A5091455958- Astrophysical Phenomena and Observations
- Pulsars and Gravitational Waves Research
- Gamma-ray bursts and supernovae
- Astrophysics and Cosmic Phenomena
- Mechanics and Biomechanics Studies
- Astronomy and Astrophysical Research
- Relativity and Gravitational Theory
- Adaptive optics and wavefront sensing
- Galaxies: Formation, Evolution, Phenomena
- Stellar, planetary, and galactic studies
- Astronomical Observations and Instrumentation
- Cosmology and Gravitation Theories
- Geophysics and Gravity Measurements
- Scientific Measurement and Uncertainty Evaluation
- High-pressure geophysics and materials
- Multidisciplinary Science and Engineering Research
- Black Holes and Theoretical Physics
- Noncommutative and Quantum Gravity Theories
University of Michigan
2020-2024
Massachusetts Institute of Technology
2024
Stanford University
2018-2019
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 The launch of NuSTAR and the increasing number binary black hole (BBH) mergers detected through gravitational wave observations have exponentially advanced our understanding BHs. Despite simplicity owed to being fully described by their mass angular momentum, BHs remained mysterious laboratories that probe most extreme environments in universe. While significant progress has been made recent decade, distribution spin not yet understood. In this work, we provide a systematic analysis...
Abstract We extend our recent work on black hole spin in X-ray binary systems to include an analysis of 189 archival NuSTAR observations from 24 sources. Using self-consistent data reduction pipelines, spectral models, and statistical techniques, we report unprecedented uniform sample 36 stellar-mass measurements based relativistic reflection. This treatment suggests that prior reports low spins a small number sources were generally erroneous: comprehensive finds those tend harbor holes with...
Abstract The proximity and duration of the tidal disruption event ASASSN-14li led to discovery narrow, blueshifted absorption lines in X-rays UV. gas seen X-ray is consistent with bound material close apocenter elliptical orbital paths, or a disk wind similar those Seyfert-1 active galactic nuclei. We present new analysis deepest high-resolution XMM-Newton Chandra spectra ASASSN-14li. Driven by relative strengths He-like H-like charge states, data require [N/C] ≥ 2.4, qualitative agreement...
Accretion is a universal astrophysical process that plays key role in cosmic history, from the epoch of reionization to galaxy and stellar formation evolution. Accreting stellar-mass black holes X-ray binaries are one best laboratories study accretion probe strong gravity—and most importantly, measure angular momentum, or spin, holes, its as powering mechanism for relativistic phenomena. Comprehensive characterization disk-corona system accreting their co-evolution, fundamental measurements...
Abstract Mrk 817 is a bright and variable Seyfert 1.2 active galactic nucleus (AGN). X-ray monitoring of with the Neil Gehrels Swift Observatory in 2022 revealed that source flux had declined to lower level than recorded at any prior point then 19 yr mission. We present an analysis deep XMM-Newton NuSTAR observations obtained this low state. The spectra reveal complex wind consisting neutral ionized absorption zones. Three separate velocity components are detected as part structured...
Abstract Accretion disks and coronae around massive black holes have been studied extensively, they are known to be coupled. Over a period of 30 yr, however, the X-ray (coronal) flux Mrk 817 increased by factor 40 while its UV (disk) remained relatively steady. Recent high-cadence monitoring finds that continua in also decoupled on timescales weeks months. These findings could require mechanical beaming innermost accretion flow, and/or an absorber shields disk broad line region (BLR) from...
The origin and distribution of stellar-mass black hole spins are a rare window into the progenitor stars supernova events that create them. Swift J1728.9-3613 is an X-ray binary, likely associated with remnant G351.9-0.9 (Balakrishnan et al. 2023). A NuSTAR spectrum this source during its 2019 outburst reveals reflection from accretion disk extending to innermost stable circular orbit. Modeling relativistic Doppler shifts gravitational redshifts imprinted on measures dimensionless spin...
Abstract The black hole candidate EXO 1846-031 underwent an outburst in 2019, after at least 25 yr quiescence. We observed the system using NuSTAR on 2019 August 3. 3–79 keV spectrum shows strong relativistic reflection features. Our baseline model gives a nearly maximal spin value of <?CDATA $a={0.997}_{-0.002}^{+0.001}$?> (1 σ statistical errors). This high nominally excludes possibility central engine harboring neutron star. Using several models, we test robustness our measurement to...
Abstract We report on Chandra grating spectra of the stellar-mass black hole GRS 1915+105 obtained during a novel, highly obscured state. As source entered this state, dense, massive accretion disk wind was detected through strong absorption lines. Photoionization modeling indicates that it must originate close to central engine, orders magnitude from outer disk. Strong, nearly sinusoidal flux variability in phase yielded key insight: is blueshifted when its column density relatively low,...
Abstract The black hole (BH) candidate XTE J2012+381 underwent an outburst at the end of 2022. We analyzed 105 NICER observations and two NuSTAR source during outburst. M ∼ 10 ⊙ BH indicate clear signs relativistic disk reflection, which we modeled to measure a spin <?CDATA $a={0.988}_{-0.030}^{+0.008}$?> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>a</mml:mi> <mml:mo>=</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>0.988</mml:mn> </mml:mrow>...
Abstract We collect new and archival optical observations of nine “black-widow” millisecond pulsar binaries. New measurements include direct imaging with the Keck, Gemini-S, MDM, Las Cumbres Observatory 2 m telescopes. This is supplemented by synthesized colors from Keck long-slit spectra. Four black-widow companions are presented here for first time. Together these data provide multicolor photometry covering a large fraction orbital phase. fit light curves (photon) heating model using...
