Naohisa Anabuki

Suzaku Observations of the Hard X-ray Variability of MCG-6-30-15: the Effects of Strong Gravity Around a Kerr Black Hole

Suzaku has, for the first time, enabled the hard X-ray variability of the Seyfert 1 galaxy MCG-6-30-15 to be measured. The variability in the 14-45 keV band, which is dominated by a strong reflection hump, is quenched relative to that at a few keV. This directly demonstrates that the whole reflection spectrum is much less variable than the power-law continuum. The broadband spectral variability can be decomposed into two components - a highly variable power-law and constant reflection - as previously inferred from other observations in the 2-10 keV band. The strong reflection and high iron abundance give rise to a strong broad iron line, which requires the inner disc radius to be at about 2 gravitational radii. Our results are consistent with the predictions of the light bending model which invokes the very strong gravitational effects expected very close to a rapidly spinning black hole.

SUZAKU OBSERVATIONS OF LOCAL ULTRALUMINOUS INFRARED GALAXIES

We report the results from our analysis of Suzaku X-ray Imaging Spectrometer (XIS) (0.5-10 keV) and Hard X-ray Detector (HXD)/PIN (15-40 keV) observations of five well-known local ultraluminous infrared galaxies: IRAS F05189 – 2524, IRAS F08572 + 3915, Mrk 273, PKS 1345 + 12, and Arp 220. The XIS observations of F05189 – 2524 and Mrk 273 reveal strong iron lines consistent with Fe Kα and changes in spectral shapes with respect to previous Chandra and XMM-Newton observations. Mrk 273 is also detected by the HXD/PIN at ~ 1.8σ. For F05189 – 2524, modeling of the data from the different epochs suggests that the change in spectral shape is likely due to the central source switching off, leaving behind a residual reflection spectrum, or an increase in the absorbing column. An increase in the covering fraction of the absorber can describe the spectral variations seen in Mrk 273, although a reduction in the intrinsic active galactic nucleus (AGN) luminosity cannot be formally ruled out. The Suzaku spectra of Mrk 273 are well fitted by a ~ 94% covering fraction model with a column density of ~ 1024 cm–2. The absorption-corrected log[L 2-10keV/L IR] ratio is consistent with those found in PG Quasars. The 0.5-10 keV spectrum of PKS 1345 + 12 and Arp 220 seem unchanged from previous observations and their hard X-ray emission is not convincingly detected by the HXD/PIN. The large column density derived from CO observations and the large equivalent width of an ionized Fe line in Arp 220 can be reconciled by an ionized reflection model. F08572 + 3915 is undetected in both the XIS and HXD/PIN, but the analysis of unpublished Chandra data provides a new measurement at low energies.

