-
PEACC -- Precision Emitter for 21 cm Array Coherent Calibration
Authors:
Kalyani Bhopi,
Morgan Cole,
Mallory Helfenbein,
Will Tyndall,
Audrey Whitmer,
Kevin Bandura,
Laura Newburgh
Abstract:
Foreground mitigation remains a central challenge for 21 cm intensity mapping experiments, which require precise, wideband calibration of telescope beams and gains. We present the Precision Emitter for 21 cm Array Coherent Calibration (PEACC), a digitally synthesized calibration source that generates Gaussian noise across a 1.2 GHz bandwidth, time-synchronized to a 1 pulse-per-second output from a…
▽ More
Foreground mitigation remains a central challenge for 21 cm intensity mapping experiments, which require precise, wideband calibration of telescope beams and gains. We present the Precision Emitter for 21 cm Array Coherent Calibration (PEACC), a digitally synthesized calibration source that generates Gaussian noise across a 1.2 GHz bandwidth, time-synchronized to a 1 pulse-per-second output from a GPS-disciplined oscillator, and optimized for aerial deployment. PEACC uses a dual-source architecture with one unit mounted on an aerial platform and a second reference unit connected directly to the radio data acquisition system; this configuration enables improved sensitivity in the low-SNR regime and direct phase measurement. The system further supports configurable band selection, allowing adaptation to various 21 cm intensity mapping telescopes. We validated PEACC through anechoic chamber measurements and by integrating the source on a drone flown over a local radio dish testbed. In both settings, the correlated channel substantially outperformed the auto-correlation channel across all signal-to-noise regimes of interest, confirming the key advantage of the dual-source architecture. To our knowledge, this is the first published demonstration of a free-space coherent calibration signal synchronized only by clocks, the first deployment of such a source on a drone, and the first published beam measurements made with such a source. Given the growing interest in drone-based calibration for 21 cm arrays, this work establishes the feasibility of high-fidelity digital calibration for next-generation 21 cm instruments, and provides a practical path towards improved foreground control and beam calibration in future arrays.
△ Less
Submitted 10 April, 2026;
originally announced April 2026.
-
FRB 20250316A: A Brilliant and Nearby One-Off Fast Radio Burst Localized to 13 parsec Precision
Authors:
The CHIME/FRB Collaboration,
:,
Thomas C. Abbott,
Daniel Amouyal,
Shion E. Andrew,
Kevin Bandura,
Mohit Bhardwaj,
Kalyani Bhopi,
Yash Bhusare,
Charanjot Brar,
Alice Cai,
Tomas Cassanelli,
Shami Chatterjee,
Jean-François Cliche,
Amanda M. Cook,
Alice P. Curtin,
Evan Davies-Velie,
Matt Dobbs,
Fengqiu Adam Dong,
Yuxin Dong,
Gwendolyn Eadie,
Tarraneh Eftekhari,
Wen-fai Fong,
Emmanuel Fonseca,
B. M. Gaensler
, et al. (62 additional authors not shown)
Abstract:
Precise localizations of a small number of repeating fast radio bursts (FRBs) using very long baseline interferometry (VLBI) have enabled multiwavelength follow-up observations revealing diverse local environments. However, the 2--3\% of FRB sources that are observed to repeat may not be representative of the full population. Here we use the VLBI capabilities of the full CHIME Outriggers array for…
▽ More
Precise localizations of a small number of repeating fast radio bursts (FRBs) using very long baseline interferometry (VLBI) have enabled multiwavelength follow-up observations revealing diverse local environments. However, the 2--3\% of FRB sources that are observed to repeat may not be representative of the full population. Here we use the VLBI capabilities of the full CHIME Outriggers array for the first time to localize a nearby (40 Mpc), bright (kJy), and apparently one-off FRB source, FRB 20250316A, to its environment on 13-pc scales. We use optical and radio observations to place deep constraints on associated transient emission and the properties of its local environment. We place a $5σ$ upper limit of $L_{\mathrm{9.9~\mathrm{GHz}}} < 2.1\times10^{25}~\mathrm{erg~s^{-1}~Hz^{-1}}$ on spatially coincident radio emission, a factor of 100 lower than any known compact persistent radio source associated with an FRB. Our KCWI observations allow us to characterize the gas density, metallicity, nature of gas ionization, dust extinction and star-formation rate through emission line fluxes. We leverage the exceptional brightness and proximity of this source to place deep constraints on the repetition of FRB 20250316A, and find it is inconsistent with all well-studied repeaters given the non-detection of bursts at lower spectral energies. We explore the implications of a measured offset of 190$\pm20$ pc from the center of the nearest star-formation region, in the context of progenitor channels. FRB 20250316A marks the beginning of an era of routine localizations for one-off FRBs on tens of mas-scales, enabling large-scale studies of their local environments.
