J/ApJ/708/1760 Flux estimations of faint X-ray sources (Getman+, 2010)
Methods for estimating fluxes and absorptions of faint X-ray sources.
Getman K.V., Feigelson E.D., Broos P.S., Townsley L.K., Garmire G.P.
<Astrophys. J., 708, 1760-1771 (2010)>
=2010ApJ...708.1760G 2010ApJ...708.1760G
ADC_Keywords: X-ray sources ; Clusters, open ; Stars, pre-main sequence
Keywords: methods: data analysis - methods: statistical - open clusters and
associations: individual (M17) - techniques: photometric -
X-rays: general - X-rays: stars
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 HII 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.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 21 2424 Simulated data to figure 3
table3.dat 17 1212 Simulated data to figure 4
table4.dat 23 2424 Simulated data to figure 5
table5.dat 27 16018 Simulated data to figure 9
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See also:
B/chandra : The Chandra Archive Log (CXC, 1999-)
J/ApJS/169/353 : Chandra sources in M17 (Broos+, 2007)
J/ApJ/660/1462 : Abundances of ONC X-ray PMS stars (Maggio+, 2007)
J/AJ/131/2164 : X-ray sources in RMC 136 (Townsley+, 2006)
J/ApJS/160/319 : COUP: observations and source lists (Getman+, 2005)
J/ApJ/613/393 : X-ray and radio sources in ρ Oph Core A (Gagne+, 2004)
J/ApJ/574/258 : X-ray-emitting young stars in the Orion nebula (Feigelson+,
2002)
http://www2.astro.psu.edu/xray/docs/TARA/ae_users_guide.html : ACIS Extract
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 5 F5.3 keV MedEt Apparent full-band median energy
7- 11 F5.3 --- Fph/Fs Ratio of the apparent simulated fluxes (1)
13- 16 F4.1 [10-7W] Lhc Log of hard-band intrinsic luminosity (erg/s)
18- 21 A4 --- Band Energy band (full=0.5-8keV hard=2-8keV)
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Note (1): Ratio of the apparent X-ray flux of simulated data from ACIS
Extract (version 2009-01-27) photometry to that inferred from flux
integration of the input spectral models.
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 5 F5.3 keV MedEt Apparent full-band median energy
7- 12 F6.3 [cm-2] NH Log of X-ray column density
14- 17 F4.1 [10-7W] Lhc Log of hard-band intrinsic luminosity; erg/s
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 5 F5.3 keV MedEt Apparent full-band median energy
7- 13 F7.5 [---] Fc/F Log of simulated intrinsic to apparent flux ratio
15- 18 F4.1 [10-7W] Lhc Log of hard-band intrinsic luminosity; erg/s
20- 23 A4 --- Band Energy band (full=0.5-8keV hard=2-8keV)
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Byte-by-byte Description of file: table5.dat
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Bytes Format Units Label Explanations
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1- 5 F5.3 keV MedE Apparent median energy
7- 12 F6.4 keV e_MedE Error on MedE
14- 17 F4.1 [10-7W] Lhc Log of hard-band intrinsic luminosity; erg/s
19- 22 A4 --- Band Energy band (full=0.5-8keV hard=2-8keV)
24- 27 I4 ct NC Net counts
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 23-Feb-2012