Article
Astronomy & Astrophysics
Ashutosh Tripathi, Biao Zhou, Askar B. Abdikamalov, Dimitry Ayzenberg, Cosimo Bambi
Summary: The Einstein-Maxwell dilaton-axion gravity theory is a string-inspired model with potential as an alternative to General Relativity. Recent studies have explored its astrophysical implications in the spectra of accreting black holes and found a constraint verified by analyzing a NuSTAR spectrum of the black hole binary EXO 1846-031. The analysis revealed a constraint on the black hole dilaton charge that is an order of magnitude more stringent than previous constraints.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Astronomy & Astrophysics
Roberto Soria, Ruican Ma, Lian Tao, Shuang-Nan Zhang
Summary: By revisiting the published results of X-ray and optical studies on the black hole candidate MAXI J0637-430, we have improved the understanding of its system parameters. This black hole is the farthest known from the Galactic Center and has the shortest period among all Galactic black hole X-ray binaries.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Article
Astronomy & Astrophysics
Hanna Sai, Xiaofeng Wang, Jianfeng Wu, Jie Lin, Hua Feng, Tianmeng Zhang, Wenxiong Li, Jujia Zhang, Jun Mo, Tianrui Sun, Shuhrat A. Ehgamberdiev, Davron Mirzaqulov, Liming Rui, Weili Lin, Xulin Zhao, Han Lin, Jicheng Zhang, Xinghan Zhang, Yong Zhao, Xue Li, Danfeng Xiang, Lingzhi Wang, Chengyuan Wu
Summary: MAXI J1820+070 is a low-mass black hole X-ray binary system with high luminosity in both optical and X-ray bands during outburst periods. Optical emission precedes X-ray emission by 20.80 +/- 2.85 days during the rebrightening process. The optical flux is influenced by the X-ray irradiation model and additional energy sources.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2021)
Article
Astronomy & Astrophysics
Shafqat Riaz, Swarnim Shashank, Rittick Roy, Askar B. Abdikamalov, Dimitry Ayzenberg, Cosimo Bambi, Zuobin Zhang, Menglei Zhou
Summary: Despite significant efforts in the past decades, we still lack a robust theoretical framework to solve the problem of spacetime singularities. Recent years have seen an increasing interest in the study of phenomenological scenarios to describe singularity-free black holes, gravitational collapses, and cosmological models. In this study, the researchers consider a recent proposal for a rotating regular black hole and measure its regularization parameter from available black hole data.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2022)
Article
Astronomy & Astrophysics
R. Taverna, L. Marra, S. Bianchi, M. Dovciak, R. Goosmann, F. Marin, G. Matt, W. Zhang
Summary: Studying the radiation emitted from black hole accretion discs is crucial in understanding the physical properties of black holes, particularly their spin. In addition to spectral analysis, polarimetry is becoming increasingly important and can provide estimates of black hole spin. Absorption effects have a significant impact on the polarization properties of the emitted radiation.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2021)
Article
Astronomy & Astrophysics
Romana Mikusincova, Michal Dovciak, Michal Bursa, Niccolo Di Lalla, Giorgio Matt, Jiri Svoboda, Roberto Taverna, Wenda Zhang
Summary: Simulated observations using X-ray polarimetry were conducted on an X-ray binary system, revealing the potential of this technique to accurately measure black hole spin and inclination. The study highlights the usefulness of X-ray polarimetry in constraining black hole spins.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2023)
Article
Astronomy & Astrophysics
P. Reig, N. D. Kylafis
Summary: The study suggests that in black hole binaries, the extended jet is an excellent candidate source of hard photons, with some soft photons being reflected back to the accretion disk via inverse Compton scattering, while most of the Comptonized, back-scattered photons escape close to the black hole.
ASTRONOMY & ASTROPHYSICS
(2021)
Article
Astronomy & Astrophysics
Giuseppe Lingetti, Enrico Cannizzaro, Paolo Pani
Summary: This article investigates the superradiant instability in scalar-tensor theories of gravitation, discussing its effects and constraints on the theories.
