Roger W. Romani
A5041320985- Pulsars and Gravitational Waves Research
- Astrophysics and Cosmic Phenomena
- Gamma-ray bursts and supernovae
- Astrophysical Phenomena and Observations
- Radio Astronomy Observations and Technology
- Geophysics and Gravity Measurements
- Dark Matter and Cosmic Phenomena
- High-pressure geophysics and materials
- Astronomical Observations and Instrumentation
- Particle Accelerators and Free-Electron Lasers
- Solar and Space Plasma Dynamics
- Particle Detector Development and Performance
- Superconducting Materials and Applications
- Astronomy and Astrophysical Research
- Galaxies: Formation, Evolution, Phenomena
- Mechanics and Biomechanics Studies
- Stellar, planetary, and galactic studies
- Neutrino Physics Research
- Nuclear Physics and Applications
- Superconducting and THz Device Technology
- Particle accelerators and beam dynamics
- Particle physics theoretical and experimental studies
- Geomagnetism and Paleomagnetism Studies
- Physics of Superconductivity and Magnetism
- Atomic and Subatomic Physics Research
Kavli Institute for Particle Astrophysics and Cosmology
2015-2024
Stanford University
2015-2024
Institute for Space Astrophysics and Planetology
2022-2024
University of Pisa
2023-2024
SLAC National Accelerator Laboratory
2011-2023
Compact Imaging (United States)
2023
Universities Space Research Association
2022
Osservatorio Astrofisico di Torino
2021
Marshall Space Flight Center
2019
Istituto Nazionale di Fisica Nucleare
2019
We present measurements of the Hubble diagram for 103 Type Ia supernovae (SNe) with redshifts 0.04 < z 0.42, discovered during first season (Fall 2005) Sloan Digital Sky Survey-II (SDSS-II) Supernova Survey. These data fill in redshift "desert" between low- and high-redshift SN surveys. combine SDSS-II new distance estimates published from ESSENCE survey, Legacy Survey, Space Telescope, a compilation nearby measurements. Combining Baryon Acoustic Oscillations SDSS Luminous Red Galaxy sample...
The Large Area Telescope (LAT) aboard the Fermi Gamma-ray Space provides an unprecedented opportunity to study gamma-ray blazars. To capitalize on this opportunity, beginning in late 2007, about a year before start of LAT science operations, we began large-scale, fast-cadence 15 GHz radio monitoring program with 40-m telescope at Owens Valley Radio Observatory (OVRO). This 1158 northern (declination>-20 deg) sources from Candidate Blazar Survey (CGRaBS) and now encompasses over 1500 sources,...
The Sloan Digital Sky Survey-II (SDSS-II) has embarked on a multi-year project to identify and measure light curves for intermediate-redshift (0.05 < z 0.35) Type Ia supernovae (SNe Ia) using repeated five-band (ugriz) imaging over an area of 300 sq. deg. survey region is stripe 2.5° wide centered the celestial equator in Southern Galactic Cap that been imaged numerous times earlier years, enabling construction deep reference image discovery new objects. Supernova observations are being...
We have assembled an 8.4 GHz survey of bright, flat-spectrum (alpha > -0.5) radio sources with nearly uniform extragalactic (|b|>10 deg) coverage for brighter than S_{4.8 GHz} = 65 mJy. The catalog is from existing observations (especially CLASS and the Wright et al. PMN-CA survey), augmented by reprocessing archival VLA ATCA data new to fill in gaps. refer this program as CRATES, Combined Radio All-sky Targeted Eight Survey. resulting provides precise positions, sub-arcsecond...
We report on the discovery of a supermassive binary black hole system in radio galaxy 0402+379, with projected separation between two holes just 7.3 pc. This is closest pair yet found by more than 2 orders magnitude. These results are based recent multifrequency observations using Very Long Baseline Array (VLBA), which reveal compact, variable, flat-spectrum, active nuclei within elliptical host 0402+379. Multiepoch from VLBA also provide constraints total mass and dynamics system. Low...
Abstract We describe Keck-telescope spectrophotometry and imaging of the companion “black widow” pulsar PSR J0952−0607, fastest known spinning neutron star (NS) in disk Milky Way. The is very faint at minimum brightness, presenting observational challenges, but we have measured multicolor light curves obtained radial velocities over illuminated “day” half orbit. model fits indicate system inclination i = 59.°8 ± 1.°9 a mass M NS 2.35 0.17 ⊙ , largest well-measured found to date. Modeling...
Fermi has provided the largest sample of γ-ray-selected blazars to date. In this work we use a complete flat spectrum radio quasars (FSRQs) detected during first year operation determine luminosity function (LF) and its evolution with cosmic time. The number density FSRQs grows dramatically up redshift ∼0.5–2.0 declines thereafter. peak in is dependent, more luminous sources peaking at earlier times; thus LF γ-ray follows luminosity-dependent similar that radio-quiet active galactic nuclei....
Launched on 2021 December 9, the Imaging X-ray Polarimetry Explorer (IXPE) is a NASA Small Mission in collaboration with Italian Space Agency (ASI). The mission will open new window of investigation—imaging x-ray polarimetry. observatory features three identical telescopes, each consisting mirror module assembly polarization-sensitive imaging detector at focus. A coilable boom, deployed orbit, provides necessary 4-m focal length. utilizes three-axis-stabilized spacecraft, which services such...
