About

Frederick Lamb is a Research Professor affiliated with The Program in Arms Control & Domestic and International Security at the Illinois Global Institute. His contact information includes an office at 1110 W. Green M/C 704 Urbana, IL 61801, and an email address at fkl@illinois.edu. He is involved in research related to arms control and security studies, contributing to the academic and policy-oriented work within the program. His role supports the mission of the program and the broader goals of the Illinois Global Institute, focusing on domestic and international security issues.

Research topics

• Physics
• Nuclear physics
• Astrophysics

Selected publications

• A More Precise Measurement of the Radius of PSR J0740+6620 Using Updated NICER Data

  arXiv (Cornell University) · 2024-06-20

  preprintOpen access

  PSR J0740+6620 is the neutron star with the highest precisely determined mass, inferred from radio observations to be $2.08\pm0.07\,\rm M_\odot$. Measurements of its radius therefore hold promise to constrain the properties of the cold, catalyzed, high-density matter in neutron star cores. Previously, Miller et al. (2021) and Riley et al. (2021) reported measurements of the radius of PSR J0740+6620 based on Neutron Star Interior Composition Explorer (NICER) observations accumulated through 17 April 2020, and an exploratory analysis utilizing NICER background estimates and a data set accumulated through 28 December 2021 was presented in Salmi et al. (2022). Here we report an updated radius measurement, derived by fitting models of X-ray emission from the neutron star surface to NICER data accumulated through 21 April 2022, totaling $\sim1.1$ Ms additional exposure compared to the data set analyzed in Miller et al. (2021) and Riley et al. (2021), and to data from X-ray Multi-Mirror (XMM-Newton) observations. We find that the equatorial circumferential radius of PSR J0740+6620 is $12.92_{-1.13}^{+2.09}$ km (68% credibility), a fractional uncertainty $\sim83\%$ the width of that reported in Miller et al. (2021), in line with statistical expectations given the additional data. If we were to require the radius to be less than 16 km, as was done in Salmi et al. (2024), then our 68% credible region would become $R=12.76^{+1.49}_{-1.02}$ km, which is close to the headline result of Salmi et al. (2024). Our updated measurements, along with other laboratory and astrophysical constraints, imply a slightly softer equation of state than that inferred from our previous measurements.

  PublisherOA PDFDOI

• A More Precise Measurement of the Radius of PSR J0740+6620 Using Updated NICER Data

  The Astrophysical Journal · 2024-10-01 · 100 citations

  articleOpen access

  Abstract PSR J0740+6620 is the neutron star with the highest precisely determined mass, inferred from radio observations to be 2.08 ± 0.07 M ⊙ . Measurements of its radius therefore hold promise to constrain the properties of the cold, catalyzed, high-density matter in neutron star cores. Previously, Miller et al. and Riley et al. reported measurements of the radius of PSR J0740+6620 based on Neutron Star Interior Composition Explorer (NICER) observations accumulated through 2020 April 17, and an exploratory analysis utilizing NICER background estimates and a data set accumulated through 2021 December 28 was presented in Salmi et al. Here we report an updated radius measurement, derived by fitting models of X-ray emission from the neutron star surface to NICER data accumulated through 2022 April 21, totaling ∼1.1 Ms additional exposure compared to the data set analyzed in Miller et al. and Riley et al., and to data from XMM-Newton observations. We find that the equatorial circumferential radius of PSR J0740+6620 is <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>12.92</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1.13</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>2.09</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> km (68% credibility), a fractional uncertainty ∼83% the width of that reported in Miller et al., in line with statistical expectations given the additional data. If we were to require the radius to be less than 16 km, as was done in Salmi et al., then our 68% credible region would become <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>R</mml:mi> <mml:mo>=</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>12.76</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1.02</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>1.49</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> km, which is close to the headline result of Salmi et al. Our updated measurements, along with other laboratory and astrophysical constraints, imply a slightly softer equation of state than that inferred from our previous measurements.

