J/A+A/598/A134 γ-ray signature in WHSP blazars (1BIGB) (Arsioli+, 2017)
Searching for γ-ray signature in WHSP blazars. Fermi-LAT detection of
150 excess signal in the 0.3-500 GeV band.
Arsioli B., Chang Y.-L.
<Astron. Astrophys., 598, A134 (2017)>
=2017A&A...598A.134A 2017A&A...598A.134A (SIMBAD/NED BibCode)
ADC_Keywords: Gamma rays ; BL Lac objects
Keywords: galaxies: active - BL Lacertae objects: general -
radiation mechanisms: non-thermal - gamma rays: diffuse background -
gamma rays: general
Abstract:
A direct search of γ-ray emission centered on multifrequency
selected candidates is a valuable complementary approach to the
standard search adopted in current γ-ray Fermi-LAT catalogs. Our
sources are part of the 2WHSP sample that was assembled with the aim
of providing targets for Imaging Atmospheric Cherenkov Telescopes
(IACT). A likelihood analysis based on their known position enabled us
to detect 150 γ-ray excess signals that have not yet been
reported in previous γ-ray catalogs (1FGL, 2FGL, 3FGL). By
identifying new sources, we solve a fraction of the extragalactic
isotropic γ-ray background (IGRB) composition, improving the
description of the γ-ray sky.
We perform data reduction with the Fermi Science Tools using positions
from 400 high synchrotron peaked (HSP) blazars as seeds of tentative
γ-ray sources; none of them have counterparts from previous
1FGL, 2FGL and 3FGL catalogs. Our candidates are part of the 2WHSP
sample (currently the largest set of HSP blazars). We focus on HSPs
characterized by bright synchrotron component with peak flux
νf(ν)≥10-12.1erg/cm2/s, testing the hypothesis of having
a γ-ray source in correspondence to the WHSP positions. Our
likelihood analysis considers the 0.3-500GeV energy band, integrating
over 7.2yr of Fermi-LAT observation and making use of the Pass 8 data
release.
From the 400 candidates tested, a total of 150 2WHSPs showed excess
γ-ray signature: 85 high-significance detections with test
statistic (TS)>25, and 65 lower-significance detections with TS
between 10 to 25. We assume a power law spectrum in the 0.3-500GeV
band and list the spectrum parameters describing all 150 new
γ-ray sources. We study the γ-ray photon spectral index
distribution, the likelihood of detection according to the synchrotron
peak brightness (figure of merit parameter), and plot the measured
γ-ray LogN-LogS of HSP blazars, also discussing the portion of
the IGRB that has been resolved by the present work. We also report on
four cases where we could resolve source confusion and find
counterparts for unassociated 3FGL sources with the help of
high-energy TS maps together with multifrequency data. The 150 new
γ-ray sources are named with the acronym 1BIGB for the first
version of the Brazil ICRANet Gamma-ray Blazar catalog, in reference
to the cooperation agreement supporting this work.
Description:
Based on the position of a potential γ-ray source, we downloaded
Pass 8 processed events from the public Fermi-database6 that includes
all photons recorded in a region of interest (ROI) of 25° radius
from the candidate's position, for the whole 7.2yr of observations
(MM/DD/YYYY: 08/04/2008 to 11/04/2015). In our analysis we used the
Fermi Science Tools (v10r0p5), performing binned analysis to deal with
the long integration time.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
tablea1.dat 86 150 The 150 new gamma-ray signatures detected down
to TS>10 level
tablea2.dat 52 30 *List of 30 2WHSPs detected with the largest
significance within our gamma-ray likelihood
analysis, all having TS>45 based Pass 8
Fermi-LAT data when integrating over 7.2yr
of observations
--------------------------------------------------------------------------------
Note on tablea2.dat: All those cases were re-evaluated based on Pass 7 data,
integrating over the first 4yr of mission; in order to reproduce the setup
used to prepare the 3FGL catalog (see Sect. 3.4 for the setup description).
