J/A+A/693/A62 eRO-ExTra catalog (Grotova+, 2025)
eRO-ExTra: eROSITA extragalactic non-AGN X-ray transients and variables in
eRASS1 and eRASS2.
Grotova I., Rau A., Salvato M., Buchner J., Goodwin A.J., Liu Z.,
Malyali A., Merloni A., Tubin-Arenas D., Homan D., Krumpe M., Nandra K.,
Shirley R., Anderson G.E., Arcodia R., Bahic S., Baldini P., Buckley D.A.H.,
Ciroi S., Kawka A., Masterson M., Miller-Jones J.C.A., Di Mille F.
<Astron. Astrophys. 693, A62 (2025)>
=2025A&A...693A..62G 2025A&A...693A..62G (SIMBAD/NED BibCode)
ADC_Keywords: Surveys ; X-ray sources
Keywords: catalogs - galaxies: nuclei - X-rays: galaxies
Abstract:
The eROSITA telescope aboard the Spectrum Roentgen Gamma (SRG)
satellite provides an unprecedented opportunity to explore the
transient and variable extragalactic X-ray sky due to the sensitivity,
sky coverage, and cadence of the all-sky survey. While previous
studies showed the dominance of regular active galactic nuclei (AGN)
variability, a small fraction of sources expected in such a survey
arise from more exotic phenomena such as tidal disruption events
(TDEs), quasi-periodic eruptions, or other short-lived events
associated with supermassive black hole accretion. This paper
describes the systematic selection of X-ray extragalactic transients
found in the first two eROSITA all-sky surveys (eRASS) that are not
associated with known AGN prior to eROSITA observations.
We generate a variability sample using the data from the first and
second eRASS, which includes sources with variability significance and
fractional amplitude larger than four in the 0.2-2.3keV energy
band, discovered between December 2019 and December 2020, and located
in the Legacy Survey DR10 (LS10) footprint. When possible, transients
are associated with optical LS10 counterparts. The properties of these
counterparts are used to exclude stars and known active galaxies. The
sample is additionally cleaned from known AGN using pre-eROSITA SIMBAD
and the Million Quasars Catalog (Milliquas) classifications, archival
optical spectra, and archival X-ray data. We explore archival X-ray
variability, long-term (2-2.5 years) eROSITA light curves, and peak
X-ray spectra to characterize the X-ray properties of the sample.
Sources with radio counterparts are identified using the Rapid ASKAP
Continuum Survey (RACS) and Karl G. Jansky Very Large Array Sky Survey
(VLASS).
We present a catalog of 304 extragalactic eROSITA transients
and variables not associated with known AGN, called eRO-ExTra. More
than 90% of sources are associated with reliable LS10 optical
counterparts. For each source, we provide archival X-ray data from
Swift, ROSAT, and XMM-Newton, the eROSITA long-term light curve with
light curve classification, as well as the best power law fit spectral
results at the peak eROSITA epoch. Reliable spectroscopic and
photometric redshifts, both archival and from follow-up data, are
provided for more than 80% of the sample. Several sources in the
catalog are eROSITA discovered known TDE candidates. In addition, 31
sources are radio detected. The origin of radio emission needs to be
further identified.
The eRO-ExTra transients constitute a relatively clean parent sample
of non-AGN variability phenomena associated with massive black holes.
The eRO-ExTra catalog includes more than 95% of sources discovered in
X-rays with eROSITA for the first time, making it a valuable resource
for studying unique nuclear transients.
Description:
This is the catalog of extragalactic non-AGN X-ray transients and
variables found in the first two eROSITA all-sky surveys (eRASS). The
catalog contains 304 unique sources with variability significance and
fractional amplitude larger than 4 between eRASS1 and eRASS2 in the
0.2-2.3keV energy band. More than 90% of sources are associated
with reliable LS10 optical counterparts, properties of which were used
to exclude stars and regular or known AGN. For each source, we provide
archival X-ray data from Swift, ROSAT and XMM-Newton, the eROSITA
long-term lightcurve, which includes eRASS1-4 (5 if available), with
lightcurve classification as well as the best power-law fit spectral
results at the peak eROSITA epoch. Spectroscopic and photometric
redshifts, both archival and from follow-up data, are provided for
more than 90% of the sample. The eRO-ExTra catalog is the largest of
its kind to date with more than 95% of sources discovered in X-rays
with eROSITA for the first time.
