arXiv subjects

Aiko Miyamoto

Publications and source records attributed to Aiko Miyamoto.

6 recordsLinked to original sources

arXiv2026

The Geometry of Ultra-Fast Outflows Probed by Soft X-ray Variability in PDS 456

Constraining the location and geometry of ultra-fast outflows (UFOs) is essential for identifying where they are launched and how they are accelerated. We investigate the soft X-ray variability of the luminous quasar PDS 456 using simultaneous March 2024 observations with XRISM/Xtend and NuSTAR. A model-independent comparison between the flare and quiescent phases reveals spectral variability around 1 keV in the rest frame, while the hard X-ray spectral shape remains nearly unchanged. Broadband spectral fitting shows that the soft X-ray structure is well described by a partial-covering low-ionization UFO with $\log (ξ/(\mathrm{erg~cm~s^{-1}})) \simeq 3.1$ and $v_{\mathrm{out}} \simeq 0.30c$. Time-sliced spectral analysis further reveals significant variability in the covering fraction of this absorber. Interpreting this variability as transverse motion across the X-ray source, we constrain the crossing velocity to be $v_{\mathrm{cross}} \lesssim 5 \times 10^{-3}c$ and derive a lower limit on the absorber distance of $r \gtrsim 4 \times 10^3 R_{\mathrm{g}}$. This location is substantially farther out than the high-ionization UFO previously inferred at ~200-600 $R_{\mathrm{g}}$, while the two phases have comparable outflow velocities. The resulting velocity-distance structure disfavors a self-similar magnetocentrifugal wind and instead suggests either radiation-pressure acceleration following a Castor-Abbott-Klein-like velocity law or compact magnetic acceleration through magnetic reconnection. These results demonstrate that soft X-ray partial-covering variability can provide a geometrical probe of UFOs and directly connect spectral variability to wind acceleration.

astro-ph.HE↗

arXiv2026

Low-Noise SiPM Light Readout and ASIC-Based Charge Readout of a Liquid Argon Time Projection Chamber for MeV Gamma-Ray Measurements

We have developed a compact liquid argon time projection chamber (LArTPC), NanoGRAMS, as a technology demonstrator for the Gamma-Ray and AntiMatter Survey (GRAMS). LArTPCs have the potential to enable Compton cameras with unprecedented effective area in the MeV gamma-ray band. NanoGRAMS has an active volume of $5.12 \times 5.12 \times 10~\mathrm{cm^3}$ and is equipped with a low-noise scintillation and charge readout system. The scintillation light is detected by an array of 16 SiPMs ($6 \times 6~\mathrm{mm^2}$ each), whose signals are summed and amplified by a low-noise transimpedance amplifier operable at liquid argon temperature. Ionization electrons are read out with $3.2\,\mathrm{mm}$-pitch pixels and processed by VATA-SGD ASICs, with synchronization provided by an FPGA-based data acquisition system. We irradiated the detector with a $^{60}\mathrm{Co}$ source (1173 and $1332\,\mathrm{keV}$) and successfully detected both 1-hit and 2-hit events. The collected charge was converted to deposited energy using a phenomenological recombination model, and the detector response was evaluated with a Geant4-based Monte Carlo simulation. The reconstructed energy spectrum shows Compton edges at 963 and $1118\,keV$, consistent with the expected values. For 2-hit events, the sequence of interactions was identified, and the reconstructed back-projection image agrees with the source position. These results demonstrate the feasibility of NanoGRAMS as a Compton camera for MeV gamma-ray imaging spectroscopy.

astro-ph.IM↗

arXiv2026

Possible time-variable iron-K$α$ emission in the circumnuclear region of the Circinus galaxy

We present imaging and spatially resolved spectral analyses of eight Chandra data taken for the Circinus galaxy in $\approx$ 22 years to reveal neutral iron-K$α$ emission on a circumnuclear scale ($\sim$ 10--100 pc) and search for time variability in the emission. By simulating and taking account of point-source emission from the active galactic nucleus (AGN), we detect iron-line emission $\sim$ 20--60 pc away from the nucleus, particularly in the eastern and western regions. In the two regions, possible time variability in the line flux was also detected. Our spectral analysis then finds that the observed equivalent widths can reach $\sim$ 2 keV and the slopes of underlying continua are rather inverted with $Γ< 0$. These are consistent with a scenario in which the iron emission originates from clouds illuminated by AGN X-rays; our result could provide the first extragalactic example of AGN X-ray echoes. In this scenario, we estimated the physical sizes of the illuminated clouds based on the timescale of variability to be less than 6 pc. Furthermore, we compared the iron emission distribution with the cold molecular distribution inferred by Atacama Large Millimeter/submillimeter Array (ALMA) observation of CO($J$=3--2), revealing that in the region of bright iron-line emission, the molecular emission seems to be weak. This might suggest that the AGN X-ray emission affects the chemical composition in the form of AGN feedback.

