Search for TeV emission from the region around PSR B1706-44 with the H.E.S.S. experiment

0.21 MB·English

by  H. E. S. S. Collaboration

Astronomy & Astrophysics manuscript no. pwn˙1706 February 2, 20108
(DOI: will be inserted by hand later)
Search for TeV emission from the region around PSR B1706–44
with the H.E.S.S. experiment
1 2 3 4 5 1
F. Aharonian , A.G. Akhperjanian , K.-M. Aye , A.R. Bazer-Bachi , M. Beilicke , W. Benbow ,
D. Berge1, P. Berghaus6 ⋆, K. Bernlo¨hr1,7, C. Boisson8, O. Bolz1, C. Borgmeier7, I. Braun1, F. Breitling7,
A.M. Brown3, J. Bussons Gordo9, P.M. Chadwick3, L.-M. Chounet10, R. Cornils5, L. Costamante1,20,
B. Degrange10, A. Djannati-Ata¨i6, L.O’C. Drury11, G. Dubus10, T. Ergin7, P. Espigat6, F. Feinstein9,
10 10 12 1 9 10 1 13
P. Fleury , G. Fontaine , Y. Fuchs , S. Funk , Y.A. Gallant , B. Giebels , S. Gillessen , P. Goret ,
3 14 5 12 1 1
C. Hadjichristidis , M. Hauser , G. Heinzelmann , G. Henri , G. Hermann , J.A. Hinton ,
W. Hofmann1, M. Holleran15, D. Horns1, O.C. de Jager15, I. Jung1,14 ⋆⋆, B. Kh´elifi1, Nu. Komin7,
5 A. Konopelko1,7, I.J. Latham3, R. Le Gallou3, A. Lemi`ere6, M. Lemoine10, N. Leroy10, T. Lohse7,
0 A. Marcowith4, C. Masterson1,20, T.J.L. McComb3, M. de Naurois16, S.J. Nolan3, A. Noutsos3,
0
2 K.J. Orford3, J.L. Osborne3, M. Ouchrif16,20, M. Panter1, G. Pelletier12, S. Pita6, G. Pu¨hlhofer1,14,
M. Punch6, B.C. Raubenheimer15, M. Raue5, J. Raux16, S.M. Rayner3, I. Redondo10,20⋆⋆⋆, A. Reimer17,
n
17 5 18 16 1 2 12 7
O. Reimer , J. Ripken , L. Rob , L. Rolland , G. Rowell , V. Sahakian , L. Saug´e , S. Schlenker ,
a
17 17 7 17 8 19 7
J R. Schlickeiser , C. Schuster , U. Schwanke , M. Siewert , H. Sol , R. Steenkamp , C. Stegmann ,
4 J.-P. Tavernet16, R. Terrier6, C.G. Th´eoret6, M. Tluczykont10,20, G. Vasileiadis9, C. Venter15,
2 P. Vincent16, B. Visser15, H.J. V¨olk1, and S.J. Wagner14

