Title: Interstellar Scintillation
1Interstellar Scintillation micro-arcsecond
scale structure in AGN
- Hayley Bignall (JIVE)
- J-P Macquart (Kapteyn Institute, Groningen)
- Dave Jauncey, Jim Lovell, Tasso Tzioumis (ATNF)
- Lucyna Kedziora-Chudczer (U. Sydney)
2Outline
- IDV and ISS some background
- Latest results for the fast scintillator,
PKS 1257-326 - Brief overview of last weeks workshop in
Dwingeloo Interstellar scintillation of
Extragalactic Radio Sources
3 Discovery of IDV
- 1984 flicker - timescales 2-10 days at 2.7 GHz
(Heeschen) - "Intraday variability" (IDV Witzel et al. 1986,
Heeschen et al. 1987) - Debate over origin intrinsic vs scintillation
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5Regimes of scintillation
STRONG SCATTERING
WEAK SCATTERING
Fresnel scale rF(lL/2p)1/2
tref
Log time scale
tweak
tdiff
Log frequency
6PKS 0405-385 the first intra-hour variable
- Kedziora-Chudczer et al. (1997)
8.6 GHz
4.8 GHz
2.3 GHz
1.4 GHz
7PKS 0405-385 ISS model
RMS fractional variations as a function of
frequency
8PKS 0405-385
- Rapid variability interpreted as interstellar
scintillation (ISS) by Kedziora-Chudczer et al.
(1997) - Still a high brightness temperature (D1000
required) using standard model of Galactic
electron density (TC93) - Model of Rickett et al. (2002) implies nearby
screen (3-30 pc) Tb reduced to 2x1013 K
9PKS 1257-326 the third intra-hour variable
- The second well-studied IHV?! is J18193845
(Dennett-Thorpe de Bruyn, 2000), discovered
with WSRT - PKS 1257-326 was discovered serendipitously in
2000, in ATCA data at 4.8 and 8.6 GHz - ID quasar at z1.256 (Perlman et al. 1998),
B18.7 - X-ray flux 2x10-13 erg cm-2 s-1 (0.1-2 keV)
- Flat radio spectrum ltSgt 0.3 Jy
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11Two-station time delay
- Simultaneous VLA/ATCA observations
- Performed in 2002 May, 2003 Jan, March
- 2 consecutive days, 2 frequencies
- 4.86 GHz, 8.46 GHz, 100 MHz bandwidth
- Only 2.8 h common visibility low elevations
- Secondary calibrator PKS 1255-316 1o separation,
non-IDV (? 1), 2 Jy - Arcsecond-scale structure subtracted
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14Time delay, May 13-14 2002
VLA
ATCA
May 13, 4.9 GHz
May 13, 8.5 GHz
Flux density (0.2-0.4 Jy)
May 14, 4.9 GHz
May 14, 8.5 GHz
Time (4 hour range)
15Time delay, Jan 10 2003
Jan 10, 4.9 GHz
Jan 10, 8.5 GHz
Flux density (0.2-0.4 Jy)
VLA
ATCA
Time (4 hour range)
16Time delay, Mar 6-7 2003
VLA
ATCA
Mar 6, 4.9 GHz
Mar 6, 8.5 GHz
Flux density (0.2-0.4 Jy)
Mar 7, 4.9 GHz
Mar 7, 8.5 GHz
Time (4 hour range)
17Fitting to a constant time delay (May data)
c2
Time delay (0-1000 s)
18Fitting to a constant time delay (Jan data)
c2
Time delay (0-1000 s)
19Fitting to a constant time delay (March data)
c2
Time delay (0-1000 s)
20Flux density difference, before and after
applying time shift (March data)
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224.8 GHz
8.6 GHz
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25Fitting time delay annual cycle
- Free parameters are
- Velocity of scattering screen (vRA, vdec)
- Characteristic length scale s0
- Axial ratio and position angle of anisotropy, R,
b - Data ? J-Ps fitting code combined c2
minimization ? fits! - (work in progress)
26S01.5x105 km vRA27 km s-1 Vdec6 km
s-1 R10 B-40o
27S0105 km vRA27 km s-1 Vdec6 km s-1 R5.6 B-40o
28LSR
29Implications
- If rF105 km at 4.8 GHz (l6.25 cm), then screen
distance L30 pc - For best fit, source cant be bigger than 100x40
mas ? Tb 3 x 1012 K
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33PKS 1257-326
- Combined time delay annual cycle is a neat
method of constraining scintillation parameters - Still much more to get out of the data! e.g
- intrinsic variations and frequency dependence
- polarization (cf Rickett et al. 2002)
- Behaviour of PKS 1257-326 is remarkably similar
to J18193845! - What makes these sources special?
34- A small workshop held at ASTRON/JIVE, Dwingeloo,
the Netherlands, 5-7 April 2004 - SOC de Bruyn, Jauncey, Bignall, Macquart,
Gurvits - 25 participants, most gave talks
- Plenty of discussion time
35Summary of ISS workshop
- Majority of presentations were on radio IDV/ISS
in AGN observations and theory/modelling. - Several presentations on VLBI results
- A few on the ISM, scattering screens
- Two talks on scintillation of GRBs
- All presentations will soon appear online at
http//www.jive.nl/meetings/iss_workshop - Some points of discussion
36ISS workshop some of the topics discussed
- Lovell MASIV Survey 700 sources observed, only
one J1819! Are 1257 and J1819 special sources,
or on a special line-of-sight (or both?!) - Walker IDV scattering screens clues from
pulsar spectroscopy - Scintillation arc analysis (Stinebring et al.)
- Anisotropic scattering, thin screens
- Fast scintillators dont need special scatterers,
just local examples of a population which
pervades the Galactic disk - Other talks related to ISM/screens Cordes (the
Galaxy is grossly undersampled) Fuhrmann
37ISS workshop some of the topics discussed
- Macquart diffractive scintillation in
J18193845 modelling implies minimum Tb 1015 K - Rickett scintillation arc analysis finds
different limits on source angular size - Conflicting results need to be reconciled
J18193845 dynamic spectrum
38ISS workshop some of the topics discussed
- The (very few!) fast scintillators allow fairly
detailed modelling (Earth Orbit Synthesis), but
to do the same with the slower scintillators
requires much more dedicated observing - Jauncey monitoring programs like Ceduna, GAVRT
- Future instruments? The ATA, other SKA
demonstrators.
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