About

Jonathan C. Pober is an Associate Professor of Physics at Brown University. His research group focuses on developing new techniques for studying the Epoch of Reionization and the Cosmic Dawn, periods when the first stars and galaxies illuminated the early Universe. Using low-frequency radio astronomy, his work aims to detect highly-redshifted 21 cm line emission from neutral hydrogen during these early cosmic epochs. The research involves overcoming significant challenges in extracting this hydrogen signal from various radio signals, both human-generated and astrophysical, through the development of innovative experiments and analysis techniques. Pober's work is at the forefront of creating novel analysis approaches and applying them to data from cutting-edge experiments. He holds a PhD from the University of California, Berkeley, earned in 2013, along with a Master's degree from Berkeley, a MPhil from the University of Cambridge, and a Bachelor's degree from Haverford College. His academic background and research contributions position him as a leading figure in the field of radio cosmology and early Universe studies.

Research topics

• Physics
• Astrophysics
• Astronomy
• Particle physics

Selected publications

• RadioAstronomySoftwareGroup/pyuvdata: v3.2.6

  Zenodo (CERN European Organization for Nuclear Research) · 2026-04-13

  otherOpen access

  This patch version improves memory usage in the UVFits reader, fixes a bug in reading MS caltables with multiple times, and adds support for Python 3.14! What's Changed Fixing a few new warnings... by @kartographer in https://github.com/RadioAstronomySoftwareGroup/pyuvdata/pull/1655 Improve memory usage in uvfits reader by @bhazelton in https://github.com/RadioAstronomySoftwareGroup/pyuvdata/pull/1651 Bug fix for reading ms caltables with multiple times by @rlbyrne in https://github.com/RadioAstronomySoftwareGroup/pyuvdata/pull/1653 fully support python 3.14 by @bhazelton in https://github.com/RadioAstronomySoftwareGroup/pyuvdata/pull/1659 Prep for version 3.2.6 by @bhazelton in https://github.com/RadioAstronomySoftwareGroup/pyuvdata/pull/1661 Full Changelog: https://github.com/RadioAstronomySoftwareGroup/pyuvdata/compare/v3.2.5...v3.2.6

  PublisherDOI

• Limits on the 21 cm Power Spectrum at <i>z</i> = 6.5–7.0 from Murchison Widefield Array Observations

  The Astrophysical Journal · 2025-08-05 · 12 citations

  articleOpen access

  Abstract This paper presents the spherically averaged 21 cm power spectrum derived from Epoch of Reionization (EoR) observations conducted with the Murchison Widefield Array (MWA). The analysis uses EoR0-field data, centered at (R.A. = 0 h , decl. = −27 ∘ ), collected between 2013 and 2023. Building on the improved methodology described in C. M. Trott et al. (2024), we incorporate additional data quality control techniques introduced in C. D. Nunhokee (2020). We report the lowest-power-level limits on the EoR power spectrum at redshifts z = 6.5, z = 6.8, and z = 7.0. These power levels, measured in the east–west polarization, are (30.2) 2 mK 2 at k = 0.18 h Mpc −1 , (31.2) 2 mK 2 at k = 0.18 h Mpc −1 , and (39.1) 2 mK 2 at k = 0.21 h Mpc −1 , respectively. The total integration time amounts to 268 hr. These results represent the deepest upper limits achieved by the MWA to date and provide the first evidence of the heated intergalactic medium at redshifts z = 6.5 to 7.0.

