A5049624884- Astrophysical Phenomena and Observations
- Pulsars and Gravitational Waves Research
- Mechanics and Biomechanics Studies
- Gamma-ray bursts and supernovae
- Astrophysics and Cosmic Phenomena
- High-pressure geophysics and materials
- Scientific Measurement and Uncertainty Evaluation
- Particle Accelerators and Free-Electron Lasers
- Geophysics and Sensor Technology
- Solar and Space Plasma Dynamics
- Astronomy and Astrophysical Research
- Geophysics and Gravity Measurements
- Magnetic confinement fusion research
- Astrophysics and Star Formation Studies
- Planetary Science and Exploration
- Superconducting Materials and Applications
- Astronomical Observations and Instrumentation
- Stellar, planetary, and galactic studies
- Astro and Planetary Science
New York University
2023
University of Southampton
2019-2023
University of Groningen
2019-2023
New York University Abu Dhabi
2022-2023
Astronomy and Space
2021
Abstract We present the first X-ray polarization measurements of GX 339–4. IXPE observed this source twice during its 2023–2024 outburst, once in soft-intermediate state and again a soft state. The observation taken intermediate shows significant (4 σ ) degree P X = 1.3% ± 0.3% angle θ −74° 7° only 3–8 keV band. FORS2 at Very Large Telescope simultaneously, detecting optical B , V R I bands (between ∼0.1% ∼0.7%), all roughly aligned with polarization. also detect discrete jet knot from radio...
We present a comprehensive study of the flaring mode transitional millisecond pulsar (tMSP) PSR J1023+0038 during its X-ray sub-luminous state, using strictly simultaneous X-ray, UV, optical, and radio observations. The flares exhibit UV optical counterparts coincide with brightest flare observed in past decade, reaching 1.2,mJy at 6,GHz lasting ∼1,hour. During flare, polarisation drops from ≃1.4% to ≃0.5%, indicating emergence an unpolarised component. propose that thickening disc, which...
We present a detailed spectral and temporal analysis of the black-hole candidate MAXI~J1535$-$571 using NICER observations in September October 2017. focus specifically on hard-intermediate state when source shows type-C quasi-periodic oscillations (QPOs). fitted time-averaged spectrum rms phase-lag spectra QPO with one-component time-dependent Comptonization model. found that corona contracts from $\sim 10^4$ to 3 \times 10^3$ km as frequency increases 1.8$ Hz 9.0$ Hz. The fits suggest...
We present the first X-ray spectropolarimetric results for Cygnus X-1 in its soft state from a campaign of five IXPE observations conducted during 2023 May-June. Companion multiwavelength data are likewise shown. The 2-8 keV X-rays exhibit net polarization degree PD=1.99%+/-0.13% (68% confidence). signal is found to increase with energy across IXPE's bandpass. polarized an energy-independent angle PA=-25.7+/-1.8 deg. East North This consistent being aligned Cyg X-1's AU-scale compact radio...
We studied the outburst evolution and timing properties of recently discovered X-ray transient MAXI J1348-630 as observed with NICER. produced fundamental diagrams commonly used to trace spectral evolution, power density spectra study fast variability. The main is similar that in black hole transients. source evolved from hard state, through hard- soft-intermediate states, into soft state rise, back reverse during decay. At end outburst, underwent two reflares peak fluxes ~1 ~2 orders...
ABSTRACT MAXI J1535−571 is a black-hole X-ray binary that in 2017 exhibited very bright outburst which reached peak flux of up to 5 Crab the 2–20 keV band. Given high flux, several space observatories obtained unprecedented signal-to-noise data key parts outburst. In our previous paper, we studied corona hard-intermediate state (HIMS) with Insight-HXMT. this focus on study soft-intermediate (SIMS) through spectral-timing analysis 26 NICER detections type-B quasi-periodic oscillations (QPOs)....
Black hole low-mass X-ray binaries (BH LMXBs) evolve in a similar way during outburst. Based on the spectrum and variability, this evolution can be divided into three canonical states: low/hard, intermediate high/soft state. BH LMXBs from low/hard to state through some outbursts (here called "full outbursts"). However, other cases, undergo which source never reaches state, here "Failed-Transition outburst" (FT outbursts). From sample of 56 undergoing 128 outbursts, we find that $\sim$36%...
