J/A+A/684/A208 Unassociated Fermi-LAT sources seen with eROSITA (Mayer+, 2024)
Searching for X-ray counterparts of unassociated Fermi-LAT sources and
rotation-powered pulsars with SRG/eROSITA.
Mayer M.G.F., Becker W.
<Astron. Astrophys. 684, A208 (2024)>
=2024A&A...684A.208M 2024A&A...684A.208M (SIMBAD/NED BibCode)
ADC_Keywords: X-ray sources ; Gamma rays ; Pulsars
Keywords: stars: neutron - pulsars: general - gamma rays: general -
X-rays: general
Abstract:
The latest source catalog of the Fermi-LAT telescope contains more
than 7000 gamma-ray sources at GeV energies, with the two dominant
source classes thought to be blazars and rotation-powered pulsars.
Despite continuous follow-up efforts, around 2600 sources have no
known multiwavelength association.
Our target is the identification of possible (young and recycled)
pulsar candidates in the sample of unassociated gamma-ray sources
via their characteristic X-ray and gamma-ray emission. To achieve
this, we cross-match the Fermi-LAT catalog with the catalog of X-ray
sources in the western Galactic hemisphere from the first four all-sky
surveys of eROSITA on the SRG (Spektrum-Roentgen-Gamma) mission. We
complement this by identifying X-ray counterparts of known pulsars
detected at gamma-ray and radio energies in the eROSITA data.
We use a Bayesian cross-matching scheme to construct a probabilistic
catalog of possible pulsar-type X-ray counterparts to Fermi-LAT
sources. Our method combines the overlap of X-ray and gamma-ray source
positions with a probabilistic classification (into pulsar and blazar
candidates) of each source based on its gamma-ray properties and a
prediction on the X-ray flux of pulsar- or blazar-type counterparts.
Finally, an optical and infrared counterpart search is performed to
exclude coronally emitting stars and active galactic nuclei from our
catalog. We provide a catalog of our prior gamma-ray-based
classifications of all 2600 unassociated sources in the Fermi-LAT
catalog, with around equal numbers of pulsar and blazar candidates.
Our final list of candidate X-ray counterparts to suspected new
high-energy pulsars, cleaned for spurious detections and sources with
obvious non-pulsar counterparts, contains around 900 X-ray sources,
the vast majority of which lies in the 95% gamma-ray error ellipse. We
predict between 30 and 40 new pulsars among our top 200 candidates,
with around equal numbers of young and recycled pulsars. This
candidate list may serve as input to future follow-up campaigns,
looking directly for pulsations or for the orbital modulation of
possible binary companions, where it may allow for a drastic reduction
in the number of candidate locations to search. We furthermore detect
the X-ray counterparts of 15 known rotation-powered pulsars, which
were not seen in X-rays before.
Description:
We have conducted a probabilistic cross-matching analysis between the
14-yr catalog of Fermi-LAT γ-ray sources (4FGL-DR4), and the
SRG/eROSITA X-ray catalog based on four all-sky surveys.
The file "catalog.dat" is the full version of Table 4 in our paper,
presenting the full list of candidates with a probability of being a
pulsar-type counterpart PiPSR>0.02. This list was cleaned from
spurious X-ray sources and sources with obvious non-pulsar
multiwavelength identifications.
The file "cand.dat" gives the corresponding list of sources which
failed visual inspection.
