-
MNRAS 000, 1–12 (2017) Preprint 15 January 2019 Compiled using
MNRAS LATEX style file v3.0
MAGIC and Fermi -LAT gamma-ray results onunassociated HAWC
sources
M. L. Ahnen1, S. Ansoldi2,20, L. A. Antonelli3, C. Arcaro4, D.
Baack5, A. Babić6, B. Banerjee7, P. Bangale8, U. Barresde
Almeida8,9, J. A. Barrio10, J. Becerra González11, W. Bednarek12,
E. Bernardini4,13,23, R. Ch. Berse5, A. Berti2,24,W.
Bhattacharyya13, A. Biland1, O. Blanch14, G. Bonnoli15, R.
Carosi15, A. Carosi3, G. Ceribella8, A. Chatterjee7,S. M. Colak14,
P. Colin8, E. Colombo11, J. L. Contreras10, J. Cortina14, S.
Covino3, P. Cumani14, P. Da Vela15, F. Dazzi3,A. De Angelis4, B. De
Lotto2, M. Delfino14,25, J. Delgado14, F. Di Pierro4, A.
Domı́nguez10, D. Dominis Prester6, D. Dorner16,M. Doro4, S.
Einecke5, D. Elsaesser5, V. Fallah Ramazani17, A.
Fernández-Barral4,14? D. Fidalgo10, M. V. Fonseca10,L. Font18, C.
Fruck8, D. Galindo19, R. J. Garćıa López11, M. Garczarczyk13, M.
Gaug18, P. Giammaria3, N. Godinović6,D. Gora13, D. Guberman14, D.
Hadasch20, A. Hahn8, T. Hassan14, M. Hayashida20, J. Herrera11, J.
Hose8, D. Hrupec6,K. Ishio8, Y. Konno20, H. Kubo20, J. Kushida20,
D. Kuveždić6, D. Lelas6, E. Lindfors17, S. Lombardi3, F.
Longo2,24,M. López10, C. Maggio18, P. Majumdar7, M. Makariev21, G.
Maneva21, M. Manganaro11, K. Mannheim16, L. Maraschi3,M. Mariotti4,
M. Mart́ınez14, S. Masuda20, D. Mazin8,20, K. Mielke5, M. Minev21,
J. M. Miranda15, R. Mirzoyan8,A. Moralejo14, V. Moreno18, E.
Moretti8, T. Nagayoshi20, V. Neustroev17, A. Niedzwiecki12, M.
Nievas Rosillo10, C. Nigro13,K. Nilsson17, D. Ninci14, K.
Nishijima20, K. Noda14, L. Nogués14, S. Paiano4, J. Palacio14, D.
Paneque8, R. Paoletti15,J. M. Paredes19, G. Pedaletti13, M.
Peresano2, M. Persic2, P. G. Prada Moroni22, E. Prandini4, I.
Puljak6, J. R. Garcia8,I. Reichardt4, W. Rhode5, M. Ribó19, J.
Rico14, C. Righi3, A. Rugliancich15, T. Saito20, K. Satalecka13, T.
Schweizer8,J. Sitarek12,20, I. Šnidarić6, D. Sobczynska12, A.
Stamerra3, M. Strzys8, T. Surić6, M. Takahashi20, L. Takalo17, F.
Tavecchio3,P. Temnikov21, T. Terzić6, M. Teshima8,20, N.
Torres-Albà19, A. Treves2, S. Tsujimoto20, G. Vanzo11, M.
VazquezAcosta11, I. Vovk8, J. E. Ward14, M. Will8, D. Zarić6,
(MAGIC Collaboration), A. Albert26, R. Alfaro27, C. Alvarez28,R.
Arceo28, J. C. Arteaga-Velázquez29, D. Avila Rojas27, H.A. Ayala
Solares30, A. Becerril27, E. Belmont-Moreno27,S. Y. BenZvi31, A.
Bernal32, J. Braun33, K. S. Caballero-Mora28, T. Capistrán34, A.
Carramiñana34, S. Casanova35,M. Castillo29, U. Cotti29, J.
Cotzomi36, S. Coutiño de León34, C. De León36, E. De la
Fuente37, R. Diaz Hernandez34,S. Dichiara32, B. L. Dingus26, M. A.
DuVernois33, J. C. Dı́az-Vélez37, R. W. Ellsworth38, K. Engel39,
O. Enriquez-Rivera40, D. W. Fiorino39, H. Fleischhack41, N.
Fraija32, J. A. Garćıa-González27, F. Garfias32, A.
González-Muñoz27,M. M. González32, J. A. Goodman39, Z.
Hampel-Arias33, J. P. Harding26, S. Hernandez27, F.
Hueyotl-Zahuantitla28,C. M. Hui42, P. Hüntemeyer41, A. Iriarte32,
A. Jardin-Blicq43, V. Joshi43, S. Kaufmann28, A. Lara40, R. J.
Lauer44,W. H. Lee32, D. Lennarz45, H. León Vargas27, J. T.
Linnemann46, A. L. Longinotti34, G. Luis-Raya47, R.
Luna-Garćıa48,R. López-Coto43, K. Malone30, S. S. Marinelli46, O.
Martinez36, I. Martinez-Castellanos39, J. Mart́ınez-Castro48, H.
Mart́ınez-Huerta49, J. A. Matthews44, P. Miranda-Romagnoli50, E.
Moreno36, M. Mostafá30, A. Nayerhoda35, L. Nellen51, M.
Newbold52,M. U. Nisa31, R. Noriega-Papaqui50, R. Pelayo48, J.
Pretz30, E. G. Pérez-Pérez47, Z. Ren44, C. D. Rho31, C.
Rivière39, D. Rosa-González34, M. Rosenberg30, E. Ruiz-Velasco43,
F. Salesa Greus35, A. Sandoval27, M. Schneider53, M. Seglar
Arroyo30,G. Sinnis26, A. J. Smith39, R. W. Springer52, P.
Surajbali43, I. Taboada45†, O. Tibolla28, K. Tollefson46, I.
Torres34,T. N. Ukwatta26, G. Vianello54, L. Villaseñor36, F.
Werner43, S. Westerhoff33, J. Wood33, T. Yapici31, G. Yodh55, A.
Zepeda49,H. Zhou26, J. D. álvarez29, (HAWC Collaboration), M.
Ajello56 L. Baldini57 G. Barbiellini58,59 B. Berenji60 E.
Bissaldi61,62
R. D. Blandford63 R. Bonino64,65 E. Bottacini63,66 T. J.
Brandt67 J. Bregeon68 P. Bruel69 R. A. Cameron63 R. Caputo70
P. A. Caraveo71 D. Castro72,67 E. Cavazzuti73 G. Chiaro71 S.
Ciprini74,75 D. Costantin76 F. D’Ammando77,78 F. de Palma62,79
A. Desai56 N. Di Lalla57 M. Di Mauro63 L. Di Venere61,62 A.
Domı́nguez80 C. Favuzzi61,62 Y. Fukazawa81 S. Funk82 P.
Fusco61,62
F. Gargano62 D. Gasparrini74,75 N. Giglietto61,62 F.
Giordano61,62 M. Giroletti77 T. Glanzman63 D. Green83,67 I. A.
Grenier84
S. Guiriec85,67 A. K. Harding67 E. Hays67 J.W. Hewitt86‡ D.
Horan69 G. Jóhannesson87,88 M. Kuss89 S. Larsson90,91I. Liodakis63
F. Longo58,59 F. Loparco61,62 P. Lubrano75 J. D. Magill83 S.
Maldera64 A. Manfreda57 M. N. Mazziotta62
I.Mereu92 P. F. Michelson63 T. Mizuno93 M. E. Monzani63 A.
Morselli94 I. V. Moskalenko63 M. Negro64,65 E. Nuss68
N. Omodei63 M. Orienti77 E. Orlando63 J. F. Ormes95 M.
Palatiello58,59 V. S. Paliya56 M. Persic58,96 M.
Pesce-Rollins89
V. Petrosian63 F. Piron68 T. A. Porter63 G. Principe82 S.
Rainò61,62 B. Rani67 M. Razzano89,97 S. Razzaque98 A.