ABSTRACT The black hole candidate and X-ray binary MAXI J1535−571 was discovered in 2017 September. During the decay of its discovery outburst, before returning to quiescence, source underwent at least four reflaring events, with peak luminosities ∼1035–36 erg s−1 (d/4.1 kpc)2. To investigate nature these flares, we analysed a sample NICER (Neutron star Interior Composition Explorer) observations taken almost daily cadence. In this work, present detailed spectral timing analysis evolution...
We present a systematic spectral-timing analysis of fast appearance/disappearance type-B quasi-periodic oscillation (QPO), observed in four NICER observations MAXI J1348-630. By comparing the spectra period with and without QPO, we found that main difference appears at energy bands above ~2 keV, suggesting QPO emission is dominated by hard Comptonised component. During transition, change relative contribution disk was observed. The flux decreased while increased from non-QPO to QPO. However,...
We study the properties of type-C quasi-periodic oscillation (type-C QPO) MAXI J1348-630 during its 2019 outburst and reflare with NICER. This is first time that evolution QPOs studied an reflare. found QPO are similar to those observed in other black-hole systems outburst. suggests physical processes responsible for same a also FWHM high-frequency broadband component changes significantly energy. energy-dependent fractional rms amplitude phase lags from 0.5 keV 12 keV. increases up 2-3 then...
Transitional millisecond pulsars are an emerging class of sources that link low-mass X-ray binaries to radio in binary systems. These alternate between a pulsar state and active low-luminosity disc state. During the state, these exhibit two distinct emission modes (high low) unpredictably, abruptly, incessantly. optical pulsations observed only during high mode. The root cause this puzzling behaviour remains elusive. This paper presents results most extensive multi-wavelength campaign ever...
In high-mass X-ray binaries (HMXBs), the compact object accretes strong stellar wind of an O-B supergiant companion star. flux variations alter wind's ionization state and optical line profiles, which are important in determination orbital parameters system. We analyzed state-dependent variability profiles by separating components coming from star’s atmosphere accreted stream matter located between star accretion disk (i.e. focused wind). then determined radial velocities intensities...
Abstract We use the rms and lag spectra of type-C quasiperiodic oscillation (QPO) to study properties Comptonization region (aka corona) during low/hard hard-intermediate states main outburst reflare MAXI J1348−630. simultaneously fit time-averaged energy spectrum source fractional phase-lag QPO with time-dependent model VKOMPTH. The data can be explained by two physically connected coronae interacting accretion disk via a feedback loop X-ray photons. best-fitting consists corona ∼10 3 km...
We present a comprehensive study of the flaring mode transitional millisecond pulsar (tMSP) PSR J1023+0038 during its X-ray sub-luminous state, using strictly simultaneous X-ray, UV, optical, and radio observations. The flares exhibit UV optical counterparts coincide with brightest flare observed in past decade, reaching 1.2 mJy at 6 GHz lasting ~1 hour. During flare, polarization drops from ~1.4% to ~0.5%, indicating emergence an unpolarized component. propose that thickening disc, which...
In high-mass X-ray binaries (HMXBs), the compact object accretes strong stellar wind of an O-B supergiant companion star. flux variations alter wind's ionization state and optical line profiles, which are key in determination orbital parameters system. Using method Fourier Disentangling, we decomposed spectral contributions from atmosphere close to photosphere accreted stream matter (i.e. focused wind). High-resolution spectroscopy Cyg X-1 its hard soft-intermediate states revealed...
We present a detailed X-ray spectral and variability study of the full 2018 outburst MAXI J1727-203 using NICER observations. The lasted approximately four months. Spectral modelling in 0.3-10 keV band shows presence both soft thermal hard Comptonised component. analysis these components that evolved through soft, intermediate states during outburst. find (disc) component was detected throughout almost entire outburst, with temperatures ranging from ~0.4 keV, at moment maximum luminosity, to...
