J/MNRAS/512/3858 Study of highly variable XMMSL2 sources (Li+, 2022)
Populations of highly variable X-ray sources in the XMM-Newton slew survey.
Li D., Starling R.L.C., Saxton R.D., Pan H.-W., Yuan W.
<Mon. Not. R. Astron. Soc. 512, 3858 (2022)>
=2022MNRAS.512.3858L 2022MNRAS.512.3858L (SIMBAD/NED BibCode)
ADC_Keywords: X-ray sources ; Positional data ; Cross identifications ;
Photometry ; Redshifts
Keywords: surveys - X-rays: general - galaxies: active - stars: flare -
X-rays: binaries
Abstract:
We present the identifications of a flux-limited sample of highly
variable X-ray sources on long time-scales from the second catalogue
of the XMM-Newton SLew survey (XMMSL2). The carefully constructed
sample, comprising 265 sources (2.5 per cent) selected from the XMMSL2
clean catalogue, displayed X-ray variability of a factor of more than
10 in 0.2-2 keV compared to the ROSAT All Sky Survey. Of the sample
sources, 94.3 per cent are identified. The identification procedure
follows a series of cross-matches with astronomical data bases and
multiwavelength catalogues to refine the source position and identify
counterparts to the X-ray sources. Assignment of source type utilizes
a combination of indicators including counterparts offset, parallax
measurement, spectral colours, X-ray luminosity, and light-curve
behaviour. We identified 40 per cent of the variables with stars, 10
per cent with accreting binaries, and at least 30.4 per cent with
active galactic nuclei. The rest of the variables are identified as
galaxies. It is found that the mean effective temperatures of the
highly variable stars are lower than those of less variable stars. Our
sample of highly variable AGN tend to have lower black hole masses,
redshifts, and marginally lower soft X-ray luminosities compared to
the less variable ones, while no difference was found in the Eddington
ratio distributions. Five flaring events are tidal disruption events
published previously. This study has significantly increased the
number of variable sources in XMMSL2 with identifications and provides
greater insight on the nature of many o f the sources, enabling
further studies of highly variable X-ray sources.
Description:
Variability is known to be one of the key characteristics of the X-ray
sky. Since the early days of X-ray astronomy, the study of the
temporal properties of X-ray radiation, alongside spectral and imaging
studies, has been a powerful tool with which to explore the radiation
processes and nature of X-ray sources, ranging from stellar coronal
activity, to accreting stellar compact objects, and to active galactic
nuclei (AGN). The XMM-Newton SLew survey (XMMSL), with its large and
nearly homogeneous sky coverage and comparable soft X-ray sensitivity
to that of the RASS, is well suited for the study of long-term
variability of relatively faint X-ray sources, and for the discovery
of X-ray flaring and transient events. It contains data taken with the
EPIC-pn camera during slew observations.
In this paper, we first search for long-term variable soft X-ray
sources from the XMMSL2 clean catalogue by comparing the source fluxes
with those measured in the earlier RASS, and then perform
multiwavelength identification for those highly variable sources using
various archival data bases as SIMBAD and NED.
As detailed in the section 2 sample selection as been made from the
XMMSL2 clean catalogue in the 0.2-2 keV band folowing criteria on
DetML, Ext and FX parameters. To select long-term variable sources, we
compared the XMMSL2 soft band fluxes of the initial sample with those
measured in RASS2RXS. The HILIGT tool allows to convert count to
erg/s/cm2 for fluxes. We calculated ratios between the XMMSL2 and
RASS fluxes (or upper limits) and selected sources with a flux ratio
greater than 10 for the 265 sources. Next, we proceed to cross-math
with SIMBAD and NED in order to retreive object names counterpart from
other catalogues as Gaia, ALL/NEOWise, Swift-XRT and 3XMM/4XMM-DR9. As
results, we present in table.dat the photometric properties and
