J/ApJ/836/50 Chandra observations of IC 10 (Laycock+, 2017)
The X-ray binary population of the nearby dwarf starburst galaxy IC 10:
variable and transient X-ray sources.
Laycock S., Cappallo R., Williams B.F., Prestwich A., Binder B.,
Christodoulou D.M.
<Astrophys. J., 836, 50-50 (2017)>
=2017ApJ...836...50L 2017ApJ...836...50L (SIMBAD/NED BibCode)
ADC_Keywords: X-ray sources ; Binaries, X-ray ; Galaxies, nearby
Keywords: galaxies: starburst; X-rays: binaries
Abstract:
We have monitored the Cassiopeia dwarf galaxy (IC 10) in a series of
10 Chandra ACIS-S observations to capture its variable and transient
X-ray source population, which is expected to be dominated by High
Mass X-ray Binaries (HMXBs). We present a sample of 21 X-ray sources
that are variable between observations at the 3σ level, from a
catalog of 110 unique point sources. We find four transients (flux
variability ratio greater than 10) and a further eight objects with
ratios >5. The observations span the years 2003-2010 and reach a
limiting luminosity of >1035erg/s, providing sensitivity to X-ray
binaries in IC 10 as well as flare stars in the foreground Milky Way.
The nature of the variable sources is investigated from light curves,
X-ray spectra, energy quantiles, and optical counterparts. The purpose
of this study is to discover the composition of the X-ray binary
population in a young starburst environment. IC 10 provides a sharp
contrast in stellar population age (<10My) when compared to the
Magellanic Clouds (40-200My) where most of the known HMXBs reside. We
find 10 strong HMXB candidates, 2 probable background Active Galactic
Nuclei, 4 foreground flare-stars or active binaries, and 5 not yet
classifiable sources. Complete classification of the sample requires
optical spectroscopy for radial velocity analysis and deeper X-ray
observations to obtain higher S/N spectra and search for pulsations. A
catalog and supporting data set are provided.
Description:
A monitoring series of 7x15ks Chandra/ACIS observations, spaced at
roughly six-week intervals was obtained during 2009-2010.
A pair of very deep ACIS-S3 observations (2x45ks) made in 2006
November provide a reference data set for improved source positions
and spectral information.
The original Wang+ (2005, J/MNRAS/362/1065) Chandra (ACIS-S3)
observation of 30ks made in 2003 was included in our analysis.
The complete listing of 10 observation identifiers (ObsIDs) comprising
the data set is summarized in Table 1.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 63 11 Chandra observations of IC 10
table2.dat 296 111 Chandra ACIS-S source catalog of IC 10
fig3.dat 55 52 Light-curves of strongly variable X-ray sources
with Ratio>10 and σVar>3, 2003-2010
fig4.dat 55 120 Light-curves of moderately variable X-ray sources
selected according to 5<Ratio<10 and
σVar>3
fig5.dat 55 176 Light-curves of variable X-ray sources selected
according to Ratio<5 and σVar>3
--------------------------------------------------------------------------------
See also:
B/chandra : The Chandra Archive Log (CXC, 1999-2014)
J/A+A/424/125 : Carbon stars in IC10 (Demers+, 2004)
J/ApJS/150/19 : ChaMP. I. First X-ray source catalog (Kim+, 2004)
J/MNRAS/362/1065 : XMM/Chandra study of IC 10 (Wang+, 2005)
J/AJ/133/2393 : UBVRI phot. in 7 Local Group dwarfs galaxies (Massey+, 2007)
J/MNRAS/388/1198 : Be/X-ray binaries in Small Magellanic Cloud (McBride+, 2008)
J/PAZh/35/829 : Star clusters in IC 10 (Tikhonov+, 2009)
J/ApJ/721/1368 : X-ray emission from the Sombrero galaxy (Li+, 2010)
J/ApJS/192/10 : Chandra ACIS survey in 383 nearby galaxies. I. (Liu, 2011)
J/ApJS/193/31 : M33 Chandra ACIS survey: final catalog (Tullmann+, 2011)
J/AJ/150/94 : Chandra Local Volume Survey. I. (Binder+, 2015)
J/ApJS/216/10 : DUSTiNGS. I. The Good Source Catalog (Boyer+, 2015)
J/ApJS/218/9 : Deep XMM-Newton survey of M33 (Williams+, 2015)
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 7 F7.1 d MJD ? Modified Julian Date of the observation
9- 19 A11 "Y/M/D" Date UT date of observation
20- 21 A2 --- Day2 Other days of observation
23- 27 I5 --- ObsID Chandra ObsID
29 A1 --- f_ObsID Flag on ObsID (1)
31- 34 F4.1 ks Exp [8/81] Exposure time
36- 37 I2 h RAh ? Hour of right ascension (J2000)
39- 40 I2 min RAm ? Minute of right ascension (J2000)
42- 43 I2 s RAs ? Second of right ascension (J2000)
45 A1 --- DE- Sign of declination (J2000)
46- 47 I2 deg DEd ? Degree of declination (J2000)
49- 50 I2 arcmin DEm ? Arcminute of declination (J2000)
52- 53 I2 arcsec DEs ? Arcsecond of declination (J2000)
55- 60 F6.2 deg Roll [10/340]? Roll angle
62- 63 I2 --- Nsrc [19/63] Number of unique point sources detected (2)
--------------------------------------------------------------------------------
Note (1): Flag as follows:
a = Obsid 03953 used about half of the CCD area in subarray mode.
b = Merged 2006 data set referred to as obsid 57082 consists of the nearly
contiguous ObsIDs 07082 and 08458, which had identical pointings.