astro-ph.GA↗

arXiv2025

Unraveling the structure of the stratified ultra-fast outflows in PDS 456 with XRISM

Multiple clumpy wind components ($v_{out}\sim0.2-0.3c$) in the luminous quasar PDS 456 have recently been resolved by XRISM in the Fe-K band for the first time. In this paper, we investigate the structure of ultra-fast outflows (UFOs) using coordinated observations from XRISM, XMM-Newton, and NuSTAR, along with the self-consistently calculated photoionization model \texttt{PION}. Our results reveal a stratified ionization structure, characterized by a relation between wind velocity and ionization parameter $v_{out}\proptoξ^{(0.14\pm0.04)}$. To evaluate the impact of the screening effect, we tested all possible order permutations of six \texttt{PION} components. We find that highly ionized UFOs ($\logξ>4.5$) are insensitive to their relative positions, whereas the soft X-ray UFO ($\logξ\sim3$ and $v_{out}\sim0.27c$) and the lowest-ionized hard X-ray UFO ($\logξ\sim4.1$ and $v_ {out}\sim0.23c$) are statistically favored -- based on the evidence from both the C-statistic and Bayesian analysis -- to occupy the middle and innermost layers, respectively. This suggests a possible trend where slower UFOs are launched from regions closer to the supermassive black hole (SMBH). The soft X-ray UFO is found to be thermally unstable, regardless of its relative position. However, its location remains unclear. Our sequence analysis and its similarity to hard X-ray UFOs suggest that they may be co-spatial, while variability constraints support its location within the broad-line region at sub-parsec scales. Simulations with the gate-valve opened XRISM show that high-resolution soft X-ray data can enhance the reliability of our results. Furthermore, simulations with the future X-ray mission NewAthena demonstrate its capability to resolve the absorber sequence and spatial distributions, enabling the determination of UFO structures and their roles in AGN feedback.

astro-ph.HE↗

arXiv2025

XL-Calibur measurements of polarised hard X-ray emission from the Crab

We report measurements of the linear polarisation degree (PD) and angle (PA) for hard X-ray emission from the Crab pulsar and wind nebula. Measurements were made with the XL-Calibur ($\sim$15-80 keV) balloon-borne Compton-scattering polarimeter in July 2024. The polarisation parameters are determined using a Bayesian analysis of Stokes parameters obtained from X-ray scattering angles. Well-constrained ($\sim$8.5$σ$) results are obtained for the polarisation of the $\sim$19-64 keV signal integrated over all pulsar phases: PD=(25.1$\pm$2.9)% and PA=(129.8$\pm$3.2)$^\circ$. In the off-pulse (nebula-dominated) phase range, the PD is constrained at $\sim$4.5$σ$ and is compatible with the phase-integrated result. The PA of the nebular hard X-ray emission aligns with that measured by IXPE in the 2-8 keV band for the toroidal inner region of the pulsar wind nebula, where the hard X-rays predominantly originate. For the main pulsar peak, PD=(32.8$^{+18.2}_{-28.5}$)% and PA=(156.0 $\pm$ 21.7)$^\circ$, while for the second peak (inter-pulse), PD=(0.0$^{+33.6}_{-0.0}$)% and PA=(154.5 $\pm$ 34.5)$^\circ$. A low level of polarisation in the pulsar peaks likely does not favour emission originating from the inner regions of the pulsar magnetosphere. Discriminating between Crab pulsar emission models will require deeper observations, e.g. with a satellite-borne hard X-ray polarimeter.

astro-ph.HE↗

arXiv2025

XL-Calibur Polarimetry of Cyg X-1 Further Constrains the Origin of its Hard-state X-ray Emission

The balloon-borne hard X-ray polarimetry mission XL-Calibur observed the Black Hole X-ray Binary (BHXRB) Cygnus X-1 (Cyg X-1) during its nearly six-day Long Duration Balloon (LDB) flight from Sweden to Canada in July 2024. The XL-Calibur observations allowed us to derive the most precise constraints to date of the Polarization Degree (PD) and Polarization Angle (PA) of the hard X-ray emission from a BHXRB. XL-Calibur observed Cyg X-1 in the hard state and measured a $\sim$19-64 keV PD of ($5.0^{+2.7}_{-3.0}$)% at a PA of $-28^{\circ}\pm 17^{\circ}$, with an 8.7% chance probability of detecting larger PDs than the one observed, given an unpolarized signal. The XL-Calibur results are thus comparable to the 2-8 keV PD and PA found by IXPE, with a similar agreement between the hard X-ray PA and the radio jet direction. We also discuss the implications of our polarization measurements in the context of models describing the origin of the broadband X-ray and $γ$-ray emission, to which XL-Calibur provides independent constraints on any proposed emission modeling.

astro-ph.HE↗