A5009220087- Astrophysical Phenomena and Observations
- Pulsars and Gravitational Waves Research
- Gamma-ray bursts and supernovae
- Astrophysics and Cosmic Phenomena
- Mechanics and Biomechanics Studies
- Astronomical Observations and Instrumentation
- High-pressure geophysics and materials
- Astronomy and Astrophysical Research
- Stellar, planetary, and galactic studies
- Geophysics and Gravity Measurements
- Astro and Planetary Science
- Geophysics and Sensor Technology
- Earthquake Detection and Analysis
- Adaptive optics and wavefront sensing
- Radio Astronomy Observations and Technology
- Galaxies: Formation, Evolution, Phenomena
- Particle Accelerators and Free-Electron Lasers
- Superconducting Materials and Applications
- Particle Detector Development and Performance
- Nuclear physics research studies
- Solar and Space Plasma Dynamics
- Atomic and Molecular Physics
- Relativity and Gravitational Theory
- Advanced X-ray Imaging Techniques
- Astrophysics and Star Formation Studies
Brera Astronomical Observatory
2009-2025
National Institute for Astrophysics
2011-2025
University of Oxford
2015-2024
VTT Technical Research Centre of Finland
2023
John Wiley & Sons (United Kingdom)
2023
Macquarie University
2023
John Brown University
2023
Newcastle University
2022
European Space Astronomy Centre
2012-2019
University of Turku
2017
We present a systematic analysis of the fast time variability properties transient black hole binary GRO J1655-40, based on complete set RossiXTE observations. demonstrate that frequencies quasi-periodic oscillations and broad band noise components their variations match accurately strong field general relativistic particle motion in close vicinity innermost stable circular orbit, as predicted by precession model. obtain high precision measurements mass (M = (5.31 +/- 0.07) M solar masses,...
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 analyzed RXTE/PCA and HEXTE data of the transient black hole binary GX 339-4, col- lected over a time span eight years. studied properties behavior low frequency quasi periodic oscillations (QPOs) as function integrated broad-band variability spectral parameters during four outbursts (2002, 2004, 2007, 2010). Most QPOs could be classified following ABC classification that has been proposed before. Our results show can extended to include dependencies three QPO types have indeed...
We present a systematic study of the orbital inclination effects on black-hole transients fast time-variability properties. have considered all binaries that been densely monitored by Rossi XTE satellite. find amplitude low-frequency quasi periodic oscillations (QPOs) depends inclination. Type-C QPOs are stronger for nearly edge-on systems (high inclination), while type-B when accretion disk is closer to face-on (low inclination). Our results also suggest noise associated with type-C...
We report on X-ray observations of the black-hole candidate GX 339-4 during its 2006/2007 outburst. The hardness-intensity diagram all RXTE/PCA data combined shows a q-shaped track similar to that observed in previous outbursts. evolution through HID suggests early phase outburst source underwent sequence state transitions, from hard soft state, which is supported by our timing analysis. Broadband (4-200 keV) spectra, fitted with an exponentially cutoff powerlaw, show spectral component...
We have systematically studied a large sample of the neutron star low mass X-ray binaries (LMXBs) monitored by Rossi Timing Explorer (50 sources; 10000+ observations). find that hysteresis patterns between Compton dominated and thermal states, typically observed in black hole LMXBs, are also common systems. These patterns, which intermediate found when looking at evolution both colour fast variability ten systems accreting below ~ 30 % Eddington Luminosity. show does not require changes...
XSSJ1227.0-4859 is a peculiar, hard X-ray source recently positionally associated to the Fermi-LAT 1FGLJ1227.9-4852/2FGLJ1227.7-4853. Multi-wavelength observations have added information on this source, indicating low-luminosity low-mass binary (LMXB), but its nature still unclear. To progress in our understanding, we present new data from monitoring campaign performed 2011 with XMM-Newton, RXTE, and Swift satellites combine them gamma-ray Fermi AGILE satellites. We complement study...
Abstract Fast time variability is the most prominent characteristic of accreting systems and presence quasi periodic oscillations (QPOs) a constant in all systems, from cataclysmic variables to AGNs, passing through black hole neutron star X‐ray binaries enigmatic ultra‐luminous sources. In this paper, I will briefly review current knowledge QPOs binaries, mainly focussing on their observed properties, but also mentioning important models that have been proposed explain origin over last...
Quasi-periodic oscillations (QPOs) with frequencies from $\sim0.05$-$30$ Hz are a common feature in the X-ray emission of accreting black hole binaries. As QPOs originate innermost accretion flow, they provide opportunity to probe behaviour matter extreme gravity. In this paper, we present systematic analysis inclination dependence phase lags associated both Type-B and Type-C sample 15 Galactic We find that lag at QPO frequency strongly depends on inclination, evolution sign. Although soft...
