arXiv subjects

Yoshihiro Ueda

Publications and source records attributed to Yoshihiro Ueda.

At least 181 records · Page 10Linked to original sources

arXiv2013

Power Spectrum Density of long-term MAXI data

Monitor of All-sky X-ray Image (MAXI) on the International Space Station has been observing the X-ray sky since 2009 August 15. It has accumulated the X-ray data for about four years, so far. X-ray objects are usually variable and their variability can be studied by the power spectrum density (PSD) of the X-ray light curves.We applied our method to calculate PSDs of several kinds of objects observed with MAXI. We obtained significant PSDs from 16 Seyfert galaxies.For blackhole binary Cygnus X-1 there was a difference in the shape of PSD between the hard state and the soft state. For high mass X-ray binaries, Cen X-3, SMC X-1, and LMC X-4, there were several peaks in the PSD corresponding to the orbital period and the superorbital period.

astro-ph.HE↗

arXiv2013

Accretion disk and ionized absorber of the 9.7-hour dipping black hole binary MAXI J1305-704

We report the results from X-ray studies of the newly discovered black hole candidate MAXI J1305-704 based on Suzaku and Swift observations in the low/hard and high/soft states, respectively. The long Suzaku observation shows two types of clear absorption dips, both of which recur on a dip interval of 9.74 +- 0.04 hours, which we identify with the orbital period. There is also partially ionized absorption in the non-dip (persistent) emission in both the high/soft state and, very unusually, the low/hard state. However, this absorption (in both states) has substantially lower ionization than that seen in other high inclination systems, where the material forms a homogeneous disk wind. Here instead the absorption is most probably associated with clumpy, compact structures associated with the dipping material, which we see uniquely in this source likely because we view it at a very large inclination angle. A large inclination angle is also favored, together with a low black hole mass, to explain the high disk temperature seen in the fairly low luminosity high/soft state, as Doppler boosting enhances the disk temperature at high inclination. The disk radius inferred from these data is significantly smaller than that of the soft component seen in the low/hard state, supporting models where the disk is truncated at low luminosities. We find, however, that the lack of variability power on time scales of ~50 sec in the Suzaku low/hard state data is difficult to explain, even with a low mass black hole.

astro-ph.HE↗

arXiv2013

The role of the Gamma-Eddington ratio relation on the X-ray Baldwin effect in Active Galactic Nuclei

The X-ray Baldwin effect is the inverse correlation between the equivalent width (EW) of the narrow component of the iron Kalpha line and the X-ray luminosity of active galactic nuclei (AGN). A similar trend has also been observed between Fe Kalpha EW and the Eddington ratio (lambda_Edd). Using Chandra/HEG results of Shu et al. (2010) and bolometric corrections we study the relation between EW and the lambda_Edd, and find that log EW = (-0.13+/-0.03)log(lambda_Edd) + 1.47. We explore the role of the known positive correlation between the photon index of the primary X-ray continuum (Gamma) and lambda_Edd on the X-ray Baldwin effect. We simulate the iron Kalpha line emitted by populations of unabsorbed AGN considering 3 different geometries of the reflecting material: toroidal, spherical-toroidal and slab. We find that the Gamma-lambda_Edd correlation cannot account for the whole X-ray Baldwin effect, unless a strong dependence of Gamma on lambda_Edd, such as the one recently found by Risaliti et al. (2009) and Jin et al. (2012), is assumed. No clear correlation is found between EW and Gamma. We conclude that a good understanding of the slope of the Gamma-lambda_Edd relation is critical to assess whether the trend plays a leading or rather a marginal role in the X-ray Baldwin effect.

