Telecon notes, NGVLA Transients/Physics SWG 2014/10/24

(Meeting notes taken by Paul Demorest)

Meeting participants:

Geoff Bower, Jim Braatz, Paul Demorest, Walter Max-Moerbeck, Nissim Kanekar, Rachel Osten, Bryan Butler, Steve Myers, Frazer Owen, Brian Metzger, Jeremy Darling, Dan Marrone, Miguel Morales, Michael Rupen, Sarah Burke-Spolaor

Telecon Notes:

Introduction (Geoff): Aim is to develop science case for "next-gen VLA" type instrument, operating at >~ 3 GHz freq, avoiding overlap with SKA-mid and lower-freq science. Immediate goal is ~1 hour presentation for AAS workshop Jan 4. Eventually whitepaper. 3 other science working groups exist on other topics. External speaker for our session is R. Kawabe. On this call, discuss topics, try to arrive at ~3 key science drivers in broad "physics/transients/cosmology" area.

Science topics discussed during the call (with primary discussers noted):

Galactic Center pulsars (Geoff): Timing and searching for pulsars (esp MSPs) at the galactic center needs >~ 10 GHz to beat scattering. Lots of potential payoff in tests of GR, BH mass/spin, etc. Paul: Most other (non-GC) pulsar projects better done at lower freqs.

EM counterparts to GW events (Geoff): Advanced LIGO/VIRGO will be detecting poorly localized GW events during this timeframe. Followup/localization can be done similar to current VLA+GRB, etc type observations.

H20 masers around SMBHs (Jim): Currently ~150 known systems, of which ~30 are "interesting" and ~12 imaged with VLBA/GBT giving rotation curves, BH masses. Sensitivity limited, needs VLBI baselines (~1-3 km), ideally with ~GBT-scale collecting area (at K-band) on each. Could lead to ~10x increase in number of measured systems, improving H0 measurement from current ~5% to ~2%. Also probe breadown of M-sigma realation. Discussion of whether existing large telescopes are good enough to provide the long baselines: GBT is good, Bonn not great at K-band, QTT interesting but not much visibility overlap, SRT "incremental". High-redshfit masers potentially interesting, largely uncharacterized so far.

Plasma physics (Frazer): Not much connection between plasma physics and radio astronomy community. Could probe processes such as particle acceleration in cluster relics. current obs show hints of flat-spectrum emission, unexplained by theory, unexplored param space at high radio freqs. Sensitivity/FoV limited, would benefit from mosaic imaging. Other plasma-related topics include reconnection, solar physics.

Solar phyiscs (Rachel): Should have planet in habiatble zones found by mid-2020s. Radio observation can support exoplanet research, explore solar wind/weather in extrasolar systems. Bryan: Maybe should go in Cradle of Life rather than this group? Rapid response to triggers from LSST/etc (eg recent "superflare") interesting. This would benefit from large instantanous BW. "explosion" type events often occur fastest at higher freq so rapid followup interesting.

Evolution of physical constants (Nissim): Methanol and ammonia lines up to ~100 GHz useful for this. Current obs are sensitivity-limited, point sources, absoption lines. Ongoing current VLA project to do this for a few sources. wide BW needed to get multiple lines.

Redshifts vs time (Jeremy): Observing redshift change with time for individual objects. Used to be part of large optical (eg TMT) science case, has fallen off that. Needs ~10 year timespan, narrow lines (CO absorption?), averaging over many objects needed to measure cosomological component. Steve/Michael: individual object acceleration (non-cosmological) is interesting anyways.

Tidal disrpution events (Brian M): Disruption of star by BH triggers relativistic jet and synch radiation. Signal may be much stronger at higher freqs (vs ~1 GHz). Investigate AGN turn-on, probe evolution of BHs versus redshift.

Mapping molecular gas (Dan): cross-correlate with spectra from upcoming large optical surveys to map out otherwise unresolvable mol. gas. Survey speed needed.

Imaging variable sources (Michael): High-sensitivity (~us), high-resolution (~mas) imaging of ~10^4 K emission from X-ray binaries, novae, stellar outflows. Not possible with current instruments. Resolution should match sensitivity for variable sources -- no point in having nJy sensitivity on a mJy source, if that mJy source is a tenth the size of your beam. High frequencies --> large uv --> high angular res'n; we should aim at res'n such that (e.g.) a 1000 K source is 10sigma in 10 hrs at 45 GHz.

Action items

How to move forward (Geoff):

• Set up wiki (Paul/Bryan); want ~1 paragraph plus figure for each topic (everyone).
• Next telecon in ~2 weeks,
• collect more topics and/or more people.
• Should compile list of who in the group will be at AAS.