Telecon notes, NGVLA Transients/Physics SWG 2014/10/24
(Meeting notes taken by Paul Demorest)
(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
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
(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.
(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
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.
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.