J/ApJ/735/26 Chandra observations of M81 (Sell+, 2011)
Luminosity functions and point-source properties from multiple Chandra
observations of M81.
Sell P.H., Pooley D., Zezas A., Heinz S., Homan J., Lewin W.H.G.
<Astrophys. J., 735, 26 (2011)>
=2011ApJ...735...26S 2011ApJ...735...26S
ADC_Keywords: Galaxies, nearby ; X-ray sources ; Spectroscopy ; Models
Keywords: galaxies: individual (M81) - X-rays: binaries - X-rays: galaxies
Abstract:
We present an analysis of 15 Chandra observations of the nearby spiral
galaxy M81 taken over the course of six weeks in 2005 May-July. Each
observation reaches a sensitivity of ∼1037erg/s. With these
observations and one previous deeper Chandra observation, we compile a
master source list of 265 point sources, extract and fit their
spectra, and differentiate basic populations of sources through their
colors. We also carry out variability analyses of individual point
sources and of X-ray luminosity functions (XLFs) in multiple regions
of M81 on timescales of days, months, and years. We find that, despite
measuring significant variability in a considerable fraction of
sources, snapshot observations provide a consistent determination of
the XLF of M81. We also fit the XLFs for multiple regions of M81 and,
using common parameterizations, compare these luminosity functions to
those of two other spiral galaxies, M31 and the Milky Way.
Description:
We present 15 Chandra observations of M81 (ObsIDs 5935-5949; 2005 May
26-2005 Jul 6) taken specifically to explore XLF and individual
point-source variability. For our analysis, we include an additional
observation from the Chandra archive (ObsID 735; 2000 May 7). All 16
observations were taken with the Advanced CCD Imaging Spectrometer
(ACIS).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table3.dat 127 276 Merged extraction data of sources in the master
and borderline source lists
table4.dat 132 276 Merged fit data of sources in the master and
borderline source lists
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See also:
B/chandra : The Chandra Archive Log (CXC, 1999-2012)
J/ApJS/192/10 : Chandra ACIS survey in 383 nearby galaxies. I. (Liu, 2011)
J/AJ/141/129 : Chandra Transmission Grating Data Cat. (Huenemoerder+, 2011)
J/ApJS/157/59 : Ultraluminous X-ray sources in nearby galaxies (Liu+, 2005)
J/ApJS/144/213 : Chandra X-ray observations of M81 (Swartz+, 2003)
J/A+A/368/797 : Soft X-ray properties of Seyfert galaxies (Pfefferkorn+, 2001)
J/ApJ/554/202 : ROSAT X-ray observations of M81 (Immler+, 2001)
Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 3 A3 --- Seq Source index number (G1)
5- 14 F10.6 deg RAdeg Right Ascension in decimal degrees (J2000)
16- 24 F9.6 deg DEdeg Declination in decimal degrees (J2000)
26- 31 F6.3 arcmin OAA ? Average off-axis angle
33- 37 I5 ct SCts ? Total source counts
39- 44 F6.1 ct BCts ? Total background counts
46- 51 F6.1 ct Soft ? Net soft (0.5-1keV) counts
53- 57 F5.1 ct e_Soft ? Lower limit uncertainty in Soft (1)
59- 63 F5.1 ct E_Soft ? Upper limit uncertainty in Soft
65- 70 F6.1 ct Med ? Net medium (1-2keV) counts
72- 75 F4.1 ct e_Med ? Lower limit uncertainty in Med (1)
77- 80 F4.1 ct E_Med ? Upper limit uncertainty in Med
82- 87 F6.1 ct Hard ? Net hard (2-8keV) counts
89- 92 F4.1 ct e_Hard ? Lower limit uncertainty in Hard (1)
94- 97 F4.1 ct E_Hard ? Upper limit uncertainty in Hard
99-102 F4.1 % PSF ? Average PSF fraction enclosed by extraction
region
104-105 A2 --- n_Seq Source off chip (2)
107-111 F5.2 --- VarS1 ? Variability statistic (3)
113-121 A9 --- Obs1 Observations used to derive VarS1
123-127 F5.2 --- VarS2 ? Variability statistic (4)
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Note (1): A lower limit uncertainty of "0.0" indicates a "nan" value.
