如何处理Fermi LAT的数据

主要参考这里. 经过自己操作, 在变成中文, 方便以后参考. 下面以090510为例.

1. 获取数据

1.1 到网站上 http://fermi.gsfc.nasa.gov/cgi-bin/ssc/LAT/LATDataQuery.cgi

输入至少时间和地点, 就是第一项的position, 和date.

eg. 地点: 333.400, -26.767 时间: 263607783, 263608783 (这里选择1000s, 也可以选其它的时间). 如下图

下面这个保持原样

而这些数据应该到GCN上去找. 或者在LAT的catalog上.

1.2 然后点"start search", 下载两个fits文件. 一个数据, 包含PH字样, 一个仪器数据, 包含SC字样.

比如: L090905073938E0D2F37E30_PH00.fits L090905073938E0D2F37E30_SC00.fits

2. 重新生成数据文件 (刚才获取的文件是一段比较长时间的数据), bin并且生成response文件. 命令行用红色标出了.

~/Desktop/gbm-data/lat/090510$ gtselect

(要加选项 evclsmin=1 evclsmax=3, 说明在此)

Input FT1 file[L090907111446E0D2F37E46_PH00.fits] L090905073938E0D2F37E30_PH00.fits

Output FT1 file[GRB090902B_PH.fits] GRB090510_PH.fits

RA for new search center (degrees) (0:360) [265] 333.4

Dec for new search center (degrees) (-90:90) [27.33] -26.767

radius of new search region (degrees) (0:180) [10]

start time (MET in s) (0:) [273582310] 263607783

end time (MET in s) (0:) [273582335] 263607813

lower energy limit (MeV) (0:) [100]

upper energy limit (MeV) (0:) [300000]

maximum zenith angle value (degrees) (0:180) [105]

Done.

~/Desktop/gbm-data/lat/090510$ gtbin

This is gtbin version ScienceTools-v9r15p2-fssc-20090808

Type of output file (CCUBE|CMAP|LC|PHA1|PHA2) [PHA1]

Event data file name[GRB090902B_PH.fits] GRB090510_PH.fits

Output file name[GRB090902B_PH.pha] GRB090510_PH.pha

Spacecraft data file name[L090907111446E0D2F37E46_SC00.fits] L090905073938E0D2F37E30_SC00.fits

Algorithm for defining energy bins (FILE|LIN|LOG) [LOG]

Start value for first energy bin in MeV[100]

Stop value for last energy bin in MeV[300000]

Number of logarithmically uniform energy bins[100] 30

~/Desktop/gbm-data/lat/090510$ gtrspgen

This is gtrspgen version ScienceTools-v9r15p2-fssc-20090808

Response calculation method (GRB|PS) [GRB]

Spectrum file name[GRB090510_PH.pha]

Spacecraft data file name[L090905073938E0D2F37E30_SC00.fits]

Output file name[GRB090510_PH.rsp]

Time of GRB (s)[263607783]

Response function to use, Handoff|DC2|DC2A|DC2FA|DC2BA|DC2FB etc[P6_V1_DIFFUSE]

Algorithm for defining true energy bins (FILE|LIN|LOG) [LOG]

Start value for first energy bin in MeV[30] 100

Stop value for last energy bin in MeV[300000]

Number of logarithmically uniform energy bins[100] 30

注意上面如果不输入就表示默认[]中的值, 这个值是程序记住了上次输入的. 这样很有利于一直处理同一个暴, 很多内容就直接回车就可以了.

3. 用xspec拟合谱

~/Desktop/gbm-data/lat/090510$ xspec

XSPEC version: 12.5.0ac

Build Date/Time: Thu Apr 2 03:38:12 2009

XSPEC12>data GRB090510_PH.pha

***Warning: No TLMIN keyword value for response matrix FCHAN column.

Will assume TLMIN = 1.

1 spectrum in use

Spectral Data File: GRB090510_PH.pha Spectrum 1

Net count rate (cts/s) for Spectrum:1 2.488e+00 +/- 3.436e-01

Assigned to Data Group 1 and Plot Group 1

Noticed Channels: 1-30

Telescope: GLAST Instrument: LAT Channel Type: PI

Exposure Time: 27.73 sec

Using Response (RMF) File GRB090510_PH.rsp for Source 1

XSPEC12>response GRB090510_PH.rsp

Response successfully loaded.

XSPEC12>model powerlaw (此处可发挥)

Input parameter value, delta, min, bot, top, and max values for ...

1 0.01 -3 -2 9 10

1:powerlaw:PhoIndex>

1 0.01 0 0 1e+24 1e+24

2:powerlaw:norm>

========================================================================

Model powerlaw<1> Source No.: 1 Active/On

Model Model Component Parameter Unit Value

par comp

1 1 powerlaw PhoIndex 1.00000 +/- 0.0

2 1 powerlaw norm 1.00000 +/- 0.0

________________________________________________________________________

Chi-Squared = 8.416990e+10 using 30 PHA bins.

Reduced chi-squared = 3.006068e+09 for 28 degrees of freedom

Null hypothesis probability = 0.000000e+00

Current data and model not fit yet.

XSPEC12>fit 100

Chi-Squared Lvl Par # 1 2

56.7827 -1 1.05836 1.68733e-05

......

17.4616 -2 1.87492 8.42061

==============================

Variances and Principal Axes

1 2

1.3453E-04| -0.9999 0.0140

9.8143E+01| -0.0140 -0.9999

------------------------------

========================

Covariance Matrix

1 2

1.930e-02 1.372e+00

1.372e+00 9.812e+01

------------------------

========================================================================

Model powerlaw<1> Source No.: 1 Active/On

Model Model Component Parameter Unit Value

par comp

1 1 powerlaw PhoIndex 1.87492 +/- 0.138941

2 1 powerlaw norm 8.42061 +/- 9.90575

________________________________________________________________________

Chi-Squared = 17.46 using 30 PHA bins.

Reduced chi-squared = 0.6236 for 28 degrees of freedom

Null hypothesis probability = 9.389053e-01

XSPEC12>cpd /xw

XSPEC12>plot ufspec

上面PhoIndex=1.87492就是我们想要的. 图像结果如下