Interaction of the SNR with The Surrounding Medium

1. The Interstellar Medium (ISM) 2. Radio Telescopes 3. The Supernova Remnants (SNRs) & CO

Useful Readings

Burton, W.B. et al. 1991, “The Galactic Interstellar Medium”

Spitzer, L. 1978, “Physical Processes In The Interstellar Medium”

Dickey, J.M. & Lockman, F.J. 1990, ARA&A

The Four Components of the Interstellar Medium

Component Temperature [K]

Density [atoms/cm3]

Main Constituents

HI Clouds 50 – 150 1 – 1000 Neutral hydrogen; other atoms ionized

Intercloud Medium (HII)

103 - 104 0.01 Partially ionized H; other atoms

fully ionized

Coronal Gas 105 - 106 10-4 – 10-3 All atoms highly ionized H

Molecular Clouds 20 - 50 103 - 105 Neutral gas; dust and

molecules

HII

HII+dust

HI+dust+molecules

Star

How do we detect the ISM?Many tracers throughout the E-M spectrum

Spectral emission linese.g. H (optical), HI (radio), CO (millimeters), recombination

lines (H109 in the radio) Spectral absorption lines

e.g. HI, Ca, Na, Fe Thermal continuum emission

e.g. PAH emission (12m), HII regions (radio, infrared, optical, millimeter, …), hot, diffuse plasma (Xray)

Nonthermal continuum emissione.g. synchrotron emission from the magnetoionic medium

Absorption and Scatteringe.g. dust grains (Xray, UV, optical)

Reflectione.g. dust grains (optical light)

)1()0()(

eSeIISId

dI

Spectral Line Sources

Neutral hydrogen (H I ) spin-flip transition

Recombination lines (between high-lying atomic states)

Molecular lines (CO, OH, etc.)

Neutral hydrogen (HI) can be traced by observing this radio emission

- naturally narrow width of this line makes it an ideal diagnostic of interstellar hydrogen because the strength of the line depends on the density and temperature of the hydrogen gas.

The observation of the 21cm line of hydrogen marked the birth of spectral-line radio astronomy.

Observing Neutral Hydrogen:The 21-cm (radio) line

Observations of the 21-cm Line

All-sky map of emission in the 21-cm line

G a l a c t i c p l a n e

Observations of the 21-cm Line

HI clouds moving towards Earth

(from redshift/blueshift of line)

HI clouds moving away from Earth

Individual HI clouds with different radial velocities resolved

HI Shells and Supernova Remnants: SNR G327.7+0.4

The HI around a supernova remnant (SNR) is also modified by the remnant

HI ring around SNR G327.7+0.4

The Most Easily Observed Molecules in Space

The Most Common Molecule in Space:

Use CO as a tracer for H2 in the ISM.

H2 = Molecular Hydrogen can be detected by far ultraviolet absorption and emission:

- very difficult to observe.

But: Where there’s H2, there’s also CO - cloud may contain only 1 CO per 10,000 H2, - enough to see

• CO = Carbon Monoxide Radio emission• OH = Hydroxyl Radio emission.

• CO emission lines show molecular cloud complexes.

• Stars apparently form in these dense regions.

A common view of the ISM?

BBU CO GRS

CGPS HI

Tracing the ISM Life CycleSupernova Explosions

Star Formation

Hot Gas:Bubbles, shells,

& chimneys

Diffuse WNM

Molecular Clouds

Cold atomic clouds

Stellar WindsHII regions

Planetary Nebulae

Nucleosynthesis

H2, CO and other molecular lines

Masers

HI absorption

HI emission

Fluorescence of an H envelope NII, OII, H, etc.

Thermal continuum

Dredge up spectral linesMetals in the ISM

Far-UV and Xray continuum,

H, OVI spectral lines

Electromagnetic Radiation

Wavelength

Radio Detection techniques developed from meter-wave to submillimeter-wave: = 1 meter = 300 MHz

= 1 mm = 300 GHz

What looks dark in one wavelength may look bright in another.

Light Pollution

Earth at Night Credit: C. Mayhew & R. Simmon (NASA/GSFC), NOAA/ NGDC, DMSP Digital Archive

What do Radio Astronomers measure?

Luminosity of a source: L = dE/dt erg/s Flux of a source at distance R:

S = L/4R2 erg/s/cm2

• Flux measures how bright a star is. In optical astronomy, this is measured in magnitudes, a logarithmic measure of flux.

• Intensity: If a source is extended, its surface brightness varies across its extent. The surface brightness is the intensity, the amount of flux that originates from unit solid angle of the source:

I = dS/d erg/s/cm2/steradian

|u ()|2

|u ()|2

Radiometer Equation For an unresolved source, the detection sensitivity of a radio

telescope is determined by the effective area of the telescope and the “noisiness” of the receiver

For an unresolved source of a given flux, S, the expected antenna temperature is given by

kTA = ½ Ae,maxS The minimum detectable TA is given by

TA = Ts/(B)

where Ts is the system temperature of the receiver, B is the bandwidth and is the integration time, and is of order unity depending on the details of the system. The system temperature measures the noise power of the receiver (Ps = BkTs). In Radio Astronomy, detection is typically receiver noise dominated.

How do radio telescopes work?

Sources of Radio Emission

1. Blackbody (thermal)2. Continuum sources 3. Spectral line sources

Blackbody Sources

Peak in cm-wave radio requires very low temperature: mT = 0.2898 cm K

Cosmic Microwave Background is about the only relevant blackbody source

Ignored in most work – essentially constant source of static (same in all directions) and much weaker than static produced by instrumentation itself

Continuum Sources

Due to relativistic electrons:

Synchrotron radiation

Bremsstrahlung Quasars, Active Galactic Nuclei, Pulsar

s, Supernova Remnants, etc. Used by ALFALFA for calibration

H I spectral line from galaxy shifted by expansion of universe (“recession velocity”) and broadened by rotation

Frequency

What is Resolution?

SN typesType Ia

Disruption of a binary system:

SNR

Type II

Core-Collapse:Neutron Star or a black hole SNR

Why SNe?

SN 1987A discovered by I. Shelton 02/24/87 (originally from Winnipeg!)

Neutrinos!(a SN explosion releases 1053 ergs,erg=10-7 J)

Why Study SNRs ?

•Interstellar Medium : Dynamics, Energetics, Magnetic Field

•Tracking the elements we are made of!

• Nearby Laboratory to study physics in extreme conditions: Neutron Stars & Black Holes (QED, General Relativity, Gravitational Waves)

Survey of Molecular Clouds around Galactic SNRs

Yamamoto, F.; Hasegawa, T.; Sawada, T.; Sugimoto, M.; Naitoh, S.; Handa, T.; Sofue, Y.

IAU 8th Asian-Pacific Regional Meeting

Survey of Molecular Clouds around Galactic SNRs

The Environment of Tycho: Possible Interaction with the Molecular Cloud

Lee, Jae-Joon; Koo, Bon-Chul; Tatematsu, Keni'chi

2004ApJ...605L.113L

Type Ia, 1572, d=2.3 Kpc

Thank you for your attention