Swift Broadband Modelling

Transcription

Swift Broadband Modelling!
Joint XRT–UVOT SED Fitting!
Stephen Holland
Swift Science Centre
[email protected]
http://swift.gsfc.nasa.gov/
Fermi–Swift Data Analysis Workshop
8–12 Nov 2010, NASA/GSFC
1
Joint XRT–UVOT Spectral Fitting
GRB 050525A
2
XRT Spectral Fitting
What we did on Wednesday and Thursday.
3
Generate the XRT Spectrum
4
UVOT “Spectral” Fitting
Download the UVOT Data
•  Swift Data Archive
•  Get (or create) the SKY images
sw00351588000u??_sk.img
where ?? Is the filter code
5
6
Examine the UVOT Data
Determine which UVOT SKY images (or summed SKY
images to use.
Examine the light curves to find a good epoch.
There should be a UVOT exposure in each filter near the
SED epoch .
7
Use the Six Broadband Filters
Good:
v
(λ0 = 5402 Å, FWHM = 750 Å)
b
(λ0 = 4329 Å, FWHM = 980 Å)
u
(λ0 = 3501 Å, FWHM = 875 Å)
uvw1 (λ0 = 2634 Å, FWHM = 700 Å)
uvm2 (λ0 = 2231 Å, FWHM = 510 Å)
uvw2 (λ0 = 2030 Å, FWHM = 760 Å)
Not Good:
white (λ0 = 3471 Å, FWHM = 2600 Å)
8
9
10
Pick the SED Epoch
1000 s
Use the text report file generated by uvotproduct
to determine which exposures to use
11
Pick the UVOT Exposures
Unbinned Data for V sky images:
No Exposure t-trig
dt net_rate
0
19.5 648.1
9.9 0.3012
1
19.4 822.4
9.9 0.2878
2
19.5 1054.0
9.9 0.2471
3
19.4 1226.9
9.9 0.0927
4
19.4 1399.9
9.9 0.4681
5
19.5 1566.1
9.9 0.5654
6
19.5 1739.9
9.9 0.3892
7
19.4 1913.3
9.9 0.3434
8
196.6 6155.7 99.9 0.0208
9
196.6 7591.1 99.9 –0.1185
+/–
0.2249
0.2224
0.2254
0.2057
0.2775
0.2965
0.2931
0.3265
0.0577
0.0902
mag
19.19
19.24
19.41
20.47
18.71
18.51
18.91
19.05
22.09
99.00
+/–
0.81
0.84
0.99
2.41
0.64
0.57
0.82
1.03
3.01
99.00
n_sig
1.35
1.30
1.10
0.45
1.71
1.94
1.35
1.06
0.36
0.00
EXTNAME
vv263608423E
vv263608597E
vv263608829E
vv263609002E
vv263609175E
vv263609341E
vv263609515E
vv263609688E
vv263613841I
vv263615276I
Repeat for each filter.
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UVOT Exposures to Use
SKY file + extension
sw00351588000uvv_sk.img+4
sw00351588000ubb_sk.img+3
sw00351588000uuu_sk.img+4
sw00351588000uw1_sk.img+2
sw00351588000um2_sk.img+3
sw00351588000uw2_sk.img+3
Start Time (s)
864.1
1142.6
1118.2
1093.8
1068.6
1019.7
Convert photometry from each image into a “spectrum” with one channel
13
Set Up Region Files
14
Create Region Files
Source Region
fk5;circle(22:14:12.50,-26:34:59.1,2.5”)
Background Region
fk5;circle(22:14:13.861,-26:34:57.03,9")
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UVOT2PHA
Uvot2pha converts UVOT image or event data into a .pha file that XSpec can
use.
> uvot2pha
Input (img or evt) filename[ ]: sw00351588000uvv_sk.img+4
Source region file name[ ]: src.reg
Background region file name[ ]: bkg.reg
Output source PHA filename[ ]: vv_src.pha
Output background PHA filename[ ]: vv_bkg.pha
Response file name[ ]: CALDB
Repeat for each SKY exposure.