Reimer99,63
O. Reimer99,63 C. Sgrò89 E. J. Siskind100 G. Spandre89 P.
Spinelli61,62 H. Tajima101,63 M. Takahashi102 J. B. Thayer63
D. J. Thompson67 D. F. Torres103,104 E. Torresi105 E. Troja67,83
J. Valverde69 K. Wood106 M. Yassine58,59
(Fermi-LATCollaboration),
(Affiliations can be found after the references)
Accepted XXX. Received YYY; in original form ZZZ
© 2017 The Authors
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2 The MAGIC, HAWC and Fermi-LAT Collaborations
ABSTRACTThe HAWC Collaboration released the 2HWC catalog of TeV
sources, in which 19show no association with any known high-energy
(HE; E & 10 GeV) or very-high-energy (VHE; E & 300 GeV)
sources. This catalog motivated follow-up studies by boththe MAGIC
and Fermi -LAT observatories with the aim of investigating
gamma-rayemission over a broad energy band. In this paper, we
report the results from the firstjoint work between HAWC, MAGIC and
Fermi -LAT on three unassociated HAWCsources: 2HWC J2006+341, 2HWC
J1907+084∗ and 2HWC J1852+013∗. Although nosignificant detection
was found in the HE and VHE regimes, this investigation showsthat a
minimum 1◦ extension (at 95% confidence level) and harder spectrum
in theGeV than the one extrapolated from HAWC results are required
in the case of 2HWCJ1852+013∗, while a simply minimum extension of
0.16◦ (at 95% confidence level) canalready explain the scenario
proposed by HAWC for the remaining sources. Moreover,the hypothesis
that these sources are pulsar wind nebulae is also investigated in
detail.
Key words: gamma rays: general – gamma rays: individual: (2HWC
J2006+341,2HWC J1907+084∗, 2HWC J1852+013∗) – pulsars: general
1 INTRODUCTION
The synergy of current gamma-ray observatories is aunique
opportunity to explore the Universe between afew tens of MeV to
hundreds of TeV. The study of sucha broad energy band can be
accomplished by means ofdifferent detection techniques. At the
highest energies arethe Water Cherenkov arrays, such as the High
AltitudeWater Cherenkov (HAWC) Observatory, which is sensitiveto
cosmic and gamma rays between 100 GeV and 100TeV. A large effective
area and high duty cycle makeHAWC an optimal instrument to perform
survey studieson multi-TeV sources. Other detection techniques
acheivea better sensitivity than HAWC at energies below
ap-proximately 10 TeV: the Imaging Atmospheric CherenkovTelescope
(IACT) technique, as implemented by the MajorAtmospheric Gamma-ray
Imaging Cherenkov (MAGIC)telescopes, provides better angular and
energy resolution.However, the duty cycle of such atmospheric
Cherenkovtelescopes is greatly reduced by high-intensity
backgroundlight or non-optimal weather conditions at night. At
evenlower energies (∼ GeV), detectors on board satellites, likethe
Fermi-Large Area Telescope (LAT), are used to detectgamma rays.
This instrument has a high duty cycle, awide field of view (FoV) of
20% of the sky and very goodgamma/hadron separation.
HAWC has published two catalogs of TeV sources:1HWC for sources
in the inner Galactic plane using 275days of data with a
configuration of approximately one-third of the full array
(HAWC-111; Abeysekara et al. 2016),and 2HWC for almost the entire
sky using 507 days of thecompleted HAWC detector (Abeysekara et al.
2017c). Thesecond catalog improves over the first with respect to
ex-posure time, detector size and angular resolution, resultingin a
significant improvement in sensitivity. As done for theprevious
catalog, 2HWC data was analyzed using a binnedlikelihood method
described in Younk et al. (2015). In this
? [email protected]† [email protected]‡
[email protected]
method a source model needs to be assumed for all sourcesin the
sky. The model for each source is characterized by thesource
morphology and its spectrum. For the 2HWC anal-ysis, HAWC used two
different approaches: (1) a point-likesearch adopting a spectrum
defined by a power-law func-
tion, dN/dE = N0(EE0
)−Γ(with N0 the normalization, E0
the pivot energy and Γ the spectral index), with spectral in-dex
Γ = 2.7, and (2) extended source searches with a sourcemorphology
modeled as a uniform disk of 0.5◦, 1◦ and 2◦in radius and spectral
index Γ = 2.0. The total number ofsources identified in this
catalog was 39, of which 19 were notassociated with any previously
reported TeV source withinan angular distance of 0.5◦. All 2HWC
sources presented atest statistic (TS) above 25 (equivalent to a
pre-trial signifi-cance of ∼ 5σ).
The 2HWC catalog motivated follow-up studies withH.E.S.S.
(López-Coto et al. 2017), VERITAS (Park et al.2017) and also MAGIC
and Fermi-LAT. In this work, wefocused on the 19 sources with no
high-energy (HE; E & 10GeV) or very-high-energy (VHE; E &
300 GeV) associa-tion, in order to provide new multi-wavelength
informationof candidates without a lower energy counterpart. After
eval-uating those sources, a short list of three targets was
se-lected: 2HWC J2006+341 (RA = 301.55◦, Dec = 34.18◦),2HWC
J1907+084∗ (RA = 286.79◦, Dec = 8.50◦) and2HWC J1852+013∗ (RA =
283.01◦, Dec = 1.38◦). Thesesources were chosen because they lie in
the FoV of previ-ous MAGIC observations, allowing MAGIC to analyze
thesesources without performing new dedicated observations.
Even though the HAWC spectra of each source weredetermined using
a likelihood fit, the 2HWC catalog didnot use a likelihood method
to describe multiple sources si-multaneously. In the 2HWC catalog,
the asterisk of 2HWCJ1907+084* and 2HWC J1852+013* indicates that
thesources were near another source with larger significance
andthus their characterization may be influenced by
neighboringsources. 2HWC J2006+340, 2HWC J1907+084* and
2HWCJ1852+013* were detected in the point source search
withsignificances of 6.10σ, 5.80σ and 8.50σ, respectively.
Thecorresponding photon index and flux normalization valuesobtained
in the 2HWC catalog are listed in Table 1. Their
MNRAS 000, 1–12 (2017)
mailto:[email protected]:[email protected]@unf.edu
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MAGIC and Fermi-LAT results on HAWC sources 3
Table 1. Coordinates, photon index, flux at the pivot energy (7
TeV) and energy range for the analyzed sources. Values are
provided
in the 2HWC catalog, except for the energy range, which was
obtained in a dedicated analysis. Only statistical uncertainties
are shown.
Based on a study of the Crab Nebula by HAWC (Abeysekara et al.
2017b), the systematic uncertainty can be divided into
severalcomponents: 0.10◦ in angular resolution, 0.2 in photon
index, and 50% in flux normalization.
RA Dec l b 1σ stat. error Photon index Flux normalization Energy
range
[◦] [◦] [◦] [◦] [◦] [×10−15 TeV−1cm−2s−1] [TeV]2HWC J2006+341
301.55 34.18 71.33 1.16 0.13 2.64 ± 0.15 9.6 ± 1.9 1 – 862HWC
J1907+084∗ 286.79 8.50 42.28 0.14 0.27 3.25 ± 0.18 7.3 ± 2.5 0.18 –
102HWC J1852+013∗ 283.01 1.38 34.23 0.50 0.13 2.90 ± 0.10 18.2 ±
2.3 0.4 – 50
Table 2. Distance in degrees between the four MAGIC wobble
pointing positions (W1, W2, W3 and W4) and the selected
2HWCsources. The total time after data quality cuts, in hours,
achieved by MAGIC in each case is also shown.
W1 W2 W3 W4
Distance [◦] ttotal [h] Distance [◦] ttotal [h] Distance [◦]
ttotal [h] Distance [◦] ttotal [h]2HWC J2006+341 0.5 16.0 0.9 14.0
0.4 16.3 1.0 14.8
2HWC J1907+084∗ 0.5 1.0 1.2 1.0 0.7 1.3 1.1 0.92HWC J1852+013∗
1.1 30.8 0.7 28.8 1.2 29.6 0.6 27.5
corresponding energy range is computed with a dedicatedHAWC
analysis (see Section 2.1) and also given in the ta-ble.
