Transcript atmospheric extinction

Supporting material for Lecture 3:
Gamma-Ray Bursts and their counterparts
Light extinction:
Atmospheric absorption
Galactic extinction by dust and gas
GRBs are brief flashes of soft -ray radiation (100 keV),
discovered in the 1970’s, the origin of which was not known
until 1997
CGRO-BATSE
Early Multiwavelength Counterparts
(z = 0.937)
(z = 6.29)
(z = 1.6)
Bloom et al. 2008
atmospheric extinction
The amount of atmospheric extinction depends on the altitude
of an object, being lowest at the zenith and at a maximum near
the horizon. It is calculated by multiplying the standard
atmospheric extinction curve by the mean airmass calculated
over the duration of the observation:
Airmass = sec(z), z = zenith angle
Spectrum of star HD144470: the only line produced in the
Stellar atmosphere is He 7065, the rest are telluric
The Milky Way in Infrared (2MASS survey)
Note the Galactic Plane
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Extinction curves of our Galaxy and Magellanic Clouds
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2175 Å: graphite or PAH?
Dust suppression along given sight lines is estimated from
COBE Infrared maps:
Schlegel, Finkbeiner, Davis 1998, ApJ, 500, 525
Neutral gas in our Galaxy absorbs thru photoelectric effect.
This is predominantly neutral hydrogen (HI): the Lyman limit
occurs at 912 Å = 13.6 eV
At frequencies higher than 13.6 eV part of the X-ray flux is
Absorbed, in a frequency-dependent way
Morrison & McCammon (1983, ApJ, 270, 119) have
computed this dependence in the 0.03 - 10 keV energy
interval, taking into account cosmic abundances
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Hydrogen atom
One  = 21 cm (1420 MHz) photon is emitted when the proton
And electron spins flip from parallel to antiparallel.
Radio and far infrared images of M81 (3.6 Mpc)
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The Antennae
(22 Mpc)
White: optical
Blue: radio (21cm)
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High-z QSO spectra
(Becker et al. 2001)
The Intergalactic medium
Absorbs radiation:
Lyman alpha forest
And Lyman continuum
In high redshift quasars:
intervening absorption by
Clouds of neutral hydrogen
Elihu Boldt
The Extreme Universe: Some Views From Here
Closing lecture, 3rd INTEGRAL Workshop:
The Extreme Universe, Taormina, September 14-18 1998
Astrophysical Letters & Communications Vol. 37, 1999
arXiv:astro-ph/9902040