Article
Astronomy & Astrophysics
Arghajit Jana
Summary: By collecting spectral data of black hole X-ray binaries (BIIXBs) across different spectral states, the study explores the spectral properties and correlations among different spectral parameters. Interesting correlations and uncertain phenomena are observed in different spectral states.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Article
Astronomy & Astrophysics
Magnus Axelsson, Alexandra Veledina
Summary: The geometry of the inner accretion flow in the hard and hard-intermediate states of X-ray binaries is studied using observations of the black hole X-ray binary MAXI J1820+070 during its 2018 outburst. The study focuses on the evolution of timing properties, particularly the variability frequencies of the iron K alpha line. Results show significant changes in the reflector distance and iron line profile during the hard-to-soft transition, supporting a truncated disc/inner flow geometry.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2021)
Article
Astronomy & Astrophysics
Pengcheng Yang, Guobao Zhang, David M. Russell, Joseph D. Gelfand, Mariano Mendez, Jiancheng Wang, Ming Lyu
Summary: Studying the correlation between UV/optical and X-ray emissions in low-mass X-ray binary systems can provide valuable insights into the accretion process. In this study, the authors analyzed the data from the BH-LMXB Swift J1753.5-0127 during its 12-year outburst and found a strong correlation between the UV/optical and X-ray emissions during the hard states of the outburst.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Article
Astronomy & Astrophysics
Alireza Allahyari, Lijing Shao
Summary: The study tests the no-hair theorem using quasi-periodic oscillations in the relativistic precession model, applying the Kerr-Q and Hartle-Thorne metrics to derive expressions for quasi-periodic frequencies. A degeneracy in constraining spin and quadrupole parameters complicates the measurement of their values. By proposing a novel test using the Hartle-Thorne metric, it is found that there is strong evidence suggesting the Kerr black hole as the source of the central object in GRO J1655-40.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Astronomy & Astrophysics
F. M. Vincentelli, P. Casella, D. M. Russell, M. C. Baglio, A. Veledina, T. Maccarone, J. Malzac, R. Fender, K. O'Brien, P. Uttley
Summary: This study presents the results of the fast X-ray/infrared variability analysis of the black hole transient MAXI J1535-571, showing a strong asymmetric anticorrelation between X-ray and near-IR light curves. The detection of a near-IR QPO and simultaneous X-ray QPO at approximately the same frequency suggests a possible misalignment between the disc and jet in scenarios for fast IR variability.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2021)
Article
Astronomy & Astrophysics
Shafqat Riaz, Michal Szanecki, Andrzej Niedzwiecki, Dimitry Ayzenberg, Cosimo Bambi
Summary: This paper studies the impact of returning radiation on relativistic reflection spectra from black hole accretion disks, finding systematic uncertainties in measurement properties when neglecting returning radiation; NICER simulations show overestimation of disk inclination and black hole spin parameter at low viewing angles, with no bias at high viewing angles, and consistent iron abundance estimation. In extreme cases, returning radiation flattens radial emissivity and produces uncompensated residuals, potentially affecting interpretation of data from future X-ray missions. NuSTAR observations above 10 keV show different conclusions from NICER simulations, such as the ability to obtain a high iron abundance.
ASTROPHYSICAL JOURNAL
(2021)
Article
Astronomy & Astrophysics
S. Harikrishna, K. Sriram
Summary: This study investigates the connection between type-B quasi-periodic oscillations (QPOs) and the hot flow in the inner accretion disc region in black hole X-ray binaries. Spectral and timing studies were conducted on 23 observations, revealing differences in the spectral properties between type-C and type-B QPOs, suggesting that a jet could be responsible for the type-B QPOs. Further research is needed to confirm this scenario.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Article
Mathematics
Cosimo Bambi
Summary: Einstein's theory of General Relativity, a pillar of modern physics, has been mainly tested in the weak field regime for decades, but recent years have seen significant progress in testing the theory in the strong field regime with black holes and neutron stars data.
ARABIAN JOURNAL OF MATHEMATICS
(2022)
Article
Astronomy & Astrophysics
Zuobin Zhang, Honghui Liu, Askar B. Abdikamalov, Dimitry Ayzenberg, Cosimo Bambi, Menglei Zhou
Summary: In this study, the spins of black holes were measured using the continuum-fitting and the iron-line methods, and three NuSTAR observations of the black hole binary GRS 1716-249 were analyzed. The analysis confirmed the Kerr nature of the black hole in GRS 1716-249 and provided stringent constraints on possible deviations from the predictions of general relativity.
