J/ApJS/209/9 Unidentified gamma-ray sources. IV. X-ray (Paggi+, 2013)
Unveiling the nature of the unidentified gamma-ray sources.
IV. The Swift catalog of potential X-ray counterparts.
Paggi A., Massaro F., D'Abrusco R., Smith H.A., Masetti N., Giroletti M.,
Tosti G., Funk S.
<Astrophys. J. Suppl. Ser., 209, 9 (2013)>
=2013ApJS..209....9P 2013ApJS..209....9P
ADC_Keywords: Gamma rays ; Cross identifications ; X-ray sources ;
Photometry, UBVRI ; Photometry, ultraviolet ; BL Lac objects
Keywords: catalogs - galaxies: active - gamma rays: galaxies -
radiation mechanisms: non-thermal - X-rays: galaxies
Abstract:
A significant fraction (∼30%) of the high-energy γ-ray sources
listed in the second Fermi Large Area Telescope (LAT) catalog are
still of unknown origin, having not yet been associated with
counterparts at lower energies. To investigate the nature of these
enigmatic sources, we present an extensive search of X-ray sources
lying in the positional uncertainty region of a selected sample of
these unidentified gamma-ray sources (UGSs) that makes use of all
available observations performed by the Swift X-ray Telescope before
2013 March 31, available for 205 UGSs. To detect the fainter sources,
we merged all the observations covering the Fermi LAT positional
uncertainty region at a 95% level of confidence of each UGS. This
yields a catalog of 357 X-ray sources, finding candidate X-ray
counterparts for ∼70% of the selected sample. In particular, 25% of
the UGSs feature a single X-ray source within their positional
uncertainty region, while 45% have multiple X-ray sources. For each
X-ray source, we also looked in the corresponding Swift UVOT merged
images for optical and ultraviolet counterparts, also performing
source photometry. We found ultraviolet-optical correspondences for
∼70% of the X-ray sources. We searched several major radio, infrared,
optical, and ultraviolet surveys for possible counterparts within the
positional error of the sources in the X-ray catalog to obtain
additional information on their nature. Applying the kernel density
estimation technique to infrared colors of Wide-Field Infrared Survey
Explorer counterparts of our X-ray sources we select six γ-ray
blazar candidates. In addition, comparing our results with previous
analyses, we select 11 additional γ-ray blazar candidates.
Description:
The initial sample considered in our analysis is constituted by the
299 unidentified gamma-ray sources (UGSs) in the 2FGL catalog that do
not present any γ-ray analysis flag (Nolan et al. 2012,
Cat. J/ApJS/199/31).
After Fermi was launched, the Swift XRT Survey of Fermi Unassociated
Sources was started in order to perform follow-up observations of the
unidentified gamma-ray sources (UGSs) in an attempt to find their
potential X-ray counterparts (PI: A. Falcone). We analyze all data
collected between the beginning of the follow-up program until 2013
March 31. We note that 203 of the 205 UGSs that constitute our sample
have been also observed in the optical and UV by UVOT. We then
produced for each X-ray observation the corresponding merged UVOT
event files, adopting standard procedures.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 164 357 Catalog of XRT-PC detected sources in the positional
uncertainty region of each UGS as reported in the 2FGL
table2.dat 251 357 UVOT counterparts to the XRT-PC detected sources with
their photometric properties
table3.dat 51 194 XRT-PC sources featuring a USNO-B counterpart within
the positional error
table4.dat 24 62 UGSs without XRT-PC counterparts in the Fermi LAT
positional uncertainty region
table5.dat 72 29 XRT-PC counterparts to γ-ray blazar-like sources
selected according to Papers I and V.