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arXiv2013

The 37-month MAXI/GSC source catalog in the high Galactic-latitude sky

We present the catalog of high Galactic-latitude ($|b|>10^{\circ}$) X-ray sources detected in the first 37-month data of Monitor of All-sky X-ray Image (MAXI) / Gas Slit Camera (GSC). To achieve the best sensitivity, we develop a background model of the GSC that well reproduces the data based on the detailed on-board calibration. Source detection is performed through image fit with the Poisson likelihood algorithm. The catalog contains 500 objects detected in the 4--10 keV band with significance of $s_{\rm D, 4-10 keV} \geq 7$. The limiting sensitivity is $\approx 7.5\times10^{-12}$ ergs cm$^{-2}$ s$^{-1}$ ($\approx 0.6$ mCrab) in the 4--10 keV band for 50% of the survey area, which is the highest ever achieved as an all-sky survey mission covering this energy band. We summarize the statistical properties of the catalog and results from cross matching with the Swift/BAT 70-month catalog, the meta-catalog of X-ray detected clusters of galaxies, and the MAXI/GSC 7-month catalog. Our catalog lists the source name (2MAXI), position and its error, detection significances and fluxes in the 4--10 keV and 3--4 keV bands, their hardness ratio, and basic information of the likely counterpart available for 296 sources.

astro-ph.HE↗

arXiv2013

MAXI/GSC Discovery of the Black Hole Candidate MAXI J1305-704

We present the first results on the new black hole candidate, MAXI J1305-704, observed by MAXI/GSC. The new X-ray transient, named as MAXI J1305-704, was first detected by the MAXI-GSC all-sky survey on 2012 April 9 in the direction to the outer Galactic bulge at (l,b)=(304.2deg,-7.6deg). The Swift/XRT follow-up observation confirmed the uncatalogued point source and localized to the position at (13h06m56s.44,-70d27'4".91). The source continued the activity for about five months until 2012 August. The MAXI/GSC light curve in the 2--10 keV band and the variation of the hardness ratio of the 4-10 keV to the 2-4 keV flux revealed the hard-to-soft state transition on the the sixth day (April 15) in the brightening phase and the soft-to-hard transition on the ~60th day (June 15) in the decay phase. The luminosity at the initial hard-to-soft transition was significantly higher than that at the soft-to-hard transition in the decay phase. The X-ray spectra in the hard state are represented by a single power-law model with a photon index of ~2.0, while those in the soft state need such an additional soft component as represented by a multi-color disk blackbody emission with an inner disk temperature ~0.5--1.2 keV. All the obtained features support the source identification of a Galactic black-hole binary located in the Galactic bulge.

astro-ph.HE↗

arXiv2013

A New Cluster of Galaxies towards the Galactic Bulge, Suzaku J1759-3450

We observed an extended X-ray source designated as Suzaku J1759-3450 with the Suzaku and Chandra observations towards 1RXS J175911.0-344921, which is an unidentified X-ray source listed in the ROSAT Bright Source Catalogue. A conspicuous emission line at 6 keV was also found in the Suzaku J1759-3450 spectrum. Assuming the emission line to be K emission from He-like Fe ions, we inferred Suzaku J1759-3450 to be an extragalactic object located at z = 0.13. The radial profile of the surface brightness in the 0.5-10 keV band was explained well with an isothermal beta-model of r_c = 1.61' and beta = 0.78. The X-ray spectrum was well reproduced by an optically-thin thermal plasma with the electron temperature of kT_e = 5.3 keV attenuated by the photoelectric absorption of N_H = 2.3 x 10^21 cm^-2. The bolometric X-ray luminosity of L_X (r < r_500) = 4.3 x 10^44 erg s^-1 is consistent with that expected from the L_X-T relation of clusters of galaxies. In terms of the spatial extent, the X-ray spectrum, and the bolometric luminosity of the X-ray emitting gas, we concluded that Suzaku J1759-3450 is a new cluster of galaxies.

astro-ph.HE↗

arXiv2013

Suzaku View of the Swift/BAT Active Galactic Nuclei. V. Torus Structure of Two Luminous Radio-loud AGNs (3C 206 and PKS 0707-35)