The paper is structured as follows: in Section 2, thedata
analysis for MAGIC and Fermi-LAT observations arepresented.
Description of the specific HAWC analysis on theselected sources is
also included. The observations and re-sults, for each source
separately, are shown in Section 3.Discussion and conclusion can be
found in Sections 4 and 5,respectively.
2 DATA ANALYSIS
2.1 HAWC
The HAWC Observatory is the second generation of ground-based
gamma-ray extensive air shower arrays, located inSierra Negra,
Mexico (19.0◦N, 97.3◦ W, 4100 m a.s.l.), andsuccessor to the
Milagro Gamma-ray Observatory. The cur-rent system, inaugurated on
March 20 2015, is comprisedof 300 water Cherenkov detectors (WCD)
over an area of22,000 m2. Science operations began before detector
com-pletion, under the HAWC-111 configuration. The
angularresolution of HAWC varies with event size (fraction of
photo-multiplier tubes reporting a signal or fhit) from 0.17◦ to
1.0◦(Abeysekara et al. 2017b). HAWC operates with > 95%
dutycycle with a large FoV of 15% of the sky, which allows it
toscan two-thirds of the sky every 24 hours.
Information presented here on 2HWC J2006+341,2HWC J1907+084* and
2HWC J1852+013* is taken mostlyfrom the 2HWC catalog Abeysekara et
al. (2017c). The onlyexception is the energy range shown in Table
1. The likeli-hood analysis in HAWC is computed over fhit bins,
whichcan be considered an energy estimator. However, the fhitbins
depend strongly on the declination and spectral hard-ness of each
source, and so does this fhit/energy correla-tion. The energy range
is then given as a constraint on thephoton distribution as a
function of fhit for each separatesource. Following Abeysekara et
al. (2017c), we take the en-ergy range as the boundaries within
which the events con-tribute to the 75% of the TS value.
2.2 MAGIC
MAGIC is a stereoscopic system of two 17 m diame-ter IACTs
situated on the Canary island of La Palma,Spain (28.8◦N, 17.8◦ W,
2225 m a.s.l.). The current systemachieves an integral sensitivity
of 0.66 ± 0.03% of the CrabNebula flux (CU) in 50 hours of
observation above 220 GeV(Aleksić et al. 2016). The energy
threshold in stereoscopicmode is as low as 50 GeV at low zenith
angles under darkobservational conditions (Aleksić et al.
2012).
The analysis presented in this work is performed usingthe
standard MAGIC analysis software (MARS; Zanin et al.2013). The
significance is computed following Eq. 17 of Li &Ma (1983).
Differential and integral flux upper limits (ULs)are calculated
using the Rolke algorithm (Rolke et al. 2005)with a confidence
level (CL) of 95%, assuming a Poissonianbackground and a total
systematic uncertainty of 30%.
As mentioned above, the three analyzed sources wereincluded in
the FoV of former MAGIC observations. Thesearchival data were taken
using the false-source trackingmode, or wobble-mode: the telescopes
point at four differ-ent positions located 0.4◦ from the nominal
source, whichallows us to evaluate the background simultaneously
(Fominet al. 1994). Thus, our observations were not dedicated tothe
2HWC sources and so, their coordinates are shifted fromthe camera
center by different distances than the standardoffset of 0.4◦ (see
Figure 1). To account for their location inthe camera, the
background used in the calculation of ULswas evaluated through the
off-from-wobble-partner (OfWP)method (Zanin et al. 2013). Table 2
summarizes the dis-tances between the camera center and the 2HWC
sourcesat the four different wobble positions. The total
observationtime, after data quality cuts, for each case is also
quoted inTable 2. It is worth highlighting that the MAGIC
sensitivitydepends on the angular offset from the pointing
direction.However, after the MAGIC upgrade of 2011–2012, the
sensi-tivity at offset angles larger than 0.4◦ improved
considerablyas shown by Aleksić et al. (2016). For the analysis
performedin this work, and given the range of angular offsets for
allthe candidates, the sensitivity remains between ∼ 0.6 − 1.0%
CU.
Observations of 2HWC J1852+013∗ were carried out en-
MNRAS 000, 1–12 (2017)
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4 The MAGIC, HAWC and Fermi-LAT Collaborations
tirely under dark conditions, i.e. in absence of moonlight.
Onthe other hand, 2HWC J2006+341 and 2HWC J1907+084∗
were observed with nominal high-voltage at background lev-els
ranging between 1 and 8 times the brightness of the darksky due to
different Moon phases. The higher the moonlightlevel, the brighter
is the night sky background and therefore,stronger cuts to the
signal are applied during this analysis,following the prescription
of Ahnen et al. (2017). This istaken into account by selecting
appropriate Monte Carlo-simulated gamma-ray and background data to
match theobservational conditions. The background data are used
forthe computation of the gamma/hadron separation throughthe Random
Forest (RF), a multi-dimensional classificationalgorithm based on
decision trees (Albert et al. 2008).
Since the three HAWC sources each have a maximumsignificance in
the point-source HAWC maps, they may bepoint-like sources for MAGIC
as well. Therefore, we analyzethe candidates under two hypotheses:
we assume that thesources are point-like for MAGIC (point spread
function;PSF . 0.10◦, beyond a few hundred GeV) or are extendedwith
a radius of 0.16◦. Larger extensions cannot be adopteddue to the
OfWP method and the standard 0.4◦ offsetapplied in the wobble
pointing mode, because the expectedregion of gamma-ray emission
from the 2HWC source andthe background regions selected to compute
flux ULs wouldoverlap.
2.3 Fermi-LAT
The LAT on board the Fermi Gamma-Ray Space Telescopehas
continuously monitored the sky since 2008. It is sensitiveto HE
gamma rays between 20 MeV and ∼1 TeV (Atwoodet al. 2009) and scans
the entire sky every 3 hours. For thiswork we used data taken
between 2008 August and 2017February based on the Pass 8 SOURCE
photon reconstruc-tion. The Pass 8 data offer two primary benefits
for thestudy of HE gamma-ray sources: a greater acceptance
com-pared with previous LAT reconstructions and an improvedPSF with
a 68% containment angle less than 0.2◦ above 10GeV that is nearly
constant with increasing energy (Atwoodet al. 2013).
For each source of interest we analyze energies between10 GeV
and 1 TeV using the standard binned likelihoodframework provided by
the Fermi Science Tools (v10r01p01).Data within a 10◦ radius of
interest were binned into 8 en-ergy bins per decade and a spatial
bin size of 0.05◦. We usedthe recommended Galactic and isotropic
backgrounds1.
We did not extend our analysis to lower energies fortwo primary
reasons: for any HAWC source to be detectedat lower energies, it
must be detectable at >10 GeV with theLAT, unless the HAWC and
LAT emission is produced bya different component; and this
high-energy cut suppressesphotons from gamma-ray pulsars and
Galactic diffuse emis-sion in the plane. As a source model for this
analysis weuse the Third Catalog of Hard Fermi-LAT Sources for
point
1 Galactic interstellar emission model: gll iem v06. f
its,Isotropic: iso P8R2 SOURCE V6 v06.txt. Please
see:http://fermi.gsfc.nasa.gov/ssc/data/access/lat/
BackgroundModels.html
sources (3FHL; Ajello et al. 2017) and the Fermi
GalacticExtended Source (FGES) catalog for extended sources
(Ack-ermann et al. 2017).
Using ∼8.5 years of Pass 8 data, we search for newsources
separately testing both a point or extended sourceat the location
of the HAWC candidate. The spectrum ofthe source is modeled as a
simple power law. After initiallyfitting a putative point source at
the HAWC position, theposition is re-localized. The normalization
of other sourceswithin 5◦ are left as free parameters in the fit.
To search fora possible extended source, we use a uniformly
illuminateddisk with a radius of 0.2◦ as the initial spatial model.
Thef ermipy package (Wood et al. 2017) fits both the radius
andcentroid of the possible extended source. If a
statisticallysignificant source is not found, ULs at the position
of the2HWC source are computed at 95% CL using a Bayesianmethod.
