Analysis of extended sources with the EPIC cameras - XMM-Newton

Analysis of extended sources withthe EPIC cameras7 th ESAC SAS WorkshopJune 19 – 22, 2007Matthias EhleXMM-Newton Science Operations CentreXMM-Newton1

Status• Analysis of extended sources is complex, challenging and time-consuming• There is currently neither an “official” SAS recipe, nor a simple thread• Some tasks cannot be accomplished with SAS. They require FTOOLS or homemadesoftware; Several groups were/are independently working in this field…• But (since 2005) XMM-Newton EPIC Background working group (BGWG):“A steering and supervising committee to provide the user with clear informationon the EPIC Background and (SAS)-Tools to treat the EPIC Background correctlyfor various TBD scenarios”http://xmm.esac.esa.int/external/xmm_sw_cal/background/ (also info on RGS/OM bkg.)– A table summarizing the temporal, spectral and spatial properties of EPICbackground components– Progress & Meetings of the XMM-Newton EPIC Background working group– Products• XMM-Newton Extended Source Analysis Software package, ESAS• XMM-Newton 'blank sky' background files & related software• Filter wheel closed data• Other scripts• Links to related papersXMM-NewtonMatthias Ehle2

Why?• Diagnostics of interstellar matter via SNR• Diffuse emission in nearby galaxies (halos, starburst winds)and groups of galaxies• Study of astrophysical jets (proto-stars, active galacticnuclei)• Temperature and metallicity profiles in clusters of galaxies...• ... is my favourite source extended or not?XMM-NewtonMatthias Ehle3

Why is it so difficult? XMM-NewtonMatthias Ehle4

Why is it so difficult (again)?XMM-NewtonMatthias Ehle5

Which background to use (I)?• Often no statistically useful background region in the observationfield-of-view use “blank sky fields” to generate backgroundspectra• Recommended option (files produced for BGWG by Read & Carter, Uni. Leicester):http://xmm.esac.esa.int/external/xmm_sw_cal/background/blank_sky.shtml– a superposition of many (~200) pointed observations of pipelineproduct data from the 2XMM reprocessing– background event files (spectral) & exposure maps (spatial analysis):• MOS1 & MOS2: full-frame mode• PN: full-frame & extended full frame mode• Each filter mode combination event file available (thin, medium or thick)• twelve different instrument-filter-mode combinations• For each event list: two types of exposure map; vignetted and nonvignetted• two types of background event lists: unfilled & refilledXMM-NewtonMatthias Ehle6

Using the blank sky field background• On the left is shown an image created from a pn events file with sources removed,and on the right, the image of the events file after the event filling procedure• Blank-Sky Fields exist as event lists, with DET[XY] column onlyXMM-NewtonMatthias Ehle7

Using the blank sky field background (cntd(cntd.)Software available related to background files (shell scripts calling SAS/FTOOLS):– Skycast: to cast an EPIC background dataset onto the sky, at the position given by aninput template event dataset (e.g. the event file you are interested in producing abackground for); attcalc– BGrebinimage2SKY_2006: to re-bin and re-project exposure maps onto the sky to thespatial scale and sky position of a user-input image.– SelectRADec: to select events from a certain area of the sky, specifying a rightascension and declination (J2000), and the maximum distance from this position oneis prepared to consider. A final event file and exposure map is produced.Caveats: Variations in spectra…1. … with count rate &2. … over the sky:Note the higher count rate of the galacticcentre due to higher levels of soft X-ray emissionGalactic CentreGalactic Anti-centreNorth Galactic PoleSouth Galactic PoleXMM-NewtonMatthias Ehle8

Background re-normalization• You need to normalize the blank-skyfield background to the quiescent levelobserved during your observationWhat do you do if yourobservation falls here?• for example, 40 ksec of cleaned data• in Blank-sky: exposure time = 2245ksec ratio = 56.1 (or use other, moresophisticated scaling methods…)• divide the BS-extracted image by56.1 and subtract the resultant imagefrom the original users image• Similar scaling for BS backgroundspectraXMM-NewtonMatthias Ehle9

