NextNext GenerationGeneration VLBIVLBI

Michael Bietenholz York University TheThe RoleRole ofof VLBIVLBI

• Resolution! VLBI provides a resolution which cannot be routinely matched in any other band, typically 1 milliarcsec at 5 GHz, down to 20 micro-arcsec at 345 GHz • Sensitive to high brightness temperatures and thus mostly non- thermal emission. Radio is relatively extinction-free • Very wide range of science applications: AGN, explosive events (FRB, GRB, SNe, TDE...), masers, pulsars, radio stars • Astrometry: parallaxes, proper motions, ICRF • Canada was a pioneer in VLBI (Penticton & Algonquin, 1967) VLBI Developments • More VLBI-capable telescopes coming online: . MeerKAT / South Africa . ASKAP / Australia . African VLBI Network Sicaya, Peru . FAST / China • Sicaya / Peru Kuntunse, Ghana • Space-VLBI: Millimetron (Spektr-M) project • Calibration strategies (multi-view, wide-field observations with in-beam calibrators) millimetron.ru • Higher recording bandwidths • Using remote atomic clocks over optical fibre links

MeerKAT, South Africa FAST, China VLBI Astrometry

• Phase-referenced differential astrometry with VLBI today can measure positions with ~10 micro-arcsec or better • With SKA-1: accuracies of 3~5 micro-arcsec; parallaxes of ~4% out to Galactic centre; proper motions of 0.2 km/s in one year at 2 kpc • Accuracy better than that obtainable with GAIA • VLBI astrometry may be required to accurately calibrate GAIA parallaxes • VLBI is not affected by dust: can do Galactic centre and star-forming regions • VLBI is only feasible for brightness temperatures > 107 K, in other words, mostly non-thermal sources like masers, chromospherically active young stars (mostly low-mass), pulsars (and AGN; GAIA will see largely stars) • VLBI measurements allow – tomographic mapping of the star-forming regions and of the Galaxy. – Parallax accuracy at 3 kpc (~50pc) are sufficient to resolve structure in spiral arms which have widths of ~100's of pc VLBI of Galactic Sources

• Many of the sources (active stars, pulsars) are relatively faint. • Sensitive, long baselines, such as provided by MeerKAT or SKA with either European or Australian antennas, are crucial for astrometry of Galactic sources

Figure: a simulated population of 12 GHz masers

van Langevelde & Quiroga-Nu ñes Astrometry of Galactic Masers and Pulsars

• Early results from Reid et al. 2010 • Trigonometric parallaxes to masers in Galactic star-forming regions. Distance error bars mostly smaller than dots! 12 GHz Methanol masers

H2O masers

Reid et al 2009; Galaxy image R. Hurt: Pulsar Proper Motions

• Observing pulsars near the Galactic centre will allow tests of general relativity, determine the mass of the Galactic centre black hole as well as characterize the interstellar medium near the Galactic centre • Accurate positions and proper motions (as well as pulsar timing) will be key to these science goals • Although many are expected to exist, none have so far been detected, so any pulsars near Galactic centre will be faint • Pulsars in the rest of the Galaxy have high proper Proper motion of the Galactic centre magnetar, motions (~250 km/s) thought to PSR J1745-2900, at only 0.1 pc from Sgr A*, be due to an initial "kick" measured by VLBI (Bower et al 2015) Scattering: Pico-arcsec Astrometry

Figure: Ue-Li Pen

 Radiation from pulsars is scattered and reaches the Earth via multi-path propagation. Recent VLBI observations (Brisken et al 2010) have shown that it is possible to use this scattering screen as a billion-km baseline, and resolve motions of ~50 pico-arcsecs (Pen et al 2014)  Low frequency: Penticton & Algonquin  Pulsar binary orbits  Pulsar magnetosphere structure  ISM structure  Pulsar timing arrays (obtain distances) VLBI for Transients Speed Distance Typical for … Angular velocity 20 km/s 10 kpc Star 0.4 mas/yr

5000 Nova, Cataclysmic 10 kpc 2 mas/week km/s Variable c 10 kpc Relativistic 0.7 mas/hour 20000 10 Mpc Supernova 0.4 mas/yr km/s c 100 Mpc Relativistic 0.6 mas/yr

VLBI follow-up will be crucial for determining the proper motions (including expansion) expected in a wide range of transients. Short transients are expected to be small because of light-travel time arguments, and thus of scales for which VLBI resolution is required for followup Recurrent Nova RS Ophiuci O’Brien et al. 2006 Relativistic Expansion: Gamma-Ray

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GRB 030329 was associated with supernova 2003dh VLBI measurements: by Taylor, Pihlstrom et al. show clear super-luminal motion, and then deceleration, with transition to non-relativistic regime at t ~1yr SN 1986J: Black Hole with Jets?

Speculative cartoon: 2003 Contours, red: 5 GHz Blue → white: 15 GHz

2014 5 GHz

• Could SN 1986J host an accreting black hole with jets, where the jets produce the NE hot-spot and the faint SW extension?

Bietenholz & Bartel, 2017 SN 1986J: Black Hole with Jets?

Speculative cartoon: 2003 Contours, red: 5 GHz Blue → white: 15 GHz

2014 5 GHz

• Could SN 1986J host an accreting black hole with jets, where the jets produce the NE hot-spot and the faint SW extension?

More generally: GRB & SN morphology, CSM structure, relation to SNe VLBI for Transients: Example • The most energetic known neutrino (2 PeV) was detected by the IceCube Neutrino Observatory at the South Pole in Dec 2012. It was officially called HESE-35, but known as "Big Bird" • A single particle – about as transient as you can get! • VLBI observations were crucial in identifying a variable quasar PKS B1424-418 (z = 1.52) as the origin of Big Bird (Kadler et al., 2016) Image: IceCube Collaboration. Gravitational Lensing

• We’re on the verge of a z = 3.2 huge increase in source

known gravitational zlens = 0.35 lenses with Euclid LSST in optical/IR and ASKAP, MeerKAT, SKA in radio (Lens not • SKA1 MID will detect visible in 5 radio) 10 new, radio-loud M

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galaxy as well as dark matter profile Event Horizon Telescope

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Image: H. Falcke Use mm-wave (350 GHz) VLBI to obtain highest angular resolution of SgrA*, M87 and other nearby SMBH: image black hole shadow