Swift - XRT - Part II Fermi-Swift GRB Data Analysis Workshop

Transcription

1 Swift - XRT - Part II Fermi-Swift GRB Data Analysis Workshop Judy Racusin with thanks to Kim Page and Davide Donato Nov 8-12, Goddard Space Flight Center

2 Outline GRB A bright long burst with BAT/XRT overlap, WT pileup, and a bright flare WT settling - discussion not example WT pileup xrtgrblc - semi-automatic LC generation flare LC fitting XSPEC spectral fits WT or PC alone WT/PC joint fit time dependent fitting

3 xrtpipeline ======================================= Running SWIFT XRT pipeline Task: xrtpipeline Version: Release Date: ======================================= Source RA position (degrees or hh mm ss.s) or POINT or OBJECT[OBJECT] Source DEC position (degrees or dd mm ss.s) or POINT or OBJECT[OBJECT] Target Archive Directory Path[] Stem for FITS input files [i.e. sw ][] sw Directory for outputs[] xrt

4 GRB A Download only seg 000 data all other segs only add last couple data points (normally use all, but will take too long for now) WT settling mode WT mode PC mode

5 xrtgrblc Handy HEASARC tool that does many steps for you xrtpipeline xselect Pile-up correction LC formation & binning xrtgrblc evtfiles=<event files> mkffiles=<makefilter files> xhdfiles=<xrt headers> attfiles=<attitude files> outdir=<output dir> outstem=<stem for output files> srcra=<source RA> srcdec=<source Dec> minenergy=<minimum energy> maxenergy=<maximum energy> splitenergy=<soft/hard split>

6 WT Settling Mode enabled Jan 10, 2010 Settling phase during last of spacecraft maneuver Pushes LC back for earlier observations Short gap before normal WT mode due to image mode Moving spacecraft and source makes analysis very difficult

7 WT Pile-up Pile-up = multiple photons hit same pixel between readouts Event looks like flux and energy of all photons added together = spectrum is wrong Photons focused at center of PSF -> remove center of PSF and then account for missing flux knowing PSF shape Romano et al. 2006, A&A, 456, 917

8 WT Pile-up To estimate exclusion annulus for count rate bins (<100, , , etc. cts/s) Fit spectrum in circular regions around source See where photon index stabilizes or grades stabilize Use different extraction region for different count rate bins, estimate PSF correction using PSF model in CALDB, then apply to raw light curve This is very labor intensive, and can be left as an exercise Romano et al. 2006, A&A, 456, 917

9 xrtgrblc Handy HEASARC tool that does many steps for you xrtpipeline xselect Pile-up correction LC formation & binning can add multiple segments xrtgrblc evtfiles=<event files> mkffiles=<makefilter files> xhdfiles=<xrt headers> attfiles=<attitude files> outdir=<output dir> outstem=<stem for output files> srcra=<source RA> srcdec=<source Dec> minenergy=<minimum energy> maxenergy=<maximum energy> splitenergy=<soft/hard split>

10 xrtgrblc xrtgrblc clobber=yes evtfiles= xrt/sw xpcw3po_cl.evt, xrt/sw xwtw2po_cl.evt mkffiles= xrt/ sw s.mkf, xrt/sw s.mkf xhdfiles= /xrt/hk/sw xhd.hk, /xrt/hk/ sw xhd.hk attfiles= /auxil/sw sat.fits, /auxil/sw sat.fits outdir= xrtlc outstem=sw srcra= srcdec= minenergy=0.3 maxenergy=10.0 splitenergy=0.0 cleanspec=no cutlowbins=no cutlowbinspc=no cutlowbinswt=yes gapintv="200" minpccnts="60" pcframetime="0" trigtime=" " wtframetime=" " evtfiles= all of the event files from xrtpipeline(po_cl = pointed and cleaned) mkffiles=filter files from xrtpipeline, xhdfiles=house keeping files from data attfiles=space craft attitude files, outdir= where you want to put your outputs outstem=sw srcra= GRB RA, srcdec= GRB Dec - look up RA/Dec in GCN or Leicester site minenergy=0.3, maxenergy=10.0 splitenergy= no split (0.0) or energy to get multiple band lightcurves

11 xrtgrblc Magically have counts light curve (ignore flux light curve) sw _xpwetsrcb_ lc.gif background arf files pha files for source and regions and all correction factors in info.fits file

12 LC fitting (QDP) Manipulating the LC files to be read by QDP TIMEBIN=TIMEDEL/2; RATECOR ; ERRORCOR]' grb_wt.lc fdump clobber=yes wrap=yes align=yes prhead=no ftcopy clobber=yes 'sw _xwtetsra.lc[2][col TIME ; showrow=no infile=grb_wt.lc+2 outfile=grb_wt_lc.qdp columns=" " rows="-" TIMEBIN=TIMEDEL/2; RATECOR ; ERRORCOR]' grb_pc.lc ftcopy clobber=yes 'sw _xpcetsra.lc[2][col TIME ; fdump clobber=yes wrap=yes align=yes prhead=no showcol=no showrow=no showunit=no infile=grb_pc.lc+2 outfile=grb_pc_lc.qdp columns=" " rows="-" cat grb_wt_lc.qdp grb_pc_lc.qdp > grb_lc.qdp