The origin of the extragalactic $\gamma$-ray background (EGB) has been debated for some time. { EGB comprises emission from resolved and unresolved sources, such as blazars, star-forming galaxies radio galaxies, well radiation truly diffuse processes.} This letter focuses on blazar source class, most numerous detected population, presents an updated luminosity function spectral energy distribution model consistent with observations performed by {\it Fermi} Large Area Telescope (LAT). We show...
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 Most of the light from blazars, active galactic nuclei with jets magnetized plasma that point nearly along line sight, is produced by high-energy particles, up to around 1 TeV. Although are known be ultimately powered a supermassive black hole, how particles accelerated such high energies has been an unanswered question. The process must related magnetic field, which can probed observations polarization jets. Measurements radio optical polarization—the only range available until...
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...
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We have demonstrated the use of superconducting transition edge sensors for wide-band detection individual photons from mid infrared (IR), through optical, and into far ultraviolet (UV). These tungsten are squares about 18 μm on a side detect single photon events above threshold 0.3 eV (4 wavelength), with an energy resolution 0.15 full width at half maximum, risetime (falltime) .5 μs (60 μs). The calibration data extend up to UV cutoff fiber optic feed 3.5 (350 nm).
view Abstract Citations (368) References (35) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Gamma-Ray Pulsars: Emission Zones and Viewing Geometries Romani, Roger W. ; Yadigaroglu, I. -A. There are now a half dozen young pulsars detected in high energy photons by the Compton GRO, showing variety of emission efficiencies pulse profiles. We present here calculation pattern on sky model which posits $\gamma$-ray production charge depleted gaps outer...
For massive black hole binaries produced in galactic mergers, we examine the possibility of inspiral induced by interaction with field stars. We model evolution such for a range galaxy core and binary parameters, using numerical results from literature to compute binary's energy angular momentum loss rates due stellar encounters including effect back-action on find that only small fraction systems can merge within Hubble time via unassisted dynamics. External perturbations may, however,...
We present precise phase-connected pulse timing solutions for 16 gamma-ray-selected pulsars recently discovered using the Large Area Telescope (LAT) on Fermi Gamma-ray Space plus one very faint radio pulsar (PSR J1124-5916) that is more effectively timed with LAT. describe analysis techniques including a maximum likelihood method determining times of arrival from unbinned photon data. A major result this work improved position determinations, which are crucial multi-wavelength follow up. For...
Chandra X-Ray Observatory imaging has shown that equatorial tori, often with polar jets, are very common in young pulsar wind nebulae (PWNe). These structures interesting both for what they reveal about the relativistic itself and (nearly) model-independent measurement of neutron star spin orientation provide. The latter is a particularly valuable probe emission models physics. We describe here procedure fitting simple three-dimensional torus to X-ray data, which provides robust estimates...
The Sloan Digital Sky Survey-II Supernova Survey has identified a large number of new transient sources in 300 deg2 region along the celestial equator during its first two seasons three-season campaign. Multi-band (ugriz) light curves were measured for most sources, which include solar system objects, galactic variable stars, active nuclei, supernovae (SNe), and other astronomical transients. imaging survey is augmented by an extensive spectroscopic follow-up program to identify SNe, measure...
We report on optical spectroscopy of 165 flat spectrum radio quasars (FSRQs) in the Fermi 1LAC sample, which have helped allow a nearly complete study this population. FSRQs show significant evidence for non-thermal emission even optical; degree depends γ-ray hardness. They also smaller virial estimates hole mass than quasar sample. This appears to be largely due preferred (axial) view FSRQ and non-isotropic (H/R ∼ 0.4) distribution broad-line velocities. Even after correction bias, higher...
We describe a uniform all-sky survey of bright blazars, selected primarily by their flat radio spectra, that is designed to provide large catalog likely gamma-ray AGN. The defined sample has 1625 targets with and X-ray properties similar those the EGRET spread uniformly across |b| > 10 deg sky. also report progress toward optical characterization sample; objects known R < 23, 85% have been classified 81% measured redshifts. One goal this program focus attention on most interesting...
We present the first results of VLBA Imaging and Polarimetry Survey (VIPS), a 5 GHz VLBI survey 1127 sources with flat radio spectra. Through automated data reduction imaging routines, we have produced publicly available I, Q, U images detected polarized flux density from 37% sources. also developed an algorithm to use each source's I image automatically classify it as pointlike source, core jet, compact symmetric object (CSO) candidate, or complex source. Using Sloan Digital Sky (SDSS),...
The Large Area Telescope on board the Fermi satellite observed a gamma-ray flare in Crab Nebula lasting for approximately nine days April of 2011. source, which at optical wavelengths has size ≈11 lt-yr across, doubled its flux within eight hours. peak photon was (186 ± 6) × 10−7 cm−2 s−1 above 100 MeV, corresponds to 30-fold increase compared average value. During flare, new component emerged spectral energy distribution, peaked an (375 26) MeV maximum. observations imply that emission...
We present ugriz light curves for 146 spectroscopically-confirmed or spectroscopically-probable Type Ia supernovae (SNe) from the 2005 season of Sloan Digital Sky Survey-II Supernova (SN) survey. The have been constructed using a photometric technique that we call scene modeling, which is described in detail here; major feature SN brightnesses are extracted stack images without spatial resampling convolution image data. This procedure produces accurate photometry along with estimates...