  PublisherDOI

• Snowmass 2021 Cosmic Frontier White Paper: The Dense Matter Equation of State and QCD Phase Transitions

  arXiv (Cornell University) · 2022-09-15 · 1 citations

  preprintOpen access

  Our limited understanding of the physical properties of matter at ultra-high density, high proton/neutron number asymmetry, and low temperature is presently one of the major outstanding problems in physics. As matter in this extreme state is known to only exist stably in the cores of neutron stars (NSs), complementary measurements from electromagnetic and gravitational wave astrophysical observations of NSs, combined with terrestrial laboratory constraints and further theoretical investigations, hold the promise to provide important insight into the properties of matter in a region of the quantum chromodynamics phase space that is otherwise inaccessible. This multidisciplinary endeavor imposes the following requirements for facilities and resources in the upcoming decade and beyond: * A next generation of gravitational wave detectors to uncover more double NS and neutron star-black hole mergers; * Sensitive radio telescopes to find the most massive and fastest spinning NSs; * Large-area, high-time-resolution and/or high angular resolution X-ray telescopes to constrain the NS mass-radius relation; * Suitable laboratory facilities for nuclear physics experiments to constrain the dense matter equation of state; * Funding resources for theoretical studies of matter in this regime; * The availability of modern large-scale high performance computing infrastructure. The same facilities and resources would also enable significant advances in other high-profile fields of inquiry in modern physics such as the nature of dark matter, alternative theories of gravity, nucleon superfluidity and superconductivity, as well as an array of astrophysics, including but not limited to stellar evolution, nucleosynthesis, and primordial black holes.

  PublisherOA PDFDOI

• Constraining the Neutron Star Mass-Radius Relation and Dense Matter Equation of State with NICER. III. Model Description and Verification of Parameter Estimation Codes

  Zenodo (CERN European Organization for Nuclear Research) · 2021-04-22

  datasetOpen access

  This deposit includes the synthetic NICER data sets along with the necessary auxiliary files used in the cross-verification efforts of the parameter estimation procedures used by Miller et al. (2019) and Riley et al. (2019) to analyze the NICER data of the millisecond pulsar PSR J0030+0451. The parameters assumed in generating the synthetic data are are detailed in the ApJ Letter listed above. Three sets of files are provided corresponding to the following comparison exercises described in the ApJ Letter: 1. Ultra-compact neutron stars with R/M~3 (see Section 2.3 of Letter) -- the tar.gz file and it's MD5 checksum are: multiple_imaging_validation.tar.gz (dd7a02b2ccf0a45da4e9d3a779d3b9c4) 2. A neutron star with a single, uniform-temperature, circular hot spot (see Section 3.1 of Letter) -- the tar.gz file and it's MD5 checksum are: one_spot_synthetic_NICER_data.tar.gz (87b9ca80259b34d76746ef18802a75ec) 3. A neutron star with two different, Uniform-Temperature, circular hot spots (see Section 3.2 of Letter) -- the tar.gz file and it's MD5 checksum are: two_spot_synthetic_NICER_data.tar.gz (75374adc0cea2bc1039f6169548cc719) A readme file contained within each tarball provides detailed information about the file sets used and the parameter values assumed in generating the synthetic data sets.

  PublisherDOI

• Constraining the Neutron Star Equation of State with NICER

  43rd COSPAR Scientific Assembly. Held 28 January - 4 February · 2021-01-01

  article
  Publisher

• The Radius of PSR J0740+6620 from NICER and XMM-Newton Data

  2021 · 33 citations

  • Physics
  • Astrophysics
  • Nuclear physics

  Abstract PSR J0740+6620 has a gravitational mass of 2.08 ± 0.07 M ⊙ , which is the highest reliably determined mass of any neutron star. As a result, a measurement of its radius will provide unique insight into the properties of neutron star core matter at high densities. Here we report a radius measurement based on fits of rotating hot spot patterns to Neutron Star Interior Composition Explorer (NICER) and X-ray Multi-Mirror (XMM-Newton) X-ray observations. We find that the equatorial circumferential radius of PSR J0740+6620 is <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>13.7</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1.5</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>2.6</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> km (68%). We apply our measurement, combined with the previous NICER mass and radius measurement of PSR J0030+0451, the masses of two other ∼2 M ⊙ pulsars, and the tidal deformability constraints from two gravitational wave events, to three different frameworks for equation-of-state modeling, and find consistent results at ∼1.5–5 times nuclear saturation density. For a given framework, when all measurements are included, the radius of a 1.4 M ⊙ neutron star is known to ±4% (68% credibility) and the radius of a 2.08 M ⊙ neutron star is known to ±5%. The full radius range that spans the ±1 σ credible intervals of all the radius estimates in the three frameworks is 12.45 ± 0.65 km for a 1.4 M ⊙ neutron star and 12.35 ± 0.75 km for a 2.08 M ⊙ neutron star.