We present the results from broad-band X-ray spectral analysis of 3C 206 and PKS 0707-35 with Suzaku and Swift/BAT, two of the most luminous unobscured and obscured radio-loud active galactic nuclei with hard X-ray luminosities of 10^{45.5} erg s^{-1} and 10^{44.9} erg s^{-1} (14--195 keV), respectively. Based on the radio core luminosity, we estimate that the X-ray spectrum of 3C 206 contains a significant (~ 60% in the 14--195 keV band) contribution from the jet, while it is negligible in PKS 0707-35. We can successfully model the spectra with the jet component (for 3C 206), the transmitted emission, and two reflection components from the torus and the accretion disk. The reflection strengths from the torus are found to be R_{torus} (= Ω/2π) = 0.29 +- 0.18 and 0.41 +- 0.18 for 3C 206 and PKS 0707-35, respectively, which are smaller than those in typical Seyfert galaxies. Utilizing the torus model by Ikeda et al. (2009), we quantify the relation between the half opening angle of a torus (θ_{oa}) and the equivalent width of an iron-K line. The observed equivalent width of 3C 206, < 71 eV, constrain the column density in the equatorial plane to N_{H}^{eq} < 10^{23} cm^{-2}, or the half opening angle to θ_{oa} > 80^\circ if N_{H}^{eq} = 10^{24} cm^{-2} is assumed. That of PKS 0707-35, 72 +- 36 eV, is consistent with N_{H}^{eq} ~ 10^{23} cm^{-2}. Our results suggest that the tori in luminous radio-loud AGNs are only poorly developed. The trend is similar to that seen in radio-quiet AGNs, implying that the torus structure is not different between AGNs with jets and without jets.

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arXiv2013

Broad Band X-Ray Spectra of Two Low-luminosity Active Galactic Nuclei NGC 1566 and NGC 4941

We report the first broad band X-ray spectra of the low luminosity active galactic nuclei (LLAGN) NGC 1566 (type 1.5) and NGC 4941 (type 2) observed with Suzaku and Swift/BAT covering the 0.5-195 keV band. Both targets have hard X-ray luminosities of ~ 10^{41-42} ergs/s in the 15-55 keV band. The spectra of the nucleus are well reproduced by a sum of partially or fully covered transmitted emission and its reflection from the accretion disk, reprocessed emission from the torus accompanied by a strong narrow iron-Kαline, and a scattered component (for NGC 4941). We do not significantly detect a broad iron-Kαline from the inner accretion disk in both targets, and obtain an upper limit on the corresponding solid angle of Ω/2π< 0.3 in NGC 1566. The reflection strength from the torus is moderate, Ω/2π=0.45^{+0.13}_{-0.10} in NGC 1566 and Ω/2π=0.64^{+0.69}_{-0.27} in NGC 4941. Comparison of the equivalent width of the narrow iron-Kαline with a model prediction based on a simple torus geometry constrains its half-opening angle to be θ_oa ~ 60-70 degree in NGC 4941. These results agree with the obscured AGN fraction obtained from hard X-ray and mid-infrared selected samples at similar luminosities. Our results support the implication that the averaged covering fraction of AGN tori is peaked at L 10^{42-43} ergs/s but decreases toward lower luminosities.

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arXiv2013

Luminosity-dependent unification of Active Galactic Nuclei and the X-ray Baldwin effect