The assumed spectral indices are 2.0, 3.0 and theindex reported in
the 2HWC catalog (see Table 1). Extendedsource ULs are computed
assuming a radius of 0.16◦, forcomparison with the limits placed by
MAGIC.
3 OBSERVATIONS AND RESULTS
In the following section, we describe the different regionsof
the sky that contain the three selected sources, alongwith the
corresponding observations and results. MAGICdifferential ULs are
listed in Table 3, while Fermi-LAT in-tegral ULs (above 10 GeV) are
quoted in Table 4 for bothpoint-like and extended hypotheses.
Figure 1 presents theMAGIC significance skymaps for 2HWC J2006+341
and2HWC J1907+084∗ assuming an extended source with a0.16◦ radius.
A smaller 1◦× 1◦ MAGIC significance skymapcentered in 2HWC
J1852+013∗ is shown in Figure 2. Theskymap of the entire FoV for
this source will be included ina dedicated MAGIC paper on the
surrounding region thatis in preparation. The flat significance
field displayed in allskymaps is compatible with background in the
entire FoV.The multiwavelength spectral energy distribution (SED)
foreach 2HWC source is presented in Figure 3.
3.1 2HWC J2006+341
2HWC J2006+341 is in the FoV (at ∼ 0.63◦) of the com-pact
radio/optical nebula G70.7+1.2, which is thought tobe powered by a
pulsar/binary system interacting with asurrounding molecular cloud.
An unidentified source, 3FHLJ2004.2+3339, was detected at the
position of this putativebinary system. Therefore, VHE gamma-ray
emission fromthe G70.7+1.2 region could be expected due to the
interac-tion between the pulsar wind with both the stellar wind
ofthe companion star and the molecular cloud.
MAGIC observed 3FHL J2004.2+3339 with an ex-tended range of
zenith angles from 5◦ to 50◦. The total datasample amounts to ∼ 61
hours of good quality data fromApril 2015 to August 2016. No
significant signal is found inthe direction of 2HWC J2006+341 as
either a point-like orextended source. In order to calculate the
integral flux ULs,MAGIC adopts a power-law distribution with photon
indexΓ = 2.64, following the HAWC results. Under point-like
as-sumption, the integral UL, computed at 95% CL for
energiesgreater than 300 GeV, is 4.0× 10−13 photons cm−2s−1,
while
MNRAS 000, 1–12 (2017)
http://fermi.gsfc.nasa.gov/ssc/data/access/lat/BackgroundModels.htmlhttp://fermi.gsfc.nasa.gov/ssc/data/access/lat/BackgroundModels.html
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MAGIC and Fermi-LAT results on HAWC sources 5
Table 3. MAGIC differential ULs (at 95% CL) for 2HWC J2006+341,
2HWC J1907+084∗ and 2HWC J1852+013∗ assuming a power-law spectrum
with spectral index of Γ = 2.64, 3.25, and 2.90, respectively. ULs
for both point-like (. 0.10◦) and extended (∼ 0.16◦radius)
assumptions are shown in each case. Due to low statistics, ULs at
the highest energy ranges are not always computed for 2HWCJ2006+341
and 2HWC J1907+084∗
Energy range 2HWC J2006+341 2HWC J1907+084∗ 2HWC J1852+013∗
[GeV] [photons cm−2s−1]Point-like Extended Point-like Extended
Point-like Extended
139.2 – 300.0 2.6×10−11 6.2×10−11 7.1×10−11 3.1×10−10 1.7×10−11
4.6×10−11300.0 – 646.3 1.4×10−12 1.0×10−11 8.0×10−12 1.7×10−11
8.6×10−13 4.9×10−12646.3 – 1392.5 2.5×10−13 1.3×10−12 2.5×10−12
2.3×10−12 9.0×10−14 3.9×10−131392.5 – 3000.0 6.0×10−14 9.9×10−14
1.7×10−13 1.0×10−12 6.7×10−14 1.2×10−133000.0 – 6463.3 1.8×10−14
2.7×10−14 – 1.4×10−13 7.6×10−15 1.3×10−146463.3 – 13924.8 –
9.5×10−15 – 1.3×10−14 1.1×10−14 5.5×10−14
for 0.16◦ radius, it increases to 3.3× 10−12 photons cm−2s−1.On
the other hand, the integral UL for a point-like sourcein the
direction of 3FHL J2004.2+3339 is 4.3 × 10−13 pho-tons cm−2s−1 for
energies above 300 GeV and assuminga power-law index of 2.6. In the
GeV regime, no knownFermi catalog source is found to be coincident
with 2HWCJ2006+341. The closest Fermi-LAT source is the
alreadymentioned 3FHL J2004.2+3339 (coincident within the
errorswith 3FGL J2004.4+338, Acero et al. 2015). This source
hasbeen searched extensively for pulsations (Clark et al.
2017).Using the analysis method described in Section 2.3, no
sig-nificant (TS ≥ 25) source is detected using either the pointor
extended source models.
3.2 2HWC J1907+084∗
2HWC J1907+084∗ is located at ∼ 0.79◦ from 1HWCJ1904+080c,
included in the first HAWC survey. 1HWCJ1904+080c was detected with
a pre-trial significance of5.14σ, which motivated MAGIC follow-up
observations. Thecoordinates were not coincident with any known TeV
source,although it was close (at 0.3◦) to a Fermi-LAT
gamma-rayhotspot ( 300 GeV and indexΓ = 3.25 are 2.8 × 10−12
photons cm−2s−1 and 4.6 × 10−12photons cm−2s−1 for the point-like
and extended hypothe-ses, respectively. MAGIC does not find any
significant excessat the position of 1HWC J1904+080c either, which
leads toan integral flux UL for energies greater than 300 GeV of4.1
× 10−12 photons cm−2s−1, assuming a power-law spec-trum of Γ = 2.6.
From the Fermi-LAT, the Pass 8 analy-sis yields no significant
emission in the direction of 2HWCJ1907+084∗, either during the
point-like or the extendedanalysis.
3.3 2HWC J1852+013∗
2HWC J1852+013∗ is located in the FoV of the W44 SNR,as well as
in the FoV of the established VHE sources HESSJ1858+020 and HESS
J1857+026 (subdivided in 2 emissionsites MAGIC J1857.2+0263 and
MAGIC J1857.6+0297;MAGIC Collaboration et al. 2014). The region was
thusextensively observed by the MAGIC collaboration. 2HWCJ1852+013∗
is also located at 0.56◦ away from 3FGLJ1852.8+0158, which is
classified as a probable young pul-sar using machine learning
techniques (Saz Parkinson et al.2016).
The dataset used by MAGIC here comprises approx-imately 120
hours of dark quality data, taken from April2013 to June 2014, with
a span in zenith range from 25◦to 50◦. MAGIC does not find any
excess in the directionof 2HWC J1852+013∗. Adopting Γ = 2.90, the
constraining95% CL integral ULs are 3.8×10−13 photons cm−2s−1 for
thepoint-like search and 1.7×10−12 photons cm−2s−1 for the
ex-tended search. Specific background selection using OfWPwas
applied in this case, ensuring that no background con-trol region
overlaps with any of the several VHE emittingsources in the FoV. As
per the previous sources, ULs aregiven for E > 300 GeV. Neither
cataloged nor new sourcesfrom the Pass 8 analysis arises in the
Fermi-LAT analysisof 2HWC J1852+013∗.
