Nicer - Revision history

Thalhammer: Update on RMF/ARF selection

2025-04-10T13:31:29Z

Update on RMF/ARF selection

Thalhammer: /* Background generation: */

2023-06-07T10:34:07Z

Background generation:

Thalhammer at 10:09, 7 June 2023

2023-06-07T10:09:14Z

Thalhammer at 10:06, 7 June 2023

2023-06-07T10:06:36Z

Thalhammer: /* Issues to keep in mind: */

2023-06-07T09:33:51Z

Issues to keep in mind:

Berger at 09:20, 7 June 2023

2023-06-07T09:20:53Z

Thalhammer at 01:19, 17 March 2021

2021-03-17T01:19:55Z

Thalhammer: Wiki page for NICER data extraction

2021-03-17T01:17:31Z

Wiki page for NICER data extraction

New page

== NICER data extraction ==

NICER is a soft X-ray observatory on board the ISS. Biggest difference to many
other modern X-ray satellites are its silicon drift detectors and X-ray
concentrators (instead of focusing mirrors), which together do not permit
imaging capabilities. While this simplifies the data extraction, it is also required
to simulate a background for each observation. Previously downloaded
NICER observations can be found under /satdata/X-ray/nicer/.

=== Preparation:===

To apply the the latest calibration and filtering, first run
'xtiprepare'. The script will produce cleaned event
files inside the subdirectory 'reprocessed' inside 'prepdir'.

<pre>
#!/bin/csh

set datadir = /satdata/X-ray/nicer/data/2200570101
set prepdir = '/userdata/data/$user/where/ever/you/want'

xtiprepare --datadir=$datadir --prepdir=$prepdir
</pre>

If you notice an increased background in the resulting spectra, you
can apply additional filter criteria during the preparation. See
'xtiprepare --help' for more information.

=== Spectrum and Light-curve Extraction:===

To produce light-curves, spectra and apply barycenter correction
'xtiextract' can be used as follows.

<pre>
#!/bin/csh

set prepdir = '/userdata/data/$user/where/ever/you/want'
set dirname = 'extraction_123'

xtiextract --name=$dirname --prepdir=$prepdir

</pre>

The produced spectrum and light-curve can then be found in the
subdirecory 'dirname' in $prepdir. Currently no observation-specific
response files are generated, but instead soft links to the current ARF
& RMF files included in the CALDB are generated.

=== Background generation: ===

As we cannot produce a background spectrum from an off-source region on the
detector, a background spectrum has to be modeled. Currently there are two
different tools available for that purpose. One based on external parameters
during the observation (i.e., space weather, solar angle and cutoff-rigidity of
earths B-field) amd one based on the internal distribution of measured events.
Both are still in active development and might not be able to produce realistic
spectra for all observations. In that case a simple reference observation of one
of the RXTE background fields might be used instead. 
Both tools are further described on the instruments webpage: 
https://heasarc.gsfc.nasa.gov/docs/nicer/tools/nicer_bkg_est_tools.html

=== Issues to keep in mind: ===

Feel free to expand this list whenever you came across any new issues.

''' Optical loading: '''

When optical light is reflected onto the detectors, this can
significantly increase the low-energy background below 3keV. This is
most significant for solar angles below ~70 degrees. However, due to
its position on the ISS this can also happen at any solar angle when
light is reflected by other part of the ISS.

''' Polar Horns: '''

Unlike other observatories in LEO the ISS is on an orbit with a quite
high inclination of 51.6 degrees. This means the ISS passes through
the so called polar horn regions, where the outer Van Allen belt reach
LEO. These regions can feature an increased population of energetic
electrons, which can induce a strong background signal in NICER,
particular at higher energies. 
See this "science nugget" for more information: 
https://heasarc.gsfc.nasa.gov/docs/nicer/science_nuggets/20180809.html

''' Overly aggressive filtering: '''

It can happen, that e.g. optical loading leads to a filter parameter
exceeding the standard filter criteria for most of certain
observations. Such an observation might still be of interest, however.
In that case one might want to increase the allowed range e.g. for
"underonly_range" in "xtiprepare".

''' Large event files: '''

The downloaded eventfiles are generally compressed and are extracted to memory
before the data processing. This fails for large eventfiles of several GB.
In this case one has to unzip the file event_cl/niXXXXXXXXXX_0mpu7_ufa.evt.gz
before running xtiprepare.