The existence of an anti-correlation between the equivalent width (EW) of the narrow core of the iron Kalpha line and the luminosity of the continuum (i.e. the X-ray Baldwin effect) in type-I active galactic nuclei has been confirmed over the last years by several studies carried out with XMM-Newton, Chandra and Suzaku. However, so far no general consensus on the origin of this trend has been reached. Several works have proposed the decrease of the covering factor of the molecular torus with the luminosity (in the framework of the luminosity-dependent unification models) as a possible explanation for the X-ray Baldwin effect. Using the fraction of obscured sources measured by recent X-ray and IR surveys as a proxy of the half-opening angle of the torus, and the recent Monte-Carlo simulations of the X-ray radiation reprocessed by a structure with a spherical-toroidal geometry by Ikeda et al. (2009) and Brightman & Nandra (2011), we test the hypothesis that the X-ray Baldwin effect is related to the decrease of the half-opening angle of the torus with the luminosity. Simulating the spectra of an unabsorbed population with a luminosity-dependent covering factor of the torus as predicted by recent X-ray surveys, we find that this mechanism is able to explain the observed X-ray Baldwin effect. Fitting the simulated data with a log-linear L_{2-10keV}-EW relation, we found that in the Seyfert regime (L_{2-10keV}< 10^44.2 erg s^-1) luminosity-dependent unification produces a slope consistent with the observations for average values of the equatorial column densities of the torus of log N_H^T > 23.1. In the quasar regime (L_{2-10 keV}> 10^44.2 erg s^-1) a decrease of the covering factor of the torus with the luminosity slower than that observed in the Seyfert regime (as found by recent hard X-ray surveys) is able to reproduce the observations for 23.2 < log N_H^T < 24.2.

astro-ph.CO↗

arXiv2013

A comparative analysis of virial black-hole mass estimates of moderate-luminosity active galactic nuclei using Subaru/FMOS

We present an analysis of broad emission lines observed in moderate-luminosity active galactic nuclei (AGNs), typical of those found in X-ray surveys of deep fields, with the aim to test the validity of single-epoch virial black hole mass estimates. We have acquired near-infrared (NIR) spectra of AGNs up to z ~ 1.8 in the COSMOS and Extended Chandra Deep Field-South Survey, with the Fiber Multi-Object Spectrograph (FMOS) mounted on the Subaru Telescope. These low-resolution NIR spectra provide a significant detection of the broad Halpha line that has been shown to be a reliable probe of black hole mass at low redshift. Our sample has existing optical spectroscopy which provides a detection of MgII, a broad emission line typically used for black hole mass estimation at z > 1. We carry out a spectral-line fitting procedure using both Halpha and MgII to determine the virial velocity of gas in the broad line region, the monochromatic continuum luminosity at 3000 A, and the total Halpha line luminosity. With a sample of 43 AGNs spanning a range of two decades in luminosity (i.e., L ~ 10^44-46 ergs/s), we find a tight correlation between the continuum and line luminosity with a distribution characterized by = 1.52 and a dispersion sigma = 0.16. There is also a close one-to-one relationship between the FWHM of Halpha and of MgII up to 10000 km/s with a dispersion of 0.14 in the distribution of the logarithm of their ratios. Both of these then lead to there being very good agreement between Halpha- and MgII-based masses over a wide range in black hole mass (i.e., M_BH ~ 10^7-9 M_sun). We do find a small offset in MgII-based masses, relative to those based on Halpha, of +0.17 dex and a dispersion sigma = 0.32. In general, these results demonstrate that local scaling relations, using MgII or Halpha, are applicable for AGN at moderate luminosities and up to z ~ 2.

astro-ph.CO↗

arXiv2013

Spectral Evolution of a New X-ray Transient MAXI J0556-332 Observed by MAXI, Swift, and RXTE