Which background to use (II)?• Alternative approach use “model” to generate background spectra• Recommended option: (tool produced for BGWG by Snowden & Kuntz, US GOF):XMM-ESAS: Extended Source Analysis Software packagehttp://xmm.esac.esa.int/external/xmm_sw_cal/background/epic_esas.shtml– Allows to model quiescent particle background both spectrally & spatially forMOS detectors (support for pn is planned)– Produces background spectra for user-defined regions of the detectors andbackground images.– Output files are FITS standard & can be used in spectral fitting packages (e.g.,Xspec) or with FITS image display software (e.g., fv or ds9).– XMM-ESAS is based on the software used for the background modelingdescribed in Snowden, Collier & Kuntz (2004, ApJ, 610, 1182).– Package currently consists of both PERL scripts (calling SAS tasks) & standaloneFortran 77 programs. Goal: transform into proper SAS meta-task.XMM-NewtonMatthias Ehle10

Background flare removal: the ESAS way• Instead of GTIs from count-rate limits > 10 keV - XMM-ESAS: filtering in user def. bandFilter limitsGaussian FitHigh count rate excursions due to soft protons rather thanhigher-energy particles (which would produce increase in cornerdata)SAS task “espfilt” is under development…Strong soft proton flaring data not useful for study ofdiffuse emission; 2 ks left are likely to be stillcontaminatedXMM-NewtonMatthias Ehle11

Which background to use (II)?• Method: corner pixels are a measure of the particle background• Use as many known parametersas possible rather than relying onlocal bkg determinations and blankskybackground data sets• E.g., use FWC data, RASS, softproton distribution, archivedobservation data setsXMM-NewtonMatthias Ehle12

Which background to use (II)?• Model the Quiescent Particle Background (QPB) (after removal offlaring background)• Determine the corner spectral parameters: high-energy power law slope [2.4-12.0keV] and hardness ratio [(2.5-5.0)/(0.4-0.8)] from the observation data setXMM-NewtonMatthias Ehle13

Which background to use (II)?• Quiescent Particle Background (QPB)Mean QPB spectrum derived from unexposed corner pixel data from all public screeneddata (~76 Msec for each camera). MOS1 black, MOS2 blue.Red lines: two regions used to measure hardness ratio (HR)Green line: fitted power law above 2.4 keVHR & slope used for parameterization of QPB; Prominent background lines are labeled.Both continuum and line contributions are both position and temporally varyingXMM-NewtonMatthias Ehle14

Which background to use (II)?• Model the Quiescent Particle Background (QPB) (after removal offlaring background)• Determine the corner spectral parameters: high-energy power law slope [2.4-12.0keV] and hardness ratio [(2.5-5.0)/(0.4-0.8)] from the observation data set• Search an archived-observation data base for observations with similar parameters• Augment the observation data set corner spectra with data from the archivedobservationdata base• Scale the Filter Wheel Closed (FWC) spectra (treat each CCD separately) for theregion of interest by the ratio of the augmented observation corner spectra to theFWC corner spectra• Combine augmented & corrected corner-region spectra from different CCDs,correctly weighted, to form single bkg spectrum for object regionXMM-NewtonMatthias Ehle15

Addition: Filter wheel closed data• Filter wheel closed (FWC) data– from calibration obs. with filter wheel in closed position– Released in September 2006: stacked collections of FWC dataavailable for MOS and pn• What for?– closed position blocking X-rays & soft protons from outside– Cosmic rays, however, still penetrate to the detectors allows clean measure of following (internal) bkg components:• high energy particles producing charge directly in CCDs• particle induced X-rays (continuum and fluorescent lines), generatedinside the camera• electronic readout noise (at lowest energies)• Components are distributed non-homogeneously!• BGWG provides them for MOS & PN, different filters & modes…XMM-NewtonMatthias Ehle16