  PublisherDOI

• Improved Limits on the 21 cm Signal at <i>z</i> = 6.5–7.0 with the Murchison Widefield Array Using Gaussian Information

  The Astrophysical Journal · 2025-09-30

  articleOpen access

  Abstract We explore the properties of interferometric data from high-redshift 21 cm measurements using the Murchison Widefield Array (MWA). These data contain the redshifted 21 cm signal, contamination from continuum foreground sources, and radiometric noise. The 21 cm signal from the Epoch of Reionization (EoR) is expected to be highly Gaussian, which motivates the use of the power spectrum as an effective statistical tool for extracting astrophysical information. We find that foreground contamination introduces non-Gaussianity into the distribution of measurements and then use this information to separate Gaussian from the non-Gaussian signal. We present improved upper limits on the 21 cm EoR power spectrum from the MWA using a Gaussian component of the data, based on the existing analysis from C. D. Nunhokee et al. 2025. This is extracted as the best-fitting Gaussian to the measured data. Our best 2 σ (thermal+sample variance) limit for 268 hr of data improves from (30.2 mK) 2 to (23.0 mK) 2 at z = 6.5 for the East–West polarization, and from (39.2 mK) 2 to (21.7 mK) 2 = 470 mK 2 in North–South. The best limits at z = 6.8 ( z = 7.0) improve to P &lt; (25.9 mK) 2 ( P &lt; (32.0 mK) 2 ) and k = 0.18 h Mpc −1 ( k = 0.21 h Mpc −1 ). Results are compared with realistic simulations, which indicate that leakage from foreground contamination is a source of the non-Gaussian behavior.

  PublisherDOI

• Detecting the 21 cm Signal of the Cosmic Dark Ages

  ArXiv.org · 2025-04-11

  preprintOpen accessSenior author

  The cosmic "Dark Ages" is the period between the last scattering of the Cosmic Microwave Background (CMB) and the appearance of the first luminous sources, spanning redshifts $1100\gtrsim z\gtrsim 30$. The only way to observe this period is by examining the 21 cm hyperfine transition line of neutral hydrogen HI, which -- given the high redshifts (and hence long wavelengths) -- must be observed from outside the Earth's ionosphere. Given the faintness of the signal, concepts for a radio array on the lunar far side (where large collecting areas can be deployed and radio frequency interference is minimal) have been proposed, like FarView or FARSIDE, but designs are still in the preliminary stages. This paper studies multiple aspects of array design to determine the impact of different design decisions on sensitivity to the Dark Ages 21 cm power spectrum. We do so by using the sensitivity package 21cmSense to model and simulate various array configurations. We present a fiducial design based on a modification of the FarView concept, which consists of a collecting area of $\sim2.5\,\rm{km}^{2}$ with 82,944 tightly packed dual-polarization dipoles grouped into 5,184 correlated elements, or subarrays, delivering a $&gt;10σ$ detection of the $z=30$ signal with a five year lifetime. We find that, beyond mere collecting area, the most important factor in achieving this sensitivity is the presence of very short baselines that can only be realized with small, closely packed antennas.

  PublisherOA PDFDOI

• Limits on the 21 cm power spectrum at z=6.5-7.0 from MWA observations

  ArXiv.org · 2025-05-14 · 2 citations

  preprintOpen access

  This paper presents the spherically-averaged 21 cm power spectrum derived from Epoch of Reionization (EoR) observations conducted with the Murchison Widefield Array (MWA). The analysis uses EoR0-field data, centered at (RA$=0h$, DEC$=-27^{\circ}$), collected between 2013 and 2023. Building on the improved methodology described in Trott et al. 2020, we incorporate additional data quality control techniques introduced in Nunhokee et al. 2024. We report the lowest power level limits on the EoR power spectrum at redshifts $z=6.5$, $z=6.8$, and $z=7.0$. These power levels, measured in the East-West polarization, are $(30.2)^2$ mK$^2$ at $k=0.18\, h$ Mpc$^{-1}$, $(31.2)^2$ mK$^2$ at $k=0.18\, h$ Mpc$^{-1}$ and $(39.1)^2$ mK$^2$ at $k=0.21\, h$ Mpc$^{-1}$ respectively. The total integration time amounts to 268 hours. These results represent the deepest upper limits achieved by the MWA to date and provide the first evidence of heated intergalactic medium (IGM) at redshifts $z=6.5$ to $7.0$.