We omitted eRASS3-4(5) fluxes for 1eRASS J113028.2-080612, 1eRASS
J053016.3-412535 and 1eRASS J060056.2-293922, since their detailed
follow-up and analysis will be presented in Tubin-Arenas et al., in
prep.
We omitted information about archival X-ray observations for eRASSU
J074426.3+291606, since the extracted data describes a galaxy nearby,
and the correct counterpart is a smaller nearby galaxy
(arXiv:2301.05484).
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
catalog.dat 2121 304 eRO-ExTra catalog
--------------------------------------------------------------------------------
See also:
J/A+A/682/A34 : SRG/eROSITA all-sky survey catalogs (eRASS1) (Merloni+, 2024)
Byte-by-byte Description of file: catalog.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 23 A23 --- ERO Official IAU name of the source from
Merloni et al. (2024A&A...682A..34M 2024A&A...682A..34M) or
source name in the format eRASSU
Jhhmmss.s-ddmmss (ERO_NAME)
25- 44 F20.16 deg RAdeg eROSITA Right Ascension (ICRS) from
eRASS:5 (cumulative catalogue of 4(5)
eRASS) (ERO_RA)
46- 66 F21.17 deg DEdeg eROSITA Declination (ICRS) from eRASS:5
(ERO_DEC)
68- 85 F18.16 arcsec ePos 1-sigma position uncertainty from eRASS:5
(ERO_POSERR)
87- 98 E12.6 mW/m2 FeRASS1 Source flux in energy band 0.2-2.3keV in
eRASS1 (EROFLUXeRASS1)
100- 111 E12.6 mW/m2 FeRASS2 Source flux in the energy band 0.2-2.3keV
in eRASS2 (EROFLUXeRASS2)
113- 124 E12.6 mW/m2 FeRASS3 ? Source flux in the energy band
0.2-2.3keV in eRASS3 (EROFLUXeRASS3)
126- 137 E12.6 mW/m2 FeRASS4 ? Source flux in the energy band
0.2-2.3keV in eRASS4 (EROFLUXeRASS4)
139- 150 E12.6 mW/m2 FeRASS5 ? Source flux in the energy band
0.2-2.3keV in eRASS5 (EROFLUXeRASS5)
151 A1 --- l_FeRASS1 [u] u for upper limit flux (99.7%) in
FeRASS1
152- 163 E12.6 mW/m2 e_FeRASS1 ? Error flux (68%) in energy band
0.2-2.3keV in eRASS1
(EROFLUXERR_eRASS1)
164 A1 --- l_FeRASS2 [u] u for upper limit flux (99.7%)
in FeRASS2
165- 176 E12.6 mW/m2 e_FeRASS2 ? Error flux (68%) in energy band
0.2-2.3keV in eRASS2
(EROFLUXERR_eRASS2)
177 A1 --- l_FeRASS3 [u] u for upper limit flux (99.7%)
in FeRASS3
178- 189 E12.6 mW/m2 e_FeRASS3 ? Error flux (68%) in energy band
0.2-2.3keV in eRASS3
(EROFLUXERR_eRASS3)
190 A1 --- l_FeRASS4 [u] u for upper limit flux (99.7%)
in FeRASS4
191- 202 E12.6 mW/m2 e_FeRASS4 ? Error flux (68%) in energy band
0.2-2.3keV in eRASS4
(EROFLUXERR_eRASS4)
203 A1 --- l_FeRASS5 [u] u for upper limit flux (99.7%)
in FeRASS5
204- 215 E12.6 mW/m2 e_FeRASS5 ? Error flux (68%) in energy band
0.2-2.3keV in eRASS5
(EROFLUXERR_eRASS5)
217- 236 F20.16 --- Amp Amplitude of variability between eRASS1
and eRASS2 (Amplitude)
238- 256 F19.16 --- Signi Significance of variability between
eRASS1 and eRASS2 (Significance)
258 I1 --- LCClass [1/4] eROSITA lightcurve class
(ERO_LCCLASS) (1)
260- 300 A41 d ERODate MJD dates of eROSITA observations:
(MJD1,..,MJD), N =1,2,3,4,
(5, if available) (ERO_DATE)
