J/ApJ/923/75 X-ray/UV/opt counterparts of 4FGL gamma-ray sources (Kerby+, 2021)
Multiwavelength spectral analysis and neural network classification of
counterparts to 4FGL unassociated sources.
Kerby S., Kaur A., Falcone A.D., Eskenasy R., Hancock F., Stroh M.C.,
Ferrara E.C., Ray P.S., Kennea J.A., Grove E.
<Astrophys. J., 923, 75 (2021)>
=2021ApJ...923...75K 2021ApJ...923...75K
ADC_Keywords: Gamma rays; X-ray sources; Photometry, UBV; Active gal. nuclei;
BL Lac objects; Pulsars
Keywords: Gamma-ray sources ; X-ray sources ; Blazars ; Pulsars ;
Neural networks ; Classification
Abstract:
The Fermi-LAT unassociated sources represent some of the most
enigmatic gamma-ray sources in the sky. Observations with the
Swift-XRT and -UVOT telescopes have identified hundreds of likely
X-ray and UV/optical counterparts in the uncertainty ellipses of the
unassociated sources. In this work we present spectral fitting results
for 205 possible X-ray/UV/optical counterparts to 4FGL unassociated
targets. Assuming that the unassociated sources contain mostly pulsars
and blazars, we develop a neural network classifier approach that
applies gamma-ray, X-ray, and UV/optical spectral parameters to yield
a descriptive classification of unassociated spectra into pulsars and
blazars. From our primary sample of 174 Fermi sources with a single
X-ray/UV/optical counterpart, we present 132 Pbzr>0.99 likely
blazars and 14 Pbzr<0.01 likely pulsars, with 28 remaining
ambiguous. These subsets of the unassociated sources suggest a
systematic expansion to catalogs of gamma-ray pulsars and blazars.
Compared to previous classification approaches our neural network
classifier achieves significantly higher validation accuracy and
returns more bifurcated Pbzr values, suggesting that multiwavelength
analysis is a valuable tool for confident classification of Fermi
unassociated sources.
Description:
The unassociated sources of the Fermi-LAT 4FGL catalog are comprised
of gamma-ray sources of unknown astrophysical nature and no known
counterpart (see Abdollahi+ 2020, J/ApJS/247/33).
After 10 continuous years of observations, the 4FGL-DR2 catalog
(Ballet+ 2020arXiv200511208B 2020arXiv200511208B) contains 5064 sources in total, of which
over 1300 are unassociated; 1410 4FGL sources are targets for the
Swift-XRT survey of unassociated sources. By observing the
unassociated gamma-ray sources, the Swift program provides
high-resolution X-ray, UV, and visual observations to find
lower-energy counterparts to the unassociated sources. This survey is
a further development after previously analyzing unassociated 3FGL
sources (detailed in Kerby+ 2021, J/AJ/161/154) and has covered
approximately 500 4FGL unassociated targets with >4ks of observations
each.
So far Swift has detected possible X-ray counterparts within the
Fermi-LAT uncertainty ellipse of 208 4FGL unassociated sources, with
some unassociated sources having multiple possible X-ray counterparts.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table3.dat 85 174 *Fermi-LAT features for the unassociated sample
investigated in this work, along with Swift-XRT and
-UVOT parameters for all possible X-ray/UV/optical
counterparts (single counterpart)
table4.dat 82 31 *Fermi-LAT features for the unassociated sample
investigated in this work, along with Swift-XRT and
-UVOT parameters for all possible X-ray/UV/optical
counterparts (multiple X-ray counterparts)
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Note on table3.dat: Only unassociated sources with a single possible
counterpart are included in this table, and sources are organized
based on Pbzr, listing likely pulsars and likely blazars separately.
Note on table4.dat: Only unassociated sources with a multiple notable
X-ray sources within the Fermi-LAT uncertainty ellipse are included here.