  PublisherOA PDFDOI

• Altitude estimation of radio frequency interference sources via interferometric near-field corrections

  Publications of the Astronomical Society of Australia · 2025-01-01 · 5 citations

  articleOpen accessSenior author

  Abstract Radio-frequency interference (RFI) presents a significant obstacle to current radio interferometry experiments aimed at the Epoch of Reionization. RFI contamination is often several orders of magnitude brighter than the astrophysical signals of interest, necessitating highly precise identification and flagging. Although existing RFI flagging tools have achieved some success, the pervasive nature of this contamination leads to the rejection of excessive data volumes. In this work, we present a way to estimate an RFI emitter’s altitude using near-field corrections. Being able to obtain the precise location of such an emitter could shift the strategy from merely flagging to subtracting or peeling the RFI, allowing us to preserve a higher fraction of usable data. We conduct a preliminary study using a two-minute observation from the Murchison-Widefield Array (MWA) in which an unknown object briefly crosses the field of view, reflecting RFI signals into the array. By applying near-field corrections that bring the object into focus, we are able to estimate its approximate altitude and speed to be $11.7$ km and 792 km/h, respectively. This allows us to confidently conclude that the object in question is in fact an airplane. We further validate our technique through the analysis of two additional RFI-containing MWA observations, where we are consistently able to identify airplanes as the source of the interference.

  PublisherOA PDFDOI

• The Impact of Foregrounds on Dark Ages Measurements with the Highly Redshifted 21 cm Line

  The Astrophysical Journal · 2025-08-22 · 1 citations

  articleOpen access1st authorCorresponding

  Abstract Studies of the cosmic dark ages (30 ≲ z ≲ 150) using the highly redshifted 21 cm line of neutral hydrogen offer unparalleled amounts of cosmological information, and recent years have seen the refinement of concepts for such experiments (e.g., CoDEX and FarView), nominally feasible with technology and resources in the next one to two decades. This work studies how the “foreground wedge”—a term in the 21 cm cosmology literature referring to the contamination of power spectrum modes through the combination of smooth-spectrum foreground emission and the frequency-dependent point-spread function of a radio interferometer—manifests at these very high redshifts. We find the effect is more significant than at epoch of reionization redshifts targeted by current ground-based experiments, with foreground avoidance techniques (which discard all k modes falling within the wedge) typically losing 1 order of magnitude of sensitivity. Given the extreme faintness of the 21 cm signal from the cosmic dark ages and the very high sky temperatures (the dominant source of noise) at low radio frequencies, we conclude that some level of foreground subtraction will be necessary to enable dark ages 21 cm cosmology with experiments of the scale believed to be achievable in the near term.

  PublisherOA PDFDOI

• The Impact of Foregrounds on Dark Ages Measurements with the Highly Redshifted 21 cm Line

  ArXiv.org · 2025-07-30

  preprintOpen access1st authorCorresponding

  Studies of the cosmic dark ages ($30 \lesssim z \lesssim 150$) using the highly redshifted 21 cm line of neutral hydrogen offer unparalleled amounts of cosmological information, and recent years have seen the refinement of concepts for such experiments (e.g. CoDEX and FarView), nominally feasible with technology and resources in the next one to two decades. This work studies how the "foreground wedge" -- a term in the 21 cm cosmology literature referring to the contamination of power spectrum modes through the combination of smooth-spectrum foreground emission and the frequency-dependent point spread function of a radio interferometer -- manifests at these very high redshifts. We find the effect is more significant than at Epoch of Reionization redshifts targeted by current ground-based experiments, with foreground avoidance techniques (which discard all $k$ modes falling within the wedge) typically losing an order of magnitude of sensitivity. Given the extreme faintness of the 21 cm signal from the cosmic dark ages and the very high sky temperatures (the dominant source of noise) at low radio frequencies, we conclude that some level of foreground subtraction will be necessary to enable dark ages 21 cm cosmology with experiments of the scale believed to be achievable in the near term.