Filter Wheel Closed Data: MOS• MOS FWC Data: spectral & spatial propertiesVery strong Al K & Si K fluorescentinstrumental lines ( 1.49 keV and 1.75 keV)on top of continuum. Other fluorescent lines athigher energies; strong low-energy tail due todetector noiseXMM-NewtonMatthias Ehle17

Filter Wheel Closed Data: PN• PN FWC data: spectral & spatial propertiesXMM-NewtonMatthias Ehle18

Using the Extended Source Analysis Software• XMM-ESAS comes together with detailed Users manual, supporting calibration files,& example data set (covering spectral & imaging aspects; Galaxy Cluster A 1795)• Model uses data from unexposed (to the sky) corners of MOS detector (alsoarchived), filter-wheel-closed data, ROSAT All-Sky Survey data• Avoids use of blank-sky data: include to an un-known level contributions of cosmicbackground, residual soft proton contamination, & solar wind charge exchangecontamination.Results of ESAS & blank-sky methodsin good agreement (uncertainties atlarge annuli smaller using theXMM-ESAS method).Discrepancy between XMM-Newton &Chandra (Vikhlinin et al., 2005) is beingstudied..Temperature Profile A 1795XMM-NewtonMatthias Ehle19

Spectral analysis• Some results from XMM-ESAS (Abell 1795):Observed spectrumModel particle bkg.Model bkg. subtractedBridge where fluorescentlines affect the data (notmodeled)Filter wheel closedspectrum: strongfluorescent lines on top ofcontinuum, low energy taildue to detector noiseDiscrepancydue to residualsoft protoncontaminationFitted MOS1 &MOS2 spectrabkg. NOT subtractedXMM-NewtonMatthias Ehle20

Xspectricks• Add RASS (Rosat All Sky Survey) data of your source to constraint soft(< 2.4 keV) part– see ESAS & HEASARC X-Ray Background Tool athttp://heasarc.gsfc.nasa.gov/cgi-bin/Tools/xraybg/xraybg.pl• Variable Al (1.49 keV) & Si (1.75 keV) fluorescent instrumental lines:ignore this energy range (ESAS) and model them in Xspec• Aim at linking or freezing as many as possible fit parameters (seeESAS cookbook):• Cluster model: bknpow/b + gauss + gauss + con*con*Res. soft proton bkg. Al-1.49keV Si-1.75keV MOS1&2 solid angleCosmic bkg.(apec + (apec + apec + pow)*wabs +LHB-0.1keV cool halo-0.1keV hot halo-0.25keV unres.bkg.apec*wabs)cluster emissionXMM-NewtonMatthias Ehle21

Image smoothingIn Principle: asmooth inset=unsmoothed.img outset=smoothed.img sigma=2.5smoothstyle=simple convolversttyle=gaussian(smoothstyle=adaptive available as well)Or use adapt-900 from the XMM-ESAS package: adaptive smoothing of backgroundsubtracted & exposure corrected images (can merge MOS1 & MOS2)Abell 1795 (0.35-1.25 keV) observed counts & bkg-subtracted & exp. corrected, smoothed imageXMM-NewtonMatthias Ehle22

Further scripts: Fin/FoutFout• Estimation of the residual Soft Proton (SP) flare contamination– shell script to perform the Fin/Fout ratio calculation– Method described in Molendi et al. (2004, A&A 419, 837)– Runs on EPIC event files (MOS1, MOS2 and/or pn), to estimateamount of residual SP flare contamination (after attempts havebeen made to clean the event files using GTI filtering)• Script compares area-corrected count rates in the in-FOV (beyond10 arcminutes) and out-of-FOV regions of the detector. The higherthe in-FOV to out-of-FOV ratio, the more the file is contaminatedby SPs:– Ratio < 1.15 : File is not contaminated by SPs.– Ratio 1.15-1.3 : File is slightly contaminated by SPs.– Ratio 1.3-1.5 : File is very contaminated by SPs.– Ratio > 1.5 : File is extremely contaminated by SPs.• Not suited for extended sources filling the entire field of viewXMM-NewtonMatthias Ehle23