The file "prior.dat" provides the result of our machine-learning based
prior classification of gamma-ray sources into possible
young/millisecond pulsars and blazars, in addition to the
corresponding input parameters from the 4FGL-DR4 catalog.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
catalog.dat 716 909 Full list of candidates with a probability of
being a pulsar-type counterpart PiPSR>0.02
cand.dat 726 193 Corresponding list of sources which failed
visual inspection
prior.dat 356 2577 Result of our machine-learning based prior
classification of gamma-ray sources into
possible young/millisecond pulsars and blazars
visinspec/* . 594 Diagnostic plots showing the investigated
gamma-ray sources and their X-ray and
multiwavelength counterparts
--------------------------------------------------------------------------------
See also:
IX/67 : Incremental Fermi LAT 4th source cat. (4FGL-DR3)
(Fermi-LAT col., 2022)
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- 3 I3 --- Seq Rank of X-ray source by match probability
5- 27 A23 --- 4eRASS eROSITA source ID following IAU naming
conventions (4eRASS JHHMMSS.s+DDMMSS)
29- 46 F18.14 deg RAdeg Right ascension (ICRS) of X-ray source
48- 68 F21.17 deg DEdeg Declination (ICRS) of X-ray source
70- 87 F18.15 arcsec epos One-sigma positional error of X-ray source
89-108 F20.15 --- DetLike X-ray detection likelihood
110-127 F18.15 --- ExtLike X-ray extent likelihood
129-149 F21.19 ct/s CR X-ray count rate in 0.2-2.3keV
151-171 E21.15 mW/m2 FeRASS X-ray source flux in 0.2-2.3keV,
determined via an energy conversion
factor from the count rate
173-190 A18 --- Name4FGL Name of gamma-ray source in 4FGL-DR4
catalog
192-194 A3 --- Class2-4FGL Class of low-probability association of
gamma-ray source in 4FGL-DR4 catalog
196-220 A25 --- Assoc2-4FGL Low-probability association of gamma-ray
source in 4FGL-DR4 catalog
222-239 F18.14 deg RA4deg 4FGL right ascension (ICRS) of gamma-ray
source
241-261 F21.17 deg DE4deg 4FGL declination (ICRS) of gamma-ray
source
263-281 F19.16 arcmin amaj4FGL Semi-major axis of gamma-ray 95% error
ellipse
283-300 F18.16 arcmin bmin4FGL Semi-minor axis of gamma-ray 95% error
ellipse
302-322 F21.17 deg phi4FGL Position angle of gamma-ray error
ellipse on the sky
324-341 F18.14 deg-2 nu4FGL Density of eRASS:4 X-ray sources within a
2 deg radius around gamma-ray source
343-362 F20.17 --- ExpField Expectation value for the number of X-ray
chance alignments (denominator in Eq. 4)
364-384 E21.15 mW/m2 F4FGL gamma-ray source flux in the range
100 MeV - 100 GeV
386-404 F19.17 --- PriorPSR Prior probability for a source to be a
pulsar, rather than blazar, based on its
gamma-ray properties
406-428 E23.15 --- Prioryoungold Prior probability for a source to be a
young pulsar, rather than millisecond
pulsar, based on its gamma-ray properties
430-448 F19.17 --- dmahalanobis Mahalanobis distance, i.e. the distance
between X-ray and gamma-ray source
positions, normalized by the total
positional error in the given direction
450-468 F19.17 --- BFpos Purely positional Bayes factor of the
association, i.e. value of
Eq. 4 with c = 1.
470-487 F18.16 --- logFluxratio Logarithmic gamma-to-X-ray flux ratio
489-509 F21.18 --- PriorfrAGN Likelihood ratio, assuming AGN nature, of
having a match rather than a background
X-ray source based on only X-ray and
gamma-ray fluxes (Eqs. 6 and 7)
511-529 F19.17 --- PriorfrYNG Likelihood ratio, assuming young pulsar
nature, of having a match rather than a
background X-ray source based on only
X-ray and gamma-ray fluxes (Eqs. 6 and 7)
531-549 F19.17 --- PriorfrMSP Likelihood ratio, assuming millisecond
pulsar nature, of having a match rather
than a background X-ray source based on
only X-ray and gamma-ray fluxes
(Eqs. 6 and 7)
551-569 F19.17 --- PiPSR Combined posterior probability (Eq. 8)
for the given X-ray and gamma-ray source
to be matched, and to be of pulsar nature
571-593 E23.15 --- PiAGN Combined posterior probability (Eq. 8)