Type I Ultraluminous Infrared Galaxies: Transition Stage from ULIRGs to QSOs

We examine whether the ultraluminous infrared galaxies that contain a type I Seyfert nucleus (a type I ULIRG) are in the transition stage from ULIRGs to quasi-stellar objects (QSOs). To inspect this issue, we compare the black hole (BH) mass, the bulge luminosity and the far infrared luminosity among type I ULIRGs, QSOs and elliptical galaxies. As a result, we find the following results; (1) The type I ULIRGs have systematically smaller BH masses in spite of the comparable bulge luminosity relative to QSOs and elliptical galaxies. (2) The far-infrared luminosity of most type I ULIRGs is larger than the Eddington luminosity. We show that above results do not change significantly for 3 type I ULIRGs that we can estimate the visual extinction from the column density. Also, for all 8 type I ULIRGs, we investigate the effect of uncertainties of BH mass measurments and our sample bias, so that it turns out that our results do not alter even if we consider above two effects. In addition, Anabuki (2004) revealed that their X-ray properties are similar to those of the narrow line Seyfert 1 galaxies. These would indicate that active galactic nuclei (AGNs) with a high mass accretion rate exist in the type I ULIRGs. Based on all of these findings, we conclude that it would be a natural interpretation that type I ULIRGs are the early phase of BH growth, namely the missing link between ULIRGs and QSOs. Moreover, by comparing our results with a theoretical model of a coevolution scenario of a QSO BH and a galactic bulge, we show clearly that this explanation would be valid.We examine whether the ultraluminous infrared galaxies that contain a type 1 Seyfert nucleus (a type I ULIRG) are in the transition stage from ULIRGs to quasi-stellar objects (QSOs). To investigate this issue, we compare the black hole (BH) mass, the bulge luminosity, and the far-infrared luminosity among type I ULIRGs, QSOs, and elliptical galaxies. As a result, we find the following results: (1) The type I ULIRGs have systematically smaller BH masses in spite of the comparable bulge luminosity relative to QSOs and elliptical galaxies. (2) The far-infrared luminosity of most type I ULIRGs is larger than the Eddington luminosity. We show that the above results do not change significantly for three type I ULIRGs for which we can estimate the visual extinction from the column density. Also, for all eight type I ULIRGs, we investigate the effect of uncertainties of BH mass measurements and our sample bias to make sure that our results are not altered even if we consider the above two effects. In addition, Anabuki recently revealed that their X-ray properties are similar to those of the narrow-line Seyfert 1 galaxies. These would indicate that active galactic nuclei (AGNs) with a high mass accretion rate exist in type I ULIRGs. On the basis of all of these findings, we conclude that it would be a natural interpretation that type I ULIRGs are the early phase of BH growth, namely, the missing link between ULIRGs and QSOs. Moreover, by comparing our results with a theoretical model of a coevolution scenario of a QSO BH and a galactic bulge, we show clearly that this explanation could be valid.

X-Ray Evidence of a Buried Active Galactic Nucleus in UGC 5101

We present X-ray observations of the ultraluminous infrared galaxy, UGC 5101, thought to contain a buried active galactic nucleus (AGN) based on observations in other wave bands. We detected an absorbed hard component at greater than 3 keV, as well as soft emission in the energy range 0.5-2 keV. The soft X-ray component, possibly due to a modestly dust-obscured extended starburst, has an absorption-corrected 0.5-2 keV X-ray luminosity of LX(0.5-2 keV) = 1.2 × 1041 ergs s-1. The 0.5-2 keV X-ray-to-infrared luminosity ratio is a factor of ~5 lower than typical values for a normal starburst, suggesting that this extended starburst is unlikely to be energetically dominant in UGC 5101. The most plausible origin of the absorbed hard component is the putative buried AGN. The 6.4 keV Fe Kα emission line has a modest equivalent width (~400 eV), suggesting that this hard component is direct emission from the AGN, rather than a scattered component. The absorption-corrected 2-10 keV X-ray luminosity of the buried AGN was estimated to be LX(2-10 keV) ~ 5 × 1042 ergs s-1. The intrinsic 2-10 keV X-ray luminosity and the 2-10 keV X-ray-to-infrared luminosity ratio are both comparable to values measured for Mrk 463, a Seyfert 2 galaxy of similar infrared luminosity.

Soft x-ray imager (SXI) onboard ASTRO-H

Soft X-ray Imager (SXI) is a CCD camera onboard the ASTRO-H satellite which is scheduled to be launched in 2015. The SXI camera contains four CCD chips, each with an imaging area of 31mm x 31 mm, arrayed in mosaic, covering the whole FOV area of 38′ x 38′. The CCDs are a P-channel back-illuminated (BI) type with a depletion layer thickness of 200 _m. High QE of 77% at 10 keV expected for this device is an advantage to cover an overlapping energy band with the Hard X-ray Imager (HXI) onboard ASTRO-H. Most of the flight components of the SXI system are completed until the end of 2013 and assembled, and an end-to-end test is performed. Basic performance is verified to meet the requirements. Similar performance is confirmed in the first integration test of the satellite performed in March to June 2014, in which the energy resolution at 5.9 keV of 160 eV is obtained. In parallel to these activities, calibrations using engineering model CCDs are performed, including QE, transmission of a filter, linearity, and response profiles.