ASTROPHYSICAL JOURNAL
(2022)
Article
Astronomy & Astrophysics
Shafqat Riaz, Askar B. Abdikamalov, Dimitry Ayzenberg, Cosimo Bambi, Haiyang Wang, Zhibo Yu
Summary: This article investigates the impact of a disk-like corona on the measurement of system properties and testing the Kerr nature of a black hole by simulating observations of a black hole binary. The study finds that while the astrophysical properties of the accretion disk can be well recovered, it is more challenging to constrain the geometric properties of the black hole spacetime.
ASTROPHYSICAL JOURNAL
(2022)
Article
Astronomy & Astrophysics
Ashutosh Tripathi, Askar B. Abdikamalov, Dimitry Ayzenberg, Cosimo Bambi, Victoria Grinberg, Honghui Liu, Menglei Zhou
Summary: In this study, the hypothesis of Kerr black hole was tested with a stellar-mass black hole in GRS 1915+105 by analyzing five disk-dominated RXTE spectra and one reflection-dominated Suzaku spectrum. The combination of the constraints from the continuum-fitting and the iron line methods has the potential to provide more stringent tests of the Kerr metric.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2022)
Article
Astronomy & Astrophysics
Honghui Liu, Jiachen Jiang, Zuobin Zhang, Cosimo Bambi, Long Ji, Lingda Kong, Shu Zhang
Summary: The low-mass X-ray binary GX 339-4 underwent a new outburst in 2021, during which the flux rapidly alternated between low and high states. Time-resolved spectral analysis revealed that the flux changes occurred primarily in the hard X-ray band. The variability was attributed to the reflected emission from the inner accretion disc and the power-law continuum from the corona.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Article
Astronomy & Astrophysics
Honghui Liu, Yuhan Fu, Cosimo Bambi, Jiachen Jiang, Michael L. Parker, Long Ji, Lingda Kong, Liang Zhang, Shu Zhang, Yuexin Zhang
Summary: We analyzed three observations of GRS 1915+105 in 2017 and found strong absorption lines from highly ionized iron in the disk wind outflowing at a velocity of about 1000 km/s. Two of the observations showed significant oscillations in their light curves, corresponding to the kappa state of GRS 1915+105. The variation in the ionization state of the disk wind follows the X-ray continuum on timescales ranging from hundreds of seconds to months, with the wind's radial location consistent with thermal driving. The mass-loss rate due to the outflowing wind is comparable to the mass accretion rate in the inner disk, indicating the important role of the disk wind in the accretion system.
ASTROPHYSICAL JOURNAL
(2022)
Article
Astronomy & Astrophysics
Swarnim Shashank, Shafqat Riaz, Askar B. Abdikamalov, Cosimo Bambi
Summary: X-ray reflection spectroscopy is a leading technique for studying black hole accretion disks, but its accuracy relies on the reflection models used. This study uses a general relativistic magnetohydrodynamic code and ray-tracing techniques to test the capability of current reflection models in recovering the correct input parameters.
ASTROPHYSICAL JOURNAL
(2022)
Article
Astronomy & Astrophysics
Honghui Liu, Cosimo Bambi, Jiachen Jiang, Javier A. Garcia, Long Ji, Lingda Kong, Xiaoqin Ren, Shu Zhang, Shuangnan Zhang
Summary: We analyze the relativistic reflection spectra of GX 339-4 during its 2021 outburst and find strong relativistic reflection signatures indicating a high black hole spin and an intermediate disk inclination angle. The hard-to-soft transition is accompanied by an increasing disk temperature and a softening corona emission, while the inner disk radius remains stable. The corona height, assuming a lamppost geometry, stays close to the black hole across the state transition. Including Comptonization, the scattering fraction parameter decreases during the transition. Our analysis with a reflection model designed for hot accretion disks supports the scenario of corona property variations during the state transition.
