NICER Spectral Analysis Workflow: High-Level Products, XSPEC Usage

NICER/IXPE Workshop July/August 2024 NICER High Level Products Craig Markwardt (NASA/GSFC) & NICER Team GSFC 1

Summary NICER Spectroscopy Extracting Using in XSPEC Choosing and Specifying Background Models NICER Light curves 2

NICER Workflow Overview NICER Data (from archive) Level 1 nicerl2 (calibration, screening) Level 2 nicerl3-spect (extract, responses, bkg, syserr) nicerl3-lc (extract) This Presentation Level 3 Spectrum Light Curve Responses & Bkg 3

High Level Products Overview The two main high-level products are nicerl3-spect spectral extraction nicerl3-lc light curve extraction See example notebook NICER_data_reduction These tools are part of HEASoft and designed to be One-stop-shopping tools that extract the product, background, responses, etc. Same / similar parameters Same support for various tasks like background estimation 4

Spectral Analysis Workflow Assume you have already run nicerl2 and have a cleaned event list and filter file Run nicerl3-spect to extract products Load into XSPEC and start analysis 5

How to run nicerl3-spect DEMO Run nicerl3-spect /path/to/1234567890 clobber=YES Path to Observation Tool automatically searches for nicerl2 s products and uses them Background File OR Model + Sky ARF + Bkg RMF Source Spectrum ( pha file) Cleaned Event file ( cl file) nicerl3-spect Responses ( arf and rmf ) Filter File ( mkf file) XSPEC Load Script 6

Spectral Choices How Much Data? Screening when running nicerl2 (not nicerl3) Background settings Background Model? Background Output? Language? SCORPEON 3C50 Space Weather XSPEC Model File XSPEC .xcm Python (pyXspec) Don t be afraid of experimenting a little! 7

XSPEC But what do I do with all these products? Answer: the XSPEC load file will load all the data, responses and backgrounds for this product XSPEC command @ni1234567890mpu7_load.xcm See example notebook Fitting_Spectra DEMO 8

Example XSPEC Spectrum 9

Background Subtraction and Modeling NICER is a non-imaging instrument A background model is required to estimate background during a given observation NICER has three active background models SCORPEON adjustable template model 3C50 library model Space Weather library model Each model is trained on different variables Since 2022, all three background models are available through standard processing No separate downloads 10

Background Model Overview Characteristic SCORPEON 3C50 Space Weather Template / Parameterized Model Type Library Library COR_SAX Overshoots HBG (15-18 keV) HREJ COR_SAX KP Training Variables Background File Optional XSPEC Model Always Produces Estimate? X-ray Sky Backgrounds? Noise Peak NO NO Average Average Average Light Curves? Works with Light Leak Data? (<0.6 keV) 11

Library Models vs Template Models Library Model: 3C50 Template Model: SCORPEON IBG: 15-17 keV Events HREJ: PI Ratio-Rejected Events Measure basis vector of each unique component Make smoothed version of template as XSPEC model Normalized based on known telemetry (overshoots, etc.) Application: predict norms from telemetry & load into XSPEC Break parameter space into cells, measure background in each cell (library of spectra) Application: calculate exposure in each cell, make weighted sum of library spectra 12

SCORPEON Overview Best use of SCORPEON is an XSPEC model Background MODELING, not subtracting Adjust background with source model No oversubtraction Sane parameter limits prevent over- fitting You can create a subtractable background file if desired 13

How to Estimate Background Background estimation is automatic when using standard nicerl3-* extraction pipelines For spectra: SCORPEON model For light curves: SCORPEON file When running product tools nicerl3-_________ bkgmodeltype=3c50 14

Background Guidance Try SCORPEON first, with model output This is the default Even if you are interested in narrow energy range, fit full 0.25-18 keV range Use cstat or pgstat if possible When you fit your source spectrum, you will also be fitting the background (GOOD!) More discussion in Pitfalls presentation 3C50 and Space Weather can also be good They are background files, not models, which are subtracted from your spectrum Over/under subtraction can be a problem, so limit energy range 15

Light Curves The tool for light curve extraction is nicerl3-lc Works the same way as spectral extraction You MUST run nicerl3-spect first! See example notebook Light_Curve_Plots 16

How to run nicerl3-spect Run nicerl3-lc /path/to/1234567890 50-200 10.0 Path to Observation PI Range Time Bin Energy = PI * (10 eV) so 50-200 is 0.5-2 keV Cleaned Event file ( cl file) Source Light Curve nicerl3-lc Background Light Curve Filter File ( mkf file) Sky ARF & RMF Background RMF (from running nicerl3-spect) 17

Light Curve Choices Choose background model, time bin size, and energy range Energy Range Background Model? Time Bin PI Bin Range PI = Energy / (10 eV) SCORPEON Space Weather (slow) In seconds Don t be afraid of experimenting a little! 18

Conclusions You should now know how to extract spectral and light curve products choose and specify background models 19