4 DISCUSSION
Given that the largest population of TeV emitters inour Galaxy
are pulsar wind nebulae (PWNe; see e.g.H.E.S.S. Collaboration et
al. 2018a), the selected candidatesmay be expected to be this
source type. However, the lackof a detection by either MAGIC or
Fermi-LAT complicatesthe identification of these sources. In order
to investigatetheir possible PWN nature, we look for detected
pulsars nearthese 2HWC sources using the ATNF catalog2
(Manchesteret al. 2005). According to the characteristic ages of
the pul-sars around the three selected 2HWC sources (all above afew
tens of kyr), if these pulsars had high initial kick veloci-ties,
they could now be significantly offset from their initialpositions
and have left behind an old PWN with no com-pact object powering
it. In this case, the pulsar position isshifted from the PWN, and
without injection of magnetic
2 http://www.atnf.csiro.au/people/pulsar/psrcat/
MNRAS 000, 1–12 (2017)
-
6 The MAGIC, HAWC and Fermi-LAT Collaborations
-4 -3 -2 -1 0 1 2 3 4
287.5 287.0 286.5 286.0 285.5 285.0
9.5
9.0
8.5
8.0
7.5
7.0
RA [degrees]
Dec
[deg
rees
]
PSF
1HWC J1904+080c
2HWC J1907+084*
W1
W4
W2
W3
3FGL J1904.9+0818
302.5 302.0 301.5 301.0 300.5 300.0 299.5
35.0
34.5
34.0
33.5
33.0
32.5
RA [degrees]
Dec
[deg
rees
]
PSF
3FHL J2004.2+3339
2HWC J2006+341
W3
W1 W2
W4
Figure 1. MAGIC significance skymaps for the FoV of 2HWC
J2006+341 and 2HWC J1907+084∗, searching for sources of ∼ 0.16◦
radius.The four different wobble positions, to which MAGIC pointed
during the 3FHL J2004.2+3339 and 1HWC J1904+080c observations,
are
tagged with W1, W2, W3 and W4 in white color. MAGIC PSF is shown
in orange at the left bottom in each panel. Left panel: Skymap
of the observations at the direction of 3FHL J2004.2+3339
(yellow diamond). This FoV contains 2HWC J2006+341 (orange
diamond)located at ∼ 0.63◦ from the nominal position of MAGIC
observations. Centered at the position of 2HWC J2006+341, the
orange dashedcircle corresponds to the assumed extension of 0.16◦
used for the MAGIC analysis. The HAWC contours (4σ, 5σ and 6σ) are
shown asgreen solid lines. Right panel: Skymap for the observations
of the 1HWC J1904+080c (yellow diamond) FoV in which 2HWC
J1907+084∗
(orange diamond) is enclosed. Dashed orange circle represents
the 0.16◦ MAGIC extended assumption, while HAWC contours (at
thelevel of 5σ) are shown as green solid lines. The position of the
closest Fermi-LAT source, 3FGL J1904.9+0818, is marked as a
reddiamond.
Table 4. Fermi-LAT 95% CL flux ULs, above 10 GeV, assuming
point-like source and extended source a radius of 0.16◦.
ΓHAWC Γ=2.0 Γ = 3.0Point-like Extended Point-like Extended
Point-like Extended
[×10−11 photons cm−2s−1] [×10−11 photons cm−2s−1] [×10−11
photons cm−2s−1]J2006+341 2.4 4.4 2.3 4.7 2.4 4.2J1907+084* 3.1 3.1
2.7 2.7 3.2 3.2
J1852+013* 2.1 3.7 2.0 3.3 2.0 3.7
flux, the nebula’s emission is expected to be dominated
byinverse Compton(IC).
PSR J2004+3429 is the closest known pulsar to 2HWCJ2006+341 at a
separation of 0.40◦, and is the only onewithin a 1◦ radius. This
pulsar lies at a distance of 10 kpc,displays a spin-down power of
ÛE = 5.8 × 1035 erg s−1 andhas a characteristic age of τ = 18 kyr.
Although energeticenough to power a TeV PWN (see H.E.S.S.
Collaborationet al. 2018b), the distance between 2HWC J2006+341
andPSR J2004+3429 makes this connection improbable: giventhe
characteristic age of 18 kyr, an offset of 0.40◦ (∼ 70pc) could
only be explained with an improbably large kickvelocity for the
pulsar of ∼ 4000 km s−1. The mean 2-Dspeed for both young and old
(< 3 Myr) pulsars was deter-mined to be only 307 ± 47 km s−1 by
Hobbs et al. (2005)with a study involving a subsample of ∼ 50
pulsars’ propermotion. The offset may be cosiderably less when
consider-
ing HAWC systematic and statistical errors on the 2HWCsource
location of 0.40◦± 0.10◦syst± 0.13◦stat . Assuming themost
constraining possible value, 0.24◦, the necessary kickvelocity
would decrease to ∼ 2300 km s−1. This value is notfar away from the
fastest known pulsar at ∼ 1500 km s−1(Hobbs et al. 2005), though
that value is also uncertain giventhe distance model applied. The
highest speed for a pulsarwith a well-measured distance is only 640
km s−1. Therefore,we conclude that it is unlikely that PSR
J2004+3429 is di-rectly responsible for the emission detected by
HAWC. Onthe other hand, Linden et al. (2017) evaluated the
proba-bility of random association between 15 2HWC sources andtheir
nearby pulsars, including 2HWC J2006+341 and PSRJ2004+3429. For
this case, they obtained a chance overlapof only 8% (assuming a
source extension of 0.9◦ as providedin the 2HWC catalog by
assigning the halo-like structures
MNRAS 000, 1–12 (2017)
-
MAGIC and Fermi-LAT results on HAWC sources 7
Figure 2. 1◦× 1◦ MAGIC significance skymap, looking for
0.16◦extended sources around 2HWC J1852+013∗, whose position
isdepicted as an orange diamond. Dashed orange circle shows the
extension of 0.16◦ analyzed by MAGIC, whilst the green solid
linecorresponds to the 8σ HAWC contour.
visible in the residual skymaps to 2HWC J2006+341, whichpresents
its own uncertainties).
There are two pulsars within 0.50◦ of 2HWCJ1907+084∗: PSR
J1908+0833 at 0.30◦, and PSRJ1908+0839 at 0.33◦. The former is
located at a distance of∼ 11 kpc, with a characteristic age of τ =
4.1 Myr and a spin-down power of ÛE = 5.8×1032 erg s−1. The very
low spin-downpower and old age make it unlikely to be currently
poweringa TeV PWN. Alternatively, PSR J1908+0839, at 8.3 kpc
andwith a characteristic age of τ = 1.2 Myr, is more energeticwith
ÛE = 1.5× 1034 erg s−1, so a relation between this pulsarand the
2HWC source cannot be initially ruled out. As donefor 2HWC
J2006+341, we calculate the kick velocity for thepulsar, now with
an offset of 0.33◦ and a characteristic ageof 1.2 Myr. The obtained
velocity is ∼ 40 km s−1, which islow relative to the average kick
velocity observed throughproper motion studies but remains to be a
valid possibility(see Figure 4b from Hobbs et al. 2005). This
velocity stayswithin the young pulsars’ 2-D speed distribution even
con-sidering HAWC uncertanties (0.33◦± 0.10◦syst± 0.27◦stat).We can
compare PSR J1908+0839 with the pulsar hostedby Geminga, a
well-known TeV PWN detected by Mila-gro (Abdo et al. 2009) and
recently by HAWC (Abeysekaraet al. 2017a). Geminga’s pulsar
displays a spin-down powerof ÛE = 3.25 × 1034 erg s−1, very similar
to that shown byPSR J1908+0839, but its distance is ∼ 30 times
smaller(dGeminga = 250 pc). Given the similar spin-down power,
thenebula PSR J1908+0839 powers should also have a compara-ble
luminosity with respect to Geminga’s PWN, which would
lead to a flux around three orders of magnitude smaller thanthe
flux of Geminga and undetectable by HAWC. Therefore,it is unlikely
that 2HWC J1907+084∗ and PSR J1908+0839are associated with one
another.
Finally, the closest pulsar to the source 2HWCJ1852+013∗ is PSR
J1851+0118, offset by only 0.10◦. Thispulsar lies at a distance of
5.6 kpc and has a charac-teristic age of ∼ 100 kyr (Yao et al.
2017). If both ob-jects are related the required pulsar velocity is
a reason-able value of ∼ 100 km s−1, though this may be as high as∼
245 km s−1 when considering the largest offset given by0.10◦±
0.10◦syst± 0.13◦stat . However, this pulsar has a rel-atively low
spin-down power, ÛE = 7.2 × 1033 erg s−1, whichalong with its high
characteristic age make it unlikely toaccelerate particles that can
emit gamma rays in the TeVregime. To quantitatively test this
scenario, we use the Naimasoftware3 to model the relativistic
parent population of thenon-thermal gamma-ray emission accounting
for different ra-diative models (see Zabalza 2015). To obtain the
emissivityof the electron population that gave rise to the
gamma-rayemission seen by HAWC, we assume that IC is the dom-inant
radiative process and that the electron spectrum isdefined by a
simple power law. The target photon field forthis process is
expected to be a combination of cosmic mi-crowave background (CMB)
and infrared (IR) photons. Theassumed energy densities in each case
are standard Galacticvalues of uCMB = 0.25 eV cm−3 and uIR = 0.30
eV cm−3.With such features, the total energy carried by
electronsabove ∼ 10 TeV needed to explain HAWC detection wouldbe
We(> 10 TeV) ∼ 6.0 × 1046 erg.
