Methods for estimating fluxes and absorptions of faint X-ray sources

Research output: Contribution to journalArticle

37 Citations (Scopus)

Abstract

X-ray sources with very few counts can be identified with low-noise X-ray detectors such as the Advanced CCD Imaging Spectrometer on board the Chandra X-ray Observatory. These sources are often too faint for parametric spectral modeling using well-established methods such as fitting with XSPEC. We discuss the estimation of apparent and intrinsic broadband X-ray fluxes and soft X-ray absorption from gas along the line of sight to these sources, using nonparametric methods. Apparent flux is estimated from the ratio of the source count rate to the instrumental effective area averaged over the chosen band. Absorption, intrinsic flux, and errors on these quantities are estimated from comparison of source photometric quantities with those of high signal-to-noise spectra that were simulated using spectral models characteristic of the class of astrophysical sources under study. The concept of this method is similar to the long-standing use of color-magnitude diagrams in optical and infrared astronomy, with X-ray median energy replacing color index and X-ray source counts replacing magnitude. Our nonparametric method is tested against the apparent spectra of 2000 faint sources in the Chandra observation of the rich young stellar cluster in the M 17 H II region. We show that the intrinsic X-ray properties can be determined with little bias and reasonable accuracy using these observable photometric quantities without employing often uncertain and time-consuming methods of nonlinear parametric spectral modeling. Our method is calibrated for thermal spectra characteristic of stars in young stellar clusters, but recalibration should be possible for some other classes of faint X-ray sources such as extragalactic active galactic nuclei.

Original languageEnglish (US)
Pages (from-to)1760-1771
Number of pages12
JournalAstrophysical Journal
Volume708
Issue number2
DOIs
StatePublished - Jan 1 2010

Fingerprint

estimating
x rays
infrared astronomy
method
color-magnitude diagram
imaging spectrometers
H II regions
noise spectra
astronomy
active galactic nuclei
low noise
line of sight
modeling
charge coupled devices
observatories
astrophysics
spectrometer
observatory
diagram
broadband

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

@article{1669c2af29fd45d9a31d58850f5d03fc,
title = "Methods for estimating fluxes and absorptions of faint X-ray sources",
abstract = "X-ray sources with very few counts can be identified with low-noise X-ray detectors such as the Advanced CCD Imaging Spectrometer on board the Chandra X-ray Observatory. These sources are often too faint for parametric spectral modeling using well-established methods such as fitting with XSPEC. We discuss the estimation of apparent and intrinsic broadband X-ray fluxes and soft X-ray absorption from gas along the line of sight to these sources, using nonparametric methods. Apparent flux is estimated from the ratio of the source count rate to the instrumental effective area averaged over the chosen band. Absorption, intrinsic flux, and errors on these quantities are estimated from comparison of source photometric quantities with those of high signal-to-noise spectra that were simulated using spectral models characteristic of the class of astrophysical sources under study. The concept of this method is similar to the long-standing use of color-magnitude diagrams in optical and infrared astronomy, with X-ray median energy replacing color index and X-ray source counts replacing magnitude. Our nonparametric method is tested against the apparent spectra of 2000 faint sources in the Chandra observation of the rich young stellar cluster in the M 17 H II region. We show that the intrinsic X-ray properties can be determined with little bias and reasonable accuracy using these observable photometric quantities without employing often uncertain and time-consuming methods of nonlinear parametric spectral modeling. Our method is calibrated for thermal spectra characteristic of stars in young stellar clusters, but recalibration should be possible for some other classes of faint X-ray sources such as extragalactic active galactic nuclei.",
author = "Getman, {Konstantin V.} and Feigelson, {Eric D.} and Broos, {Patrick S.} and Townsley, {Leisa K.} and Garmire, {Gordon P.}",
year = "2010",
month = "1",
day = "1",
doi = "10.1088/0004-637X/708/2/1760",
language = "English (US)",
volume = "708",
pages = "1760--1771",
journal = "Astrophysical Journal",
issn = "0004-637X",
publisher = "IOP Publishing Ltd.",
number = "2",

}

Methods for estimating fluxes and absorptions of faint X-ray sources. / Getman, Konstantin V.; Feigelson, Eric D.; Broos, Patrick S.; Townsley, Leisa K.; Garmire, Gordon P.