302- 313 E12.6 cm-2 NH Galactic equivalent neutral hydrogen
column density in the line of sight (NH)
315- 332 F18.16 --- Gamma Photon index for the peak eRASS
(ERO_GAMMA)
334- 353 F20.18 --- e_Gamma Error photon index (68%) for the peak
eRASS (EROGAMMAERR)
355- 366 A12 --- CstatDOF C-statistic per degree of freedom, used
to assess the goodness of fit
(EROCSTATDOF)
368- 379 E12.6 mW/m2 FMod Source flux in energy band 0.2-2.3keV for
the peak eRASS (EROFLUXMOD)
381- 392 E12.6 mW/m2 e_FMod Error flux (68%) in energy band
0.2-2.3keV for the peak eRASS
(EROFLUXMOD_ERR)
394- 397 F4.1 --- ARCHFlag [0/2] Archival X-ray constraints
(ARCH_FLAG) (2)
399- 641 A243 d ARCHDate MJD dates of N archival observations:
(X1,..,X) (ARCH_DATE)
643- 934 A292 mW/m2 ARCHFlux Source flux of N archival observations:
(F1,..,F) in energy band 0.2-2.0keV
(ARCH_FLUX)
936-1043 A108 mW/m2 e_ARCHFlux Error flux (68%) of N archival
observations: (Ferr1,..,Ferr) in
energy band 0.2-2.0keV;
-1=flux upper limit (99.7%)
(ARCHFLUXERR)
1045-1426 A382 --- ARCHInst Instruments of N archival observations
(Instrument_1,.., Instrument_)
(ARCH_INSTRUMENT)
1428-1439 E12.6 --- bias Probability weighting introduced by
Xray_proba prior
(NWAYbiasLS10Xrayproba) (3)
1441-1448 F8.5 --- DistFac logarithm of the ratio of the prior and
posterior from separation, positional
error, and number density
(NWAYdistbayesfactor) (3)
1450-1457 F8.6 --- DistPost Distance posterior probability comparing
this association vs. no association
(NWAYdistpost) (3)
1459-1466 F8.6 --- psingle Distance posterior probability comparing
this association vs. no association
weighted by the prior
(NWAYpsingle) (3)
1468-1475 F8.6 --- pany For each entry in the X-ray catalogue,
the probability that there is a
counterpart (NWAYpany) (3)
1477-1484 F8.6 --- pi Relative probability of the eROSITA/LS10
match (NWAYpi) (3)
1486-1490 I5 --- LRel Integer denoting the camera and filter
set used in Legacy survey DR10 (LS10),
which will be unique for a given
processing run of data (LS10_RELEASE)
1492-1497 I6 --- LBrickID LS10 Brick ID (LS10_BRICKID)
1499-1503 I5 --- LObjID Catalog object number within this
LS10 brick (LS10_OBJID)
1505-1524 F20.16 deg RALdeg Right Ascension (J2000) of the
LS10 counterpart (LS10_RA)
1526-1545 F20.16 deg DELdeg Declination (J2000) of the
LS10 counterpart (LS10_DEC)
1547-1558 E12.6 deg-2 LRAIvar Inverse variance of RA, excluding
astrometric calibration errors
(LS10RAIVAR)
1560-1571 E12.6 deg-2 LDEIvar Inverse variance of DEC, excluding
astrometric calibration errors
(LS10DECIVAR)
1573-1584 E12.6 3.63uJy Fg LS10 model flux g (LS10FLUXG)
1586-1597 E12.6 3.63uJy Fr LS10 model flux r (LS10FLUXR)
1599-1610 E12.6 3.63uJy Fi LS10 model flux i (LS10FLUXI)
1612-1623 E12.6 3.63uJy Fz LS10 model flux z (LS10FLUXZ)
1625-1636 E12.6 3.63uJy FW1 LS10 model flux W1 (LS10FLUXW1)
1638-1649 E12.6 3.63uJy FW2 LS10 model flux W2 (LS10FLUXW2)
1651-1662 E12.6 3.63uJy-2 FIvarg Inverse variance of flux g