table6.dat 64 37 XRT-PC counterparts to γ-ray blazar-like sources
selected with the KDE technique
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See also:
I/284 : The USNO-B1.0 Catalog (Monet+ 2003)
J/ApJS/209/10 : Unidentified γ-ray sources. V. (Massaro+, 2013)
J/ApJS/208/25 : Swift X-ray observations of 1FGL sources (Takeuchi+, 2013)
J/ApJS/207/16 : BL Lac candidates for TeV observations (Massaro+, 2013)
J/ApJS/207/4 : Unidentified γ-ray sources. III. Radio (Massaro+, 2013)
J/ApJS/206/17 : New gamma-ray blazar candidates in the 3PBC (Maselli+, 2013)
J/ApJS/206/13 : Blazars with γ-ray counterparts. II. (Massaro+, 2013)
J/ApJS/206/12 : Blazars with γ-ray counterparts. I. (D'Abrusco+, 2013)
J/A+A/551/A142 : 7 year Swift-XRT point source catalog (1SWXRT) (D'Elia+, 2013)
J/ApJS/199/31 : Fermi LAT second source catalog (2FGL) (Nolan+, 2012)
J/A+A/541/A160 : X & gamma-ray observations of selected blazars (Giommi+, 2012)
J/ApJ/742/66 : New Fermi/LAT extragalactic sources (Teng+, 2011)
J/ApJ/716/30 : SED of Fermi bright blazars (Abdo+, 2010)
J/ApJ/709/1407 : SED of the Fermi blazars (Li+, 2010)
J/MNRAS/403/945 : Swift/XRT obs. of unidentified IBIS sources (Landi+, 2010)
J/A+A/458/245 : Obs. of 2 Unidentified Gamma-ray Sources (La Palombara+, 2006)
J/A+A/379/755 : Radio data of X- and gamma-ray loud blazars (Venturi+, 2001)
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 A4 --- --- [2FGL]
5- 16 A12 --- 2FGL 2nd Fermi LAT catalog ID (JHHMM.m+DDMM)
18- 22 A5 --- --- [SWXRT]
23- 38 A16 --- Swift Swift/XRT source ID (JHHMMSS.s+DDMMSS)
40- 62 A23 --- OName Other source name (1)
64- 65 I2 h RAh XRT Hour of Right Ascension (J2000)
67- 68 I2 min RAm XRT Minute of Right Ascension (J2000)
70- 75 F6.3 s RAs XRT Second of Right Ascension (J2000)
77 A1 --- DE- XRT Sign of the Declination (J2000)
78- 79 I2 deg DEd XRT Degree of Declination (J2000)
81- 82 I2 arcmin DEm XRT Arcminute of Declination (J2000)
84- 88 F5.2 arcsec DEs XRT Arcsecond of Declination (J2000)
90- 93 F4.2 arcsec ePos [3.5/9.1] Position error
95- 99 I5 s Exp XRT-PC exposure time
101-106 F6.2 ct/ks D-CR Count rate by DETECT
108-112 F5.2 ct/ks e_D-CR Uncertainty in D-CR
114-114 I1 --- Sig [2/5] Signal-to-noise threshold above which
source is detected
116-121 F6.2 ct/ks S-CR Count rate by OSTA
123-127 F5.2 ct/ks e_S-CR Uncertainty in S-CR
129-133 F5.2 --- SNR [0.22/91.12] Signal-to-Noise
135-150 A16 --- Xcat List of catalogs cross-matched (2)
152-156 A5 --- Blaz γ-ray blazar-like source (3)
158-164 F7.5 --- z [0.0061/1.725]? Redshift from literature
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Note (1): If more than one counterpart is found, the order we choose for the
the alternate name is: NVSS, FIRST, SUMSS, WENSS, WISE, SDSS, 6DFGS, NED.
Note (2): Results of the cross-matching with the catalogs discussed in
Section 4 within the positional error reported in column ePos.
Code as follows:
N = NVSS (Condon et al. 1998, Cat. VIII/65);
F = FIRST (Becker et al. 1995ApJ...450..559B 1995ApJ...450..559B; Cat. VIII/90);
S = SUMSS (Sydney University Molonglo Sky Survey; Bock et al.
1999AJ....117.1578B 1999AJ....117.1578B; Mauch et al. 2003, Cat. VIII/81);
W = WENSS (Rengelink et al. 1997, Cat. VIII/62);
w = WISE (Wright et al. 2010AJ....140.1868W 2010AJ....140.1868W; Cat. II/311);
M = 2MASS (Skrutskie et al. 2006, Cat. VII/233);
UK = UKIDSS (Lawrence et al. 2007, Cat. II/319);
s = SDSS (SDSS-dr9; e.g., Paris et al. 2012, Cat. VII/269);
6 = 6DFGS (Jones et al. 2004MNRAS.355..747J 2004MNRAS.355..747J, 2009, Cat. VII/259);
g = GALEX (GR6; Martin et al. 2005ApJ...619L...1M 2005ApJ...619L...1M);
o = UVOT (optical filter);
u = UVOT (UV filter);
U = USNO-B (Monet et al. 2003, Cat. I/284);
C = CSC (Chandra Source Catalog; e.g., Evans et al. 2010ApJS..189...37E 2010ApJS..189...37E)
Note (3): Method as follows:
WISE = according to Massaro et al. (Paper II, 2013, Cat. J/ApJS/206/13);
WENSS = according to Massaro et al. (Paper V, 2013, Cat. J/ApJS/209/10);
KDE = according to the KDE technique (Kernel Density Estimation)
as discussed in Section 6.1.