Note (2): The number of unique point sources detected in each observation after
combining wavdetect lists from the S (0.3-1.5keV), B (0.3-8keV), and
H (2.5-8keV) energy bands.
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 I3 --- Seq [1/111] Running sequence number
5- 8 A4 --- --- [CXOU]
9- 24 A16 --- CXOU Chandra coordinate-based identifier
(JHHMMSS.S+DDMMSS)
26- 32 A7 --- W05 Cross reference (1)
34- 46 A13 --- SrcID Soure identifier within the observation (2)
48- 59 F12.10 deg RAdeg Right Ascension in decimal degrees (J2000) (3)
61- 73 F13.10 deg DEdeg Declination in decimal degrees (J2000) (3)
75- 78 F4.2 deg Err95 [0.2/6] Positional uncertainty radius
at 95% confidence (4)
80- 81 I2 --- NP [2/10] Number of observations source was in FoV
of ACIS S-3 detector
83- 84 I2 --- NB [0/10] Number of observations source was
detected in 0.3-8keV band
86- 94 F9.7 ct/s <CRate> [0.0002/0.2]?=0 Average 0.3-8keV band
count rate (4)
97-105 E9.3 ct/s RMS [/0.06]?=0 Root-mean-squared 0.3-8keV band
count rate (4)
107-115 E9.3 ct/s Min [/0.03]?=0 Minimum observed 0.3-8keV band
count rate
117-125 E9.3 ct/s e_Min [/0.002]?=0 Error in Min
127-135 E9.3 ct/s Max [/0.2]?=0 Maximum observed 0.3-8keV band
count rate
137-145 E9.3 ct/s e_Max [/0.003]?=0 Error in Max
147-155 E9.3 ct/s Range [/0.2]?=0 Range of observed fluxes; Max-Min
157-165 F9.5 --- Ratio [0/118] Ratio of Max/Min count rates
167-171 F5.2 --- Var [0.06/56]?=0 Variability index σvar (5)
173-180 F8.2 ct NCts [1/22632]?=0 Net counts across all observations
182-186 I5 --- Events [0/28667] Total number of events (6)
188-193 F6.1 eV EMed [732/7951]?=0 Median energy of events (6)
195-201 F7.2 eV e_EMed [47/3069]?=0 Standard deviation in EMed
203-205 I3 --- EvBack [0/236] Number of events in background
annulus region (7)
207-212 F6.1 eV EMedB [74/7952]?=0 Median energy of events in
background annulus region (7)
214-220 F7.2 eV e_EMedB [26/3367]?=0 Standard deviation in EMedB
222-231 F10.7 --- QDx [-1.3/2.2]?=0 Spectral Slope Quantile QDx (8)
233-245 F13.7 --- e_QDx [-1000/-0.02]?=0 Lower 1σ bound on QDx
247-256 F10.7 --- E_QDx [-0.6/1.6]?=0 Upper 1σ bound on QDx
258-267 F10.7 --- QDy [0.007/3]?=0 Spectral Slope Quantile QDy (8)
269-278 F10.7 --- e_QDy [-3/-0.007]?=0 Lower 1σ bound on QDy
280-289 F10.7 --- E_QDy [0.01/2.5]?=0 Upper 1σ bound on QDy
291-296 A6 --- VarCl Variable X-ray source code(s) (9)
--------------------------------------------------------------------------------
Note (1): Cross reference to Wang+ (2005, J/MNRAS/362/1065) source
sequential number. Letter code:
X = XMM (J/MNRAS/362/1065/table1; <[WWW2005] XP NN> for Simbad;
C = Chandra (J/MNRAS/362/1065/table2; <[WWW2005] XA NN> for Simbad).
Note (2): That provided the best detection.
Note (3): After astrometric correction described in paper.
Note (4): Derived from Hong (2005ApJ...635..907H 2005ApJ...635..907H) formula.
Note (5): Equal to (Max-Min)/(eMin2+eMax2)0.5
Note (6): In source extraction region, accumulated over all observations
with positive detection.
Note (7): Accumulated over all observations with positive detection.
Note (8): For accumulated event file by Hong+ (2004ApJ...614..508H 2004ApJ...614..508H) algorithm.
Note (9): Variable X-ray source code as follows:
T = Transient (Ratio > 10);
TC = Transient Candidate;
V = Variable;
X = X-ray binary;
S = Stellar Corona;
A = AGN;
U = unclassified.
--------------------------------------------------------------------------------
Byte-by-byte Description of file: fig[345].dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 2 I2 --- Seq [1/90] Source identifier (1)
4- 18 F15.9 d MJD Modified Julian Date of observation
20- 35 F16.14 ct/s NCR [/0.2] Net count rate
37- 52 F16.14 ct/s e_NCR [/0.004]? Uncertainty in NCR
54- 55 A2 --- Band Band/Limit code (2)
--------------------------------------------------------------------------------
Note (1): Note that Src 46 is IC 10 X-2 and Src 20 is IC 10 X-1.
Note (2): Code as follows:
H = 2.5-8 keV;
B = 0.3-8 keV;
S = 0.3-1.5 keV;
UL = Upper limit.
--------------------------------------------------------------------------------
History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 08-Sep-2017