16
Run Uvot2pha on all Exposures
uvot2pha sw00351588000uvv_sk.img+4 src.reg bkg.reg
uvot2pha sw00351588000ubb_sk.img+3 src.reg bkg.reg
uvot2pha sw00351588000uuu_sk.img+4 src.reg bkg.reg
uvot2pha sw00351588000uw1_sk.img+2 src.reg bkg.reg
uvot2pha sw00351588000um2_sk.img+3 src.reg bkg.reg
uvot2pha sw00351588000uw2_sk.img+3 src.reg bkg.reg
vv_src.pha vv_bkg.pha CALDB
bb_src.pha bb_bkg.pha CALDB
uu_src.pha uu_bkg.pha CALDB
w1_src.pha w1_bkg.pha CALDB
m2_src.pha m2_bkg.pha CALDB
w2_src.pha w2_bkg.pha CALDB 17
18
Bewarned and Beware
•  Counts are source + background
•  Only interpolate the source counts Fermi–Swift Data Analysis Workshop
19
Shift to a Common Epoch I
uvotshiftpha
infile =
intime =
outfile =
outtime =
alpha = -0.90
(cleanup = yes)
(history = yes)
(clobber = no)
(chatter = 1)
(mode = ql) Fermi–Swift Data Analysis Workshop
Input .pha file
Time (s) since BAT trigger of the input file
Output .pha file
Time (s) since BAT trigger to shift to
Power-law index: f(t) = f(t0)*(t/t0)^alpha
Delete temporary files?
Write history block
Clobber existing files?
Verbosity level
20
Shift to a Common Epoch II
•  Use UVOTSHIFTPHA
•  > uvotshiftpha vv_src.pha 864.1 vv_src_1000.pha 1000
–0.90 •  Need an estimate of the light curve decay index (alpha)
fν(t)
= fν(t0) ( t / t0 )α
α= −0.90 ± 0.06
21
Shift to a Common Epoch III
uvotshiftpha vv_src.pha 864.1 vv_src_1000.pha 1000
uvotshiftpha bb_src.pha 1142.6 bb_src_1000.pha 1000
uvotshiftpha uu_src.pha 1118.2 uu_src_1000.pha 1000
uvotshiftpha w1_src.pha 1093.8 w1_src_1000.pha 1000
uvotshiftpha m2_src.pha 1068.6 m2_src_1000.pha 1000
uvotshiftpha w2_src.pha 1019.7 w2_src_1000.pha 1000
–0.90
–0.90 –0.90 –0.90 –0.90 –0.90 22
Read the Data into XSpec
XSPEC version: 12.6.0s
Build Date/Time: Thu Sep 30 12:39:22 2010
XSPEC12>data 1:1 vv_src_1000.pha 1:2 bb_src_1000.pha 1:3 uu_src_1000.pha 1:4
w1_src_1000.pha 1:5 m2_src_1000.pha 1:6 w2_src_1000.pha Number of spectra read ..... 6
6 spectra in use
Spectral Data File: vv_src_1000.pha Spectrum 1
Net count rate (cts/s) for Spectrum:1 2.166e-01 +/- 2.133e-01 (32.2 % total)
Assigned to Data Group 1 and Plot Group 1
Noticed Channels: 1
Telescope: SWIFT Instrument: UVOTA Channel Type: PHA
Exposure Time: 19.46 sec
Using Background File
vv_bkg.pha
Background Exposure Time: 19.46 sec
Using Response (RMF) File
/Volumes/Apps_and_Docs/caldb/data/swift/uvota/cpf/rsp/
swuvv_20041120v105.rsp for Source 1
23
And Now… Physics!
Milky Way
Host
dust & gas
dust & gas
Intrinsic Spectrum
redshift = z
z = 0
Not to scale
24
Model Details
!XSPEC12>model redden*phabs*zdust*zphabs*power
1.  Intrinsic spectrum of the afterglow (powerlaw)
•  Power law spectrum
powerlaw: a simple photon power law. A(E) = KE−α
par1 = a
photon index of power law (dimensionless)
norm= K
photons keV–1cm–2s–1 at 1 keV
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Model Details
1.  Photoelectic absorption in the host (zphabs)
zphabs: photoelectric absorption at a redshift of z. M(E) = exp[ −nH σ( E[1+z] ) ]
par1 = nH
par2 = z
equivalent hydrogen column
(in units of 1022 atoms cm−2)
redshift
26
Model Details
1.  Dust extinction in the host (zdust)
•  Pei (1992)
zdust: extinction by dust grains. par1 = extinction law
par2 = E(B−V) par3 = RV
par4 = z
1=Milky Way, 2=LMC, 3=SMC
reddening in host (mag)
ratio of total to selective extinction
(mag)
redshift
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Model Details
1.  Galactic photoelectic absorption (phabs)
phabs: Galactic photoelectric absorption. M(E) = exp[ −nH σ( E ) ]
par1 = nH
equivalent hydrogen column
(in units of 1022 atoms cm−2)
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Model Details
1.  Galactic dust extinction (redden)
•  Cardelli et al. (1987)
zdust: Interstellar extinction. par1 = E(B−V) Fermi–Swift Data Analysis Workshop
reddening (mag)
29
Set up the Model
XSPEC12>model redden*phabs*zdust*zphabs*power
30
Set up the Model I
Input parameter value, delta, min, bot, top, and max values for ...