Alternatively, we consider the cooling time of theseelectrons
(tcool), which is computed as follows (Aharonian2004):
tcool = 3 · 108(
EeGeV
)−1 ( ueV/cm3
)−1[yr] (1)
where Ee = 10 TeV is the electron energy and u is the
totalenergy density of the medium. In this case, we account for
ICand synchrotron losses and hence, assuming a temperatureof ∼ 25 K
for the IR photon field (Moderski et al. 2005), ucan be described
as:
u ' B2
8π+uCMB
(1 + 0.01 · Ee
TeV
)−3/2+uIR
(1 + 0.1 · Ee
TeV
)−3/2(2)
where B is the magnetic field. We use the aforementioned en-ergy
densities for the CMB and IR photon fields, and for themagnetic
field we assume the minimum possible value givenby the interstellar
magnetic field, B = 3 µG, as there is nomeasured value for the
source. Under these assumptions, thecooling time is tcool ∼ 57 kyr.
Given the spin-down powerof PSR J1851+0118, ÛE = 7.2 × 1033 erg
s−1, the total en-ergy released by the pulsar during the tcool
period wouldbe W ′e ∼ 1.3 × 1046 erg. Consequently, even assuming
thatall the energy released by the pulsar was used to
accelerateelectrons above 10 TeV, there would not be enough
energyto power a PWN with the gamma-ray brightness detected
3 naima.readthedocs.org
MNRAS 000, 1–12 (2017)
naima.readthedocs.org
-
8 The MAGIC, HAWC and Fermi-LAT Collaborations
by HAWC. According to our model, such a PWN would re-quire an
energy injection greater than ∼ 6.0×1046 erg, whichis already
higher than W ′e. The low B and uIR used in thiscalculation of
tcool provide maximum values for both tcooland the injected pulsar
energy, W ′e. Higher uIR value wouldproduce higher losses and
therefore, a smaller We. However,an extremely high value for uIR
(well above 2 eV cm−3, theIR energy density observed around
Cassiopea A and one ofthe highest for a Galactic TeV source) would
be needed todecrease We below 1046 erg. We do not consider more
com-plex scenarios in which ÛE or B change with time. The
sameparent population study was applied to 2HWC J1907+084∗
and we reach the same conclusions that corroborated
thenon-relation with the surrounding pulsars.
MAGIC and LAT ULs also help to constrain our under-standing of
the spectrum and morphology of these HAWCsources. The SEDs for the
three candidate PWNe are shownin Figure 3. MAGIC and Fermi-LAT
analyses are computedwith the photon index provided by HAWC (see
Table 1). Inthe cases of 2HWC J2006+341 and 2HWC J1907+084∗,
theMAGIC and LAT extended ULs are at the level of theHAWC spectrum
considering HAWC systematic errors of0.2 in the photon index and
50% in the flux normalization.However, point-like hypotheses are in
contradiction withHAWC results below energies of ∼ 4 TeV and ∼ 900
GeV,respectively. Therefore, it is expected that these two
2HWCsources are extended, with at least a radius of ∼ 0.16◦. Onthe
other hand, both MAGIC and Fermi-LAT results on2HWC J1852+013∗ are
incompatible with the HAWC spec-trum below energies of ∼ 10
TeV.
These results can be understood in two ways: 2HWCJ1852+013∗ is
much more extended than the assumed radiusof 0.16◦, which would
increase MAGIC and Fermi-LAT ULsabove the flux estimated by HAWC;
or the source does notemit in the sub-TeV regime, consistent with
the constrainingULs obtained by both MAGIC and the LAT. In the
latercase, the spectral shaped of 2HWC J1852+013∗ would havea
harder spectrum in the sub-TeV regime, and a minimumenergy of
around 10 TeV, instead of 400 GeV, should beassumed (see Table 1).
To constrain the former case, wecalculated LAT ULs for disks of
larger radii. For a disk of1.0◦ radius the LAT UL at energies >
0.2 TeV is within 1σstatistical errors of the measured HAWC flux,
extrapolatedto lower energies. However, this would also require a
harderspectrum in the GeV regime so as to not exceed LAT ULsat
lower energies. Additionally, as reported in the 2HWCcatalog
Abeysekara et al. (2017c), there may be a significantcontribution
from diffuse galactic emission at the location of2HWC J1852+013* to
which HAWC would be sensitive andMAGIC would not.
5 CONCLUSION
After the release of the 2HWC catalog, MAGIC and Fermi-LAT
performed dedicated analyses on three new TeV sourcesdetected by
the wide FoV observatory HAWC. None of themwere detected at lower
energies and no hotspot was foundnear them. However, owing to the
increased time and goodquality data of most of the MAGIC and the
Fermi-LATobservations, constraints on the extension of the
sourceswere possible. With this aim, we performed both
point-like
and extended source searches. For 2HWC J2006+341 and2HWC
J1907+084∗, a radius of ∼ 0.16◦ is viable given lim-its from the
extended source search by MAGIC. For 2HWCJ1852+013∗, MAGIC and
Fermi-LAT results with respect toHAWC spectra suggest a much larger
extension or a harderspectrum below ∼ 10 TeV. Moreover, we find
that none of theknown pulsars in the vicinity of 2HWC J2006+341,
2HWCJ1907+084∗ or 2HWC J1852+013∗ are likely to directlypower these
objects. It may be that these 2HWC sourcesare PWN created by as yet
un-detected pulsars, or havesome other origin such as a Galactic
supernova remnant.More sensitive observations in the near future
will providevaluable information on the nature of these sources and
helpto disentangle features in the crowded regions.
ACKNOWLEDGEMENTS
The MAGIC Collaboration would like to thank theInstituto de
Astrof́ısica de Canarias for the excellentworking conditions at the
Observatorio del Roque de losMuchachos in La Palma. The financial
support of theGerman BMBF and MPG, the Italian INFN and INAF,
theSwiss National Fund SNF, the ERDF under the SpanishMINECO
(FPA2015-69818-P, FPA2012-36668, FPA2015-68378-P,
FPA2015-69210-C6-2-R, FPA2015-69210-C6-4-R,FPA2015-69210-C6-6-R,
AYA2015-71042-P, AYA2016-76012-C3-1-P, ESP2015-71662-C2-2-P,
CSD2009-00064),and the Japanese JSPS and MEXT is gratefully
acknowl-edged. This work was also supported by the Spanish Centrode
Excelencia “Severo Ochoa” SEV-2012-0234 and SEV-2015-0548, and
Unidad de Excelencia “Maŕıa de Maeztu”MDM-2014-0369, by the
Croatian Science Foundation(HrZZ) Project 09/176 and the University
of Rijeka Project13.12.1.3.02, by the DFG Collaborative Research
CentersSFB823/C4 and SFB876/C3, and by the Polish MNiSzWgrant
745/N-HESS-MAGIC/2010/0.The HAWC Collaboration acknowledges the
supportfrom: the US National Science Foundation (NSF) the
USDepartment of Energy Office of High-Energy Physics; theLaboratory
Directed Research and Development (LDRD)program of Los Alamos
National Laboratory; Consejo Na-cional de Ciencia y Tecnoloǵıa
(CONACyT), México (grants271051, 232656, 260378, 179588, 239762,
254964, 271737,258865, 243290, 132197, 281653)(Cátedras 873,
1563),Laboratorio Nacional HAWC de rayos gamma; L’OREALFellowship
for Women in Science 2014; Red HAWC, México;DGAPA-UNAM (grants
IG100317, IN111315, IN111716-3,IA102715, 109916, IA102917,
IN112218); VIEP-BUAP;PIFI 2012, 2013, PROFOCIE 2014, 2015; the
Universityof Wisconsin Alumni Research Foundation; the Instituteof
Geophysics, Planetary Physics, and Signatures at LosAlamos National
Laboratory; Polish Science Centre grantDEC-2014/13/B/ST9/945;
Coordinación de la Investi-gación Cient́ıfica de la Universidad
Michoacana; RoyalSociety - Newton Advanced Fellowship 180385.
