SNR 1E 0102.2-7219 as an X-ray calibration standard in the 0.5−1.0 keV bandpass and its application to the CCD instruments aboardChandra,Suzaku,SwiftandXMM-Newton

Abstract

Context. The flight calibration of the spectral response of charge-coupled device (CCD) instruments below 1.5 keV is difficult in general because of the lack of strong lines in the on-board calibration sources typically available. This calibration is also a function of time due to the effects of radiation damage on the CCDs and/or the accumulation of a contamination layer on the filters or CCDs. Aims. We desire a simple comparison of the absolute effective areas of the current generation of CCD instruments onboard the following observatories: Chandra ACIS-S3, XMM-Newton (EPIC-MOS and EPIC-pn), Suzaku XIS, and Swift XRT and a straightforward comparison of the time-dependent response of these instruments across their respective mission lifetimes. Methods. We have been using 1E 0102.2-7219, the brightest supernova remnant in the Small Magellanic Cloud, to evaluate and modify the response models of these instruments. 1E 0102.2-7219 has strong lines of O, Ne, and Mg below 1.5 keV and little or no Fe emission to complicate the spectrum. The spectrum of 1E 0102.2-7219 has been well-characterized using the RGS gratings instrument on XMM-Newton and the HETG gratings instrument on Chandra. As part of the activities of the International Astronomical Consortium for High Energy Calibration (IACHEC), we have developed a standard spectral model for 1E 0102.2-7219 and fit this model to the spectra extracted from the CCD instruments. The model is empirical in that it includes Gaussians for the identified lines, an absorption component in the Galaxy, another absorption component in the SMC, and two thermal continuum components with different temperatures. In our fits, the model is highly constrained in that only the normalizations of the four brightest lines/line complexes (the O vii Heα triplet, O viii Lyα line, the Ne ix Heα triplet, and the Ne x Lyα line) and an overall normalization are allowed to vary, while all other components are fixed. We adopted this approach to provide a straightforward comparison of the measured line fluxes at these four energies. We have examined these measured line fluxes as a function of time for each instrument after applying the most recent calibrations that account for the time-dependent response of each instrument. Results. We performed our effective area comparison with representative, early mission data when the radiation damage and contamination layers were at a minimum, except for the XMM-Newton EPIC-pn instrument which is stable in time. We found that the measured fluxes of the O vii Heα r line, the O viii Lyα line, the Ne ix Heα r line, and the Ne x Lyα line generally agree to within ±10% for all instruments, with 38 of our 48 fitted normalizations within ±10% of the IACHEC model value. We then fit all available observations of 1E 0102.2-7219 for the CCD instruments close to the on-axis position to characterize the time dependence in the 0.5−1.0 keV band. We present the measured line normalizations as a function of time for each CCD instrument so that the users may estimate the un...

Different Accretion Heating of the Neutron Star Crust during Multiple Outbursts in MAXI J0556–332

“…We also use the multiplicative model constant to allow for normalization offsets between the Chandra and XMM-Newton observatories. For the Chandra data we used a constant of 1 and for the various XMM-Newton detectors-MOS1, MOS2, and pn the constants were calculated from Table 5 of Plucinsky et al (2017;C 0.983 …”

“…Due to the small number of counts per bin in the Swift/XRT spectra (0.3-10 keV), they were fit separately with W-statistics (background-subtracted Cash statistics) using the same N H and distance as used for the Chandra and XMM-Newton spectral fitting. We allow for a normalization offset of C 0.872 XRT = (Plucinsky et al 2017). Figure 1 shows the MAXI (top panel) and Swift/XRT (middle panel) light curves of J0556.…”

X-ray spectral analysis of the neutron star in SNR 1E 0102.2−7219

“…We provide the list of all observations used for our analysis in Table 1. We point the readers to Plucinsky et al (2017); Vogt et al (2018);Alan et al (2019) for detailed comments on these observations.…”

“…The supernova remnant E0102 has been extensively observed by Chandra, and used as a calibration source to model the response of the CCD instruments (Plucinsky et al 2017;Alan et al 2019). However, the background X-ray flux from E0102 around the compact object reported by Vogt et al (2018) is extremely strong, necessitating the high angular resolution of the Chandra X-ray Observatory.…”

“…Note: Our background model is wabs*tbabs*(apec + gaussian + gaussian + gaussian + gaussian). We use N H, M W and N H, S M C values reported in Plucinsky et al (2017) for our analysis. The tbabs component utilises the SMC values given in Russell & Dopita (1992) to model intrinsic absorption in the SMC.…”