J/A+A/661/A88 Gaia/Chandra X-ray sources in Galactic center (Schmitt+, 2022)
The nature of the X-ray sources constituting the 6.7 keV
Galactic ridge emission.
Schmitt J.H.M.M., Czesla S., Schneider P.C., Freund S., Robrade J.
<Astron. Astrophys., 661, A88 (2022)>
=2022A&A...661A..88S 2022A&A...661A..88S (SIMBAD/NED BibCode)
ADC_Keywords: X-ray sources ; Photometry ; Optical
Keywords: stars: activity - stars: coronae - X-rays: diffuse background
Abstract:
We reanalyze the deep Chandra X-ray observations near the Galactic
center and show that reliable identifications of X-ray sources can be
obtained with the Gaia EDR3 data to investigate which types of stellar
sources are responsible for the X-ray emission observed from the
Galactic ridge (GRXE). In the central 3 arcmin region 318 X-ray
sources are detected, about one-third of which can be identified with
objects listed in Gaia EDR3; however, only 22 objects have parallaxes
and colors and can be placed into a color-magnitude diagram and thus
be identified as coronal X-ray emitters. A rather large fraction of
the X-ray sources cannot be identified with Gaia EDR3 entries, and we
discuss the optical brightnesses of these sources. We analyze the
counting events obtained in the 6.7 keV iron line spectral region and
show that they are mainly caused by background events; however, 237
events can be associated with the detected X-ray sources, and we carry
out an intensity measurement of the whole iron line complex. Our
analysis shows that the mean energy of this iron line complex is
located at a wavelength of ~=1.87Å, where a variety of emission
lines of iron ions in ionization stages FeXXIII-FeXXV are located;
another line at 7.0 keV is only marginally detected, while the
fluorescent 6.4 keV neutral iron line is clearly not seen. We
demonstrate that only a few of the detected X-ray sources are
responsible for the bulk of the observed iron line emission. We
discuss to what extent coronal emission can be held responsible and
demonstrate that M dwarfs and active binary systems like RS CVn
systems do not significantly contribute to the observed emission;
instead, it appears that the Galactic ridge emission is produced by
optically fainter sources. Among the known population of cataclysmic
variables, polars and dwarf novae appear to be the most promising
candidates as main contributors to the GRXE.
Description:
For our study of the X-ray source population we use the 2.0 version of
the Chandra source catalog (CSC), which the Chandra project considers
to be the most complete catalog of X-ray sources detected by the
Chandra X-ray Observatory.
In Table A.1 we provide a list of all Chandra sources that can be
matched to Gaia with a geometric association probability of at least
10%; in Table A.1 we purposely include identifications with rather low
probability to demonstrate that the derived sample is quite
insensitive to the precise cutoff value chosen.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
tablea1.dat 78 103 List of Gaia matched X-ray sources in
Chandra core region
--------------------------------------------------------------------------------
See also:
I/355 : Gaia DR3 Part 1. Main source (Gaia Collaboration, 2022)
IX/57 : The Chandra Source Catalog (CSC), Release 2.0 (Evans+, 2019)
Byte-by-byte Description of file: tablea1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 16 A16 --- Chandra Chandra Name (JHHMMSS.s+DDMMSS)
18- 36 I19 --- GaiaDR3 Gaia DR3 name
38- 41 F4.2 --- Prob Geometric association probability
43- 49 F7.4 mag gmag ?=- g magnitude
51- 56 F6.4 mag BP-RP ?=- Gaia BP-RP colour index
58- 64 F7.4 mas Parallax ?=- Gaia parallax
66- 72 F7.4 --- RPlx ?=- Gaia parallax over error
74- 78 A5 --- Flag Flag (Star for coronal source)
--------------------------------------------------------------------------------
History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 15-Feb-2023