ABSTRACT Binary supermassive black hole (SMBH) systems result from galaxy mergers, and will eventually coalesce due to gravitational wave (GW) emission if the binary separation can be reduced ≲0.1 pc by other mechanisms. Here, we explore a self-lensing SMBH model for sharp (duration ∼1 h), quasi-regular X-ray flares – dubbed quasi-periodic eruptions recently observed two low-mass active galactic nuclei: GSN 069 RX J1301.9+2747. In our model, is ∼edge-on, such that each gravitationally lenses...
Abstract We present deep X-ray and radio observations of the fast blue optical transient (FBOT) AT 2020xnd/ZTF 20acigmel at z = 0.2433 from 13 days to 269 after explosion. 2020xnd belongs category optically luminous FBOTs with similarities archetypal event 2018cow. shows emission reaching L ν ≈ 8 × 10 29 erg s −1 Hz 20 GHz 75 post-explosion, accompanied by rapidly fading soft peaking X 6 42 . Interpreting in context synchrotron radiation explosion’s shock interaction environment, we find...
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 rms-intensity diagram for black hole transients. Using observations taken with Rossi X-ray timing explorer we study relation between root mean square (rms) amplitude of variability and net count-rate during 2002, 2004 2007 outbursts binary GX 339-4. find that rms-flux previously observed hard state in binaries does not hold other states, when different relations apply. These can be used as a good tracer accretion regimes. identify hard, soft intermediate states diagram....
We studied the low-frequency quasi-periodic oscillations (LFQPOs) in black hole GRO J1655−40 during 2005 outburst, using data from Rossi X-ray Timing Explorer. All LFQPOs could be identified as either type B or C previously proposed classification schemes. In soft state of outburst type-C reached frequencies that are among highest ever seen for holes. At peak ultraluminous state, power spectrum showed two simultaneous, non-harmonically related peaks which we a type-B and QPO. The...
We report on the first 180 days of Rossi X-Ray Timing Explorer observations outburst black hole candidate IGR J17091–3624. This source exhibits a broad variety complex light curve patterns including periods strong flares alternating with quiet intervals. Similar in X-ray curves have been seen (up to now) unique system GRS 1915+105. In context variability classes defined by Belloni et al. for 1915+105, we find that J17091–3624 shows ν, ρ, α, λ, β, and μ as well which resemble χ class, all...
We present a systematic analysis of the complete set observations black hole (BH) binary XTE J1550-564 obtained by Rossi X-ray Timing Explorer. study fast time variability properties source and determine spin through relativistic precession model. Similarly to what is observed in BH GRO J1655-40, frequencies QPOs broad band noise components match general particle motion close compact object predicted The combination two simultaneously quasi-periodic oscillation (QPO) together with dynamical...
We present Neutron Star Interior Composition Explorer X-ray and Arcminute Microkelvin Imager Large Array radio observations of a rapid hard-to-soft state transition in the black hole transient MAXI J1820+070. During from hard to soft switch between two particular types quasiperiodic oscillations (QPOs) was seen power density spectra, type-C type-B, along with drop strength broadband variability brief flare 7-12 keV band. Soon after this (~1.5-2.5 hr) strong observed that corresponded launch...
ABSTRACT We present the radio and X-ray monitoring campaign of 2019/2020 outburst MAXI J1348–630, a new black hole binary (BH XRB) discovered in 2019 January. observed J1348–630 for ∼14 months band with MeerKAT Australia Telescope Compact Array, X-rays Swift/XRT. Throughout outburst, we detected tracked evolution compact transient jets. Following main system underwent at least four hard-state-only re-flares, during which jets were again detected. For major rise, quenching reactivation jets,...
Quasi-periodic oscillations (QPOs) are often present in the X-ray flux from accreting stellar-mass black holes (BHs). If they due to relativistic (Lense-Thirring) precession of an inner accretion flow which is misaligned with disc, iron emission line caused by irradiation disc will rock systematically between red and blue shifted during each QPO cycle. Here we conduct phase-resolved spectroscopy a $\sim2.2$ Hz type-C BH binary GRS 1915+105, observed simultaneously NICER NuSTAR. We apply...
ABSTRACT The X-ray light curves of accreting black holes and neutron stars in binary systems show various types quasi-periodic oscillations (QPOs), the origin which is still debated. relativistic precession model identifies QPO frequencies with fundamental time-scales from General Relativity, has been proposed as a possible explanation certain such oscillations. Under specific conditions (i.e. detection particular QPOs triplet) can be used to obtain self-consistent measurements mass spin...
Abstract This paper reports the first detection of polarization in X-rays for atoll-source 4U 1820−303, obtained with Imaging X-ray Polarimetry Explorer (IXPE) at 99.999% confidence level (CL). Simultaneous polarimetric measurements were also performed radio Australia Telescope Compact Array. The IXPE observations 1820−303 coordinated Swift Telescope, Neutron Star Interior Composition Explorer, and Nuclear Spectroscopic Array aiming to obtain an accurate spectral model covering a broad...