J/AJ/161/154 3FGL X-ray Analysis and ML (Kerby+, 2021)
X-ray spectra and multiwavelength machine learning classification for likely
counterparts to Fermi 3FGL unassociated source.
Kerby S., Kaur A., Falcone A.D., Stroh M.C., Ferrara E.C., Kennea J.A.,
Colosimo J.
<Astron. J. 161, 154 (2021)>
=2021AJ....161..154K 2021AJ....161..154K (SIMBAD/NED BibCode)
ADC_Keywords: X-ray sources; Pulsars; Active gal. nuclei
Keywords: gamma-ray sources - X-ray sources - active galactic nuclei - pulsars
Abstract:
We conduct X-ray spectral fits on 184 likely counterparts to Fermi-LAT
3FGL unassociated sources. Characterization and classification of
these sources allows for more complete population studies of the
high-energy sky. Most of these X-ray spectra are well fit by an
absorbed power law model, as expected for a population dominated by
blazars and pulsars. A small subset of 7 X-ray sources have spectra
unlike the power law expected from a blazar or pulsar and may be
linked to coincident stars or background emission. We develop a
multiwavelength machine learning classifier to categorize unassociated
sources into pulsars and blazars using gamma- and X-ray observations.
Training a random forest procedure with known pulsars and blazars, we
achieve a cross-validated classification accuracy of 98.6%. Applying
the random forest routine to the unassociated sources returned 126
likely blazar candidates (defined as Pbzr>90%) and 5 likely pulsar
candidates (Pbzr<10%). Our new X-ray spectral analysis does not
drastically alter the random forest classifications of these sources
compared to previous works, but it builds a more robust classification
scheme and highlights the importance of X-ray spectral fitting. Our
procedure can be further expanded with UV, visual, or radio spectral
parameters or by measuring flux variability.
Description:
Using archival Swift-XRT observations near detected possible X-ray
counterparts to Fermi-LAT unassociated 3FGL gamma-ray sources, we
conduct power law X-ray fitting for 184 X-ray excesses (noting and
excluding three loading contaminants). After sifting out seven
additional spectra which require individual analysis, we execute
random forest classification by combining our fit X-ray parameters
with catalog gamma-ray parameters to obtain the probability that each
source is a blazar, a pulsar, or still uncategorized.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
3fglfits.dat 145 187 X-ray fit and ML classification results
(tables 3 and 4 of the paper)
--------------------------------------------------------------------------------
See also:
J/ApJS/218/23 : Fermi LAT third source catalog (3FGL) (Acero+, 2015)
Byte-by-byte Description of file: 3fglfits.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 13 A13 --- 3FGLName Fermi-LAT 3FGL catalog name (JHHMM.m+DDMM)
15- 31 A17 --- SwFS3Name Swift-XRT X-ray excess name
(JHHMMSS.s+DDMMSS)
33- 34 I2 h RAh Right ascension (J2000)
36- 37 I2 min RAm Right ascension (J2000)
39- 43 F5.2 s RAs Right ascension (J2000)
45 A1 --- DE- Declination sign (J2000)
46- 47 I2 deg DEd Declination (J2000)
49- 50 I2 arcmin DEm Declination (J2000)
52- 56 F5.2 arcsec DEs Declination (J2000)
58- 63 F6.3 --- PLSlope ? X-ray fit photon index, 0.2-10keV
65- 69 F5.3 --- E_PLSlope ? Photon index positive uncertainty
71- 75 F5.3 --- e_PLSlope ? Photon index negative uncertainty
77- 85 E9.3 mW/m2 Flux ? X-ray fit flux, 0.2-10keV
87- 95 E9.3 mW/m2 E_Flux ? X-ray flux positive uncertainty
97-105 E9.3 mW/m2 e_Flux ? X-ray flux negative uncertainty
107-109 I3 --- fitDOF ? X-ray fit degrees of freedom
111-116 F6.2 --- fitCstat ? X-ray fit C-statistic
118-122 F5.3 --- BlazarProb ? Random forest blazar probability
124-145 A22 --- Notes Error message (1)
--------------------------------------------------------------------------------
Note (1): Error message as follows:
symmetricslopeuncert = photon index uses default symmetric uncertainty
uncert_error = XSPEC:steppar routine unable to converge uncertainties
Table1oddball = unusual photon index with analysis in Table 1 of paper
unconverged_fit = X-ray fit unconverged
optical_loading = Excess attributed to optical loading in Swift-XRT
--------------------------------------------------------------------------------
Acknowledgements:
Steve Kerby, sek289(at)psu.edu
(End) Patricia Vannier [CDS] 08-Dec-2020