We present a detailed study of the evolution Galactic black hole transient GRS 1716-249 during its 2016-2017 outburst at optical (Las Cumbres Observatory), mid-infrared (Very Large Telescope), near-infrared (Rapid Eye Mount telescope), and ultraviolet (the Neil Gehrels Swift Observatory Ultraviolet/Optical Telescope) wavelengths, along with archival radio X-ray data. show that optical/near-infrared UV emission source mainly originates from multi-temperature accretion disk, while are...
We present long-term (2012-2022) optical monitoring of the candidate black hole X-ray binary Swift J1910.2-0546 with Faulkes Telescopes and Las Cumbres Observatory (LCO) network. Following its initial bright 2012 outburst, we find that source displayed a series at least 7 quasi-periodic, high amplitude (~3 mags) reflares in 2013, recurrence time increasing from ~42 days to ~49 days. In 2014, experienced mini-outburst two peaks optical. also study recent 2022 outburst wavelengths, perform...
ABSTRACT We present a novel method for measuring the lags of (weak) variability components in neutron-star and black-hole low-mass X-ray binaries (LMXBs). For this we assume that power cross-spectra these sources consists number are coherent different energy bands, but incoherent with one another. The technique is based on fitting simultaneously spectrum (PS) Real Imaginary parts cross-spectrum (CS) combination Lorentzian functions. show that, because PS LMXBs insensitive to signals large...
We report on a long-term optical monitoring of the neutron star X-ray binary Centaurus X-4 performed during last 13.5 years. This source has been in quiescence since its outburst 1979. Our reveals overall evolution accretion disc; we detect short-duration flares, likely originating also disc, superimposed with small-amplitude (< 0.1 mag) ellipsoidal modulation from companion due to geometrical effects. A (~2300 days) downward trend, followed by shorter (~1000 upward one, is observed disc...
We present the first X-ray polarization measurements of GX 339-4. IXPE observed this source twice during its 2023-2024 outburst, once in soft-intermediate state and again a soft state. The observation taken intermediate shows significant ($4\sigma$) degree P = $1.3\% \pm 0.3\%$ angle $\theta$ -74\degree $\pm$ 7\degree only 3 - 8 keV band. FORS2 at VLT simultaneously detecting optical B, V, R, I bands (between $0.1%$ $0.7\%$), all roughly aligned with polarization. also detect discrete jet...
Abstract Low Mass X-ray binaries (LMXBs) are binary systems where one of the components is either a black hole or neutron star and other less massive star. It challenging to unambiguously determine whether LMXB hosts In last few decades, multiple observational works have tried, with different levels success, address this problem. paper, we explore use machine learning tackle challenge. We train random forest classifier identify type compact object using energy spectrum in range 5-25 keV...
ABSTRACT The evolution of accreting X-ray binary systems is closely coupled to the properties their donor stars. Consequently, we can constrain evolutionary track a system by establishing nature its donor. Here, present far-ultraviolet (far-UV) spectroscopy transient neutron-star low-mass J1858 in different accretion states (low-hard, high-hard, and soft). All these spectra exhibit anomalous N v, C iv, Si He ii lines, suggesting that star has undergone CNO processing. We also determine...
ABSTRACT In X-ray observations of hard state black hole binaries (BHXRBs), rapid variations in accretion disc and coronal power-law emission are correlated show Fourier-frequency-dependent time lags. On short ($\sim$0.1 s) time-scales, these lags thought to be due reverberation therefore may depend strongly on the geometry corona. Low-frequency quasi-periodic oscillations (QPOs) flux that have been suggested arise because geometric changes corona, possibly general relativistic Lense–Thirring...
Transitional millisecond pulsars are an emerging class of sources that link low-mass X-ray binaries to radio in binary systems. These alternate between a pulsar state and active low-luminosity disc state. During the state, these exhibit two distinct emission modes (high low) unpredictably, abruptly, incessantly. optical pulsations observed only during high mode. The root cause this puzzling behaviour remains elusive. This paper presents results most extensive multi-wavelength campaign ever...