[Paper Review] Next Generation Very Large Array Memo No. 9 Science Working Group 4: Time Domain, Fundamental Physics, and Cosmology

Geoffrey C. Bower, Paul Demorest+21 more|arXiv (Cornell University)|Oct 21, 2015

Radio Astronomy Observations and Technology4 references3 citations

TL;DR

This paper outlines transformative science opportunities for the Next Generation Very Large Array (ngVLA) in time-domain astronomy, fundamental physics, and cosmology, focusing on detecting electromagnetic counterparts to gravitational waves, timing pulsars near the Galactic Center black hole, and enabling high-precision astrometry. The ngVLA’s enhanced sensitivity, wide frequency coverage (1–115 GHz), long baselines (up to 300 km), and high dynamic range imaging will enable breakthroughs in probing black hole physics, cosmic distance scales, and plasma processes in extreme environments.

ABSTRACT

We report here on key science topics for the Next Generation Very Large Array in the areas of time domain, fundamental physics, and cosmology. Key science cases considered are pulsars in orbit around the Galactic Center massive black hole, Sagittarius A*, electromagnetic counterparts to gravitational waves, and astrometric cosmology. These areas all have the potential for ground-breaking and transformative discovery. Numerous other topics were discussed during the preparation of this report and some of those discussions are summarized here, as well. There is no doubt that further investigation of the science case will reveal rich and compelling opportunities.

Motivation & Objective

• To identify and prioritize high-impact scientific opportunities for the ngVLA in time-domain phenomena, fundamental physics, and cosmology.
• To address the critical need for detecting electromagnetic counterparts to gravitational wave events from compact object mergers.
• To enable precise timing of pulsars orbiting the Galactic Center supermassive black hole, Sagittarius A*, for testing general relativity.
• To advance astrometric cosmology by measuring cosmic distances and probing dark energy through maser and intensity mapping techniques.
• To define technical requirements for ngVLA that support these transformative science cases, including sensitivity, bandwidth, and array configuration.

Proposed method

• Leverage the ngVLA’s 10× greater collecting area and 10× longer baselines (up to 300 km) compared to the JVLA and ALMA to achieve milliarcsecond resolution and high surface brightness sensitivity.
• Utilize a dense core with km-scale baselines to image compact, bright features embedded in extended emission, such as relativistic jets and relic structures.
• Implement wideband, high-time-resolution observations across 1–115 GHz to enable robust spectral index measurements and detect variable or transient radio sources.
• Employ real-time processing and high data rate systems to monitor slower transients (e.g., tidal disruption events, radio flares) over hours to days.
• Integrate VLBI techniques with ngVLA to achieve sub-mas relative astrometry and absolute position accuracy via long-baseline baselines up to 5000 km.
• Design observing modes with continuous 1 GHz bandwidth and 25 kHz spectral resolution to resolve narrow-line profiles in masers and detect circularly polarized emission.

Experimental results

Research questions

• RQ1 Can the ngVLA detect and characterize electromagnetic counterparts to gravitational wave events from neutron star and black hole mergers with sufficient sensitivity and time resolution?
• RQ2 What is the feasibility of detecting and timing pulsars in tight orbits around Sagittarius A* to test general relativity and probe black hole spin and mass?
• RQ3 How can ngVLA enable high-precision astrometry of cosmic masers and intensity mapping to constrain cosmological parameters and dark energy?
• RQ4 What technical configurations and observing modes are required to detect low-level, variable radio emission from exoplanet space weather and stellar winds?
• RQ5 How can the ngVLA’s wideband, high-dynamic-range imaging resolve compact, bright features in extended emission regions such as radio relics and jets?

Key findings

• The ngVLA can image the radio relic in A2256 with 3 arcsec resolution and 20:1 S/N in 25 hours using a 400-pointing mosaic at 10–50 GHz, assuming 3× VLA collecting area and 12m antennas.
• A 10–50 GHz observation of A2256 with 3× VLA sensitivity and compact configuration can achieve 100 nJy RMS sensitivity, enabling robust spectral index measurements across a decade of frequency.
• For exoplanet space weather, the ngVLA can detect ionized winds from M dwarfs at 10 pc with 100 nJy RMS at 10 GHz for 5σ detection at 100× solar mass loss rate, and 50 nJy RMS at 5 pc for 25× solar mass loss rate.
• The ngVLA can detect circularly polarized emission at 20% of total intensity from a 10 pc source with L_r ≈ 10^13 erg/s/Hz in 5 minutes, requiring 100 nJy sensitivity over 500 MHz bandwidth.
• For astrometry, at least 20% of ngVLA’s collecting area must be dedicated to baselines up to 5000 km in both east-west and north-south directions to achieve sub-mas absolute position accuracy.
• Spectral observing modes with 1 GHz contiguous bandwidth and 25 kHz resolution are essential for resolving narrow-line maser profiles and enabling high-precision astrometry.