Note (2): Flag as follows:
OC = Off Chip.
NA = Not Applicable/Available. This occurs in the case of the variability
statistic when the source is only on the chips in one of
ObsIDs 5935-5949 or off the ObsID 735 chips.
Note (3): As defined in equation 1 between ObsIDs 5935-5949.
Note (4): As defined in equation 1 between the merged observation and ObsID 735.
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 A3 --- Seq Source index number (G1)
5- 6 A2 --- f_Seq [OC ] OC: Off chip
8- 12 A5 --- Model Model type: plaw=power law, or bbod=blackbody
14 A1 --- n_Model [ab] Note on Model type (5)
16- 19 F4.2 --- Param ? Photon Index (plaw) or kT (bbod) of Model
21- 24 F4.2 --- e_Param ? Lower limit uncertainty in Param (6)
26- 29 F4.2 --- E_Param ? Upper limit uncertainty in Param (6)
31- 38 E8.2 --- Norm ? Model normalization (7)
40- 47 E8.2 --- e_Norm ? Lower limit uncertainty in Norm (6)
49- 56 E8.2 --- E_Norm ? Upper limit uncertainty in Norm (6)
58- 63 F6.2 10+22/cm2 NH ? The H I column density (8)
65- 70 F6.2 10+22/cm2 e_NH ? Lower limit uncertainty in NH (6)
72- 76 F5.2 10+22/cm2 E_NH ? Upper limit uncertainty in NH (6)
78- 83 F6.1 --- CStat ? Total best-fit C-Statistic (for the source
and background models together)
85- 88 I4 --- DOF [1012/1016]? Degrees of Freedom (9)
90- 95 F6.2 10+30W Lum ? The 0.5-8 keV luminosity (10)
97-100 F4.2 10+30W e_Lum ? Lower limit uncertainty in Lum (6)
102-106 F5.2 10+30W E_Lum ? Upper limit uncertainty in Lum (6)
108-132 A25 --- Com Comments about source extraction (11)
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Note (5): Flag as follows:
a = Sherpa's JD pileup model (Davis 2001ApJ...562..575D 2001ApJ...562..575D) was used in
addition to the power-law fit.
b = See Swartz et al. (2003, Cat. J/ApJS/144/213) for model parameters.
Note (6): A value of "0.0" indicates a "NA" value. This occurs when: in the
case of source 62, the model is too complicated to be listed in the
table; Sherpa fails to find the confidence interval; the source has
zero flux so that Photon Index or kT is not defined. A "9.99"
indicates that the parameter was frozen during the spectral fitting.
Note (7): In units of photons/keV/cm2/s at 1keV for the power-law model and
L39/(D10)2, where L39 is the source luminosity in units of
1039erg/s and D10 is the distance to the source in units of
10 kpc for the blackbody model.
Note (8): The best-fit column density for the source which includes galactic
foreground and intrinsic source absorption. A value of "0.04"
indicates that the best-fit is on the galactic foreground minimum
column density (the lower bound will then be "0.0").
Note (9): For the source and background models together.
Note (10): The uncertainties are estimated by scaling the luminosity by the
uncertainty in the counts, which was calculated from the 90%
Bayesian confidence intervals, (Kraft et al. 1991ApJ...374..344K 1991ApJ...374..344K).
Note (11): "RS ObsID" indicates that the source was on the readout streak in
the specified ObsID. "POC ObsID" indicates that the source was
partially off of the chip in the specified ObsID. "S#" indicates
the Swartz source number that this source is matched to
(Cat. J/apJS/144/213, <[SGM2003] NNN> in Simbad. "VC #" indicates
that the source was very close to another source.
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Global notes:
Note (G1): A "B" before the number refers to a borderline source
not part of the master source list.
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 29-Nov-2012