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See also:
J/A+A/598/A17 : The 2WHSP catalog (Chang+, 2017)
Byte-by-byte Description of file: tablea1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 5 A5 --- --- [1BIGB]
7- 22 A16 --- 1BIGB Source name (JHHMMSS.d+DDMMSS) (1)
23- 25 A3 --- n_1BIGB [abc ] Note on 1BIGB (2)
27- 35 F9.5 deg RAdeg Right ascension (J2000)
37- 45 F9.5 deg DEdeg Declination (J2000)
47 A1 --- l_z Lower limit flag on z (3)
48- 52 F5.3 --- z Redshift from literature (4)
53 A1 --- u_z [?] Uncertainty flag on z
55- 58 F4.2 --- GAMMA Spectral photon index (5)
60- 63 F4.2 --- e_GAMMA rms uncertainty on GAMMA
65- 68 F4.2 10-13ph/cm2/s/MeV N0 N0 parameter (5)
70- 73 F4.2 10-13ph/cm2/s/MeV e_N0 rms uncertainty on N0
75- 79 F5.1 --- TS Test statistic
81- 84 F4.2 10-10ph/cm2/s Flux Photon counts calculated by integrating
Eq. (1) along the energy range
1-100 GeV (Flux1-100GEv)
86 A1 --- Note [*] * indicates sources with
re-evaluated parameters in tablea2
--------------------------------------------------------------------------------
Note (1): Sources are named with the acronym 1BIGB (for the first version of
"Brazil ICRANet Gamma-ray Blazar" catalog) with coordinates corresponding to
those of 2WHSP seeds used for the likelihood analysis.
Note (2): Notes as follows:
a = source also reported in the 2FHL catalog (Ackermann et al. 2016,
Cat. J/ApJ/810/14)
b = source reported as possible counterparts of photon clustering detected
by Fermi-LAT at E>10GeV (Campana et al. 2015Ap&SS.360...65C 2015Ap&SS.360...65C)
c = Source 2WHSPJ194356.2+211821 is the single case located at |b|<10°
(Also to improve the completeness of the final sample, known HSP
sources at |b|<10° were incorporate in the 2WHSP catalog.)
Note (3): all lower-limits shown here were derived in Arsioli et al.,
Cat. J/A+A/579/A34; Chang et al., Cat. J/A+A/598/A17.
Note (4): from Shaw et al. 2013, Cat. J/ApJ/764/135b;
Pita et al., 2014A&A...565A..12P 2014A&A...565A..12P; Furniss et al., 2013ApJ...768L..31F 2013ApJ...768L..31F;
Danforth et al., 2010ApJ...720..976D 2010ApJ...720..976D; Shaw et al., 2013AJ....146..127S 2013AJ....146..127S;
Masetti et al., 2013A&A...559A..58M 2013A&A...559A..58M; Sbarufatti et al., 2005AJ....129..559S 2005AJ....129..559S;
Massaro et al., 2015Ap&SS.357...75M 2015Ap&SS.357...75M, Cat. VII/274)
Sources with currently absent redshift were given "0" value.
Note (5): The gamma-ray model parameters from Fermi Science Tools assume a
power law to describe the spectrum within the studied energy range 0.3-500GeV.
The parameters N0 and GAMMA are direct outputs from the likelihood analysis
over 7.2yr of Fermi-LAT data in the 0.3-500GeV band; those results consider
the pivot energy fixed as E0=1GeV.
The spectrum of each gamma-ray candidate is always modeled as a power law:
dN/dE=N0(E/E0)-GAMMA (equation (1)), where
E0 is a scale parameter (also known as pivot energy),
N0 is the pre-factor (flux density at the pivot energy E0), and
GAMMA is the photon spectral index for the energy range under consideration.
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Byte-by-byte Description of file: tablea2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 5 A5 --- --- [2WHSP]
6- 21 A16 --- 2WHSP 2WHSP source name (JHHMMSS.s+DDMMSS)
22 A1 --- n_2WHSP [*] Note on 2WHSP (1)
24- 27 F4.2 --- GAMMA Spectral photon index (2)
29- 32 F4.2 --- e_GAMMA rms uncertainty on GAMMA
34- 37 F4.2 10-13ph/cm2/s/MeV N0 pre-factor parameter N0 (2)
39- 42 F4.2 10-13ph/cm2/s/MeV e_N0 rms uncertainty on N0
44- 47 F4.1 --- TS4yr Test statistic based on Pass 7 data,
integrating over the first 4yr of
mission
49- 52 F4.2 10-10ph/cm2/s Flux Integral flux in the 1-100GeV energy
band
--------------------------------------------------------------------------------
Note (1): *: for two sources the power-law fitting does not converge well given
their significance is too low.
Note (2): Fitting parameter assuming a power-law model to describe the gamma-ray
spectrum in the 0.3-300GeV band (we integrated up to 300GeV following Fermi-LAT
team recommendations to work with Pass 7).
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History:
From electronic version of the journal
References:
Arsioli et al. 1BIGB SEDs. 2018MNRAS.480.2165A 2018MNRAS.480.2165A
Arsioli & Polenta LSP blazars 2018A&A...616A..20A 2018A&A...616A..20A
Chang et al. 2WHSP 2017A&A...598A..17C 2017A&A...598A..17C Cat. J/A+A/598/A17
Arsioli et al. 2BIGB 2020MNRAS.493.2438A 2020MNRAS.493.2438A Cat. J/MNRAS/493/2438
(End) Patricia Vannier [CDS] 24-May-2017