Ajay Ratheesh
A5080395605- Astrophysical Phenomena and Observations
- Astrophysics and Cosmic Phenomena
- Pulsars and Gravitational Waves Research
- Mechanics and Biomechanics Studies
- Gamma-ray bursts and supernovae
- Particle Detector Development and Performance
- High-pressure geophysics and materials
- Particle Accelerators and Free-Electron Lasers
- Radio Astronomy Observations and Technology
- Astronomical Observations and Instrumentation
- Solar and Space Plasma Dynamics
- Nuclear Physics and Applications
- Advanced X-ray and CT Imaging
- Neutrino Physics Research
- Calibration and Measurement Techniques
- Geophysics and Gravity Measurements
- Superconducting Materials and Applications
- Astro and Planetary Science
- Particle accelerators and beam dynamics
- Gyrotron and Vacuum Electronics Research
- Galaxies: Formation, Evolution, Phenomena
- Medical Imaging Techniques and Applications
- X-ray Spectroscopy and Fluorescence Analysis
- CCD and CMOS Imaging Sensors
- Scientific Measurement and Uncertainty Evaluation
Institute for Space Astrophysics and Planetology
2019-2024
National Institute for Astrophysics
2019-2023
Istituto Nazionale di Fisica Nucleare, Sezione di Pisa
2023
University of Rome Tor Vergata
2019-2022
Sapienza University of Rome
2019-2022
Tata Institute of Fundamental Research
2019-2021
Istituto Nazionale di Fisica Nucleare
2021
Marshall Space Flight Center
2019-2021
Osservatorio Astrofisico di Torino
2019
While X-ray Spectroscopy, Timing and Imaging have improved verymuch since 1962, when the first astronomical non-solar source was discovered, especially with launch of Newton/X-ray Multi-Mirror Mission, Rossi/X-ray Explorer Chandra/Advanced Astrophysics Facility, progress polarimetry has been meager. This is in part due to lack sensitive polarization detectors, fate approved missions because celestial sources appeared less polarized than expected. Only one positive measurement available until...
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...
Abstract Imaging X-ray Polarimetry Explorer (IXPE) is a Small mission by NASA and Agenzia Spaziale Italiana, launched on 2021 December 9, dedicated to investigating polarimetry allowing angular-, time-, energy-resolved observations in the 2–8 keV energy band. IXPE science observation phase since 2022 January; it comprised of three identical telescopes with grazing-incidence mirrors, each one having focal plane gas pixel detector. In this paper, we present possible guideline obtain an optimal...
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 Black hole X-ray binaries exhibit different spectral and timing properties in accretion states. The outburst of a recently discovered extraordinarily bright source, Swift J1727.8–1613, has enabled the first investigation how polarization source evolve with state. 2–8 keV degree was previously measured by Imaging Polarimetry Explorer (IXPE) to be ≈4% hard intermediate Here we present new IXPE results taken soft state, flux dominated thermal disk emission. We find that dropped...
Due to be launched in late 2021, the Imaging X-Ray Polarimetry Explorer (IXPE) is a NASA Small mission designed perform polarization measurements 2-8 keV band, complemented with imaging, spectroscopy and timing capabilities. At heart of focal plane set three polarization-sensitive Gas Pixel Detectors (GPD), each based on custom ASIC acting as charge-collecting anode. In this paper we shall review design, manufacturing, test IXPE focal-plane detectors, particular emphasis connection between...
IXPE is a Small Explorer mission that was launched at the end of 2021 to measure polarization X-ray emission from tens astronomical sources. Its focal plane detectors are based on Gas Pixel Detector, which measures by imaging photoelectron tracks in gas mixture and reconstructing their initial directions. The quality single track, then capability correctly determining original direction photoelectron, depends many factors, e.g., whether emitted low or high inclination with respect collection...
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 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 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...
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...
ABSTRACT We report spectro-polarimetric results of an observational campaign the bright neutron star low-mass X-ray binary Cyg X-2 simultaneously observed by IXPE, NICER, and INTEGRAL. Consistently with previous results, broad-band spectrum is characterized a lower-energy component, attributed to accretion disc kTin ≈ 1 keV, plus unsaturated Comptonization in thermal plasma temperature kTe = 3 keV optical depth τ 4, assuming slab geometry. measure polarization degree 2–8 band P 1.8 ± 0.3 per...