(LS10FLUXIVAR_G)
1664-1675 E12.6 3.63uJy-2 FIvarr Inverse variance of flux r
(LS10FLUXIVAR_R)
1677-1688 E12.6 3.63uJy-2 FIvari Inverse variance of flux r
(LS10FLUXIVAR_I)
1690-1699 F10.6 3.63uJy-2 FIvarz Inverse variance of flux z
(LS10FLUXIVAR_Z)
1701-1709 F9.6 3.63uJy-2 FIvarW1 Inverse variance of flux W1
(LS10FLUXIVAR_W1)
1711-1718 F8.6 3.63uJy-2 FIvarW2 Inverse variance of flux W2
(LS10FLUXIVAR_W2)
1720-1727 F8.6 --- MWtransg [0/1] Galactic transmission in g filter
in linear units (LS10MWTRANSMISSION_G)
1729-1736 F8.6 --- MWtransr [0/1] Galactic transmission in r filter
in linear units (LS10MWTRANSMISSION_R)
1738-1745 F8.6 --- MWtransi [0/1] Galactic transmission in i filter
in linear units (LS10MWTRANSMISSION_I)
1747-1754 F8.6 --- MWtransz [0/1] Galactic transmission in z filter
in linear units (LS10MWTRANSMISSION_Z)
1756-1763 F8.6 --- MWtransW1 [0/1] Galactic transmission in W1 filter
in linear units
(LS10MWTRANSMISSION_W1)
1765-1772 F8.6 --- MWtransW2 [0/1] Galactic transmission in W2 filter
in linear units
(LS10MWTRANSMISSION_W2)
1774-1776 A3 --- MType Morphological model from LS10 (LS10_TYPE)
1778-1795 F18.16 --- z ? Redshift (Z_REDSHIFT)
1797-1802 A6 --- zType Redshift type: photoz = photometric,
specz = spectroscopic (Z_TYPE)
1804-1824 A21 --- r_z Redshift origin (Z_REFERENCE)
1826-1861 A36 --- SName SIMBAD source ID (SIMBAD_NAME)
1863-1876 F14.10 deg RASdeg ? SIMBAD Right Ascension (J2000)
(SIMBAD_RA)
1878-1891 F14.10 deg DESdeg ? SIMBAD Declination (J2000) (SIMBAD_DEC)
1893-1909 A17 --- SType SIMBAD main type (SIMBAD_TYPE)
1911-1920 A10 --- TNS Transient Name Server (TNS) source name
(TNS_NAME)
1922-1937 F16.12 deg RATdeg ? TNS Right Ascension (TNS_RA)
1939-1956 F18.14 deg DETdeg ? TNS Declination (TNS_DEC)
1958-1975 F18.12 d TNSDate ? MJD TNS discovery date (TNS_DATE)
1977-2007 A31 --- VLASS The Very Large Array Sky Survey (VLASS)
(VLASS_NAME)
2009-2026 F18.14 deg RAVdeg ? VLASS Right Ascension (VLASS_RA)
2028-2046 F19.15 deg DEVdeg ? VLASS Declination (VLASS_DEC)
2048-2065 F18.16 mJy FVLASS ? VLASS total flux density at 3GHz
(VLASS_FLUX)
2067-2091 A25 --- RACS Rapid ASKAP Continuum Survey (RACS)
(RACS_NAME)
2093-2102 F10.6 deg RARdeg ? RACS Right Ascension (RACS_RA)
2104-2113 F10.6 deg DERdeg ? RACS Declination (RACS_DEC)
2115-2121 F7.3 mJy FRACS ? RACS total flux density at 0.88GHz
(RACS_FLUX)
--------------------------------------------------------------------------------
Note (1): eROSITA lightcurve class as follows:
1 = decline
2 = flare
3 = brightening
4 = other
Note (2): Archival X-ray constraints as follows:
0 = not constraining UL
1 = constraining UL
2 = previously detected
Note (3): see Salvato et al. (2018MNRAS.473.4937S 2018MNRAS.473.4937S) for clarification.
--------------------------------------------------------------------------------
Acknowledgements:
Iuliia Grotova, grotova(at)mpe.mpg.de
(End) Patricia Vannier [CDS] 04-Dec-2024