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J/MNRAS/388/849     NGC253 XMM observations                  (Barnard+, 2008)

A multi-coloured survey of NGC253 with XMM-Newton: testing the methods used for creating luminosity functions from low-count data. Barnard R., Greening L.S., Kolb U. <Mon. Not. R. Astron. Soc., 388, 849-862 (2008)> =2008MNRAS.388..849B
ADC_Keywords: Galaxies, nearby ; X-ray sources Keywords: galaxies: individual: NGC 253 - X-rays: binaries - X-rays: general Abstract: NGC 253 is a local, starbursting spiral galaxy with strong X-ray emission from hot gas, as well as many point sources. We have conducted a spectral survey of the X-ray population of NGC 253 using a deep XMM-Newton observation. NGC 253 only accounts for ∼20 per cent of the XMM-Newton EPIC field of view, allowing us to identify ∼100 X-ray sources that are unlikely to be associated with NGC 253. Hence, we were able to make a direct estimate of contamination from, for example, foreground stars and background galaxies. X-ray luminosity functions (XLFs) of galaxy populations are often used to characterize their properties. There are several methods for estimating the luminosities of X-ray sources with few photons. We have obtained spectral fits for the brightest 140 sources in the 2003 XMM-Newton observation of NGC 253, and compare the best-fitting luminosities of those 69 non-nuclear sources associated with NGC 253 with luminosities derived using other methods. We find the luminosities obtained from these various methods to vary systematically by a factor of up to 3 for the same data; this is largely due to differences in absorption. We therefore conclude that assuming Galactic absorption is probably unwise; rather, one should measure the absorption for the population. Description: XMM-Newton observations are susceptible to periods of high background levels, caused by increased flux of solar particles. We screened the data from each of the EPIC cameras (MOS1, MOS2 and pn), to remove flaring intervals. This process resulted in ∼46ks of good time for the PN and ∼69ks for the MOS cameras. File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file tablea1.dat 44 185 Positions of X-ray sources in the XMM-Newton observations of NGC 253, along with some observed properties tablea2.dat 105 185 Spectral properties for each source from Observation 2
See also: J/ApJ/649/730 : ULX population in nearby galaxies from XMM (Winter+, 2006) B/xmm : XMM-Newton Observation Log (XMM-Newton SOC, 2007) Byte-by-byte Description of file: tablea1.dat
Bytes Format Units Label Explanations
1- 3 I3 --- [BGK2008] Source sequential number (G1) 5- 6 I2 h RAh Right ascension (J2000) 8- 9 I2 min RAm Right ascension (J2000) 11- 15 F5.2 s RAs Right ascension (J2000) 17 A1 --- DE- Declination sign (J2000) 18- 19 I2 deg DEd Declination (J2000) 21- 22 I2 arcmin DEm Declination (J2000) 24- 28 F5.2 arcsec DEs Declination (J2000) 30 A1 --- inD25 [yn] indicates whether the source is within the D25 isophotal region of NGC 253 32- 33 I2 arcsec Rs Source extraction radius 35- 39 F5.2 --- Ab/As Background-to-source area ratio 41- 44 F4.2 --- EEF Encircled energy fraction (1)
Note (1): Sources with an EEF of zero were detected, but no suitable spectra were obtained.
Byte-by-byte Description of file: tablea2.dat
Bytes Format Units Label Explanations
1- 3 I3 --- [BGK2008] Source sequential number (G1) 5- 9 I5 ct CtPN pn source counts 11- 15 I5 ct CtMOS MOS source counts 17- 26 A10 --- Mod Best fitting model (1) 27- 31 F5.3 10+22cm-2 NH ? Absorption 32- 36 F5.3 10+22cm-2 e_NH ? rms uncertainty on NH at 90% confidence level 37 A1 --- f_NH [f] f for fixed absorption 40- 44 F5.3 --- Param ? Parameter (spectral index or temperature) (2) 46- 50 F5.3 --- e_Param ? rms uncertainty on Param at 90% confidence level 52- 55 F4.2 --- Param2 ? Second parameter value (spectral index or temperature) (2) 56- 59 F4.2 --- e_Param2 ? rms uncertainty on Param2 at 90% confidence level 62- 66 F5.1 --- chi2 ? chi2 value 67 A1 --- --- [/] 68- 70 I3 --- DOF ? Degree Of Freedom (3) 72- 76 F5.3 --- gf ? Good fit probability 78- 86 F9.2 10+29W LBF ? Best-fitting luminosity 88- 96 F9.2 10+29W e_LBF ? rms uncertainty on LBF at 90% confidence level 99-105 F7.2 10+29W LSM ?=0. Standard model (Method I) luminosity
Note (1): Best-fitting models for bright sources can be as follows: PO = a power law BB = blackbody BR = bremsstrahlung 2C = a two-component model consisting of a BB plus power law Faint sources are modelled using a best-fitting power law: ----------------------------------------------------------------------------- Model NFnt NH/1020 Gamma chi2/dof [gf] Flux(pn thin) Flux (MOS med) ----------------------------------------------------------------------------- IS 7 1.3 0.4 (.03) 71/54 [0.06] 12000(200) 36000(8000) OS 36 1.3 1.23(.13) 55/44 [0.12] 4800(400) 19000(2000) ----------------------------------------------------------------------------- Note (2): Parameter (spectral index or temperature), spectral index for PO models, temperature for BB and BR models, spectral index and temperature for 2C models. Note (3): The quality of the spectrum may be deduced from the number of degrees of freedom because the spectra are grouped to a minimum number of counts per bin (brighter sources have more degrees of freedom).
Global notes: Notes (G1): Sources identified as [BGK2008] SNNN in Simbad. History: From electronic version of the journal
(End) Patricia Vannier [CDS] 24-Dec-2008
The document above follows the rules of the Standard Description for Astronomical Catalogues.From this documentation it is possible to generate f77 program to load files into arrays or line by line

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