classification of 265 highly variable sources.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table.dat 220 265 Photometric properties of out XMMSL2 variable
sources sample
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See also:
J/MNRAS/473/4937 : AllWISE ctp to ROSAT/2RXS & XMMSLEW2 catalogs
(Salvato+, 2018)
J/A+A/588/A103 : Second ROSAT all-sky survey (2RXS) source catalog
(Boller+, 2016)
J/A+A/403/247 : Variability in the ROSAT All-Sky Survey (Fuhrmeister+, 2003)
J/A+A/480/611 : XMM-Newton Slew Survey catalogue, XMMSL1 (Saxton+, 2008)
J/ApJ/792/30 : NEOWISE magnitudes for near-Earth objects (Mainzer+, 2014)
IX/10A : ROSAT All-Sky Bright Source Catalogue (1RXS) (Voges+ 1999)
V/147 : The SDSS Photometric Catalogue, Release 12 (Alam+, 2015)
IX/66 : 4XMM-DR11s serendipitous source catalogue from stacks
(Traulsen+, 2022)
IX/53 : XMM-Newton slew survey Source Catalogue, version 2.0
(XMM-SSC, 2017)
II/328 : AllWISE Data Release (Cutri+ 2013)
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
IX/58 : 2SXPS Swift X-ray telescope point source catalogue
(Evans+, 2020)
IX/55 : XMM-Newton Serendipitous Source Catalogue 3XMM-DR8
(XMM-SSC, 2018)
IX/59 : XMM-Newton Serendipitous Source Catalogue 4XMM-DR9
(Webb+, 2020)
Byte-by-byte Description of file: table.dat
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Bytes Format Units Label Explanations
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1- 23 A23 --- XMMSL2 Official name for sources detected in the
XMM-Newton slew survey (XMMSL2uniquename)
25- 37 F13.9 deg RAdeg Right ascension (J2000) (XMMSL2_RA)
39- 51 F13.9 deg DEdeg Declination (J2000) (XMMSL2_DEC)
53- 60 E8.3 mW/m2 FXMM The 0.2-2 keV source soft band flux in
the XMMSL2 (FLUX_XMMSL2) (1)
62- 69 E8.3 mW/m2 e_FXMM The error on the XMMSL2 soft band flux FX
(FLUXXMMSL2ERR)
71- 78 F8.6 pix Ext The spatial extension of the source in the
XMMSL2 soft band (EXT_XMMSL2)
80- 89 F10.5 --- DetML The detection likelihoods in the XMMSL2
soft band (DETMLXMMSL2)
91- 98 E8.3 mW/m2 FXRASS The 0.2-2 keV source soft band flux in
the RASS at the XMMSL2 source position
(FLUX_RASS)
100- 107 E8.3 mW/m2 e_FXRASS The error on the RASS soft flux FXRASS, 0
means that FXRASS is an upper limit
(FLUXRASSERR)
109- 120 F12.8 --- FXMM/FXRASS The flux ratio between FXMM and FXRASS
(FLUX_RATIO)
122- 149 A28 --- CrossID The catalogue name of the best cross-match
(IDENTIFIER)
151- 163 F13.9 deg RACdeg ? Right ascension of the identifier (J2000)
(IDENTIFIER_RA)
165- 177 F13.9 deg DECdeg ? Declination (J2000) (IDENTIFIER_DEC)
179- 185 A7 --- Type Type of the identifier (ID_TYPE)
187- 188 A2 --- f_Type Flag for the type for each source (ID_FLAG)
(2)
190- 195 F6.4 --- z ? Redshift of the galaxies and AGN when
available in SIMBAD/NED (z)
197- 201 F5.2 yr t ? Time range when the fluxes of flaring
galaxies declined by a factor of 10
203- 220 A18 --- r_CrossID The astronomical data base or catalogue
from which the best match has been
selected (ID_RESOURCE) (3)
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Note (1): Flux derived from an absorbed power-law spectrum of slope 1.7 and
NH = 3 * 1020 cm-2. We keep the highest flux for sources with
more than one XMMSL2 detection.
Note (2): The type for each source as follows:
1 = Star, 94 sources in our sample
2 = AGN, 76 sources in our sample
3 = Non-interacting binary, 6 sources in our sample
4 = Accreting binary, 27 sources in our sample
5 = Galaxy, 47 sources in our sample
6 = Unclear, 11 sources in our sample
no = No counterparts, 4 sources in our sample
Note (3): The data base or catalogue are SIMBAD, NED, and WISEx_Gaiax. The x in
WISEx_Gaiax refers to the number of AllWISE and Gaia-DR2 associations
For example, WISE1_Gaia2 means that the XMMSL2 X-ray source had one
AllWISE and two Gaia-DR2 associations in the cross-matching. The mul
after SIMBAD or NED means that there is more than one counterpart,
and lc appended to the resource means that the identification of the
source has been updated after checking the X-ray light curves as
described in section 4.1 Galaxies.
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History:
From electronic version of the journal
(End) Luc Trabelsi [CDS] 14-Mar-2025