Suzaku wide-band X-ray Spectroscopy of the Seyfert 2 AGN in NGC 4945

Suzaku observed a nearby Seyfert 2 galaxy NGC4945, which hosts one of the brightest active galactic nuclei above 20 keV. Combining data from the X-ray CCD camera (XIS) and the Hard X-ray Detector (HXD), the AGN intrinsic nuclear emission and its reprocessed signals were observed simultaneously. The intrinsic emission is highly obscured with an absorbing column of ∼ 5 × 10 24 cm −2 , and was detectable only above ∼ 10 keV. The spectrum below 10 keV is dominated by reflection continuum and emission lines from neutral/ionized material. Along with a neutral iron Kα line, a neutral iron Kβ and a neutral nickel Kα line were detected for the first time from this source. The neutral lines and the cold reflection continuum are consistent with both originating in the same location. The Compton down-scattered shoulder in the neutral Fe-Kα line is ∼ 10% in flux of the narrow core, which confirms that the line originates from reflection rather than transmission. The weakness of the Compton shoulder also indicates that the reflector is probably seen nearly edge-on. Flux of the intrinsic emission varied by a factor of ∼ 2w ithin∼ 20 ks, which requires the obscuring material to be geometrically thin. Broadband spectral modeling showed that the solid angle of the neutral reflector is less than a few ×10 −2 × 2π. All this evidence regarding the reprocessed signals

X-Ray spectral variability of the seyfert galaxy NGC 4051 observed with Suzaku

We report results from a Suzaku observation of the narrow-line Seyfert 1 NGC 4051. During our observation, large amplitude rapid variability is seen and the averaged 2--10 keV flux is 8.1x10^-12 erg s^-1 cm^-2, which is several times lower than the historical average. The X-ray spectrum hardens when the source flux becomes lower, confirming the trend of spectral variability known for many Seyfert 1 galaxies. The broad-band averaged spectrum and spectra in high and low flux intervals are analyzed. The spectra are first fitted with a model consisting of a power-law component, a reflection continuum originating in cold matter, a blackbody component, two zones of ionized absorber, and several Gaussian emission lines. The amount of reflection is rather large (R ~ 7, where R=1 corresponds to reflection by an infinite slab), while the equivalent width of the Fe-K line at 6.4 keV is modest (140 eV) for the averaged spectrum. We then model the overall spectra by introducing partial covering for the power-law component and reflection continuum independently. The column density for the former is 1x10^23 cm^-2, while it is fixed at 1x10^24 cm-2 for the latter. By comparing the spectra in different flux states, we identify the causes of spectral variability. (abridged)

Wide-Band Spectroscopy of the Compton Thick Seyfert2 Galaxy Markarian 3 with Suzaku

We obtained a wide-band spectrum of the Compton-thick Seyfert 2 galaxy Mrk 3 with Suzaku. The observed spectrum was clearly resolved into weak, soft power-law emission, a heavily absorbed power-law component, cold reflection, and many emission lines. The heavily absorbed component, absorbed by gas with a column density of 1.1x10^24 cm^-2, has an intrinsic 2--10 keV luminosity of ~1.6x10^43 erg s^-1, and is considered to be direct emission from the Mrk 3 nucleus. The reflection component was interpreted as reflection of the direct light off cold, thick material; the reflection fraction

Performance of an Analog ASIC Developed for X-ray CCD Camera Readout System Onboard Astronomical Satellite

R

Observation of Crab Nebula with hard x-ray polarimeter: PHENEX

was 1.36+/-0.20. The cold material is inferred to be located > 1 pc from the central black hole of Mrk 3 due to the low ionization parameter of iron (xi < 1 erg cm s^-1) and the narrow iron line width (s < 22 eV). A Compton shoulder to the iron line was detected, but the intensity of the shoulder component was less than that expected from spherically distributed Compton-thick material. The weak, soft power-law emission is considered to be scattered light by ionized gas. The existence of many highly-ionized lines from O, Ne, Mg, Si, S, and Fe in the observed spectrum indicates that the ionized gas has a broad ionized structure, with xi=10--1000. The scattering fraction with respect to the direct light was estimated to be 0.9+/-0.2%, which indicates that the column density of the scattering region is about 3.6x10^22 cm^-2. This high-quality spectrum obtained by Suzaku can be considered a template for studies of Seyfert 2 galaxies.