  PublisherOA PDF

• NICER PSR J0740+6620 Illinois-Maryland MCMC Samples

  Figshare · 2021-04-19 · 13 citations

  dataset

  Posterior samples from the Illinois-Maryland analysis of NICER and XMM-Newton data for PSR J0030+0451. Files ending in "RM" contain only equatorial circumferential radius and gravitational mass posterior samples. Files ending in "full" contain the full set of posterior samples from each analysis. Files starting with "NICER-only" contain samples from the analysis of NICER data alone.<br> Files starting with "NICER+XMM" contain samples from the joint NICER + XMM analysis, assuming no relative calibration offset between the instruments.<br> Files starting with "NICER+XMM-relative" contain samples from the joint NICER + XMM analysis, allowing for up to a +-10% offset in the relative calibration between the instruments.

  DOI

• Nuclear Weapons and Missile Defense

  Bulletin of the American Physical Society · 2021-04-20

  article1st authorCorresponding
  Publisher

• NICER PSR J0740+6620 Illinois-Maryland MCMC Samples

  Zenodo (CERN European Organization for Nuclear Research) · 2021-04-19

  datasetOpen access

  Posterior samples from the Illinois-Maryland analysis of NICER and XMM-Newton data for PSR J0030+0451. Files ending in "RM" contain only equatorial circumferential radius and gravitational mass posterior samples. Files ending in "full" contain the full set of posterior samples from each analysis. Files starting with "NICER-only" contain samples from the analysis of NICER data alone.<br> Files starting with "NICER+XMM" contain samples from the joint NICER + XMM analysis, assuming no relative calibration offset between the instruments.<br> Files starting with "NICER+XMM-relative" contain samples from the joint NICER + XMM analysis, allowing for up to a +-10% offset in the relative calibration between the instruments.

  PublisherDOI

• Constraining the Neutron Star Mass-Radius Relation and Dense Matter Equation of State with NICER. III. Model Description and Verification of Parameter Estimation Codes

  Zenodo (CERN European Organization for Nuclear Research) · 2021-04-22 · 1 citations

  datasetOpen access

  This deposit includes the synthetic NICER data sets along with the necessary auxiliary files used in the cross-verification efforts of the parameter estimation procedures used by Miller et al. (2019) and Riley et al. (2019) to analyze the NICER data of the millisecond pulsar PSR J0030+0451. The parameters assumed in generating the synthetic data are are detailed in the ApJ Letter listed above. Three sets of files are provided corresponding to the following comparison exercises described in the ApJ Letter: 1. Ultra-compact neutron stars with R/M~3 (see Section 2.3 of Letter) -- the tar.gz file and it's MD5 checksum are: multiple_imaging_validation.tar.gz (dd7a02b2ccf0a45da4e9d3a779d3b9c4) 2. A neutron star with a single, uniform-temperature, circular hot spot (see Section 3.1 of Letter) -- the tar.gz file and it's MD5 checksum are: one_spot_synthetic_NICER_data.tar.gz (87b9ca80259b34d76746ef18802a75ec) 3. A neutron star with two different, Uniform-Temperature, circular hot spots (see Section 3.2 of Letter) -- the tar.gz file and it's MD5 checksum are: two_spot_synthetic_NICER_data.tar.gz (75374adc0cea2bc1039f6169548cc719) A readme file contained within each tarball provides detailed information about the file sets used and the parameter values assumed in generating the synthetic data sets.

  PublisherDOI

Recent grants

• Studies in Relativistic Physics and Astrophysics

  NSF · $394k · 2001–2007

• Studies in Relativistic Physics and Astrophysics

  NSF · $383k · 2007–2010

Frequent coauthors

• M. Coleman Miller

  University of Maryland, College Park

  130 shared

• Sebastien Guillot

  Institut de Recherche en Astrophysique et Planétologie

  66 shared

• Dimitrios Psaltis

  49 shared

• M. van der Klis

  The Netherlands Cancer Institute

  40 shared

• Stratos Boutloukos

  National Institute for Astrophysics

  37 shared

• Keith C. Gendreau

  34 shared

• Paul S. Ray

  United States Naval Research Laboratory

  33 shared

• Zaven Arzoumanian

  31 shared