J/A+A/690/A152 eROSITA study of the Canis Major overdensity (Saeedi+, 2024)
eROSITA (eRASS1) study of the Canis Major overdensity:
Developing a multi-wavelength algorithm for classifying faint X-ray sources.
Saeedi S., Sasaki M., Knies J., Robrade J., Heindl T., Zainab A.,
Hammerich S., Reh M., Wilms J.
<Astron. Astrophys. 690, A152 (2024)>
=2024A&A...690A.152S 2024A&A...690A.152S (SIMBAD/NED BibCode)
ADC_Keywords: X-ray sources ; Binaries, X-ray ; Binaries, cataclysmic ;
Photometry, infrared ; Optical
Keywords: Galaxy: X-rays: binaries - stars: binaries: symbiotics -
stars: binaries: cataclysmic variables
Abstract:
Using data from eROSITA(extended Roentgen Survey with an Imaging
Telescope Array) on board Spektrum-Roentgen-Gamma (Spektr-RG, SRG)
taken during the first eROSITA all-sky survey (eRASS1), we performed
the first X-ray classification and population study in the field of
the Canis Major overdensity (CMa OD), which is an elliptical-shaped
stellar overdensity located at l=-240°; b=-80°.
This study aims to identify the X-ray sources in CMa OD. We developed
a classification algorithm using multi-wavelength criteria as a
preliminary method for the classification of faint X-ray sources,
specifically in regions with a high source number density.
We used the brightness of the multi-wavelength counterparts (mainly
from infrared and optical catalogues), along with the X-ray flux and
X-ray hardness ratios (HRs) to classify the sources.
Out of a total number of 8311 X-ray sources, we classified 1029
sources as Galactic stars and binaries in the foreground, 946 sources
as active galactic nuclei (AGNs) and galaxies in the background, and
435 sources with stellar counterparts that may belong to either the MW
or CMa OD. Among the sources with a stellar counterpart, we identified
34 symbiotic star candidates, plus 335 sources, of which the infrared
(IR) counterparts have properties of M-giants in CMa OD. Moreover,
there is a known high-mass X-ray binary (HMXB, 4U 0728-25) in the
field of our study; according to the Gaia parallax of its companion,
it appears to be a member of CMa OD. There is also a recently detected
transient low-mass X-ray binary (LMXB, SRGt J071522.1-191609) is also
present; it may be a member of CMa OD based on its companion, which is
most likely highly absorbed and is thus located behind the Galactic
disk. In addition, we present the X-ray luminosity function (XLF) of
members and candidate members of CMa OD. It is dominated by sources
with luminosities of <2x1032-1033erg/s in the energy range of
0.2-2.3keV. These sources are expected to be either accreting white
dwarfs or quiescent LMXBs.
Description:
With the goal of classifying X-ray sources detected with
eROSITA, we performed a multi-wavelength analysis of the counterparts
of X-ray sources in the field of CMa OD.