0.05
0.001
0
0
10
10
1:redden:E(B-V)>0.02
1
0.001
0
0 100000
1e+06
2:phabs:nH>9.6e-3
0
3:zdust:method>3
0.1
0.01
0
0
100
100
4:zdust:E(B-V)>0.1
3.1
-0.01
0
0
10
10
5:zdust:Rv>2.93
0
-0.01
0
0
20
20
6:zdust:redshift>0.903
1
0.001
0
0 100000
1e+06
7:zphabs:nH>1
0
-0.01
0
0
10
10
8:zphabs:redshift>=6
1
0.01
-3
-2
9
10
9:powerlaw:PhoIndex>1
1
0.01
0
0
1e+24
1e+24
10:powerlaw:norm>1
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Set up the Model II
========================================================================
Model redden<1>*phabs<2>*zdust<3>*zphabs<4>*powerlaw<5> Source No.: 1 Active/On
Model Model Component Parameter Unit Value
par comp
1 1 redden
E(B-V)
2.00000E-02 frozen
2 2 phabs
nH
10^22 9.60000E-03 frozen
3 3 zdust
method
3
frozen
4 3 zdust
E(B-V)
0.100000
+/- 0.0
5 3 zdust
Rv
2.93000
frozen
6 3 zdust
redshift z
0.903
frozen
7 4 zphabs
nH
10^22 1.00000
+/- 0.0
8 4 zphabs
redshift
0.903
= 6
9 5 powerlaw PhoIndex
1.00000
+/- 0.0
10 5 powerlaw norm
1.00000
+/- 0.0
________________________________________________________________________
XSPEC12>freeze 1
XSPEC12>freeze 2
XSPEC12>thaw 6
 Galactic reddening is known
 Galactic absorption is known
 let this be a free parameter to solve for redshift
XSPEC12>renorm
32
Set the Test Statistic
!XSPEC12>statistic cstat;
Warning: Cstat statistic is only valid for Poisson data.
cstat statistic: variance weighted using standard weighting
C-statistic =
1.56 using 6 PHA bins and 1 degrees of freedom.
Current data and model not fit yet.
33
Fit the Model
XSPEC12>fit
========================================================================
par comp
1 1 redden
E(B-V)
2.00000E-02 frozen
2 2 phabs
nH
10^22 9.60000E-03 frozen
3 3 zdust
method
3
frozen
4 3 zdust
E(B-V)
8.31709E-02 +/- 0.161152 5 3 zdust
Rv
2.93000
frozen
6 3 zdust
redshift
z
0.903000
frozen
7 4 zphabs
nH
10^22 1.00000
+/- -1.00000 8 4 zphabs
redshift
0.903000
= 6
1.01831
+/- 1.89618
10 5 powerlaw norm
0.158233
+/- 2.00024
________________________________________________________________________
C-statistic =
34
Make a Plot
!XSPEC12>cpd /xw
!XSPEC12>setplot wave
!XSPEC12>plot ldata res
35
36
What if there is a UVOT Grism Spectrum?
•  UVOT grism spectra are compatible with
XSpec
•  Treat them the same as an XRT spectrum
37
Joint X-Ray and U/Optical SED
•  Add the XRT data to the UVOT data and run
Xspec again
38
Read the Data into XSpec
XSPEC version: 12.6.0s
Build Date/Time: Thu Sep 30 12:39:22 2010
XSPEC12>data 1:1 vv_src_1000.pha 1:2 bb_src_1000.pha 1:3 uu_src_1000.pha 1:4
w1_src_1000.pha 1:5 m2_src_1000.pha 1:6 w2_src_1000.pha 1:7 090510_pc_g20.pha Number of spectra read ..... 6***Warning: Detected response matrix energy bin value = 0 (or neg).
XSPEC will instead use small finite value (response file will not be altered).