△ Less
Submitted 23 June, 2025;
originally announced June 2025.
-
CHIME/FRB Outriggers: Design Overview
Authors:
The CHIME/FRB Collaboration,
Mandana Amiri,
Bridget C. Andersen,
Shion Andrew,
Kevin Bandura,
Mohit Bhardwaj,
Kalyani Bhopi,
Vadym Bidula,
P. J. Boyle,
Charanjot Brar,
Mark Carlson,
Tomas Cassanelli,
Alyssa Cassity,
Shami Chatterjee,
Jean-François Cliche,
Alice P. Curtin,
Rachel Darlinger,
David R. DeBoer,
Matt Dobbs,
Fengqiu Adam Dong,
Gwendolyn Eadie,
Emmanuel Fonseca,
B. M. Gaensler,
Nina Gusinskaia,
Mark Halpern
, et al. (44 additional authors not shown)
Abstract:
The Canadian Hydrogen Intensity Mapping Experiment (CHIME) has emerged as the world's premier facility for studying fast radio bursts (FRBs) through its fast transient search backend CHIME/FRB\@. The CHIME/FRB Outriggers project will augment this high detection rate of 2--3 FRBs per day with the ability to precisely localize them using very long baseline interferometry (VLBI). Using three strategi…
▽ More
The Canadian Hydrogen Intensity Mapping Experiment (CHIME) has emerged as the world's premier facility for studying fast radio bursts (FRBs) through its fast transient search backend CHIME/FRB\@. The CHIME/FRB Outriggers project will augment this high detection rate of 2--3 FRBs per day with the ability to precisely localize them using very long baseline interferometry (VLBI). Using three strategically located stations in North America and deploying recently developed synoptic VLBI observing techniques, the Outriggers will provide $\sim 50$~milliarcsecond localization precision for the majority of detected FRBs. This paper presents an overview of the design and implementation of the Outriggers, covering their geographic distribution, structural design, and observational capabilities. We detail the scientific objectives driving the project, including the characterization of FRB populations, host galaxy demographics, and the use of FRBs as cosmological probes. We also discuss the calibration strategies available to mitigate ionospheric and instrumental effects, ensuring high-precision localization. With two stations currently in science operations, and the third in commissioning, the CHIME/FRB Outriggers project is poised to become a cornerstone of the FRB field, offering unprecedented insights into this enigmatic cosmic phenomenon.
△ Less
Submitted 7 April, 2025;
originally announced April 2025.
-
A Digital Calibration Source for 21cm Cosmology Telescopes
Authors:
Kalyani Bhopi,
Will Tyndall,
Pranav Sanghavi,
Kevin Bandura,
Laura Newburgh,
Jason Gallicchio
Abstract:
Foreground mitigation is critical to all next-generation radio interferometers that target cosmology using the redshifted neutral hydrogen 21 cm emission line. Attempts to remove this foreground emission have led to new analysis techniques as well as new developments in hardware specifically dedicated to instrument beam and gain calibration, including stabilized signal injection into the interfero…
▽ More
Foreground mitigation is critical to all next-generation radio interferometers that target cosmology using the redshifted neutral hydrogen 21 cm emission line. Attempts to remove this foreground emission have led to new analysis techniques as well as new developments in hardware specifically dedicated to instrument beam and gain calibration, including stabilized signal injection into the interferometric array and drone-based platforms for beam mapping. The radio calibration sources currently used in the literature are broad-band incoherent sources that can only be detected as excess power and with no direct sensitivity to phase information. In this paper, we describe a digital radio source which uses Global Positioning Satellite (GPS) derived time stamps to form a deterministic signal that can be broadcast from an aerial platform. A copy of this source can be deployed locally at the instrument correlator such that the received signal from the aerial platform can be correlated with the local copy, and the resulting correlation can be measured in both amplitude and phase for each interferometric element. We define the requirements for such a source, describe an initial implementation and verification of this source using commercial Software Defined Radio boards, and present beam map slices from antenna range measurements using the commercial boards. We found that the commercial board did not meet all requirements, so we also suggest future directions using a more sophisticated chipset.
△ Less
Submitted 19 November, 2022; v1 submitted 27 January, 2022;
originally announced January 2022.