ASTROPHYSICAL JOURNAL
(2023)
Article
Astronomy & Astrophysics
Zuobin Zhang, Jiachen Jiang, Honghui Liu, Cosimo Bambi, Christopher S. Reynolds, Andrew C. Fabian, Thomas Dauser, Kristin Madsen, Andrew Young, Luigi Gallo, Zhibo Yu, John Tomsick
Summary: We present the results from a joint XMM-Newton + NuSTAR observation of the Seyfert 1 galaxy ESO 511-G030, showing that the source remained in a low flux and stable state. The broadband spectrum indicates the presence of a power-law continuum, a soft excess below 2 keV, a narrow iron Ka emission, and a high-energy cutoff. Two possible scenarios, a warm and optically thick Comptonizing corona or a relativistic reflection from a high-density inner disk, can explain the observed soft excess. All models require a low temperature for the hot corona.
ASTROPHYSICAL JOURNAL
(2023)
Review
Multidisciplinary Sciences
Cosimo Bambi
Summary: General relativity, one of the pillars of modern physics, has been predominantly tested in the weak-field regime until recently. However, advances in observational facilities have allowed for exploration of the strong-field regime, providing data for gravitational wave tests, black hole imaging, and X-ray tests of general relativity. This manuscript aims to provide a pedagogical review on X-ray tests of general relativity with black holes and compare them with gravitational wave tests and black hole imaging.
Article
Astronomy & Astrophysics
Honghui Liu, Jiachen Jiang, Zuobin Zhang, Cosimo Bambi, Andrew C. Fabian, Javier A. Garcia, Adam Ingram, Erin Kara, James F. Steiner, John A. Tomsick, Dominic J. Walton, Andrew J. Young
Summary: We conducted a high-density relativistic reflection analysis on 21 spectra of six black hole X-ray binaries in the hard state using data from NuSTAR and Swift. Our findings indicate that 76% of the observations in our sample require a disk density higher than the previously assumed 10^15 cm(-3) in reflection analysis. Stellar mass black holes have higher disk densities compared to active galactic nuclei. Our results suggest that the inner disk radius is close to the innermost stable circular orbit in the luminous hard state, and the coronal temperatures are lower than expected, which can be explained by a hybrid plasma model. The disk ionization parameter is overestimated when assuming a fixed density of 10^15 cm(-3), while the inner disk radius remains unaffected.
ASTROPHYSICAL JOURNAL
(2023)
Article
Astronomy & Astrophysics
Q. Yuan, Pankaj Kushwaha, Alok C. Gupta, Ashutosh Tripathi, Paul J. Wiita, M. Zhang, X. Liu, Anne Lahteenmaki, Merja Tornikoski, Joni Tammi, Venkatessh Ramakrishnan, L. Cui, X. Wang, M. F. Gu, Cosimo Bambi, A. E. Volvach
Summary: In this study, correlation and periodicity analyses were performed on the multiband light curves of PKS 1510-089, a flat-spectrum radio quasar. The results show correlations between gamma-ray, optical, and near-infrared emissions with no time lags, while both gamma-ray and optical/near-infrared emissions precede radio radiation. Furthermore, evidence for a quasi-periodic variation of approximately 1540 days was found in the 37 GHz light curve, suggesting periodic behaviors in the unresolved core emission. The color variability analysis reveals that the source follows a redder-when-brighter trend over time, even in the low-flux state.
ASTROPHYSICAL JOURNAL
(2023)
Article
Astronomy & Astrophysics
Swarnim Shashank, Cosimo Bambi
Summary: Gravitational-wave observations of binary black holes were used to test the Kerr hypothesis, and the results showed consistency.
Article
Astronomy & Astrophysics
Rittick Roy, Askar B. Abdikamalov, Dimitry Ayzenberg, Cosimo Bambi, Shafqat Riaz, Ashutosh Tripathi
Summary: In this paper, a relativistic reflection model is constructed to test the weak-equivalence principle in the strong gravitational field of black holes. The analysis of the reflection features of a black hole binary spectrum helps constrain possible violations of the weak-equivalence principle by massive particles and x-ray photons.
Article
Astronomy & Astrophysics
Askar B. Abdikamalov, Dimitry Ayzenberg, Cosimo Bambi, Sourabh Nampalliwar, Ashutosh Tripathi
Summary: X-ray reflection spectroscopy is a powerful technique for probing the nature of gravity around black holes in the strong-field regime. By analyzing observations of a supermassive black hole using a non-Kerr black hole model, the study confirms that astrophysical black holes are described by the Kerr metric. Although some deformation parameters are poorly constrained, the study overall recovers the Kerr solution.