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Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 A4 --- --- [2FGL]
5- 16 A12 --- 2FGL 2nd Fermi LAT catalog ID (JHHMM.m+DDMM)
18- 22 A5 --- --- [SWXRT]
23- 38 A16 --- Swift Swift/XRT source ID (JHHMMSS.s+DDMMSS)
40- 41 I2 h RAuh UVOT Hour of Right Ascension (J2000)
43- 44 I2 min RAum UVOT Minute of Right Ascension (J2000)
46- 51 F6.3 s RAus UVOT Second of Right Ascension (J2000)
53 A1 --- DEu- UVOT Sign of the Declination (J2000)
54- 55 I2 deg DEud UVOT Degree of Declination (J2000)
57- 58 I2 arcmin DEum UVOT Arcminute of Declination (J2000)
60- 64 F5.2 arcsec DEus UVOT Arcsecond of Declination (J2000)
66- 69 F4.2 arcsec Sep [0/6.5] Angular separation between X-ray and
UV sources
71- 77 F7.4 mag E(B-V) [0.01/16] Galactic extinction (4)
79- 83 I5 s ExpV ? UVOT V band exposure time
85- 89 F5.2 mag Vmag [11.46/21.22]? Swift/UVOT V band Vega magnitude
from UVOTSOURCE (5)
90- 90 A1 --- f_Vmag [*] * = filter saturation
92- 95 F4.2 mag e_Vmag ? Uncertainty in Vmag (6)
97-101 F5.2 mag Vmag2 [11.87/18.58]? Swift/UVOT V band Vega magnitude
from UVOTDETECT (5)
103-106 F4.2 mag e_Vmag2 ? Uncertainty in Vmag2 (6)
108-111 I4 s ExpB ? UVOT B band exposure time
113-117 F5.2 mag Bmag [13.12/22.03]? Swift/UVOT B band Vega magnitude
from UVOTSOURCE (5)
119-122 F4.2 mag e_Bmag ? Uncertainty in Bmag (6)
124-128 F5.2 mag Bmag2 [13.31/19.24]? Swift/UVOT B band Vega magnitude
from UVOTDETECT (5)
130-133 F4.2 mag e_Bmag2 ? Uncertainty in Bmag2 (6)
135-139 I5 s ExpU ? UVOT U band exposure time
141-145 F5.2 mag Umag [11.91/21.91]? Swift/UVOT U band Vega magnitude
from UVOTSOURCE (5)
146-146 A1 --- f_Umag [*] * = filter saturation
148-151 F4.2 mag e_Umag ? Uncertainty in Umag (6)
153-157 F5.2 mag Umag2 [11.83/21.46]? Swift/UVOT U band Vega magnitude
from UVOTDETECT (5)
158-158 A1 --- f_Umag2 [*] * = filter saturation
160-163 F4.2 mag e_Umag2 ? Uncertainty in Umag2 (6)
165-169 I5 s ExpW1 ? Swift/UVOT W1 band exposure time
171-175 F5.2 mag W1mag [11.01/22.23]? Swift/UVOT UVW1 band Vega
magnitude from UVOTSOURCE (5)
176-176 A1 --- f_W1mag [*] * = filter saturation
178-181 F4.2 mag e_W1mag ? Uncertainty in W1mag (6)
183-187 F5.2 mag W1mag2 [10.95/21.74]? Swift/UVOT UVW1 band Vega
magnitude from UVOTDETECT (5)
188-188 A1 --- f_W1mag2 [*] * = filter saturation
190-193 F4.2 mag e_W1mag2 ? Uncertainty in W1mag2 (6)
195-199 I5 s ExpM2 ? Swift/UVOT UVM2 band exposure time
201-205 F5.2 mag M2mag [10.42/22.56]? Swift/UVOT UVM2 band Vega
magnitude from UVOTSOURCE (5)
206-206 A1 --- f_M2mag [*] * = filter saturation
208-211 F4.2 mag e_M2mag ? Uncertainty in M2mag (6)
213-217 F5.2 mag M2mag2 [10.36/21.95]? Swift/UVOT UVM2 band Vega
magnitude from UVOTDETECT (5)
218-218 A1 --- f_M2mag2 [*] * = filter saturation
220-223 F4.2 mag e_M2mag2 ? Uncertainty in M2mag2 (6)
225-229 I5 s ExpW2 ? UVOT W2 band exposure time
231-235 F5.2 mag W2mag [12.23/22.8]? Swift/UVOT UVW2 band Vega magnitude
from UVOTSOURCE (5)
237-240 F4.2 mag e_W2mag ? Uncertainty in W2mag (6)
242-246 F5.2 mag W2mag2 [12.25/22.47]? Swift/UVOT UVW2 band Vega
magnitude from UVOTDETECT (5)
248-251 F4.2 mag e_W2mag2 ? Uncertainty in W2mag2 (6)
--------------------------------------------------------------------------------
Note (4): As derived by the Infrared Science Archive (IRSA).