for the given X-ray and gamma-ray source
to be matched, and to be of AGN (blazar)
nature
595-617 E23.15 --- PiYNG Combined posterior probability (Eq. 8)
for the given X-ray and gamma-ray source
to be matched, and to be of young pulsar
nature
619-641 E23.15 --- PiMSP Combined posterior probability (Eq. 8)
for the given X-ray and gamma-ray
source to be matched, and to be of
millisecond pulsar nature
643-661 F19.17 --- Pi Combined posterior probability (Eq. 8)
for the given X-ray and gamma-ray source
to be matched
663-716 A54 --- Comment Comment on the match, for instance, on
possible alternative nature of the
X-ray source
--------------------------------------------------------------------------------
Byte-by-byte Description of file: cand.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 A4 --- Seq Rank of X-ray source by match probability
6- 28 A23 --- 4eRASS eROSITA source ID following IAU naming
conventions
30- 47 F18.14 deg RAdeg Right ascension (ICRS) of X-ray source
49- 68 F20.16 deg DEdeg Declination (ICRS) of X-ray source
70- 88 F19.16 arcsec epos One-sigma positional error of X-ray
source
90-111 F22.15 --- DetLike X-ray detection likelihood
113-131 F19.15 --- ExtLike X-ray extent likelihood
133-153 F21.18 ct/s CR X-ray count rate in 0.2-2.3keV
155-175 E21.15 mW/m2 FeRASS X-ray source flux in 0.2-2.3keV,
determined via an energy conversion
factor from the count rate
177-194 A18 --- Name4FGL Name of gamma-ray source in 4FGL-DR4
catalog
196-198 A3 --- Class2-4FGL Class of low-probability association of
gamma-ray source in 4FGL-DR4 catalog
200-224 A25 --- Assoc2-4FGL Low-probability association of gamma-ray
source in 4FGL-DR4 catalog
226-243 F18.14 deg RA4deg Right ascension (ICRS) of gamma-ray
source
245-264 F20.16 deg DE4deg Declination (ICRS) of gamma-ray source
266-285 F20.17 arcmin amaj4FGL Semi-major axis of gamma-ray 95% error
ellipse
287-306 F20.17 arcmin bmin4FGL Semi-minor axis of gamma-ray 95% error
ellipse
308-327 F20.16 deg phi4FGL Position angle of gamma-ray error
ellipse on the sky
329-346 F18.14 deg-2 nu4FGL Density of eRASS:4 X-ray sources within
a 2deg radius around gamma-ray source
348-367 F20.17 --- ExpField Expectation value for the number of X-ray
chance alignments (denominator in Eq. 4)
369-389 E21.15 mW/m2 F4FGL gamma-ray source flux in the range
100MeV-100GeV
391-408 F18.16 --- PriorPSR Prior probability for a source to be a
pulsar, rather than blazar, based on
its gamma-ray properties
410-432 E23.15 --- Prioryoungold Prior probability for a source to be a
young pulsar, rather than millisecond
pulsar, based on its gamma-ray
properties
434-451 F18.16 --- dmahalanobis Mahalanobis distance, i.e. the distance
between X-ray and gamma-ray source
positions, normalized by the total
positional error in the given direction
453-472 F20.18 --- BFpos Purely positional Bayes factor of the
association, i.e. value of
Eq. 4 with c=1
474-492 F19.17 --- logFluxratio Logarithmic gamma-to-X-ray flux ratio
494-514 F21.17 --- PriorfrAGN Likelihood ratio, assuming AGN nature,
of having a match rather than a
background X-ray source based on only
X-ray and gamma-ray fluxes
(Eqs. 6 and 7)
516-534 F19.17 --- PriorfrYNG Likelihood ratio, assuming young pulsar
nature, of having a match rather than a
background X-ray source based on only
X-ray and gamma-ray fluxes
(Eqs. 6 and 7)
536-554 F19.17 --- PriorfrMSP Likelihood ratio, assuming millisecond
pulsar nature, of having a match rather
than a background X-ray source based on
only X-ray and gamma-ray fluxes
(Eqs. 6 and 7)
556-574 F19.17 --- PiPSR Combined posterior probability (Eq. 8)
for the given X-ray and gamma-ray source
to be matched, and to be of pulsar
nature
576-598 E23.15 --- PiAGN Combined posterior probability (Eq. 8)
for the given X-ray and gamma-ray source
to be matched, and to be of AGN (blazar)
nature
600-622 E23.15 --- PiYNG Combined posterior probability (Eq. 8)
