Lecture 4Radio SNRs- Interaction with ISM• SNRs/ISM effects of mutual interaction

• The problem of distance - Methods

• Radio continuum emission in SNRsInstruments and notions of observational techniques

• Interaction with surrounding ISM Observations

• Control brightness distribution and shape of the SNRs in the different wavelengths

• Can locally modify the particles acceleration mechanisms (change radio spectrum)

• Regulate the temporal evolution of parts or of the whole SNR

The ISM influenceSNRs

The problem of the distanceOne of the most serious problems to understand the physics of SNRs is the estimate of accurate distances.Methods:

• Historical SNRs with well established ages

• Optical measurements of proper motions

• Absorption HI spectra

• Associated atomic and/or molecular gas

• The controversial Σ− D relation

• Association with neighbouring objects, like HII regions

Absorption technique

Problem:• the background radio continuum source has to be bright enough or at least have a bright spot

Emission lines technique:

The main problem is to prove the physical association between the SNR and the surrounding ISM + use of Galactic rotation models and distance ambiguity

How to assess the interaction SNR-ISM?

HI and CO emission lines (the canonical way)H2 emission line (1-0 S(1) line at 2.122 mm, ratio of 2-1/1-0 S(1) lines)OH maser (1720 MHz, several advantages)High excitation molecular lines

Spectral study of non-thermal X-ray emission ( 10 keV) and gamma-ray detection

-4 km/s

-3 km/s

積分強度 (- 10 km s-1 ～ 0 km s-1)

電波連続波 20cm (背景)

Intrinsic errors > 30%

Distance ambiguity inside the Galaxy: 2 distances have the same radial velocity

積分強度 ( 0 km s-1 ～ 10 km s-1)

電波連続波 20cm (背景)

Σ – D relation

Very controversial (see Green)but useful for upper limits

Case & Bhattacharya (1998)

Σ 1GHz = 5.43 +8.16 -3.26 x 10 -17 D (-2.64 +- 0.26) W m-2 Hz-1 sr-1

The instruments

The resolving power of a single-dish telescope isQ(radians) ~ λ /D (D diameter of the antenna)

Filled aperture telescopes Dmax ~ 100m

To achieve an angular resolution comparable to that ofoptical observations it would be necessary a radiotelescope 1 million times bigger

Solution: array of several antennae doing interferometry

The resolution of the interferometer array is

Θ (radians) ~ λ /d (d maximum distance between antennae)

Since the separation between radiotelescopes may be thousands of kilometers, the angular resolution finallyachieved may reach values as small as one milli-arcsecond(the angular size of a person in the Moon surface).

FOV = λ / Diameter of single antennaeSmall antennae → FOV ↑, sensitivity ↓

The relative phase of the signals depends on the direction of arrival ofthe radio wave and the baseline distance between the antennas

I(l,m)V(u,v)= A(l,m) I(l,m) e dldm-2πi(ul+vm)∫∫1-l2-m2-∞

∞

Two-element interferometer

Earth rotation will move the source through the interferometer's beam, giving a quasi-sinusoidal interferometer output . This pattern is called a fringe pattern orsometimes interferogram.There are more "lobes" in the fringe pattern when the baseline is longer

Coverage of the uv plane with 12 hours observing

A “beam” has to be formed

Dirty image

After long processes of cleaning

The source is better resolved for a longer baseline

Interferometers are "spatial filters“

The response of an interferometer depends on the sizeof the radio source as well as its position.

They can spatially resolve sources producing verydetailed images, but filter out all extended components(see the trees but not the forest).

Therefore, they fail to estimate flux density if the size ofthe source is larger than the resolving power of thesingle antenna at the used frequency (primary beam).

Problem:

u l

FFT

Solution: to add observations from single dish observations

64 m

Parkes (Australia) Effelsberg (Germany)

100 m

VLA: 27 antennae of 25m in diameter spanning 35 km

GMRT: 30 antennae, 40 m diameter spread over 25 km

ATCA: 6 antennae 22m diameter along 6 km

http://www.astronet.ru/db/xware/msg/1226620/planetalignment_white_big.jpg.htmlhttp://deepspace.jpl.nasa.gov/dsn/images/album/dsn67.jpg

Radio continuum observations of SNRs

Radio observations were historically the earliest to provide systematic discovery and characterization of SNRs, and most SNRs are radio objects.

Puppis A

IC 443 W 44 SN 1006

W 28

W 50 / SS433

New VLA 1.4 GHz mosaic of Puppis-Acomposed of DnC + CnB VLA configurations data and single dish observations from Parkes Southern Galactic Plane Survey (McClure-Griffiths et al. 2001).