From a total number of 8311 sources, 1901 have entries in SIMBAD with
classification (see Table A.1). 507 sources have been already
identified as background sources in other catalogues. In this study,
we have successfully identified 946 new background sources and 274
candidates. We classified 1029 sources as Galactic foreground objects,
20 sources as Galacticforeground candidates, sources as stellar
objects (which may either be Galactic sources or members of CMa OD),
and sources as stellar object candidates. Out of the stellar objects,
100 sources are considered to be members of CMa OD and to be candidate
members of CMa OD. They are expected to be mainly AWD systems
according to their X-ray luminosities. Finally, 2936 sources remained
unclassified.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablea1.dat 216 8311 X-ray sources in the FOV of CMa OD
tableb1.dat 137 8311 WISE and Gaia counterpart of X-ray sources in
the field of CMa OD
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See also:
J/A+A/682/A34 : SRG/eROSITA all-sky survey catalogs (eRASS1) (Merloni+, 2024)
Byte-by-byte Description of file:tablea1.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 I4 --- No Source-ID in this paper
6- 28 A23 --- Name eROSITA ID of the source,
1eRASS JHHMMSS.s-DDMMSS
30- 39 F10.6 deg RAdeg Right ascension (J2000)
41- 50 F10.6 deg DEdeg Declination (J2000)
52- 60 F9.6 arcsec e_Pos 1 sigma positional error of the source
62- 71 E10.5 10-17W/m2 Flux Flux of the sources in 0.2-5.0keV
(in 10-14erg/s/cm-2 unit)
73- 82 E10.5 10-17W/m2 e_Flux Flux error of the sources in 0.2-5.0keV
(in 10-14erg/s/cm-2 unit)
84- 94 F11.6 --- ML Detection maximum likelihood of source
in 0.2-5.0keV
96-104 F9.6 --- HR1 Hardness ratio 1 (1)
106-113 F8.6 --- e_HR1 Hardness ratio 1 error (1)
115-123 F9.6 --- HR2 Hardness ratio 2 (1)
125-132 F8.6 --- e_HR2 Hardness ratio 2 error (1)
134-142 F9.6 --- HR3 Hardness ratio 3 (1)
144-151 F8.6 --- e_HR3 Hardness ratio 3 error (1)
153-161 F9.6 --- HR4 Hardness ratio 4 (1)
163-170 F8.6 --- e_HR4 Hardness ratio 4 error (1)
172-186 A15 --- Class Class of a source (2)
188-216 A29 --- Comment SIMBAD ID of the sources as exist in SIMBAD
data base, plus the information is source
has the problem of optical loading
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Note (1): details of calculation in the paper.
Note (2): Classes as follows:
SYM = Symbiotic Star
FG = Foreground star/system
AGN = Active Galactic Nuclei
STRL = stellar object
Cma_OD = Member of CMa OD
CAN = Candidate
NONE = Unclassified
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Byte-by-byte Description of file: tableb1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 I4 --- No Source ID in this paper
6- 14 F9.6 mag W1mag ?=0 WISE W1 magnitude of the infrared
counterpart of the X-ray source (1)
16- 23 F8.6 mag e_W1mag ?=0 Error of W1 magnitude of the infrared
counterpart of the X-ray source (1)
25- 33 F9.6 mag W2mag ?=0 WISE W2 magnitude of the infrared
counterpart of the X-ray source (1)
35- 42 F8.6 mag e_W2mag ?=0 Error of W2 magnitude of the infrared
counterpart of the X-ray source (1)
44- 52 F9.6 mag W3mag ?=0 WISE W3 magnitude of the infrared
counterpart of the X-ray source (1)
54- 61 F8.6 mag e_W3mag ?=0 Error of W3 magnitude of the infrared
counterpart of the X-ray source (1)
63- 71 F9.6 mag W4mag ?=0 WISE W4 magnitude of the infrared
counterpart of the X-ray source (1)
73- 80 F8.6 mag e_W4mag ?=0 Error of W4 magnitude of the infrared
counterpart of the X-ray source (1)
82- 90 F9.6 mag Gmag Gaia G magnitude of Gaia counterpart
of the X-ray source (1)
92- 99 F8.6 mag e_Gmag Error of G magnitude of Gaia counterpart
of the X-ray source (1)
101-109 F9.6 mag Rpmag Gaia GRP magnitude of Gaia counterpart
of the X-ray source (1)
111-118 F8.6 mag e_Rpmag Error of GRP magnitude of Gaia counterpart
of the X-ray source (1)
120-128 F9.6 mag Bpmag Gaia GBP magnitude of Gaia counterpart
of the X-ray source (1)
130-137 F8.6 mag e_Bpmag Error of GBP magnitude of Gaia counterpart
of the X-ray source (1)
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Note (1): more details in Sect. 3 and 4 of the paper.
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Acknowledgements:
Sara Saeedi, sara.saeedi(at)fau.de
(End) Patricia Vannier [CDS] 25-Sep-2024