file: fluxmap.txt crea: deh date: 2008 Jul 29 tlm : 2010 Apr 23 Subj: Content for Xjet webpage on fluxmaps 1.0 GENERAL 2.0 FLUXMAPS & PHOTOMETRY 3.0 RADIO MAPS 4.0 EVENT FILE 5.0 DOCUMENTATION 6.0 CAVEATS 1.0 GENERAL From 2008.5, we are adding Chandra X-ray fluxmaps and associated files to the downloadable images. This is in accord with our long term policy of providing processed data products and will permit users to perform X-ray photometry on their local systems in a relatively straightforward manner. During spot checking, we reproduced published values to within a factor of two, often within 20%. We feel that this is satisfactory since the CALDB has changed and we are using reprocessed data from the archives (2008). Furthermore, our products are observed values whereas published fluxes and flux densities are normally 'unabsorbed' fluxes. There are 6 maps provided for each source: 3 fluxmaps (soft, medium, and hard), a smoothed fluxmap constructed by adding the 3 band maps and applying a Gaussian smoothing, a radio map used for registration of the X-ray files, and an 'evt2' file which has been registered so as to align the nuclear X-ray emission with the corresponding radio peak. Pixel randomization has been removed from the evt file and the original data were obtained from the Chandra archive after the reprocessing of 2007. In 2010 we decided to regenerate the fluxmaps using CIAO 4.2.1 and CALDB 4.2.2. With the release (2009 Dec; CALDB 4.2) of a new model for the contamination buildup on the ACIS filters, it became obvious that our soft fluxmaps were compromised (with increasing time from 2004, the low energy effective area becomes more and more overestimated meaning soft fluxes became more and more underestimated). CALDB 4.2 contains a new contamination model which corrects this situation. At the same time, we have devised a method to replace the label "No thumbnail" with labels describing the type of file. Thus whenever you encounter these labels ("registered event file", "soft flux map", etc) you may be assured that the fluxmaps were constructed with exposure maps using the new contamination model. 2.0 FLUXMAPS & PHOTOMETRY 2.1 The processing of fluxmaps is performed in 5 steps: 1) unpack the archival data and update the ardlib file for the badpix information. 2) check for high background intervals and time-filter if necessary. Unlike an 'official' pipeline, we do not have an algorithm for this step. Rather it is a subjective decision based on the total available exposure time as well as how badly the background is affected. 3) Remove pixel randomization from the evt file and apply the latest gain map. 4) construct a regridded smoothed array of the central source and use this to determine the position of the nuclear emission. Shift the evt file to align the X-ray peak/centroid with the radio peak by doing an 'hedit' of the key words RA_NOM, DEC_NOM, TCRVL11 & 12. 5) Produce the three band maps by constructing monochromatic exposure maps and dividing them into regridded arrays (1024x1024) of each band. band nominal energy band ____ ______________ _____________ soft 0.8 0.5 - 1 keV med 1.4 1 - 2 keV hard 4 2 - 7 keV We also multiply each band map by h*nu where nu corresponds to the nominal energy. Thus the units for the flux maps are erg/cm^2/s per logical pixel. Summing the 3 band maps produces the total fluxmap which we smooth with a Gaussian and provide for visual purposes. It should not be used for photometry. Regridding is usually a factor of 4 (converting 0.492" native pixels to 0.123" logical pixels), but may differ so as to include a larger area of the sky in the fixed 1024 format ("f2"), or to improve resolution for sources which are "event rich". 2.2 Photometry can be performed by the user with the tool of his choice (e.g. DS9) by measuring any user-defined aperture on each or all of the band maps. The result requires only a single correction to accomodate the fact that all events in each band were assigned an erg value based on the nominal energy. This is most easily done by using 'dmstat' in ciao on the evt file to determine the actual mean energy of the events within the aperture. Then the measured flux is multiplied by /nominal_energy. Since this correction is normally only a few percent, it can be omitted for users without access to CIAO. An example for the soft band: dmstat "120NrR_evt2.fits[sky=region(k4ciao.reg),energy=500:1000][cols energy]" > k4.meanE 3.0 RADIO MAPS Radio maps have been obtained from gererous colleagues, from the NRAO VLA Archive Survey [NVAS; http://www.aoc.nrao.edu/~vlbacald/], from the DRAGN website [http://www.jb.man.ac.uk/atlas/], from the MERLIN archive [http://www.merlin.ac.uk/archive/], from NED [http://nedwww.ipac.caltech.edu/], or by processing archival data. Where possible we include the origin in the ASCII file accompanying each fits image. We have used AIPS to obtain an rms value for the map and the beam area in pixels, thereby allowing radio intensities to be obtained with any imaging tool. 4.0 EVENT FILE The event file we provide should be identical to the evt2 file in the Chandra archives except for the removal of pixel randomization and the registration (shifting the sky coordinates to be the same as the reference radio map). 5.0 DOCUMENTATION The construction of filenames is based on our established guidelines, and is a compromise between including useful information and ending up with unwieldly, long names. Each image whether generated by us or contributed by users should have an ASCII descriptor file. 6.0 CAVEATS We have made no effort to merge multiple observations. Normally we choose the longest available obsid. ACIS contamination buildup which reduces the effective area at lower energies is dealt with via the use of exposure maps. However, it must be remembered that the flux in the soft band will be reduced by the galactic column density and if there is additional absorption at the source, other bands may also be affected. Pileup is not normally a problem for jet knots and hotspots, but it can occur.