The Dynamic Radio Sky

Transcription

1 The Dynamic Radio Sky Exoplanet Bursts, Lunar Neutrinos, and other Exotica Joseph Lazio (Naval Research Laboratory SKA Program Development Office)

2 Who Cares? Radio transients are like butterfly collecting is the 200 th anniversary of the birth of Charles Darwin (1809 February 12) Astronomy is an observational science As is evolutionary biology Yet collecting has led to the development of evolutionary relationships.

3 Who Cares? Transient radio sources are necessarily compact Locations of explosive or dynamic events Probe fundamental physics and astrophysics Radio signals modified by intervening media and are powerful probes of those media Dispersion Scattering Faraday rotation

4 The RadioTransient Sky Science Planets Solar(!) Extrasolar Brown Dwarfs New behavior from old friends Neutron stars Radio-wave scattering Lunar neutrinos Exotica ETI Exploding black holes Technology Time Domain Observations Confusion RFI Flexible scheduling Frequency agility Data Management

5 Solar Planetary Radio Emission Solar wind loading of magnetosphere produces radio emission 1% of auroral input energy into electron cyclotron radio emission ν < 40 MHz Accurate position of radio emission remains poorly unknown, even today! viz. LOFAR observations Basic plasma physics Model for stars, brown dwarfs, other planets, Jupiter

6 Extrasolar Planetary Radio Emission HD M = 3.32 M J P = 267 d (a = AU) e = 0.23 Discovery of extrasolar planets! ~ 400 extrasolar planets Indirect detection via optical signature Detecting characterizing: What are their properties? Can we detect planets at other wavelengths? IR thermal emission detected? Magnetospheric radio (viz. Jupiter) Implications for habitability?

7 Lighthouse-like Brown Dwarfs M9 dwarf P = hr Brown dwarf magnetosphere / emission mechanism Connection to pulsar magnetosphere? Current work typically at 5 and 8 GHz Largely unexplored ~ 1 GHz TVLM (Hallinan et al. 2007)

8 Dwarf Stars Radio emission from nearby dwarf stars E.g., AD Leo with Arecibo (~ 1.5 GHz) Structure on millisecond time scales Magnetized plasma processes in stellar coronae E.g., cyclotron maser AD Leo (Osten & Bastian) Living with a Star Real world application of

9 Transient Pulsars Long-term On-off transition < 10 s Off ~ 30 days Intrinsic Pulsar wind and emission mechanism (or ETI?) ~ 1 GHz s/s s/s PSR B Modified Julian Date (Kramer et al. 2006)

10 RRATs On ~ 10 ms Off >~ 1 hr Intrinsic Pulsar emission mechanism and/or magnetosphere Frequency (MHz) Amplitude (mjy) Time J ~ 1.4 GHz (McLaughlin et al. 2005)

11 Propagation Effects Extreme scattering events are one manifestation Months to years Extrinsic Probe of intervening medium(a) Flux Density (mjy) Date J (Maitia et al. 2003)

12 Giant and Nano-giant Pulses On ~ 2 ns duration Off ~ 10 min. T B > K Brightest objects in the Universe Probes pulsar emission mechanism scattering environment? Crab pulsar (Hankins et al. 2003) 5.5 & 8.6 GHz

13 Probing the Local Group Power-law distribution of pulse strengths Longer observations means stronger pulses Majority of Local Group medium ionized ( missing baryons ) Possible probe of local intergalactic medium? Cf. FUSE, Chandra probes of tracer species (O VI, O VII, etc.)

14 Lunar Neutrinos Moon as a beam dump Ultra-high energy ν initiates particle shower E ν ~ ev (or higher?) Negative charge excess develops Coherent radio pulse Askar yan effect Hyper-GZK probe of Universe GZK effect limits our view of Universe (HiRes experiment; arxiv:astro-ph/ ) How Do Cosmic Accelerators Work? (Quarks to Cosmos) γ HiRes ν

15 GCRT J A monitoring campaign of the Galactic center λ 1 meter Roughly 20 epochs Time samplings from ~ 1 week to 1 decade Observations with Very Large Array (most) Giant Metrewave Radio Telescope Hymanet al. 2005

16 Exotica Rees (1977) predicts primordial black holes will produce radio pulses Series of searches 40 MHz 430 MHz (= 1.8 µev, Phinney & Taylor) ~ 1 TeV (Linton et al.) Interest in Fermi/GLAST searches (e.g., Dingus et al.)

17 Extraterrestrial Intelligence Radio signals can cross the Galaxy essentially unimpeded. CP 1919 was L.G.M 1 When we least expect it? Fortune favors the prepared mind The Universe is full of magical things, patiently waiting for our wits to grow sharper. Eden Phillpotts Ardipithecus ramidus Jocelyn Bell, 1967 Modified Julian Date

18 Transient Phase Space Physics: SD 2 = 2kT B (tν) 2 Raleigh-Jeans law S = 2kT B /λ 2 * Ω Observational: S = (2kT B /c 2 ) Ω ν 2 (and time res., cadence, ) Non-imaging Extension of typical pulsar processing Imaging Visibilities, sky models, residual images,

19 Transient Phase Space νw = dimensionless pulse width, uncertaintylike relation SD 2 = pseudoluminosity J. Cordes

20 Transient Phase Space Observational / empirical approach How does a telescope (SKA) compare with existing & previous searches? Arecibo, ATA, LOFAR, E VLA, LOFAR ATA Fly s Eye Gain (K/Jy) Field of View (arcminutes) 278 deg deg EVLA Fly s Eye Frequency (MHz)

21 Long Wavelength Demonstrator Array MHz 16-element dipole station At VLA site in NM Existence proof for transient detection with (sparse) aperture arrays

22 Radio Transients More than butterfly collecting! Probe fundamental physics and astrophysics Probe intervening media Increasing opportunities Both scientific & technical Imaging & non-imaging! Both A/T and Ω are important!