We report on the spectral evolution of a new X-ray transient, MAXI J0556-332, observed by MAXI, Swift, and RXTE. The source was discovered on 2011 January 11 (MJD=55572) by MAXI Gas Slit Camera all-sky survey at (l,b)=(238.9deg, -25.2deg), relatively away from the Galactic plane. Swift/XRT follow-up observations identified it with a previously uncatalogued bright X-ray source and led to optical identification. For more than one year since its appearance, MAXI J0556-332 has been X-ray active, with a 2-10 keV intensity above 30 mCrab. The MAXI/GSC data revealed rapid X-ray brightening in the first five days, and a hard-to-soft transition in the meantime. For the following ~ 70 days, the 0.5-30 keV spectra, obtained by the Swift/XRT and the RXTE/PCA on an almost daily basis, show a gradual hardening, with large flux variability. These spectra are approximated by a cutoff power-law with a photon index of 0.4-1 and a high-energy exponential cutoff at 1.5-5 keV, throughout the initial 10 months where the spectral evolution is mainly represented by a change of the cutoff energy. To be more physical, the spectra are consistently explained by thermal emission from an accretion disk plus a Comptonized emission from a boundary layer around a neutron star. This supports the source identification as a neutron-star X-ray binary. The obtained spectral parameters agree with those of neutron-star X-ray binaries in the soft state, whose luminosity is higher than 1.8x10^37 erg s^-1. This suggests a source distance of >17 kpc.

astro-ph.HE↗

arXiv2012

An X-ray Detected Group of Quiescent Early-type Galaxies at z=1.6 in the Chandra Deep Field South

(Abridged) We report the discovery of an X-ray group of galaxies located at a high redshift of z=1.61 in the Chandra Deep Field South. The group is first identified as an extended X-ray source. We use a wealth of deep multi-wavelength data to identify the optical counterpart -- our red sequence finder detects a significant over-density of galaxies at z~1.6 and the brightest group galaxy is spectroscopically confirmed at z=1.61. We measure an X-ray luminosity of L_{0.1-2.4 keV}= 1.8\pm0.6 \times 10^{43} erg/s, which then translates into a group mass of 3.2\pm0.8 \times 10^{13} M_sun. This is the lowest mass group ever confirmed at z>1.5. The deep optical-nearIR images from CANDELS reveal that the group exhibits a surprisingly prominent red sequence. A detailed analysis of the spectral energy distributions of the group member candidates confirms that most of them are indeed passive galaxies. Furthermore, their structural parameters measured from the near-IR CANDELS images show that they are morphologically early-type. The newly identified group at z=1.61 is dominated by quiescent early-type galaxies and the group appears similar to those in the local Universe. One possible difference is the high fraction of AGN (38^{+23}_{-20}%), which might indicate a role for AGN in quenching. But, a statistical sample of high-z groups is needed to draw a general picture of groups at this redshift. Such a sample will hopefully be available in near future surveys.

astro-ph.CO↗

arXiv2012

Comoving Space Density and Obscured Fraction of High-Redshift Active Galactic Nuclei in the Subaru/{\it XMM-Newton} Deep Survey

We study the comoving space density of X-ray-selected luminous active galactic nuclei (AGNs) and the obscured AGN fraction at high redshifts ($3 < z < 5$) in the Subaru/{\it XMM-Newton} Deep Survey (SXDS) field. From an X-ray source catalog with high completeness of optical identification thanks to deep optical images, we select a sample of 30 AGNs at $z > 3$ with intrinsic (de-absorbed and rest-frame 2--10 keV) luminosities of $L_{\rm X} = 10^{44-45}$ erg s$^{-1}$ detected in the 0.5--2 keV band, consisting of 20 and 10 objects with spectroscopic and photometric redshifts, respectively. Utilizing the $1/V_{\rm max}$ method, we confirm that the comoving space density of luminous AGNs decreases with redshift above $z > 3$. When combined with the {\it Chandra}-COSMOS result of Civano et al.\ (2011), the density decline of AGNs with $L_{\rm X} = 10^{44-45}$ erg s$^{-1}$ is well represented by a power law of $(1 + z)^{-6.2 \pm 0.9}$. We also determine the fraction of X-ray obscured AGNs with $N_{\rm H} > 10^{22}$ cm$^{-2}$ in the Compton-thin population to be 0.54$^{+0.17}_{-0.19}$, by carefully taking into account observational biases including the effects of photon statistics for each source. This result is consistent with an independent determination of the type-2 AGN fraction based on optical properties, for which the fraction is found to be 0.59$\pm$0.09. Comparing our result with that obtained in the local Universe, we conclude that the obscured fraction of luminous AGNs increases significantly from $z=0$ to $z>3$ by a factor of 2.5$\pm$1.1.