13 More QDP Open ascii LC file in text editor edit grb_lc.qdp READ SERR 1 2 comment out header lines with!

14 QDP Fitting Cut out flare manually - save as new file Fit flares with various models Gaussian (gaus) Lorentzian (lore) FRED (burs) sbur (smoothed FRED) QDP not very sophisticated - give it good guess, and manually tune before letting fit go at it

15 QDP node3.html qdp grb_lc_noflare.qdp /xw log x on log y on label X Time since trigger (s) label Y Count Rate (cts/s) plot hardcopy /cps

16 More QDP Fitting Choose model (pow, brkpow, brkpow2, brkpow3) In this case, I chose a triple broken power law mo brkpow3 (my fit E+09) plot fit plot 0 fit plot 1 plot

17 xrtmkarf (ancillary response file) xrtmkarf expofile= xrt/ sw xwtw2po_ex.img clobber=yes Name of the input PHA FITS file[src_wt_spec.pha] Apply PSF correction (used if extended=no)?(yes/no)[yes] Name of the output ARF FITS file[spec_wt.arf] Source X coordinate (SKY for PC and WT modes, DET for PD mode)(used if extended=no):[-1] Source Y coordinate (SKY for PC and WT modes, DET for PD mode)(used if extended=no):[-1]

18 Spectral Fitting ARF - you ve already created the arf with PSF correction RMF - in CALDB Background spectrum - already extracted for light curve Spectrum - already extracted with XSELECT Need to bin in GRPPHA (explained next) nh - to get Galactic NH Feed to XSPEC

19 GRPPHA Groups events into binned spectrum If ~200+ counts, use 20 counts per bin If low counts, use unbinned or 10 counts per bin > grppha Please enter PHA filename[] sw _xwtetsr.pha Please enter output filename[] sw _xwtetsr_grp20.pha >CHKEY RESPFILE swxwt0to2s6_ v012.rmf >CHKEY ANCRFILE specpc.arf >CHKEY BACKFILE specpcback.pi >exit

20 Galactic NH >nh Equinox (d/f 2000)[2000] RA in hh mm ss.s or degrees[] DEC in dd mm ss.s or degrees[] >> Leiden/Argentine/Bonn (LAB) Survey of Galactic HI LII, BII Requested position at X and Y pixel Search nh in 4 X 4 box Each pixel is deg deg nh calculated using all points within deg from input position RA DEC Dist nh E E E E E E E+21 LAB >> Average nh (cm**-2) 2.25E+21 LAB >> Weighted average nh (cm**-2) 2.21E+21

21 XSPEC cd xrtlc xspec data sw _xwtetsr_grp20.pha../rmf/swxwt0to2s6_ v012.rmf cpd /xw setplot en ignore bad ignore mo wabs*zwabs*pow fit 1000 fit 1000 fit 1000 plot ld res error 1-4

22 Join WT/PC Spectral Fits xspec data 1:1 sw _xwtetsr_grp20.pha data 2:2 sw _xpcetsr_grp20.pha ignore bad ignore 1: ignore 2: mo wabs*zwabs*pow =================================================================== Model wabs<1>*zwabs<2>*powerlaw<3> Source No.: 1 Active/On Model Model Component Parameter Unit Value par comp Data group: wabs nh 10^ frozen 2 2 zwabs nh 10^ / zwabs redshift frozen 4 3 powerlaw PhoIndex / powerlaw norm /- 0.0 Data group: wabs nh 10^ / zwabs nh 10^ = zwabs redshift frozen 9 3 powerlaw PhoIndex = powerlaw norm /- 0.0

23 Flux Conversion Factors need arf without psf correction fit spectrum in XSPEC flux show rate divide rate/flux = counts to flux conversion factor for whichever spectrum

24 Although this presentation has tried to cover all the basics Alternatively of how to extract XRT light-curves and spectra, there is a quick and easy way to cheat! Light-curves (and hardness ratios) and time-averaged spectra are routinely created for every XRT-detected GRB and are available online: From these pages, there are also links to the Burst Analyser, which combines BAT and XRT data to create flux light-curves in different energy bands. Similarly, if you want to create a light-curve or spectrum for a non-grb source, go to See Evans et al. (2009, MNRAS, 397, 1177), Evans et al. (2007, A&A, 469, 379) and Evans et al. (2010, A&A, 519, 102) for details. These products are completely suitable for scientific analysis and have been used in many papers.