A novel approach to detect line emission under high background in high-resolution X-ray spectra

Xiangyu Zhang; Sara Algeri; Vinay Kashyap; Margarita Karovska

doi:10.1093/mnras/stad398

A novel approach to detect line emission under high background in high-resolution X-ray spectra

Xiangyu Zhang, Sara Algeri, Vinay Kashyap, Margarita Karovska

Statistics (Twin Cities)

Research output: Contribution to journal › Article › peer-review

1 Scopus citations

Abstract

We develop a novel statistical approach to identify emission features or set upper limits in high-resolution spectra in the presence of high background. The method relies on detecting differences from the background using smooth tests and using classical likelihood ratio tests to characterize known shapes like emission lines. We perform signal detection or place upper limits on line fluxes while accounting for the problem of multiple comparisons. We illustrate the method by applying it to a Chandra LETGS + HRC-S observation of symbiotic star RT Cru, successfully detecting previously known features like the Fe line emission in the 6–7 keV range and the Iridium-edge due to the mirror coating on Chandra. We search for thermal emission lines from Ne X, Fe XVII, O VIII, and O VII, but do not detect them, and place upper limits on their intensities consistent with a ≈1 keV plasma. We serendipitously detect a line at 16.93 Å (0.732 keV) that we attribute to photoionization or a reflection component.

Original language	English (US)
Pages (from-to)	969-983
Number of pages	15
Journal	Monthly Notices of the Royal Astronomical Society
Volume	521
Issue number	1
DOIs	https://doi.org/10.1093/mnras/stad398
State	Published - May 1 2023

Bibliographical note

Funding Information:
Sara Algeri and Xiangyu Zhang are grateful for the financial support provided by the Office of the Vice President for Research at the University of Minnesota. Vinay Kashyap was supported by the NASA Contract NAS8-03060 to the Chandra X-ray Center. Margarita Karovska and Vinay Kashyap acknowledge support for this work provided via the Chandra grant GO5-16023X.

Publisher Copyright:
© 2023 The Author(s)

Keywords

binaries: symbiotic
methods: data analysis
methods: statistical
stars: individual: RT Cru X-rays: stars techniques: spectroscopic

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10.1093/mnras/stad398

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abstract = "We develop a novel statistical approach to identify emission features or set upper limits in high-resolution spectra in the presence of high background. The method relies on detecting differences from the background using smooth tests and using classical likelihood ratio tests to characterize known shapes like emission lines. We perform signal detection or place upper limits on line fluxes while accounting for the problem of multiple comparisons. We illustrate the method by applying it to a Chandra LETGS + HRC-S observation of symbiotic star RT Cru, successfully detecting previously known features like the Fe line emission in the 6–7 keV range and the Iridium-edge due to the mirror coating on Chandra. We search for thermal emission lines from Ne X, Fe XVII, O VIII, and O VII, but do not detect them, and place upper limits on their intensities consistent with a ≈1 keV plasma. We serendipitously detect a line at 16.93 {\AA} (0.732 keV) that we attribute to photoionization or a reflection component.",

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note = "Funding Information: Sara Algeri and Xiangyu Zhang are grateful for the financial support provided by the Office of the Vice President for Research at the University of Minnesota. Vinay Kashyap was supported by the NASA Contract NAS8-03060 to the Chandra X-ray Center. Margarita Karovska and Vinay Kashyap acknowledge support for this work provided via the Chandra grant GO5-16023X. Publisher Copyright: {\textcopyright} 2023 The Author(s)",

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doi = "10.1093/mnras/stad398",

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AU - Karovska, Margarita

N1 - Funding Information: Sara Algeri and Xiangyu Zhang are grateful for the financial support provided by the Office of the Vice President for Research at the University of Minnesota. Vinay Kashyap was supported by the NASA Contract NAS8-03060 to the Chandra X-ray Center. Margarita Karovska and Vinay Kashyap acknowledge support for this work provided via the Chandra grant GO5-16023X. Publisher Copyright: © 2023 The Author(s)

PY - 2023/5/1

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N2 - We develop a novel statistical approach to identify emission features or set upper limits in high-resolution spectra in the presence of high background. The method relies on detecting differences from the background using smooth tests and using classical likelihood ratio tests to characterize known shapes like emission lines. We perform signal detection or place upper limits on line fluxes while accounting for the problem of multiple comparisons. We illustrate the method by applying it to a Chandra LETGS + HRC-S observation of symbiotic star RT Cru, successfully detecting previously known features like the Fe line emission in the 6–7 keV range and the Iridium-edge due to the mirror coating on Chandra. We search for thermal emission lines from Ne X, Fe XVII, O VIII, and O VII, but do not detect them, and place upper limits on their intensities consistent with a ≈1 keV plasma. We serendipitously detect a line at 16.93 Å (0.732 keV) that we attribute to photoionization or a reflection component.

AB - We develop a novel statistical approach to identify emission features or set upper limits in high-resolution spectra in the presence of high background. The method relies on detecting differences from the background using smooth tests and using classical likelihood ratio tests to characterize known shapes like emission lines. We perform signal detection or place upper limits on line fluxes while accounting for the problem of multiple comparisons. We illustrate the method by applying it to a Chandra LETGS + HRC-S observation of symbiotic star RT Cru, successfully detecting previously known features like the Fe line emission in the 6–7 keV range and the Iridium-edge due to the mirror coating on Chandra. We search for thermal emission lines from Ne X, Fe XVII, O VIII, and O VII, but do not detect them, and place upper limits on their intensities consistent with a ≈1 keV plasma. We serendipitously detect a line at 16.93 Å (0.732 keV) that we attribute to photoionization or a reflection component.

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A novel approach to detect line emission under high background in high-resolution X-ray spectra

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