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See also:
B/swift : Swift Master Catalog (HEASARC, 2004-)
IX/43 : 1SXPS Swift X-ray telescope point source catalogue (Evans+ 2014)
IX/67 : Fermi LAT 4th source cat. (4FGL-DR3) (Fermi-LAT col., 2022)
J/A+A/333/231 : O-M stars model atmospheres (Bessell+ 1998)
J/A+A/551/A142 : 7yr Swift-XRT point source catalog (1SWXRT) (D'Elia+, 2013)
J/ApJS/208/17 : 2nd Fermi LAT cat. of gamma-ray pulsars (2PC) (Abdo+, 2013)
J/ApJS/209/9 : Unidentified gamma-ray sources. IV. X-ray (Paggi+, 2013)
J/ApJ/810/14 : Third catalog of LAT-detected AGNs (3LAC) (Ackermann+, 2015)
J/ApJ/820/8 : 3FGL sources statistical classifications (Saz Parkinson+, 2016)
J/ApJ/854/99 : The Einstein@Home gamma-ray pulsar survey. II. (Wu+, 2018)
J/ApJ/887/18 : Classif. of X-ray counterparts of 3FGL sources (Kaur+, 2019)
J/ApJS/247/33 : The Fermi LAT fourth source catalog (4FGL) (Abdollahi+, 2020)
J/AJ/161/154 : 3FGL X-ray Analysis and ML (Kerby+, 2021)
Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1 A1 --- Type Source type code (1)
3- 15 A13 --- 4FGL Target 4FGL identifier (JHHMM.m+DDMMc) (2)
17- 22 F6.2 [10-7W/cm2] logFG [-12.1/-10.2] Log γ-ray flux;
erg/s/cm2
24- 27 F4.2 --- GammaG [1.25/3.01] The γ-ray photon index
29- 33 F5.2 --- VarInd [1.23/59.61] Year-over-year γ-ray
variability index
35- 39 F5.2 --- CurvInd [0/14.3] The γ-ray curvature index
41- 56 A16 --- SwXF4 Target SwXF4 identifier (JHHMMSS.s+DDMMSS)
58- 63 F6.2 [10-7W/cm2] logFX [-13.11/-7.39] Log X-ray 0.3-10keV
flux; erg/s/cm2
65- 69 F5.2 --- GammaX [-1.6/10] X-ray photon index
71- 72 A2 --- UVOT Swift/UVOT filter used
74- 78 F5.2 mag Vmag [14.68/22.7] Apparent V band Vega
magnitude (G1)
80- 85 F6.4 --- Pbzr [0.0015/1] The blazar probability
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Note (1): Type code as follows:
a = likely pulsar, Pbzr<0.01 (14 occurrences)
b = likely blazar, Pbzr>0.99 (132 occurrences)
c = ambiguous, 0.01<Pbzr<0.99 (28 occurrences)
Note (2): Component letters "c" added on 4 objects by CDS to match the 4FGL
designations (IX/67 and Abdollahi+ 2020, J/ApJS/247/33).
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 12 A12 --- 4FGL Target 4FGL identifier (JHHMM.m+DDMM)
14- 19 F6.2 [10-7W/cm2] logFG [-12.1/-10.47] Log γ-ray flux;
erg/s/cm2
21- 24 F4.2 --- GammaG [1.7/2.71] The γ-ray photon index
26- 30 F5.2 --- VarInd [1.65/27.2] Year-over-year γ-ray
variability index
32- 36 F5.2 --- CurvInd [0.05/10.7] The γ-ray curvature
index
38- 53 A16 --- SwXF4 Target SwXF4 identifier (JHHMMSS.s+DDMMSS)
54 A1 --- f_SwXF4 [*] Flag on SwXF4 (1)
56- 61 F6.2 [10-7W/cm2] logFX [-14.1/-8.97] Log X-ray 0.3-10keV flux;
erg/s/cm2
63- 66 F4.2 --- GammaX [0.01/7.9] X-ray photon index
68- 69 A2 --- UVOT Swift/UVOT filter used
71- 75 F5.2 mag Vmag [13.37/21.7] Apparent V band Vega
magnitude (G1)
77- 82 F6.4 --- Pbzr [0.0015/1] The blazar probability
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Note (1): Flag as follows:
* = Coincident with dim catalogued stars. The UV/optical emission from
from those stars is probably not related to a pulsar or blazar,
and thus the Pbzr values should not be trusted.
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Global notes:
Note (G1): Produced using the noted UVOT filter, the closest available to the
V band central wavelength.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 17-May-2023