Note (5): Not corrected by galactic extinction.
Note (6): Upper limits are indicated with 0.00 errors.
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Byte-by-byte Description of file: table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 5 A5 --- --- [SWXRT]
6- 21 A16 --- Swift Swift designation (JHHMMSS.s+DDMMSS)
23- 27 F5.2 mag B1mag [7.1/21.5]? USNO-B first epoch blue magnitude
29- 33 F5.2 mag R1mag [6.6/20.4]? USNO-B first epoch red magnitude
35- 39 F5.2 mag B2mag [7/22.7]? USNO-B 2nd epoch blue magnitude
41- 45 F5.2 mag R2mag [6.6/21.5]? USNO-B 2nd epoch red magnitude
47- 51 F5.2 mag Imag [6/20]? USNO-B NIR magnitude
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Byte-by-byte Description of file: table4.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 A4 --- --- [2FGL]
5- 16 A12 --- 2FGL 2FGL name (JHHMM.m+DDMM)
18 A1 --- f_2FGL [*] *: Flag on 2FGL (1)
20- 24 I5 s Exp [142/10728] XRT-PC total exposure time
-------------------------------------------------------------------------------
Note (1): Sources that have a γ-ray blazar-like candidate counterpart in
their positional uncertainty region as reported by Massaro et al.
(2013, Pap. II, Cat. J/ApJS/206/13 and Pap. V, Cat. J/ApJS/209/10).
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Byte-by-byte Description of file: table5.dat table6.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 A4 --- --- [2FGL]
5- 16 A12 --- 2FGL 2FGL name (JHHMM.m+DDMM)
18- 22 A5 --- --- [SWXRT]
23- 38 A16 --- Swift Swift designation (JHHMMSS.s+DDMMSS)
40 A1 --- f_Swift [*] *: source with radio counterpart within the
positional error listed in table 1
42- 64 A23 --- AName WISE designation (JHHMMSS.ss+DDMMSS.s) or
WN0557.5+3838 (in table 5) (1)
66 A1 --- Cl [A-C ] Classification (A=most probable candidate
blazar; only for table 5) (2)
68- 72 A5 --- OType Object type (only for table 5) (3)
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Note (1): Name of the WISE counterpart (as reported by WISE All-Sky data
catalog; Cutri & et al. 2012, Cat. II/311) or of the WENSS counterpart
(as reported by WENSS catalog; Rengelink et al. 1997, Cat. VIII/62)
closer to the XRT-PC coordinates (as reported in Table 1).
Note (2): Classification for γ-ray blazar-like sources selected by
D'Abrusco et al. (Pap. I, 2013, Cat. J/ApJS/206/12), every source is
assigned to class A, B, or C depending on the probability of the WISE
source to be compatible with the model of the WISE Fermi Blazar (WFB)
locus: class A sources are considered the most probable candidate
blazars for the high-energy source, while class B and class C sources
are less compatible with the WFB locus but are still deemed as
candidate blazars. For γ-ray blazar-like sources selected by
Massaro et al. (Pap. V, 2013, Cat. J/ApJS/209/10), with A we indicate
radio sources having -1≤α1400325≤0.55 and with B those
with 0.55≤α1400325≤0.65, where α1400325 is the
radio spectral index between 325 MHz and 1.4 GHz.
Note (3): Classification of the candidate blazar according to D'Abrusco et al.
(Pap. I, 2013, Cat. J/ApJS/206/12) based on the compatibility of the
WISE source with the regions of the WFB locus model. "BZB" and "BZQ"
indicate the regions dominated by BL Lac objects and FSRQs sources
respectively, while "MIXED" indicate the region where the population
is mixed in terms of spectral classes.
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History:
From electronic version of the journal
References:
D'Abrusco et al. Paper I. 2013ApJS..206...12D 2013ApJS..206...12D Cat. J/ApJS/206/12
Massaro et al. Paper II. 2013ApJS..206...13M 2013ApJS..206...13M Cat. J/ApJS/206/13
Massaro et al. Paper III. 2013ApJS..207....4M 2013ApJS..207....4M Cat. J/ApJS/207/4
Massaro et al. Paper V. 2013ApJS..209...10M 2013ApJS..209...10M Cat. J/ApJS/209/10
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 18-Nov-2013