Number of spectra read ..... 7
7 spectra in use
Spectral Data File: vv_src_1000.pha Spectrum 1
Net count rate (cts/s) for Spectrum:1 2.166e-01 +/- 2.133e-01 (32.2 % total)
Assigned to Data Group 1 and Plot Group 1
Noticed Channels: 1
Telescope: SWIFT Instrument: UVOTA Channel Type: PHA
Exposure Time: 19.46 sec
Using Background File
vv_bkg.pha
Background Exposure Time: 19.46 sec
Using Response (RMF) File
/Volumes/Apps_and_Docs/caldb/data/swift/uvota/cpf/rsp/
swuvv_20041120v105.rsp for Source 1
39
Set up the Model I
Input parameter value, delta, min, bot, top, and max values for ...
0.05
0.001
0
0
10
10
1:redden:E(B-V)>0.02
1
0.001
0
0 100000
1e+06
2:phabs:nH>9.6e-3
0
3:zdust:method>3
0.1
0.01
0
0
100
100
4:zdust:E(B-V)>0.1
3.1
-0.01
0
0
10
10
5:zdust:Rv>2.93
0
-0.01
0
0
20
20
6:zdust:redshift>0.903
1
0.001
0
0 100000
1e+06
7:zphabs:nH>1
0
-0.01
0
0
10
10
8:zphabs:redshift>=6
1
0.01
-3
-2
9
10
9:powerlaw:PhoIndex>1
1
0.01
0
0
1e+24
1e+24
10:powerlaw:norm>1
40
Set up the Model II
========================================================================
par comp
1 1 redden
E(B-V)
2.00000E-02 frozen
2 2 phabs
nH
10^22 9.60000E-03 frozen
3 3 zdust
method
3
frozen
4 3 zdust
E(B-V)
0.100000
+/- 0.0
5 3 zdust
Rv
2.93000
frozen
6 3 zdust
redshift z
0.903
frozen
7 4 zphabs
nH
10^22 1.00000
+/- 0.0
8 4 zphabs
redshift
0.903
= 6
1.00000
+/- 0.0
10 5 powerlaw norm
1.00000
+/- 0.0
________________________________________________________________________
!XSPEC12>freeze 1
!XSPEC12>freeze 2
!XSPEC12>thaw 6
 Galactic reddening is known
 Galactic absorption is known
 let this be a free parameter to solve for redshift
!XSPEC12>renorm
!XSPEC12>statistic cstat
!XSPEC12>ignore bad
41
Fit the Model
XSPEC12>fit
========================================================================
par comp
1 1 redden
E(B-V)
2.00000E-02 frozen
2 2 phabs
nH
10^22 9.60000E-03
frozen
3 3 zdust
method
3
frozen
4 3 zdust
E(B-V)
0.183345
+/- 2.94876E-02 5 3 zdust
Rv
2.93000
frozen
6 3 zdust
redshift z
0.903000
frozen
7 4 zphabs
nH
10^22 2.84930E-05
+/- 1.50897-02 8 4 zphabs
redshift
0.903000
= 6
1.56352
+/- 4.04335E-02 10 5 powerlaw norm
2.24636E-02
+/- 7.93948E-03 ________________________________________________________________________
C-statistic =
42
43
Compute the Errors
XSPEC12>error 1.0 4
Parameter Confidence Range (1)
Apparent non-monotonicity in statistic space detected.
Current bracket values 0.218045, 0.218191
and delta stat 0.938147, 1.06405
but latest trial 0.218105 gives 1.3509
Suggest that you check this result using the steppar command.
4 0.149773 0.218118 (–0.0336263,0.0347188)
XSPEC12>error 1.0 7
***Warning: Parameter pegged at hard limit: 0
7
0 0.0186439 (0,0.0186439)
XSPEC12>error 1.0 9
Parameter Confidence Range (1)
9
1.52913
1.60761 (–0.0387441,0.0397386)
44
What Does it all Mean?
•  Host reddening: EB−V = 0.18 (−0.03, +0.03) mag
•  Host absorption: NH = 2.8 × 1017 cm−2 (rather small, ≈ 0)
•  UVOT Data Alone: Γ= 1.0
•  Joint XRT/UVOT Data: Γ= 1.56 (−0.04, +0.04) •  Cooling break between the X-ray and UV régimes
45
Exercise
•  UVOT Data Alone: Γ= 1.0
•  Joint XRT/UVOT Data: Γ= 1.56 (−0.04, +0.04) •  Cooling break between the X-ray and UV régimes
•  Try fitting a broken power law to the joint UVOT/XRT data
•  model: bknpower instead of powerlaw
•  first power law index (UVOT)
•  second power law index (XRT)
•  break energy (try 1 keV as an initial value)
46
Extra Slides
47

Swift Broadband Modelling

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