astro-ph.CO↗

arXiv2012

Slow and Fast Transitions in the Rising Phase of Outbursts from NS-LMXB transients, AqlX-1 and 4U1608-52

We analyzed the initial rising behaviors of X-ray outbursts from two transient low-mass X-ray binaries (LMXBs) containing a neutron-star (NS), Aql X-1 and 4U 1608-52, which are continuously being monitored by MAXI/GSC in 2--20 keV, RXTE/ASM in 2--10 keV, and Swift/BAT in 15--50 keV. We found that the observed ten outbursts are classified into two types by the patterns of the relative intensity evolutions in the two energy bands below/above 15 keV. One type behaves as the 15--50 keV intensity achieves the maximum during the initial hard-state period and drops greatly at the hard-to-soft state transition. On the other hand, the other type does as both the 2--15 keV and the 15--50 keV intensities achieve the maximums after the transition. The former have the longer initial hard-state ($\gtrsim$ 9 d) than the latter's ($\ltsim$5 d). Therefore, we named them as slow-type (S-type) and fast-type (F-type), respectively. These two types also show the differences in the luminosity at the hard-to-soft state transition as well as in the average luminosity before the outburst started, where the S-type are higher than the F-type in the both. These results suggest that the X-ray radiation during the pre-outburst period, which heats up the accretion disk and delays the disk transition (i.e., from a geometrically thick disk to a thin one), would determine whether the following outburst becomes S-type or F-type. The luminosity when the hard-to-soft state transition occurs is higher than $\sim 8 \times10^{36}$ erg s$^{-1}$ in the S-type, which corresponds to 4% of the Eddington luminosity for a 1.4 \Mo NS.

astro-ph.HE↗

arXiv2012

Mid and Far Infrared Properties of a Complete Sample of Local AGNs

We investigate the mid- (MIR) to far-infrared (FIR) properties of a nearly complete sample of local Active Galactic Nuclei (AGNs) detected in the Swift/BAT all sky hard X-ray (14-195 keV) survey, based on the cross correlation with the AKARI infrared survey catalogs complemented by those with IRAS and WISE. Out of 135 non-blazer AGNs in the Swift/BAT 9 month catalog, we obtain the MIR photometric data for 128 sources either in the 9, 12, 18, 22, and/or 25 um band. We find good correlation between their hard X-ray and MIR luminosities over 3 orders of magnitude (42< log lambda L_{lambda}(9, 18 um)< 45), which is tighter than that with the FIR luminosities at 90 um. This suggests that thermal emission from hot dusts irradiated by the AGN emission dominate the MIR fluxes. Both X-ray unabsorbed and absorbed AGNs follow the same correlation, implying isotropic infrared emission, as expected in clumpy dust tori rather than homogeneous ones. We find excess signals around 9 um in the averaged infrared spectral energy distribution from heavy obscured "new type" AGNs with small scattering fractions in the X-ray spectra. This could be attributed to the PAH emission feature, suggesting that their host galaxies have strong starburst activities.

