J/MNRAS/544/885 Galactic X-ray Transients in eROSITA (Maan+, 2025)
Galactic X-ray transients in the first eROSITA all sky survey.
Maan V., Katira A., Mooley K.
<Mon. Not. R. Astron. Soc. 544, 885-910 (2025)>
=2025MNRAS.544..885M 2025MNRAS.544..885M (SIMBAD/NED BibCode)
ADC_Keywords: Surveys ; X-ray sources
Keywords: (stars:) novae, cataclysmic variables - (stars:) supergiants -
X-rays: binaries
Abstract:
Although a multitude of studies have focused on targeted observations
of Galactic X-ray transients, blind surveys and population studies
have been limited. We have used the ROSAT, eROSITA and Gaia source
catalogs to find Galactic X-ray transients having timescales
<30 years. We report the properties of 738 transients found in our
search, majority of which are active stars or interacting binaries. We
have also found ∼40 compact object systems among which are at least
8 newly-identified white-dwarf systems, 3 known X-ray binaries, and
one known pulsar.
We use eROSITA (soft X-ray) spectra of the Galactic transients to show
that two distinct types of flaring systems are prevalent: one having
peak around 1keV, well fit by thermal models, and another having peak
below 0.2keV and requiring a power-law component. Our study also
reveals that single star or interacting binary systems (X-ray
transients) involving giant stars exhibit significantly higher X-ray
luminosities than systems involving only main-sequence stars or young
stellar objects. Finally, we discuss the properties of the transients
in the context of their putative emission mechanisms, the fraction of
transients with respect to the total population, and the rates of
Galactic transients expected in blind searches of the X-ray sky.
Description:
We present the catalog of the Galactic X-ray transients detected in
our transients search with eROSITA (eRASS1), ROSAT (2RXS), and Gaia
DR2 catalogues. We show that the most of the transients either show
peaked spectra or steep fall of counts in the spectra. In total, we
report the X-ray and optical properties of 738 transients classified
into the following categories:
(i) YSO: Young stellar object (105 Transients)
(ii) SS/IB : Either chromospherically active single star or interacting
binary (418 Transients)
(iii) IB: Known interacting binary not having any compact object in
the system (110 Transients)
(iv) IB/ACO: Interacting binary or accreting compact object (50 Transients)
(v) CV : Cataclysmic variable (38 Transients)
(vi) XRB : X-ray binary (3 Transients)
(vii) LPV : Long period variable (12 Transients)
(viii) PSR : Pulsar (1 Transient)
(ix) WR : Wolf Rayet (1 Transient)
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
ero-g-t.dat 336 738 Catalogue of eRASS1 Galactic transients
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See also:
J/A+A/588/A103 : Second ROSAT all-sky survey (2RXS) source catalog
(Boller+, 2016)
J/A+A/682/A34 : SRG/eROSITA all-sky survey catalogs (eRASS1) (Merloni+, 2024)
J/A+A/693/A62 : eRO-ExTra catalog (Grotova+, 2025)
Byte-by-byte Description of file: ero-g-t.dat
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Bytes Format Units Label Explanations
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1- 23 A23 --- IAUName String containing the official IAU name of
the source (1eRASS JHHMMSS.s+DDMMSS)
25- 39 F15.11 deg RAdeg Barycentric right ascension (ICRS)
at Ep=2015.5 (1)
41- 55 F15.11 deg DEdeg Barycentric declination (ICRS)
at Ep=2015.5 (1)
57- 62 F6.4 mas e_RAdeg Standard error of right ascension (1)
64- 69 F6.4 mas e_DEdeg Standard error of declination (1)
71- 82 E12.6 mW/m2 FeRASS1 eRASS1 flux in 0.2-2.3 keV band
84- 95 E12.6 mW/m2 e_FeRASS1 1-sigma combined error on eRASS1 flux
in 0.2-2.3keV band
97-108 E12.6 mW/m2 F2RXS ?=- 2RXS (ROSAT) flux in 0.1-2.4keV
band (2)
110-121 E12.6 mW/m2 e_F2RXS ?=- Error on 2RXS flux in 0.1-2.4keV
band (2)
123-130 F8.4 --- F2RXS/FeRASS1 X-ray flux ratio F2RXS/FeRASS1
132-143 F12.7 pc Dist Distance
145-156 F12.8 pc e_Dist Error in distance
158-169 E12.6 10-7W Lum Luminosity (erg/s)
171-182 E12.6 10-7W e_Lum Error in luminosity (erg/s
184-188 F5.2 mag BP-RP ?=- Gaia BP-RP colour
190-198 F9.6 mag Gmag G mag (G)
200-209 F10.6 mag GMAG Absolute G mag
211-220 F10.6 mag GMAGc ?=- Absolute_G corrected for extinction
222-230 F9.6 mag BP-RPc ?=- BP-RP corrected for reddening
232-242 A11 --- SimbadSpClass SIMBAD spectral class
244-257 F14.11 d Per ?=- Orbital or spin Period
259-288 A30 --- SimbadClass Simbad object type/classification
290-295 A6 --- SourceClass Source class from this work
297-303 F7.2 K T ?=- Effective temperature from Gaia DR2
305-310 F6.2 Rsun Rad ?=- Radius from Gaia DR2
312-316 A5 --- FinalSpClass Final adopted spectral class using
information from temperature and radius
318-326 F9.5 deg GLON [0/360] Galactic longitude
328-336 F9.5 deg GLAT Galactic latitude
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Note (1): RA and Dec are from Gaia DR2 because of Gaia's high precision and
milli arc second angular resolution.
Note (2): In order to find the flux of the sources in 2RXS, we calculated the
Energy conversion factor (ECF) of ROSAT, in a similiar way as done by eROSITA
team (Merloni et al., 2024, Cat. J/A+A/682/A34). The reported flux is
corrected for offset.
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Acknowledgements:
Vikash Maan, vikashm22(at)iitk.ac.in
(End) Patricia Vannier [CDS] 06-Oct-2025