W. Iwakiri
A5054515903- Gamma-ray bursts and supernovae
- Astronomical Observations and Instrumentation
- Astrophysical Phenomena and Observations
- SAS software applications and methods
- Pulsars and Gravitational Waves Research
- Astrophysics and Cosmic Phenomena
- Solar and Space Plasma Dynamics
- Geophysics and Gravity Measurements
- Astronomy and Astrophysical Research
- High-pressure geophysics and materials
- Mechanics and Biomechanics Studies
- Particle Detector Development and Performance
- Neutrino Physics Research
- Particle Accelerators and Free-Electron Lasers
- Statistical and numerical algorithms
- Radio Astronomy Observations and Technology
- Stellar, planetary, and galactic studies
- Dark Matter and Cosmic Phenomena
- Superconducting Materials and Applications
- Nuclear Physics and Applications
- Astro and Planetary Science
- Atomic and Subatomic Physics Research
- Earthquake Detection and Analysis
- Particle accelerators and beam dynamics
- Astrophysics and Star Formation Studies
Chiba University
2022-2025
RIKEN
2009-2025
Pioneer (United States)
2025
Boston University
2024
University of Pisa
2024
Geophysical Laboratory
2024
Providence College
2024
Lawrence Berkeley National Laboratory
2024
Southern University and Agricultural and Mechanical College
2024
The University of Texas at Arlington
2024
A black hole x-ray binary (XRB) system forms when gas is stripped from a normal star and accretes onto hole, which heats the sufficiently to emit x-rays. We report polarimetric observation of XRB Cygnus X-1 using Imaging Polarimetry Explorer. The electric field position angle aligns with outflowing jet, indicating that jet launched inner emitting region. polarization degree (4.01+-0.20)% at 2 8 kiloelectronvolts, implying accretion disk viewed closer edge-on than orbit. observations reveal...
We report the discovery of unusually bright long-duration gamma-ray burst (GRB), GRB 221009A, as observed by Neil Gehrels Swift Observatory (Swift), Monitor All-sky X-ray Image (MAXI), and Neutron Star Interior Composition Explorer Mission (NICER). This energetic was located relatively nearby (z = 0.151), allowing for sustained observations afterglow. The large luminosity low Galactic latitude (b 4.3 degrees) make 221009A a powerful probe dust in Milky Way. Using echo tomography we map...
Abstract Most of the light from blazars, active galactic nuclei with jets magnetized plasma that point nearly along line sight, is produced by high-energy particles, up to around 1 TeV. Although are known be ultimately powered a supermassive black hole, how particles accelerated such high energies has been an unanswered question. The process must related magnetic field, which can probed observations polarization jets. Measurements radio optical polarization—the only range available until...
ABSTRACT We present an X-ray spectropolarimetric analysis of the bright Seyfert galaxy NGC 4151. The source has been observed with Imaging Polarimetry Explorer (IXPE) for 700 ks, complemented simultaneous XMM–Newton (50 ks) and NuSTAR (100 pointings. A polarization degree Π = 4.9 ± 1.1 per cent angle Ψ 86° 7° east north (68 confidence level) are measured in 2–8 keV energy range. shows that could be entirely due to reflection. Given low reflection flux IXPE band, this requires, however, a...
Abstract We report on an observational campaign the bright black hole (BH) X-ray binary Swift J1727.8–1613 centered around five observations by Imaging Polarimetry Explorer. These track for first time evolution of polarization a BH across hard to soft state transition. The 2–8 keV degree decreased from ∼4% ∼3% observations, but angle remained oriented in north–south direction throughout. Based with Australia Telescope Compact Array, we find that intrinsic 7.25 GHz radio aligns polarization....
Abstract Particle acceleration mechanisms in supermassive black hole jets, such as shock acceleration, magnetic reconnection, and turbulence, are expected to have observable signatures the multiwavelength polarization properties of blazars. The recent launch Imaging X-Ray Polarimetry Explorer (IXPE) enables us, for first time, use X-ray band (2–8 keV) probe jet synchrotron emission high-synchrotron-peaked BL Lac objects (HSPs). We report discovery linear (degree Π x = 15% ± 2% electric...
We report on the first detection of linearly polarized x-ray emission from an ultra-magnetized neutron star with Imaging X-ray Polarimetry Explorer (IXPE). The IXPE 35 observations anomalous pulsar 4U 0142+61 reveal a linear polarization degree $(12\pm 1)\%$ throughout 2--8 keV band. detect substantial variation energy: is $(14\pm at 2--4 and $(41\pm 7)\%$ 5.5--8 keV, while it drops below instrumental sensitivity around 4--5 where angle swings by $\sim 90^\circ$. give us completely new...
Abstract We report the first detection of X-ray polarization bright transient Swift J1727.8−1613 with Imaging Polarimetry Explorer. The observation was performed at beginning 2023 discovery outburst, when source resided in hard state. find a time- and energy-averaged degree 4.1% ± 0.2% angle 2.°2 1.°3 (errors 68% confidence level; this translates to ∼20 σ significance detection). This finding suggests that hot corona emitting bulk detected X-rays is elongated, rather than spherical....
Abstract We present the IXPE observation of GRB 221009A, which includes upper limits on linear polarization degree both prompt and afterglow emission in soft X-ray energy band. 221009A is an exceptionally bright gamma-ray burst (GRB) that reached Earth 2022 October 9 after traveling through dust Milky Way. The Imaging Polarimetry Explorer (IXPE) pointed at 11 to observe, for first time, 2–8 keV a afterglow. set limit 13.8% 99% confidence level. This result provides constraints jet opening...
