NuSTAR CALDB Release Version: 20211020 Release Type: CALDB release ========== Contents: data/nustar/fpm/index/caldb.indx20211020 data/nustar/fpm/bcf/detabs/nuAdetabs20100101v004.fits data/nustar/fpm/bcf/detabs/nuBdetabs20100101v004.fits data/nustar/fpm/bcf/vign/nuBvign20100101v008.fits data/nustar/fpm/bcf/vign/nuAvign20100101v008.fits data/nustar/fpm/bcf/gain/nuAgain20100101v009.fits data/nustar/fpm/bcf/gain/nuBgain20100101v009.fits data/nustar/fpm/cpf/rmf/nuBcutgrprmf20100101v003.fits data/nustar/fpm/cpf/rmf/nuAnocutgrprmf20100101v003.fits data/nustar/fpm/cpf/rmf/nuBnocutdet0_20100101v003.rmf data/nustar/fpm/cpf/rmf/nuAcutdet1_20100101v003.rmf data/nustar/fpm/cpf/rmf/nuBcutdet0_20100101v003.rmf data/nustar/fpm/cpf/rmf/nuAnocutdet2_20100101v003.rmf data/nustar/fpm/cpf/rmf/nuBnocutdet1_20100101v003.rmf data/nustar/fpm/cpf/rmf/nuAcutdet0_20100101v003.rmf data/nustar/fpm/cpf/rmf/nuAnocutdet3_20100101v003.rmf data/nustar/fpm/cpf/rmf/nuBcutdet1_20100101v003.rmf data/nustar/fpm/cpf/rmf/nuAcutdet3_20100101v003.rmf data/nustar/fpm/cpf/rmf/nuBnocutdet2_20100101v003.rmf data/nustar/fpm/cpf/rmf/nuAnocutdet0_20100101v003.rmf data/nustar/fpm/cpf/rmf/nuBcutdet2_20100101v003.rmf data/nustar/fpm/cpf/rmf/nuAcutgrprmf20100101v003.fits data/nustar/fpm/cpf/rmf/nuAcutdet2_20100101v003.rmf data/nustar/fpm/cpf/rmf/nuBnocutdet3_20100101v003.rmf data/nustar/fpm/cpf/rmf/nuBnocutgrprmf20100101v003.fits data/nustar/fpm/cpf/rmf/nuBcutdet3_20100101v003.rmf data/nustar/fpm/cpf/rmf/nuAnocutdet1_20100101v003.rmf Summary of changes: This is a major update in the calibration of the NuSTAR observatory based on detailed analysis of more than nine years of observations of the Crab, utilizing both focused and stray light measurements. Details of the analysis are presented in Madsen et al. (2021) JATIS in prep. (https://arxiv.org/abs/2110.11522), which is also available via the CALDB documentation page https://heasarc.gsfc.nasa.gov/docs/heasarc/caldb/nustar/docs/fpm/index.html A summary is also available on the SOC webpage https://nustarsoc.caltech.edu/NuSTAR_Public/NuSTAROperationSite/CALDB20211020.php The overall changes between the previous (CALDB v20211004 and earlier) and this new calibration (CALDB v20211020) are primarily off-axis dependent. Users of the updated calibration may see the following changes compared to previous analysis: # A flux increase of ~5% for sources < 1 arcmin off-axis - A flux increase of ~10% for sources 1 to 2 arcmin off-axis - A flux increase of ~15% for sources > 4 arcmin off-axis # Slopes of power law model components may change by ~0.04 depending on off-axis angle # More accurate high-energy and high off-axis angle corrections # A better agreement in the FPMA and FPMB flux measurements We expect that for most NuSTAR observations this calibration update will have little or no practical change in interpretation results, especially for analysis of low signal-to-noise spectra. There is no update to NuSTARDAS required to utilize CALDB v20211020. DETABS: v004 ============ Updated the CdZnTe and Pt absorption thicknesses for all 8 NuSTAR detectors. This is based on an analysis of the Crab spectra from over 500 ks of stray light observations have been extracted independently to recover the distinct DETABS parameters for each detector. These low-energy Pt and CdZnTe absorption components are independent of observation epoch and the use of stray light observations, which by-pass the NuSTAR optics, resolves the degeneracy with vignetting corrections. RMF: v003 ========= Updated the RMFs to provide better fidelity at low energies (<4 keV) and increased the statistical precision of the RMFs. The RMF generation code has been improved to properly account for past coarse measurements of trigger threshold and noise on the shaping amplifier. The number of incident photons used in the RMF generation has been increased by a factor of ten to improve the statistical fluctuations in the quantum efficiency. The use of stray light observations, which by-pass the NuSTAR optics, resolves the degeneracy with vignetting corrections. VIGNETTING: v008 ================ Updated the vignetting files for both telescopes taking into account the above calibrations. This includes an overall absolute calibration adjustment to conform to the updated NuSTAR absolute flux calibration. The NuSTAR vignetting files have been regenerated based on analysis of the Crab spectrum from observations at various off-axis angles amounting to a total exposure time of 233 ks. An iterative fitting procedure was devised to ensure good results, treating each off-axis bin between 0 to 7 arcmin off-axis with sufficient fidelity, to produce the correction to the response function as a function of energy and off-axis angle. The previous responses had a dependency on off-axis angle in both shape and normalization, which are strongly coupled, which has been largely mitigated by the new responses. The deviations from the Crab spectrum are now less than +/- 2% below 50 keV. GAIN: v009 ========== Added a July 2021 epoch to track the long-term gain calibration of the the NuSTAR detectors. Details of the analysis can be found in the calibration memo (CAL_NuSTAR_20211020.pdf) available on the NuSTAR calibration webpage at the HEASARC linked above.