''' Active FPMs: '''

NICER has 56 focal-plane modules (FPMs) of which 52 are usually active. For
different reasons, e.g. annealing, sometimes some FPMs are switched off. And
sometimes you have excluded certain FPMs because of their increased background
(especially FPM 14 & 34). In both cases you have to be careful to scale the ARF
or generate a new one. So one should check the event files how many detectors where
active during the observation. 
More info here: https://heasarc.gsfc.nasa.gov/docs/nicer/analysis_threads/arf-rmf/

@@ Line 6: / Line 6: @@
 imaging capabilities. While this simplifies the data extraction, it is also required
 to simulate a background for each observation. <br /> Previously downloaded
-NICER observations can be found under /satdata/X-ray/nicer/.
+NICER observations can be found under /data/X-ray/nicer/.
@@ Line 47: / Line 47: @@
 The produced spectrum and light-curve can then be found in the
-subdirecory 'dirname' in $prepdir. Currently no observation-specific
+subdirecory 'dirname' in $prepdir. Observation-specific
-response files are generated, but instead soft links to the current ARF
+response files are generated and header keywords are set accordingly. It is still advisable to double-check that they are correctly loaded into e.g. ISIS.
 === Background generation: ===
@@ Line 62: / Line 61: @@
 You can switch between them using the bkgmod_ parameter of extraction.
-Only the sw-model is curreltly able to also provide background light-curves.
+Only the sw-model is currently able to also provide background light-curves.
 For more information see :<br />
 https://heasarc.gsfc.nasa.gov/docs/nicer/tools/nicer_bkg_est_tools.html

@@ Line 121: / Line 121: @@
 ''' Damage to the optical bench '''
 On May 22, 2023, between 13:00 and 14:00 UTC, NICER appears to have developed a
 visible-light leak in the X-ray Timing Instrument (XTI) optical bench. This leads to

@@ Line 95: / Line 95: @@
 observations.
 If that happens you should check the .mkf-file and see whether any of the parameters
-exceeds the default filter criteria sepcfied in the fhelp of nimaketime.
+exceeds the default filter criteria specified in the fhelp of nimaketime.
 This can be done e.g. using fplot:
    fplot *.mkf TIME "FPM_UNDERONLY_COUNT SUN_ANGLE FPM_OVERONLY_COUNT SUNSHINE "
@@ Line 120: / Line 120: @@
 More info here: https://heasarc.gsfc.nasa.gov/docs/nicer/analysis_threads/arf-rmf/
 [[Category:Data Extraction]]

← Older revision		Revision as of 01:19, 17 March 2021
Line 113:		Line 113:
	active during the observation. <br />		active during the observation. <br />
	More info here: https://heasarc.gsfc.nasa.gov/docs/nicer/analysis_threads/arf-rmf/		More info here: https://heasarc.gsfc.nasa.gov/docs/nicer/analysis_threads/arf-rmf/
		+
		+
		+	[[Category:Data Extraction]]

@@ Line 54: / Line 54: @@
 As we cannot produce a background spectrum from an off-source region on the
-detector, a background spectrum has to be modeled. Currently there are two
+detector, a background spectrum has to be modeled. Currently there are three
-different tools available for that purpose. One based on external parameters
+different tools available for that purpose (sw', '3c50' and 'scorpeon').
-during the observation (i.e., space weather, solar angle and cutoff-rigidity of
+One based on external parameters during the observation (i.e., space weather,
-earths B-field) amd one based on the internal distribution of measured events.
+solar angle and cutoff-rigidity of earths B-field), one based on the internal
-Both are still in active development and might not be able to produce realistic
+distribution of measured events and  one using both and giving the user the
-spectra for all observations. In that case a simple reference observation of one
+option to adjust/fit the different background components.
-of the RXTE background fields might be used instead.  <br />
-Both tools are further described on the instruments webpage:<br />
+You can switch between them using the bkgmod_ parameter of extraction.
 https://heasarc.gsfc.nasa.gov/docs/nicer/tools/nicer_bkg_est_tools.html
 === Issues to keep in mind:  ===

@@ Line 93: / Line 93: @@
 It can happen, that e.g. optical loading leads to a filter parameter
 exceeding the standard filter criteria for most of certain
-observations. Such an observation might still be of interest, however.
+observations.
 In that case one might want to increase the allowed range e.g. for
 "underonly_range" in "xtiprepare".

@@ Line 19: / Line 19: @@
 #!/bin/csh
-set datadir = /satdata/X-ray/nicer/data/2200570101
+set datadir = /data/X-ray/nicer/data/2200570101
 set prepdir = '/userdata/data/$user/where/ever/you/want'