Abstract The lower-energy peak of the spectral energy distribution blazars has commonly been ascribed to synchrotron radiation from relativistic particles in jets. Despite consensus regarding jet emission processes, particle acceleration mechanism is still debated. Here, we present first X-ray polarization observations PG 1553+113, a high-synchrotron-peak blazar observed by Imaging Polarimetry Explorer (IXPE). We detect an degree (10 ± 2)% along electric-vector position angle ψ X = 86° 8°....
ABSTRACT We present an X-ray spectro-polarimetric analysis of the bright Seyfert galaxy IC 4329A. The Imaging Polarimetry Explorer (IXPE) observed source for ∼500 ks, supported by XMM–Newton (∼60 ks) and NuSTAR (∼80 exposures. detect polarization in 2–8 keV band with 2.97σ confidence. report a degree 3.3 ± 1.1 per cent angle 78° 10° (errors are 1σ confidence). is consistent being aligned radio jet, albeit partially due to large uncertainties on position angle. jointly fit spectra from three...
After about 16 years since its first outburst, the transient neutron star low-mass X-ray binary XTE J1701$-$462 turned on again in September 2022, allowing for study of polarimetric characteristics by a dedicated observing program with Imaging Polarimeter Explorer (IXPE). Polarimetric studies have been expected to improve our understanding accreting weakly magnetized stars, particular, physics and geometry hot inner regions close compact object. The IXPE data two triggered observations were...
Abstract The launch of the Imaging X-ray Polarimetry Explorer (IXPE) on 2021 December 9 has opened a new window in astronomy. We report here results first IXPE observation weakly magnetized neutron star, GS 1826−238, performed 2022 March 29–31 when source was high soft state. An upper limit (99.73% confidence level) 1.3% for linear polarization degree is obtained over 2–8 keV energy range. Coordinated INTEGRAL and NICER observations were carried out simultaneously with IXPE. spectral...
Abstract We report the first >99% confidence detection of X-ray polarization in BL Lacertae. During a recent X-ray/ γ -ray outburst, 287 ks observation (2022 November 27–30) was taken using Imaging Polarimetry Explorer (IXPE), together with contemporaneous multiwavelength observations from Neil Gehrels Swift observatory and XMM-Newton soft X-rays (0.3–10 keV), NuSTAR hard (3–70 optical Calar Alto Perkins Telescope observatories. Our data suggest that IXPE energy band is at crossover...
ABSTRACT We report on the second observation of radio-quiet active galactic nucleus MCG-05-23-16 performed with Imaging X-ray Polarimetry Explorer (IXPE). The started 2022 November 6 for a net observing time 640 ks, and was partly simultaneous NuSTAR (86 ks). After combining these data those obtained in first IXPE pointing May (simultaneous XMM–Newton NuSTAR) we find 2–8 keV polarization degree Π = 1.6 ± 0.7 (at 68 per cent confidence level), which corresponds to an upper limit 3.2 99...
ABSTRACT We report on an X-ray polarimetric observation of the high-mass binary LMC X-1 in high/soft state, obtained by Imaging Polarimetry Explorer (IXPE) 2022 October. The measured polarization is below minimum detectable 1.1 per cent (at 99 confidence level). Simultaneously, source was observed with Neutron Star Interior Composition (NICER), Nuclear Spectroscopic Telescope Array (NuSTAR), and Spectrum-Rontgen-Gamma (SRG)/Astronomical Roentgen – Concentrator (ART-XC) instruments, which...
Abstract A large energy-dependent X-ray polarization degree is detected by the Imaging Polarimetry Explorer (IXPE) in high-soft emission state of black hole binary 4U 1630–47. The highly significant detection (at ≈50 σ confidence level) an unexpectedly high polarization, rising from ∼6% at 2 keV to ∼10% 8 keV, cannot be easily reconciled with standard models thin accretion disks. In this work, we compare predictions different theoretical IXPE data and conclude that observed properties are...
Abstract The Imaging X-ray Polarimetry Explorer measured with high significance the polarization of brightest Z-source, Sco X-1, resulting in nominal 2–8 keV energy band a degree 1.0% ± 0.2% and angle 8° 6° at 90% confidence level. This observation was strictly simultaneous observations performed by NICER, NuSTAR, Insight-HXMT, which allowed for precise characterization its broadband spectrum from soft to hard X-rays. source has been observed mainly state, short periods flaring. We also...
We present the results of first X-ray polarimetric observation low-mass binary 4U 1957+115, performed with Imaging Polarimetry Explorer in May 2023. The system has been a high-soft spectral state since its discovery and is thought to host black hole. ∼571 ks reveals linear polarisation degree 1.9%±0.6% angle −41.°8±7.°9 2–8 keV energy range. Spectral modelling consistent dominant contribution coming from standard accretion disc, while data suggest significant role returning radiation:...
Abstract Cir X-1 is a neutron star X-ray binary characterized by strong variations in flux during its eccentric ∼16.6 day orbit. There are also the spectral state, and it has historically shown both atoll Z state properties. We observed source with Imaging Polarimetry Explorer two orbital segments, 6 days apart, for total of 263 ks. find an polarization degree these segments 1.6% ± 0.3% 1.4% at angles 37° 5° −12° 7°, respectively. Thus, we rotation angle 49° 8° along Because accretion flow,...
We report on the first observation of a radio-quiet Active Galactic Nucleus (AGN) using polarized X-rays: Seyfert 1.9 galaxy MCG-05-23-16. This source was pointed with Imaging X-ray Polarimetry Explorer (IXPE) starting May 14, 2022 for net observing time 486 ks, simultaneously XMM-Newton (58 ks) and NuSTAR (83 ks). A polarization degree smaller than $\Pi<4.7\%$ (at 99% c.l.) is derived in 2-8 keV energy range, where emission dominated by primary component ascribed to hot corona. The...