for the given X-ray and gamma-ray source
to be matched, and to be of young pulsar
nature
624-646 E23.15 --- PiMSP Combined posterior probability (Eq. 8)
for the given X-ray and gamma-ray source
to be matched, and to be of millisecond
pulsar nature
648-666 F19.17 --- Pi Combined posterior probability (Eq. 8)
for the given X-ray and gamma-ray source
to be matched
668-726 A59 --- Comment Comment on the match, for instance, on
possible alternative nature of the
X-ray source
--------------------------------------------------------------------------------
Byte-by-byte Description of file: prior.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 18 A18 --- Name4FGL Name of gamma-ray source in 4FGL-DR4
catalog (4FGL JHHMM.m+DDMM)
20- 43 E24.16 --- PriorPSR Prior probability for a source to be a
pulsar, rather than blazar, based on its
gamma-ray properties
45- 68 E24.16 --- Prioryoungold Prior probability for a source to be a
young pulsar, rather than millisecond
pulsar, based on its gamma-ray properties
70- 82 F13.9 --- SymLon Symmetric Galactic longitude
84- 98 E15.7 --- SymLat Symmetric Galactic latitude
100-109 F10.8 --- logVarInd log variability index
111-122 F12.10 --- FracVar Fractional variability
124-132 F9.7 --- PowerLawInd Power law index, PL_Index
134-142 F9.7 --- logParInd log-parabola Index, LP_Index
144-158 E15.7 --- DeltaInd Difference between power law and
log-parabola indices,
LP_Index - PL_Index
160-175 E16.8 --- LogParBeta log-parabola beta parameter
177-191 E15.7 --- logSigCurv ? Curvature significance for the
log-parabola model LPSigCurv scales with
the source detection significance,
192 A1 --- n_logSigCurv [I] I for infinity
193-207 E15.7 --- ModSigCurv ? 3logLPSigCurv-2logSignifAvg value
208 A1 --- n_ModSigCurv [I] I for infinity
209-217 F9.7 --- EPivot Pivot Energy
219-228 F10.7 --- EFluxErr logUncEnergyFlux100-0.4logEnergy_Flux100
value
230-244 E15.7 --- SigCombined ? 3logLP_SigCurv - logVariability_Index
value
245 A1 --- n_SigCombined [I] I for infinity
246-260 E15.7 --- HR12 Hardness ratio based on bands
0.3-1.0GeV/0.05-0.3GeV
262-276 E15.7 --- HR23 Hardness ratio based on bands
1.0-3.0GeV/0.3-1.0GeV
278-292 E15.7 --- HR34 Hardness ratio based on bands
3-30GeV/1.0-3.0GeV
294-308 E15.7 --- HR45 Hardness ratio based on bands
30-1000GeV/3-30GeV
310-324 E15.7 --- K13 Curvature parameter based on bands
1.0-3.0GeV/0.3-1.0GeV/0.05-0.3GeV
326-340 E15.7 --- K24 Curvature parameter based on bands
3-30GeV/1.0-3.0GeV/0.3-1.0GeV
342-356 E15.7 --- K35 Curvature parameter based on bands
30-1000GeV/3-30GeV/1.0-3.0GeV
--------------------------------------------------------------------------------
History:
From Martin Mayer, mgf.mayer(at)fau.de
Acknowledgements:
This work is based on data from eROSITA, the soft X-ray instrument
aboard SRG, a joint Russian-German science mission supported by the
Russian Space Agency (Roskosmos), in the interests of the Russian
Academy of Sciences represented by its Space Research Institute (IKI),
and the Deutsches Zentrum fuer Luft- und Raumfahrt (DLR). The SRG
spacecraft was built by Lavochkin Association (NPOL) and its
subcontractors and is operated by NPOL with support from the Max
Planck Institute for Extraterrestrial Physics (MPE). The development
and construction of the eROSITA X-ray instrument was led by MPE, with
contributions from the Dr. Karl Remeis Observatory Bamberg & ECAP (FAU
Erlangen-Nuernberg), the University of Hamburg Observatory, the
Leibniz Institute for Astrophysics Potsdam (AIP), and the Institute
for Astronomy and Astrophysics of the University of Tuebingen, with
the support of DLR and the Max Planck Society. The Argelander
Institute for Astronomy of the University of Bonn and the Ludwig
Maximilians Universitaet Munich also participated in the science
preparation for eROSITA.
The eROSITA data shown here were processed using the eSASS software
system developed by the German eROSITA consortium.
(End) Patricia Vannier [CDS] 07-Feb-2024