astro-ph.GA↗

arXiv2012

A Candidate Active Galactic Nucleus with a Pure Soft Thermal X-ray Spectrum

We report the discovery of a candidate active galactic nucleus (AGN), 2XMM J123103.2+110648 at z = 0.13, with an X-ray spectrum represented purely by soft thermal emission reminiscent of Galactic black hole (BH) binaries in the disk-dominated state. This object was found in the second XMM serendipitous source catalogue as a highly variable X-ray source. In three separate observations, its X-ray spectrum can be represented either by a multicolor disk blackbody model with an inner temperature of kT_in~0.16-0.21 keV or a Wien spectrum Comptonized by an optically thick plasma with kT~0.14-0.18 keV. The soft X-ray luminosity in the 0.5--2 keV band is estimated to be (1.6-3.8)x10^42 erg/s. Hard emission above ~2 keV is not detected. The ratio of the soft to hard emission is the strongest among AGNs observed thus far. Spectra selected in high/low flux time intervals are examined in order to study spectral variability. In the second observation with the highest signal-to-noise ratio, the low energy (below 0.7 keV) spectral regime flattens when the flux is high, while the shape of the high energy part (1-1.7 keV) remains unchanged. This behavior is qualitatively consistent with being caused by strong Comptonization. Both the strong soft excess and spectral change consistent with Comptonization in the X-ray spectrum imply that the Eddington ratio is large, which requires a small BH mass (smaller than ~10^5M_solar.

astro-ph.HE↗

arXiv2012

The truncated disk from Suzaku data of GX 339-4 in the extreme very high state

We report on the geometry of accretion disk and high energy coronae in the strong Comptonization state (the very high/steep power law/hard intermediate state) based on a Suzaku observation of the famous Galactic black hole GX 339-4. These data were taken just before the peak of the 2006-2007 outburst, and the average X-ray luminosity in the 0.7-200 keV band is estimated to be 2.9E38 erg/s for a distance of 8 kpc. We fit the spectrum with both simple (independent disk and corona) and sophisticated (energetically coupled disk and corona) models, but all fits imply that the underlying optically thick disk is truncated significantly before the innermost stable circular orbit around the black hole. We show this directly by a comparison with similarly broadband data from a disk dominated spectrum at almost the same luminosity observed by XMM-Newton and RXTE 3 days after the Suzaku observation. During the Suzaku observation, the QPO frequency changes from 4.3 Hz to 5.5 Hz, while the spectrum softens. The energetically coupled model gives a corresponding 5+/- 8 % decrease in derived inner radius of the disk. While this is not significant, it is consistent with the predicted change in QPO frequency from Lense-Thirring precession of the hot flow interior to the disk and/or a deformation mode of this flow, as a higher QPO frequency implies a smaller size scale for the corona. This is consistent with the truncated disk extending further inwards towards the black hole.

astro-ph.HE↗

arXiv2012

Infrared and hard X-ray diagnostics of AGN identification from the Swift/BAT and AKARI all-sky surveys

We combine data from two all-sky surveys in order to study the connection between the infrared and hard X-ray (>10keV) properties for local active galactic nuclei (AGN). The Swift/Burst Alert Telescope all-sky survey provides an unbiased, flux-limited selection of hard X-ray detected AGN. Cross-correlating the 22-month hard X-ray survey with the AKARI all-sky survey, we studied 158 AGN detected by the AKARI instruments. We find a strong correlation for most AGN between the infrared (9, 18, and 90 micron) and hard X-ray (14-195 keV) luminosities, and quantify the correlation for various subsamples of AGN. Partial correlation analysis confirms the intrinsic correlation after removing the redshift contribution. The correlation for radio galaxies has a slope and normalization identical to that for Seyfert 1s, implying similar hard X-ray/infrared emission processes in both. In contrast, Compton-thick sources show a large deficit in the hard X-ray band, because high gas column densities diminish even their hard X-ray luminosities. We propose two photometric diagnostics for source classification: one is an X-ray luminosity vs. infrared color diagram, in which type 1 radio-loud AGN are well isolated from the others in the sample. The other uses the X-ray vs. infrared color as a useful redshift-independent indicator for identifying Compton-thick AGN. Importantly, Compton-thick AGN and starburst galaxies in composite systems can also be differentiated in this plane based upon their hard X-ray fluxes and dust temperatures. This diagram may be useful as a new indicator to classify objects in new and upcoming surveys such as WISE and NuSTAR.

astro-ph.HE↗