In: Astrophysical Journal, Vol. 708, No. 2, 01.01.2010, p. 1760-1771.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Methods for estimating fluxes and absorptions of faint X-ray sources

AU - Getman, Konstantin V.

AU - Feigelson, Eric D.

AU - Broos, Patrick S.

AU - Townsley, Leisa K.

AU - Garmire, Gordon P.

PY - 2010/1/1

Y1 - 2010/1/1

N2 - X-ray sources with very few counts can be identified with low-noise X-ray detectors such as the Advanced CCD Imaging Spectrometer on board the Chandra X-ray Observatory. These sources are often too faint for parametric spectral modeling using well-established methods such as fitting with XSPEC. We discuss the estimation of apparent and intrinsic broadband X-ray fluxes and soft X-ray absorption from gas along the line of sight to these sources, using nonparametric methods. Apparent flux is estimated from the ratio of the source count rate to the instrumental effective area averaged over the chosen band. Absorption, intrinsic flux, and errors on these quantities are estimated from comparison of source photometric quantities with those of high signal-to-noise spectra that were simulated using spectral models characteristic of the class of astrophysical sources under study. The concept of this method is similar to the long-standing use of color-magnitude diagrams in optical and infrared astronomy, with X-ray median energy replacing color index and X-ray source counts replacing magnitude. Our nonparametric method is tested against the apparent spectra of 2000 faint sources in the Chandra observation of the rich young stellar cluster in the M 17 H II region. We show that the intrinsic X-ray properties can be determined with little bias and reasonable accuracy using these observable photometric quantities without employing often uncertain and time-consuming methods of nonlinear parametric spectral modeling. Our method is calibrated for thermal spectra characteristic of stars in young stellar clusters, but recalibration should be possible for some other classes of faint X-ray sources such as extragalactic active galactic nuclei.

AB - X-ray sources with very few counts can be identified with low-noise X-ray detectors such as the Advanced CCD Imaging Spectrometer on board the Chandra X-ray Observatory. These sources are often too faint for parametric spectral modeling using well-established methods such as fitting with XSPEC. We discuss the estimation of apparent and intrinsic broadband X-ray fluxes and soft X-ray absorption from gas along the line of sight to these sources, using nonparametric methods. Apparent flux is estimated from the ratio of the source count rate to the instrumental effective area averaged over the chosen band. Absorption, intrinsic flux, and errors on these quantities are estimated from comparison of source photometric quantities with those of high signal-to-noise spectra that were simulated using spectral models characteristic of the class of astrophysical sources under study. The concept of this method is similar to the long-standing use of color-magnitude diagrams in optical and infrared astronomy, with X-ray median energy replacing color index and X-ray source counts replacing magnitude. Our nonparametric method is tested against the apparent spectra of 2000 faint sources in the Chandra observation of the rich young stellar cluster in the M 17 H II region. We show that the intrinsic X-ray properties can be determined with little bias and reasonable accuracy using these observable photometric quantities without employing often uncertain and time-consuming methods of nonlinear parametric spectral modeling. Our method is calibrated for thermal spectra characteristic of stars in young stellar clusters, but recalibration should be possible for some other classes of faint X-ray sources such as extragalactic active galactic nuclei.

UR - http://www.scopus.com/inward/record.url?scp=77950242005&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=77950242005&partnerID=8YFLogxK

U2 - 10.1088/0004-637X/708/2/1760

DO - 10.1088/0004-637X/708/2/1760

M3 - Article

AN - SCOPUS:77950242005

VL - 708

SP - 1760

EP - 1771

JO - Astrophysical Journal

JF - Astrophysical Journal

SN - 0004-637X

IS - 2

ER -