Visibility workshop

Welcome to the visibility workshop!

Please take notes and submit them to steven.d.christe@nasa.gov!

Introduction (by G. Hurford)

powerpoint presentation

Imaging with Visibility (by P. Saint-Hilaire)

powerpoint presentation

Visibilities on the Command Line (by P. Saint-Hilaire)

powerpoint presentation

;;CODE FOR DEMO:

	;RESTORE, 'visibility_bag_20021126.sav',/V
	RESTORE, 'visibility_bag_20021126_5min.sav',/V
	RESTORE, 'srctrack_20021126.sav',/V

vis00=vis0
;ss=WHERE(vis00.isc GE 7) & vis0=vis00[ss]
ss=WHERE(vis00.trange[0] GE anytim('2002/11/26 20:00') AND vis00.trange[0] LE anytim('2002/11/26 22:00')) & vis0=vis00[ss]

	nvis=N_ELEMENTS(vis0)
	phase_map_center=vis0[0].xyoffset	;; reference phase_map_center to fool software with


		.RUN
		vis1='bla'
		FOR i=0L, nvis-1 DO BEGIN
			IF i MOD 1000 EQ 0 THEN PRINT, i
			t=get_edges(vis0[i].trange,/mean)
			newx=INTERPOL(srctrack.X, srctrack.t, t)
			newy=INTERPOL(srctrack.Y, srctrack.t, t)
			tmp=hsi_vis_shift_mapcenter(vis0[i], [newx,newy])	;;changing the phase so that each visibility is centered on source's exact centroid position
			IF datatype(vis1) EQ 'STR' THEN vis1=tmp ELSE vis1=[vis1,tmp]
		ENDFOR;i
		END;.RUN
		vis1.xyoffset=phase_map_center	;; makes the s/w believe all the visibilities are referenced to the same xyoffset (phase_map_center)

	;RESTORE,'vis1.sav',/V

	!P.MULTI=[0,1,3]
	LOADCT,5

	ERRWEIGHT=0

	ss=WHERE(vis0.isc NE 6 AND vis0.isc GE 3) & vis0f=hsi_vis_combine(hsi_vis_edit(vis0[ss]), ERRWEIGHT=ERRWEIGHT)
	uv_smooth, vis0f, map, reconstructed_map_visibilities=rmv
	plot_map, /LIMB, map, /ISO

	ss=WHERE(vis1.isc NE 6 AND vis1.isc GE 3) & vis1f=hsi_vis_combine(hsi_vis_edit(vis1[ss]), ERRWEIGHT=ERRWEIGHT)
	uv_smooth, vis1f, map
	plot_map, /LIMB, map, /ISO



	;; compare vis0 (rchi2: 9.5) and vis1 (rchi2:5.8)
	hsi_vis_fwdfit, vis0f, CIRCLE=0, srcout=srcout, fitstddev=fitstddev

Visibility Pitfalls by R. Schwartz

;Visibilities are a Data Compression Scheme
;
;1. Calib_eventlist is our first data compression - away from single events to time bins
;
;2. Stacked eventlist is a further compression - multiple rotations are epoch folded
;
;3. Visibilities are a further compression by a factor of 6 to 12, (half rotations)
;
;4. phase & amplitude fitting is inherently linear
;
;5. Inherent problem is tension between number of roll bins and minimum phase requirement
;	 in visibility determination.  phase gap -> throw away varying fractions of otherwise good data
;
;6. Once it's in visibilities you have hidden your systematic errors
;
;7. Viz normalization is the default.  We really need to study this
;
;8. For well separated sources with structure, the roll binning problem cannot be overcome for visibilities
;
;Let's play with visibilities

hessi_data, im=im
ov = im->get(/obj, class='hsi_visibility')

help, ov
;Get them all

v = ov->getdata(/dump)
help, v,/st
;Manipulate them
vs = v[0:99]

;Set them back
vnew = ptrarr(1)
vnew[0]= ptr_new(vs)
ov->setdata, vnew

;Look at what we have now

help, ov->getdata(/dump)

Documentation

The following is a list of currently available documentation on RHESSI visibilities.

• The Visibility Documentation Guide by G. Hurford (OUT OF DATE)
• User's guide to visibilities by G. Hurford
• Visibilities How to by Andre Csillaghy
• Visibility Object The object diagram for visibilities (OUT OF DATE)
• Choosing the number of roll bins for RHESSI visibilities by G. Hurford
• Measurement and Interpretation of X-ray Visibilities with RHESSI, a poster presented at SPD 2005.
• Normalization and Visibility Clean by G. Hurford