OBSOLETE: NICER Background Estimator Tools


The ISS orbit takes NICER through a wide range of geomagnetic latitudes – each with its own background characteristics. At high latitudes, the background is dependent on space weather and the variability of the Sun. Individual observations thus have different background levels that must be understood to maximize the science return.

To calibrate the background, NICER has to date collected many megaseconds of exposure on background fields used and characterized by RXTE (Jahoda et al. 2006) and also a few select locations near some of NICER's long term and faint MSPs. These data form a database for two different and independently developed background modeling tools. At right is an example of a faint NICER source showing how well these tools capture the shape of the background spectrum.

Command-Line Interface Tools

These tools can work well and are continuing to be refined. These tools are now included within HEASoft as of version 6.31 and higher (NICERDAS 10 or higher). In addition, a different kind of background model, called SCORPEON, is now included with HEASoft.

These models can be used by Guest Observers in preparing NICER observing proposals, as well as by other NICER users who need suitable background models to use in data analysis.

Some of the discussion on this page refers to a separately downloadable version of both the 3C50 and Space Weather background models. Since both models, as well as SCORPEON, are included within HEASoft, the NICER team no longer recommends downloading background model software or files separately. These files may not be updated in the future. Therefore they are marked as OBSOLETE.

To use any of these tools, you must have a complete NICERDAS and calibration environment installed. Please use the Settting Up a NICER Analysis Environment thread if you need further help.

To report issues and bugs, please contact the NICER helpdesk by using the HEASARC Feedback Form.

OBSOLETE Tool #1: Space Weather nicer_bkg_estimator

The separately-downloadable tool nicer_bkg_estimator tool is now obsolete and is now delivered via HEASoft. The tool implements the "space weather" method (Gendreau et al., in prep.) which uses environmental data to parse the background database. This tool uses a model of the magnetic cut-off rigidity as well as space weather data in the form of the planetary Kennziffer Index, or Kp index (Bartels et al. 1939). Kp is derived from a worldwide network of magnetometers that publishes data every 3 hours. Kp ranges from 0 to 9, where low values indicate calm space weather, while higher indicate geomagnetic storms. The space weather background tool builds a library of background spectra divided amongst these environmental variables to predict a background spectrum for a given observation that is independent of the X-ray event data collected in the target observation.

This package contains functions which can be used to create an estimated NICER background spectrum based on the "environmental" model developed by the NICER Guest Observer Facility. The environmental model uses a combination of the cut-off rigidity (COR_SAX) and the Planetary K index (KP) which gives an estimate of the space weather environment. This model also uses the SUN_ANGLE parameter which helps describe the low-energy background produced by optical loading.

OBSOLETE Downloads:

0p6Fixed bug in estimation of background counts in the lightcurve generator method mk_bkg_lc_evt; improved doc string
0p5Fixed bug in deadtime correction & updated all EXPOSURE keywords
0p4aFixed bug affecting data with many GTIs, other improvements
0p2Initial alpha release

OBSOLETE 3C50 Tool #2: nibackgen3C50

The separately-downloadable tool nibackgen3C50 is now obsolete and is delivered via HEASoft. The tool implements the 3C50 background model (Remillard et al.), which makes use of a number of background proxies in the NICER data to define the basis states of the background database. These background proxies include graded event data that discriminate some X-ray events landing near the center of each detector from those interacting near the detector edge under a field aperture. Another proxy is high energy X-ray events ("out of band"), which are very unlikely to have been focused by the X-ray mirrors. The tool takes a target observation event list and pulls out the proxy data to build a predicted background spectrum from similarly selected data from the background database.

This obsolete package was designed to run as a patch on your HEASoft installation. Alternatively, one can run the tool from within an existing HEASoft installation without explicitly installing it.

Revision Information:

v7RGv5, g2019d, g2020aSupports 2018, 2019, and 2020 gain calibration; includes updated help and parameter files; and, improves functionality and logging. S0 filtering now included (see Remillard et al.)
v6RGv5, g2019d, g2020aSupports 2018, 2019, and 2020 gain calibration; includes updated help and parameter files; and, improves functionality and logging.
v5RGv5Corrected a bug that prevented the final background spectrum from being generated in some cases where the input has a very large number of GTIs.
v4RGv5Initial alpha release

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