Thanksto Scott Delay, Luciano Dı́az and Eduardo Murrieta
fortechnical support.The Fermi-LAT Collaboration acknowledges
generousongoing support from a number of agencies and
institutesthat have supported both the development and the
oper-ation of the LAT as well as scientific data analysis.
These
MNRAS 000, 1–12 (2017)
-
MAGIC and Fermi-LAT results on HAWC sources 9
include the National Aeronautics and Space Administrationand the
Department of Energy in the United States,the Commissariat à
l’Energie Atomique and the CentreNational de la Recherche
Scientifique / Institut National dePhysique Nucléaire et de
Physique des Particules in France,the Agenzia Spaziale Italiana and
the Istituto Nazionaledi Fisica Nucleare in Italy, the Ministry of
Education,Culture, Sports, Science and Technology (MEXT),
HighEnergy Accelerator Research Organization (KEK) andJapan
Aerospace Exploration Agency (JAXA) in Japan,and the K. A.
Wallenberg Foundation, the Swedish Re-search Council and the
Swedish National Space Board inSweden. This work performed in part
under DOE ContractDE-AC02-76SF00515.
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10 The MAGIC, HAWC and Fermi-LAT Collaborations
101 102 103 104 105Energy [GeV]
10 14
10 13
10 12
10 11
10 10
E2 dN dE
[TeV
cm
2 s1 ]
2HWC J2006+341Fermi-LAT point-likeFermi-LAT 0.16 radiusMAGIC
point-likeMAGIC 0.16 radiusHAWCHAWC systematics
101 102 103 104 105Energy [GeV]
10 14
10 13
10 12
10 11
10 10
10 9
10 8
E2 dN dE
[TeV
cm
2 s1 ]
2HWC J1907+084*Fermi-LAT 0.16 radiusFermi-LAT point-likeMAGIC
0.16 radiusMAGIC point-likeHAWCHAWC systematics
101 102 103 104 105Energy [GeV]
10 14
10 13
10 12
10 11
10 10
10 9
10 8
E2 dN dE
[TeV
cm
2 s1 ]
2HWC J1852+013*Fermi-LAT point-likeFermi-LAT 0.16 radiusMAGIC
point-likeMAGIC 0.16 radiusHAWCHAWC systematics
Figure 3. Spectral energy distribution from 10 GeV up to ∼ 90
TeV. In all cases, the assumed spectrum for the sources is a
power-lawfunction with photon index Γ = 2.64 for 2HWC J2006+341
(top), Γ = 3.25 for 2HWC J1907+084∗ (middle) and Γ = 2.90 for
2HWCJ1852+013∗ (bottom), as obtained by HAWC (see Table 1).
Fermi-LAT 95% confidence level ULs for 0.16◦ disk and point-like
hypothesesare shown with dashed green and light green lines,
respectively. MAGIC 95% confidence level ULs are displayed for both
a point-like
hypothesis (light orange) and a 0.16◦ radial extension (orange).
The HAWC spectrum (dark blue) is obtained for the parameters
givenin Table 1. The light blue band indicates the HAWC spectrum
taking into account 1σ systematic errors of 0.2 and 50% in the
photon
index and flux, respectively.
MNRAS 000, 1–12 (2017)
-
MAGIC and Fermi-LAT results on HAWC sources 11
1 ETH Zurich, CH-8093 Zurich, Switzerland2 Università di Udine,
and INFN Trieste, I-33100 Udine,Italy3 National Institute for
Astrophysics (INAF), I-00136Rome, Italy4 Università di Padova and
INFN, I-35131 Padova, Italy5 Technische Universität Dortmund,
D-44221 Dortmund,Germany6 Croatian MAGIC Consortium: University of
Rijeka, 51000Rijeka, University of Split - FESB, 21000 Split,
Universityof Zagreb - FER, 10000 Zagreb, University of Osijek,31000
Osijek and Rudjer Boskovic Institute, 10000 Zagreb,Croatia.7 Saha
Institute of Nuclear Physics, HBNI, 1/AF Bidhan-nagar, Salt Lake,
Sector-1, Kolkata 700064, India8 Max-Planck-Institut für Physik,
D-80805 München,Germany9 Now at Centro Brasileiro de Pesquisas
F́ısicas (CBPF),22290-180 URCA, Rio de Janeiro (RJ), Brasil10
Unidad de Part́ıculas y Cosmoloǵıa (UPARCOS), Uni-versidad
Complutense, E-28040 Madrid, Spain11 Inst. de Astrof́ısica de
Canarias, E-38200 La Laguna, andUniversidad de La Laguna, Dpto.
Astrof́ısica, E-38206 LaLaguna, Tenerife, Spain12 University of
Lódź, Department of Astrophysics, PL-90236 Lódź, Poland13
Deutsches Elektronen-Synchrotron (DESY), D-15738Zeuthen, Germany14
Institut de F́ısica d’Altes Energies (IFAE), The BarcelonaInstitute
of Science and Technology (BIST), E-08193 Bel-laterra (Barcelona),
Spain15 Università di Siena and INFN Pisa, I-53100 Siena, Italy16
Universität Würzburg, D-97074 Würzburg, Germany17 Finnish MAGIC
Consortium: Tuorla Observatory andFinnish Centre of Astronomy with
ESO (FINCA), Univer-sity of Turku, Vaisalantie 20, FI-21500
Piikkiö, AstronomyDivision, University of Oulu, FIN-90014
University of Oulu,Finland18 Departament de F́ısica, and
CERES-IEEC, UniversitatAutónoma de Barcelona, E-08193 Bellaterra,
Spain19 Universitat de Barcelona, ICC, IEEC-UB, E-08028Barcelona,
Spain20 Japanese MAGIC Consortium: ICRR, The Universityof Tokyo,
277-8582 Chiba, Japan; Department of Physics,Kyoto University,
606-8502 Kyoto, Japan; Tokai University,259-1292 Kanagawa, Japan;
The University of Tokushima,770-8502 Tokushima, Japan21 Inst. for
Nucl. Research and Nucl. Energy, BulgarianAcademy of Sciences,
BG-1784 Sofia, Bulgaria22 Università di Pisa, and INFN Pisa,
I-56126 Pisa, Italy23 Humboldt University of Berlin, Institut für
PhysikD-12489 Berlin Germany24 also at Dipartimento di Fisica,
Università di Trieste,I-34127 Trieste, Italy25 also at Port
d’Informació Cient́ıfica (PIC) E-08193,Bellaterra (Barcelona)
Spain26Physics Division, Los Alamos National Laboratory, LosAlamos,
NM, USA27Instituto de F́ısica, Universidad Nacional Autónoma
deMéxico, Ciudad de México, Mexico28Universidad Autónoma de
Chiapas, Tuxtla Gutiérrez,Chiapas, Mexico29Universidad Michoacana
de San Nicolás de Hidalgo,Morelia, Mexico30Department of Physics,
Pennsylvania State University,
University Park, PA, USA31Department of Physics & Astronomy,
University ofRochester, Rochester, NY , USA32Instituto de
Astronomı́a, Universidad Nacional Autónomade México, Ciudad de
México, Mexico33Department of Physics, University of
Wisconsin-Madison,Madison, WI, USA34Instituto Nacional de
Astrof́ısica, Óptica y Electrónica,Puebla, Mexico35Institute of
Nuclear Physics Polish Academy of Sciences,PL-31342 IFJ-PAN,
Krakow, Poland36Facultad de Ciencias F́ısico Matemáticas,
BeneméritaUniversidad Autónoma de Puebla, Puebla,
Mexico37Departamento de F́ısica, Centro Universitario de Cien-cias
Exactas e Ingenieŕıas, Universidad de Guadalajara,Guadalajara,
Mexico38School of Physics, Astronomy, and Computational Sci-ences,
George Mason University, Fairfax, VA, USA39Department of Physics,
University of Maryland, CollegePark, MD, USA40Instituto de
Geof́ısica, Universidad Nacional Autónomade México, Ciudad de
México, Mexico41Department of Physics, Michigan Technological
Univer-sity, Houghton, MI, USA42NASA Marshall Space Flight Center,
Astrophysics Office,Huntsville, AL 35812, USA43Max-Planck Institute
for Nuclear Physics, 69117 Heidel-berg, Germany44Dept of Physics
and Astronomy, University of NewMexico, Albuquerque, NM,
USA45School of Physics and Center for Relativistic Astrophysics-
Georgia Institute of Technology, Atlanta, GA, USA 3033246Department
of Physics and Astronomy, Michigan StateUniversity, East Lansing,
MI, USA47Universidad Politecnica de Pachuca, Pachuca,
Hgo,Mexico48Centro de Investigación en Computación,
InstitutoPolitécnico Nacional, Mexico City, Mexico49Physics
Department, Centro de Investigación y de Estu-dios Avanzados del
IPN, Mexico City, DF, Mexico50Universidad Autónoma del Estado de
Hidalgo, Pachuca,Mexico51Instituto de Ciencias Nucleares,
Universidad NacionalAutónoma de México, Ciudad de México,
Mexico52Department of Physics and Astronomy, University ofUtah,
Salt Lake City, UT, USA53Santa Cruz Institute for Particle Physics,
University ofCalifornia, Santa Cruz, Santa Cruz, CA,
USA54Department of Physics, Stanford University: Stanford,CA
94305âĂŞ4060, USA55Department of Physics and Astronomy.
