broad-line-region clouds. Our results indicate that the narrow-line type 1 Seyfert galaxies in this sample tend to have lower black hole masses, higher Eddington ratios, softer 2–10 keV band spectra, lower 2–10 keV luminosities and higher αox, compared with typical broad-line type 1 Seyfert galaxies, although their bolometric luminosities are similar. We illustrate these differences in properties by forming an average SED for three subsamples, based on the full width at half-maximum velocity width of the Hβ emission line.
    Preview · Article · Jan 2012 · Monthly Notices of the Royal Astronomical Society
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    Chris Done · Shane Davis · Chichuan Jin · Omer Blaes · Martin Ward
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    ABSTRACT: (Abridged) Narrow Line Seyfert 1 (NLS1) galaxies have low mass black holes and mass accretion rates close to (or exceeding) Eddington, so a standard blackbody accretion disc should peak in the EUV. However, the lack of true absorption opacity in the disc means that the emission is better approximated by a colour temperature corrected blackbody, and this colour temperature correction is large enough ($\sim 2.4$) that the bare disc emission from a zero spin black hole can extend into the soft X-ray bandpass. Part of the soft X-ray excess seen in these objects must be intrinsic emission from the disc unless the vertical structure is very different to that predicted. However, the soft excess is much broader than predicted by a bare disc spectrum, indicating some Compton upscattering by cool, optically thick material. We associate this with the disc itself, so it must ultimately be powered by mass accretion. We build an energetically self consistent model assuming that the emission thermalises at large radii, but that at smaller radii the gravitational energy is split between powering optically thick Comptonised disc emission (forming the soft X-ray excess) and an optically thin corona above the disc (forming the tail to higher energies). We show examples of this model fit to the extreme NLS1 REJ1034+396, and to the much lower Eddington fraction Broad Line Seyfert 1 PG1048+231. We use these to guide our fits and interpretations of three template spectra made from co-adding multiple sources to track out a sequence of AGN spectra as a function of $L/L_{Edd}$. The new model is publically available within the {\sc xspec} spectral fitting package.
    Full-text · Article · Jul 2011
  • Chichuan Jin · M. J. Ward · C. Done · J. Gelbord
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    ABSTRACT: We have constructed a sample of 51 unobscured Seyferts selected from a cross-correlation between the 2XMMi catalog and SDSS DR7, which included 12 Narrow Line Seyfert 1s (NLS1s). Plus in some cases we have aperture photometry from the XMM Optical Monitor. We use these data to produce Spectral Energy Distributions (SEDs), from 10keV to just shortward of 1 micron. Using a new self-consistent multi-component model comprising a disc , a Comptonised and a power-law component, we derive best-fit models to the SEDs. From these we are better able to quantify the intrinsic properties of the AGN. In particular, we find substantial spectral diversity among the sample. The characteristics of the continuum shape depends on parameters such as the profile of permitted emission lines, black hole mass and Eddington ratio, the latter being the most influential single indicator of the overall SED. The distribution of the spectral parameters confirms that NLS1s in general have softer 2-10 keV X-ray spectra, lower 2-10 keV luminosities, lower black hole masses, and higher Eddington ratios. We also correlated distinct Balmer line components ie. broad, intermediate and narrow, with the different SED components. We find that emission associated with the broad line region correlates best with the hard X-ray component, suggesting a close link between high velocity gas and central emission. Interestingly this correlation is better than that using the accretion disc component, where most of the ionising photons emerge. Unless the correlations are dominated by modelling uncertainties, this suggests that geometry of the SED components could be important. We find that the 2-10 keV luminosity strongly correlates with the underlying optical continuum redward of 5000A, possibly due to the presence of an extra component associated with the AGN (a stellar origin is unlikely based on other observations), but not from a standard accretion disc component.
    No preview · Article · May 2011
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    ABSTRACT: We have carried out a survey of long 50 ks XMM–Newton observations of a sample of bright, variable active galactic nuclei (AGN). We found a distinctive energy dependence of the variability in RX J0136.9−3510 where the fractional variability increases from 0.3 to 2 keV, and then remains constant. This is in sharp contrast to other AGN where the X-ray variability is either flat or falling with energy, sometimes with a peak at ∼2 keV superimposed on the overall trend. Intriguingly, these unusual characteristics of the variability are shared by one other AGN, namely RE J1034+396, which is so far unique showing a significant X-ray quasi-periodic oscillation (QPO). In addition, the broad-band spectrum of RX J0136.9−3510 is also remarkably similar to that of RE J1034+396, being dominated by a huge soft excess in the Extreme-UV (EUV) to soft X-ray bandpass. The bolometric luminosity of RX J0136.9−3510 gives an Eddington ratio of about 2.7 for a black hole mass (from the H beta line width) of 7.9 × 107 M⊙. This mass is about a factor of 50 higher than that of RE J1034+396, making any QPO undetectable in this length of observation. None the less, its X-ray spectral and variability similarities suggest that RE J1034+396 is simply the closest representative of a new class of AGN spectra, representing the most extreme mass accretion rates.
    Full-text · Article · Aug 2009 · Monthly Notices of the Royal Astronomical Society Letters