NuSTAR observed the black hole candidate XTE J1908$+$094 during its 2013 and 2019 outbursts. We use relativistic reflection to measure spin of through 19 different assumptions relxill flavors parameter combinations. The most favored model in terms Deviance Information Criterion (DIC) measures be $a = 0.55^{+0.29}_{-0.45}$, an inclination $\theta=27^{+2}_{-3}$ degrees ($1\sigma$ statistical errors). look at effects coronal geometry density accretion disk on prediction. All tested models...
Abstract A number of neutron stars have been observed within the remnants core-collapse supernova explosions that created them. In contrast, black holes are not yet clearly associated with (SNRs). Indeed, some observations suggest “born in dark,” i.e., without a explosion. Herein, we present multiwavelength analysis X-ray transient Swift J1728.9−3613, based on made Chandra, ESO-VISTA, MeerKAT, NICER, NuSTAR, Swift, and XMM-Newton. Three independent diagnostics indicate system likely harbors...
Abstract We present an analysis of archival Gemini g ′, r K and Keck H , s imaging this nearby short-period binary ( P B = 95.8 minutes) 2.87 ms pulsar. The heated companion is clearly detected. Direct pulsar heating provides acceptable model at the revised >700 pc parallax distance. relatively shallow light curve modulation prefers inclination i < 40°; high-latitude view a likely explanation for lack radio signatures wind dispersion or eclipse. It also explains low minimum mass and,...
We report on a study of the narrow Fe K$\alpha$ line and reflection spectrum in well-known Seyfert-2 AGN, NGC 4388. X-ray spectra summed from two extensive NICER monitoring campaigns, separated by years, show strong evidence variation direct continuum reflected emission, but only small variations obscuring gas. Fits to individual observations find strong, positive correlation between power-law photon index, $\Gamma$, flux that is commonly observed unobscured AGN. A search for reverberation...
Abstract We report on a study of the narrow Fe K α line and reflection spectrum in well-known Seyfert-2 active galactic nucleus (AGN), NGC 4388. X-ray spectra summed from two extensive NICER monitoring campaigns, separated by years, show strong evidence variation direct continuum reflected emission, but only small variations obscuring gas. Fits to individual observations find strong, positive correlation between power-law photon index, Γ, flux that is commonly observed unobscured AGN. A...
Tidal disruption events (TDEs) can potentially probe low-mass black holes in host galaxies that might not adhere to bulge or stellar-dispersion relationships. At least initially, TDEs also reveal super-Eddington accretion. X-ray spectroscopy constrain hole masses, and ionized outflows associated with Our analysis of XMM-Newton observations the TDE AT2021ehb, around 300 days post-disruption, reveals a soft spectrum be fit combination multi-color disk blackbody power-law components. Using two...
Abstract Tidal disruption events (TDEs) can potentially probe low-mass black holes (BHs) in host galaxies that might not adhere to bulge or stellar-dispersion relationships. At least initially, TDEs also reveal super-Eddington accretion. X-ray spectroscopy constrain BH masses, and ionized outflows associated with Our analysis of XMM-Newton observations the TDE AT2021ehb, around 300 days post-disruption, reveals a soft spectrum be fit combination multicolor disk blackbody power-law...
To answer NASA’s call for a sensitive X-ray observatory in the 2030s, we present High Energy Probe (HEX-P) mission concept. HEX-P is designed to provide required capabilities explore current scientific questions and make new discoveries with broadband that simultaneously measures sources from 0.2 80 keV. HEX-P’s main goals include: 1) understand growth of supermassive black holes how they drive galaxy evolution; 2) lower mass populations white dwarfs, neutron stars, stellar-mass nearby...
Type Ia supernovae, critical for studying cosmic expansion, arise from thermonuclear explosions of white dwarfs, but their precise progenitor pathways remain unclear. Growing evidence supports the ``double-degenerate'' scenario, where two dwarfs interact. The absence other companion types capable explaining observed rate, along with observations hyper-velocity interpreted as surviving companions such systems provide compelling in favor this scenario. Upcoming millihertz gravitational wave...
Accretion is a universal astrophysical process that plays key role in cosmic history, from the epoch of reionization to galaxy and stellar formation evolution. Accreting stellar-mass black holes X-ray binaries are one best laboratories study accretion probe strong gravity -- most importantly, measure angular momentum, or spin, holes, its as powering mechanism for relativistic phenomena. Comprehensive characterization disk-corona system accreting their co-evolution, fundamental measurements...
The launch of NuSTAR and the increasing number binary black hole (BBH) mergers detected through gravitational wave (GW) observations have exponentially advanced our understanding holes. Despite simplicity owed to being fully described by their mass angular momentum, holes remained mysterious laboratories that probe most extreme environments in Universe. While significant progress has been made recent decade, distribution spin not yet understood. In this work, we provide a systematic analysis...
A number of neutron stars have been observed within the remnants core-collapse supernova explosions that created them. In contrast, black holes are not yet clearly associated with remnants. Indeed, some observations suggest ``born in dark'', i.e. without a explosion. Herein, we present multi-wavelength analysis X-ray transient Swift J1728.9$-$3613, based on made Chandra, ESO-VISTA, MeerKAT, NICER, NuSTAR, Swift, and XMM-Newton. Three independent diagnostics indicate system likely harbors...