University ofCalifornia. Irvine, CA 92697, USA56Department of
Physics and Astronomy, Clemson Univer-sity, Kinard Lab of Physics,
Clemson, SC 29634-0978, USA57Università di Pisa and Istituto
Nazionale di Fisica Nucle-are, Sezione di Pisa I-56127 Pisa,
Italy58Istituto Nazionale di Fisica Nucleare, Sezione di
Trieste,I-34127 Trieste, Italy59Dipartimento di Fisica, Università
di Trieste, I-34127Trieste, Italy60California State University, Los
Angeles, Department ofPhysics and Astronomy, Los Angeles, CA 90032,
USA61Dipartimento di Fisica “M. Merlin” dell’Università e
delPolitecnico di Bari, I-70126 Bari, Italy62Istituto Nazionale di
Fisica Nucleare, Sezione di Bari,I-70126 Bari, Italy
MNRAS 000, 1–12 (2017)
-
12 The MAGIC, HAWC and Fermi-LAT Collaborations
63W. W. Hansen Experimental Physics Laboratory, KavliInstitute
for Particle Astrophysics and Cosmology, De-partment of Physics and
SLAC National AcceleratorLaboratory, Stanford University, Stanford,
CA 94305, USA64Istituto Nazionale di Fisica Nucleare, Sezione di
Torino,I-10125 Torino, Italy65Dipartimento di Fisica, Università
degli Studi di Torino,I-10125 Torino, Italy66Department of Physics
and Astronomy, University ofPadova, Vicolo Osservatorio 3, I-35122
Padova, Italy67NASA Goddard Space Flight Center, Greenbelt,
MD20771, USA68Laboratoire Univers et Particules de Montpellier,
Uni-versité Montpellier, CNRS/IN2P3, F-34095
Montpellier,France69Laboratoire Leprince-Ringuet, École
polytechnique,CNRS/IN2P3, F-91128 Palaiseau, France70Center for
Research and Exploration in Space Science andTechnology (CRESST)
and NASA Goddard Space FlightCenter, Greenbelt, MD 20771,
USA71INAF-Istituto di Astrofisica Spaziale e Fisica CosmicaMilano,
via E. Bassini 15, I-20133 Milano, Italy72Harvard-Smithsonian
Center for Astrophysics, Cam-bridge, MA 02138, USA73Italian Space
Agency, Via del Politecnico snc, 00133Roma, Italy74Space Science
Data Center - Agenzia Spaziale Italiana,Via del Politecnico, snc,
I-00133, Roma, Italy75Istituto Nazionale di Fisica Nucleare,
Sezione di Perugia,I-06123 Perugia, Italy76Dipartimento di Fisica e
Astronomia “G. Galilei”, Univer-sità di Padova, I-35131 Padova,
Italy77INAF Istituto di Radioastronomia, I-40129 Bologna,
Italy78Dipartimento di Astronomia, Università di Bologna,I-40127
Bologna, Italy79Università Telematica Pegaso, Piazza Trieste e
Trento,48, I-80132 Napoli, Italy80Grupo de Altas Enerǵıas,
Universidad Complutense deMadrid, E-28040 Madrid, Spain81Department
of Physical Sciences, Hiroshima University,Higashi-Hiroshima,
Hiroshima 739-8526, Japan82Friedrich-Alexander-Universität
Erlangen-Nürnberg,Erlangen Centre for Astroparticle Physics,
Erwin-Rommel-Str. 1, 91058 Erlangen, Germany83Department of
Astronomy, University of Maryland,College Park, MD 20742,
USA84Laboratoire AIM, CEA-IRFU/CNRS/Université ParisDiderot,
Service d’Astrophysique, CEA Saclay, F-91191 Gifsur Yvette,
France85The George Washington University, Department ofPhysics, 725
21st St, NW, Washington, DC 20052, USA86University of North
Florida, Department of Physics, 1UNF Drive, Jacksonville, FL 32224
, USA87Science Institute, University of Iceland, IS-107
Reykjavik,Iceland88Nordita, Royal Institute of Technology and
StockholmUniversity, Roslagstullsbacken 23, SE-106 91
Stockholm,Sweden89Istituto Nazionale di Fisica Nucleare, Sezione di
Pisa,I-56127 Pisa, Italy90Department of Physics, KTH Royal
Institute of Technol-ogy, AlbaNova, SE-106 91 Stockholm,
Sweden91The Oskar Klein Centre for Cosmoparticle Physics,AlbaNova,
SE-106 91 Stockholm, Sweden92Dipartimento di Fisica, Università
degli Studi di Perugia,I-06123 Perugia, Italy93Hiroshima
Astrophysical Science Center, Hiroshima
University, Higashi-Hiroshima, Hiroshima 739-8526,
Japan94Istituto Nazionale di Fisica Nucleare, Sezione di Roma“Tor
Vergata”, I-00133 Roma, Italy95Department of Physics and Astronomy,
University ofDenver, Denver, CO 80208, USA96Osservatorio
Astronomico di Trieste, Istituto Nazionaledi Astrofisica, I-34143
Trieste, Italy97Funded by contract FIRB-2012-RBFR12PM1F from
theItalian Ministry of Education, University and
Research(MIUR)98Department of Physics, University of Johannesburg,
POBox 524, Auckland Park 2006, South Africa99Institut für Astro-
und Teilchenphysik and Institut fürTheoretische Physik,
Leopold-Franzens-Universität Inns-bruck, A-6020 Innsbruck,
Austria100NYCB Real-Time Computing Inc., Lattingtown, NY11560-1025,
USA101Solar-Terrestrial Environment Laboratory, Nagoya Uni-versity,
Nagoya 464-8601, Japan102Max-Planck-Institut für Physik, D-80805
München,Germany103Institute of Space Sciences (CSICIEEC), Campus
UAB,Carrer de Magrans s/n, E-08193 Barcelona, Spain104Institució
Catalana de Recerca i Estudis Avançats(ICREA), E-08010 Barcelona,
Spain105INAF-Istituto di Astrofisica Spaziale e Fisica
CosmicaBologna, via P. Gobetti 101, I-40129 Bologna, Italy106Praxis
Inc., Alexandria, VA 22303, resident at NavalResearch Laboratory,
Washington, DC 20375, USAThis paper has been typeset from a
TEX/LATEX file prepared by
the author.
MNRAS 000, 1–12 (2017)
1 Introduction2 Data Analysis2.1 HAWC2.2 MAGIC2.3 Fermi-LAT
3 Observations and Results3.1 2HWC J2006+3413.2 2HWC
J1907+084*3.3 2HWC J1852+013*
4 Discussion5 Conclusion