34′′ x 16′′ resolution image, rms 0.5 mJy/beam

Newly detected arc-like features

Bright eastern-knot (BEK)

N-S straight filament

Asymmetric shell ∼70′ x 57′39 different pointings

The radio/X-ray comparison

– The arc-like radio features near the N-NW shock front in Puppis-A have their exact counterpart in the X-rays.

– Radio emission matches some substructure observed in the Chandra image around the BEK.

●● Thermal X-ray emission

High compression of contours around the BEK suggests an encounter between the SNR shock and dense interstellar clouds.

Green: Rosat 0.1-2 keV (Petre et al. 1996)Red: VLA 1.4 GHz

Neutron star RX J0822-4300

ROSAT

Chandra 0.4-0.7, 0.7-1.2,

The spectral properties of the synchrotron radio emission from Puppis-A

Tomographic maps between 327 and 1425 MHz

α= α=

Bright regions: α steeper than the test values -0.4 and -0.6Dark regions: flatter α

Puppis Aα = -0.49 ± 0.02

●● Spectral pattern formed by short fringes, with α alternatively steeper and flatter, mimics the “arc-like” morphology noticed along the NE, NW, and S borders.•• No spectral counterpart to the brightest radio features.

The ISM around Puppis A

Paron et al. 2008

The supernova remnant W44Castelletti G., Dubner G., Brogan C., Kassim N.E. A&A, 471, 537 (2007)

● W44 SNR (∼2 x 104 yrs old) is located at 3 kpc in a complex region of the inner Galactic Plane rich in both thermal and non-thermal sources.

–– Strong molecular emission Strong molecular emission detected to the east of W44 detected to the east of W44 (Seta et al. 2004, Reach et al. 2005)(Seta et al. 2004, Reach et al. 2005). . OH1720 MHz masers detection.OH1720 MHz masers detection.

–– PSR B1853+01 located inside PSR B1853+01 located inside the radio shell the radio shell ((PetrePetre et al. 2002)et al. 2002)..

–– GeVGeV gamma rays detected by gamma rays detected by EGRET EGRET probably associated with probably associated with W44 W44 ((3EG 1856+0114,3EG 1856+0114, Esposito et al. Esposito et al. 1996)1996)..

W44 SNR: first 74 MHz (4m) image from the VLA

FoV

~ 11

°HII G037.5+00.9

HII G036.9+00.5

HII G037.2-00.4

HII G035.6+00.1

HII G035.5-00.8HII G034.9-00.0

HII G035.0-00.5HII G034.3+00.1HII G0334.5-01.1

HII G032.9+00.6SNR Kes 79

SNR 3C396

SNR Kes 78

SNR W44HII G032.1-00.3

SNR 3C391

Several galactic and extragalactic non-thermal sources and HII regions mapped in the field

HPBW 37′′rms= 65 mJy/beam

A+B config. data

VLA 324 MHz A+B+C+D config. data

PSR B1853+01

FoV

~ 2°

.5

HPBW 13′′rms = 5 mJy/beam

Integrated spectrum of W44● Our observations at 74 and 324 MHz complete the continuum spectrum S ∝ ν-0.37±0.02.

324/1442 MHz 74/324 MHzTotal power at 324 MHz

Spatially resolved radio spectrum• Bright filaments with similar α (-0.4;-0.5) andflatter diffuse interior.- First-order Fermi mechanism operating at the shock.

● “Thermal” inverted spectrum at 74 MHz indicative of free-free absorption from ionized gas.

Spectral tomography of W44

Radio + 8 and 12 microns

Interaction with the surrounding ISM

ASTE observations discovered a clump with molecular jets

Paron et al. 2009

W50/SS433 1400 MHz,

50 pointings VLA mosaic

2 degrees

HESS J1708-410/ G343.1-2.3

0º

90º

5º

20031992

Expansion parameter m vs azimuthal angle

m=0.25

m=0.4

m=0.57

Multi-frequency study of the SNR G338.3-0.0, possible counterpart of HESS J1640-465

HPBW 50''

MOST 843 NHz

G338.3-0.0

TeVsource

MULTI-FREQUENCY GMRT OBSERVATIONS AT 235, 610, 1280 MHZ

■ TeV emission detected by HESS (Aharonian et al. 2006)(average spectral photon index = 2.42 and F ∼2.2 x 10-11 erg cm-2 s-1).

■ An X-ray object at the centroidof HESSJ1640-465 (XMM-Newton observ. Funk et al. 2007).

– TeV emission originated in a PWN and/or correlated with dense ambient medium?

235 MHz

Right Ascension

Dec

linat

ion

610 MHz

G338.3-0.0

HESS1640-465

A

B

C

Kes 79: t~ 6000 yrs, d~7-10 kpc, molecular clouds to E and SEExample of SNR expanding into a wind blown bubble

pulsating X-ray sourceVLA XMM

Lecture 4Radio SNRs- Interaction with ISM