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imagepol.fourierrotationmeasure - Function

1.1.4 Find Rotation Measure (Fourier approach)


Description

This function will only work if you attach the Imagepol tool (using open) to an image containing Stokes Q and U, and a regular frequency axis. It Fourier transforms the complex linear polarization (Q+iU) over the spectral axis to the rotation measure axis. Thus, if your input image contained RA/DEC/Stokes/Frequency, the output image would be RA/DEC/RotationMeasure. The Rotation Measure axis has as many pixels as the spectral axis.

This method enables you to see the polarization as a function of Rotation Meausure. Its main use is when searching for large RMs. See Killeen, Fluke, Zhao and Ekers (1999, preprint) for a description of this method (or http://www.atnf.csiro.au/$\sim$nkilleen/rm.ps) and its advantages over the traditional method (rotationmeasure) of extracting the Rotation Measure.

Although you can write out the complex polarization image with the argument complex, you can’t do much with it because Image tools cannot handle complex images. Hence you can also write out the complex linear polarization image in any or all of the other forms.

The argument zerolag0 allows you to force the zero lag (or central bin) of the Rotation Measure spectrum to zero (effectively by subtracting the mean of Q and U from the Q and U images). This may avoid Gibbs phenomena from any strong low Rotation Measure signal which would normally fall into the central bin.

Arguments





Inputs

complex

Output complex linear polarization image file name. Default is unset.

allowed:

string

Default:

amp

Output linear polarization amplitude image file name Default is unset.

allowed:

string

Default:

pa

Output linear polarization position angle (degrees) image file name Default is unset.

allowed:

string

Default:

real

Output linear polarization real image file name Default is unset.

allowed:

string

Default:

imag

Output linear polarization imaginary angle image file name Default is unset.

allowed:

string

Default:

zerolag0

Force zero lag to 0 ?

allowed:

bool

Default:

false

Returns
bool

Example

 
 
"""  
#  
print "\t----\t fourierrotationmeasure Ex 1 \t----"  
po.imagepoltestimage(outfile=’iquv.im’, rm=[5.0e5,1e6], nx=8, ny=8, nf=512,  
                     f0=1.4e9, bw=8e6)  
po.fourierrotationmeasure(amp=’amp’)  
ia.open(’amp’)  
ia.statistics()  
#viewer()                     # And reorder to put RM along X-axis  
#  
"""  
 

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