  PublisherOA PDFDOI

• pyuvdata v3: an interface for astronomical interferometric data sets in Python

  The Journal of Open Source Software · 2025-05-13 · 6 citations

  articleOpen access

  pyuvdata is an open-source software package that seeks to provide a well-documented, featurerich interface for many of the different data formats that exist within radio interferometry, including support for reading and writing the following formats: UVH5 (La Plante & the pyuvdata team, 2024), UVFITS (Greisen, 2016), MIRIAD (Sault et al., 1995), and measurement set (Kemball & Wieringa, 2000) visibility files.It offers read-only support for fast holographic deconvolution (FHD, Sullivan et al., 2012) and MIR (Qi, 2022) visibility save files.Additionally, pyuvdata supports reading/writing measurement set, CalFITS (Ali et al., 2017), and CalH5 (Hazelton & the pyuvdata team, 2024) calibration solutions; and reading of FHD calibration solutions.pyuvdata also provides interfaces for and handling of models of antenna primary beams, including BeamFITS (read and write, Hazelton & the pyuvdata team, 2018), CST (read-only) and MWA beam formats (read-only).It also provides interfaces for handling of data flags.

  PublisherOA PDFDOI

• Identifying Habitable Exoplanets with Radio Telescopes on the Lunar Farside

  ArXiv.org · 2025-08-19

  preprintOpen access

  The search for habitable conditions beyond Earth is a top priority in astrophysics. The discovery of habitable exoplanets beyond our solar system will require a suite of instruments providing long-term monitoring for detection (e.g. with space and ground-based radial velocity observations), spectroscopic characterization of atmospheric and surface properties, and eventually deep chronograph-aided observations from e.g. JWST, Roman Space Telescope, and the Habitable Worlds Observatory (HWO). Detection of exoplanet magnetospheres is necessary to identify the most promising targets for follow-up characterization of biosignatures with these assets, and to provide an ensemble of objects for studies of magnetospheric conditions and atmospheric composition. Only observations of low-frequency radio emission will distinguish exoplanet magnetospheres (Hallinan et al. 2021). In this white paper, we present the two lunar radio array concepts under development that would be suitable to detect these exoplanet radio emissions. In addition, we also discuss the human exploration needed prior to construction of such lunar radio arrays while highlighting preferred candidate sites (Krolikowski &amp; Elvis 2024) for the radio telescope.

  PublisherOA PDFDOI

Recent grants

• First Science from the Epoch of Reionization with the 21cm Line

  NSF · $226k · 2013–2016

• CDS&E: A Bayesian Approach to Detecting the Cosmological 21 cm Epoch of Reionization Signal

  NSF · $377k · 2019–2023

• Collaborative Research: From 21 cm Observations to Precision Reionization Science

  NSF · $222k · 2016–2019

• Collaborative Research: 21 cm Reionization Science with the MWA

  NSF · $535k · 2021–2025

Frequent coauthors

• G. Bernardi

  Istituto di Radioastronomia di Bologna

  179 shared

• Daniel Jacobs

  Arizona State University

  140 shared

• Cathryn M. Trott

  134 shared

• M. F. Morales

  124 shared

• Adam P. Beardsley

  Winona State University

  119 shared

• B. J. Hazelton

  118 shared

• Nithyanandan Thyagarajan

  Commonwealth Scientific and Industrial Research Organisation

  115 shared

• Adam Lanman

  McGill University

  111 shared

Labs

• Jonathan Pober LabPI

  Not provided

Education

• B.A.

  Haverford College

  2007

• Other

  University of Cambridge

  2008

• M.A.

  University of California, Berkeley

  2010

• Ph.D.

  University of California, Berkeley

  2013

Awards & honors

• NASA Roman Technology Fellow