1
v 1 Max-Planck-Institutfu¨r Kernphysik,P.O. Box 103980, D 69029 Heidelberg, Germany
2 2 YerevanPhysics Institute,2 Alikhanian Brothers St., 375036 Yerevan,Armenia
1 3 Universityof Durham,Department of Physics, South Road,Durham DH13LE, U.K.
5 4 Centred’EtudeSpatialedesRayonnements,CNRS/UPS,9av.duColonelRoche,BP4346,F-31029 Toulouse
1
Cedex 4, France
0 5 Universit¨at Hamburg, Institut fu¨r Experimentalphysik, LuruperChaussee 149, D 22761 Hamburg, Germany
5 6 PhysiqueCorpusculaireetCosmologie,IN2P3/CNRS,Coll`egedeFrance,11PlaceMarcelinBerthelot,F-75231
0
Paris Cedex 05, France
/
h 7 Institutfu¨r Physik, Humboldt-Universit¨atzu Berlin, Newtonstr. 15, D 12489 Berlin, Germany
p 8 LUTH,UMR 8102 du CNRS, Observatoirede Paris, Section deMeudon, F-92195 Meudon Cedex, France
- 9 Groupe d’Astroparticules de Montpellier, IN2P3/CNRS, Universit´e Montpellier II, CC85, Place Eug`ene
o
r Bataillon, F-34095 Montpellier Cedex 5, France
t 10 Laboratoire Leprince-Ringuet,IN2P3/CNRS, Ecole Polytechnique,F-91128 Palaiseau, France
s
a 11 DublinInstitute for AdvancedStudies, 5 Merrion Square, Dublin 2, Ireland
: 12 Laboratoire d’AstrophysiquedeGrenoble, INSU/CNRS,Universit´eJoseph Fourier, BP 53, F-38041 Grenoble
v
i Cedex 9, France
X 13 Serviced’Astrophysique,DAPNIA/DSM/CEA,CE Saclay, F-91191 Gif-sur-Yvette, France
r 14 Landessternwarte, K¨onigstuhl, D 69117 Heidelberg, Germany
a 15 Unit for Space Physics, North-West University,Potchefstroom 2520, South Africa
16 Laboratoire de PhysiqueNucl´eaire et de HautesEnergies, IN2P3/CNRS, Universit´es Paris VI & VII,4 Place
Jussieu, F-75231 Paris Cedex 05, France
17 Institutfu¨rTheoretischePhysik,LehrstuhlIV:WeltraumundAstrophysik,Ruhr-Universit¨atBochum,D44780
Bochum, Germany
18 Institute of Particle and Nuclear Physics, Charles University, V Holesovickach 2, 180 00 Prague 8, Czech
Republic
19 Universityof Namibia, Private Bag 13301, Windhoek,Namibia
20 European Associated Laboratory for Gamma-Ray Astronomy,jointly supported by CNRS and MPG
Accepted by Astronomy & Astrophysics
Abstract.
TheregionaroundPSRB1706–44hasbeenobservedwiththeH.E.S.S.imagingatmosphericCherenkovtelescopes
in 2003. No evidence for γ-ray emission in the TeV range was found at the pulsar position or at the radio arc
whichcorrespondstothesupernovaremnantG343.1–2.3. The99%confidencelevelfluxupperlimitatthepulsar
position isF (E>350GeV)=1.4×10−12s−1cm−2 assuming apowerlaw(dN/dE ∝E−Γ)withphotonindexof
ul
Γ=2.5 and F (E>500GeV)=1.3×10−12s−1cm−2 without an assumption on thespectral shape. The reported
ul
upperlimits correspond to 8% of theflux from an earlier detection by theCANGAROOexperiment.
Key words. Gamma rays: observations – ISM: individual objects: PSRB1706–44 – ISM: supernova remnants –
ISM: individualobjects: G343.1–2.3
1. Introduction
250
s
PSRB1706–44 is a young pulsar (spin-down age of nt
∼17kyrs) with distance estimates ranging from 1.8 to ve
E
3.2kpc with a period of 102ms and a spin-down lumi- 200
nosityofabout1%oftheCrabpulsar(3.4×1036ergs−1).
Pulsed emission has been observed at radio and X-ray
wavelengths,andinGeVγ-rays.Anextendedsynchrotron 150
nebulaaroundthiscompactobjecthasbeenfoundinradio nts60
observations(Giacani et al. 2002)withanextensionof1’– Eve40
4’andwithaflatspectrum(energyindexof0.3),andalso 100 20
inX-rays(Gotthelf et al. 2002)withanextensionof∼20” 0
andwithaphotonindexof1.34.Thesecharacteristicssug- -20
50
gest the existence of a pulsar wind nebula (PWN) pow- -40
ered by the pulsar. In the TeV range, the CANGAROO 0 0.05 0.1 0.15 0.2 0.25 0.3
q 2 (deg.)
experimentdetectedasteadyemissioncoincidentwiththe 0
0 0.05 0.1 0.15 0.2 0.25 0.3
PWN position at a level of roughly 50% of the Crab flux q 2 (deg.)
(Kifune et al. 1995; Kushida et al. 2003), suggesting that Fig.1.θ2distributioncalculatedwithrespecttothePWN
this PWN is the southern equivalent of the Crab nebula.
position. The dots denote events from the ON region,the
TheDurhamMark6collaboration(Chadwicketal.1998)
histogram are the events from the OFF region scaled by
reportedalsoasignificantdetectionabove300GeV.Aflux
the normalization factor α. The dashed vertical line indi-
upper limit above 500GeV which is compatible with the
cates the applied angular cut. The inset shows the differ-
CANGAROO flux has been derived using data from the
ence between the ON and the scaled OFF regions.
BIGRAT telescope (Rowell et al. 1998).
PSRB1706–44 is coincident with an incomplete
ing phase, GPS time stamps were used in the offline data
arc of radio emission (McAdam et al. 1993) which has
analysistoidentifyshowersobservedincoincidencebythe
been interpreted as a shell-type supernova remnant
two telescopes. This coincidence requirement allows for a
(SNR) named G343.1–2.3. This SNR has been de-
higher background rejection and thus for a better sensi-
tected only at radio wavelengths (Duncan et al. 1995)
tivity than single telescope observations. In this configu-
and may be associated with the pulsar as discussed in
ration, a source with a flux of 5% of Crab nebula can be
Bock & Gvaramadze (2002). detectedwithmorethan5σ in4.5hoursat20◦ zenithan-
We present here the results of the observation
gle. The pulsar was observed with 28-min runs in wobble
of the field of view around PSR B1706–44 with mode, whereby runs are taken pointing ±0.5◦ away from
the H.E.S.S. experiment. H.E.S.S. is an atmospheric
the pulsar position in declination. Data affected by hard-
Cherenkov detector dedicated to the observation of
ware problems or bad weather conditions were excluded
TeV γ-rays (Hofmann 2003). Situated in Namibia, the
fromanalysis.The properfunctioning ofthe detectorsys-
full four-telescope array is operational since December
temwasverifiedbynumerouschecks.Thetelescopepoint-
2003. Each telescope has a mirror area of 107 m2
ing has been confirmedby correlatinghigh PMT currents
(Bernl¨ohr et al. 2003) and is equipped with a cam-
with bright stars in the field of view. The trigger rate of
era consisting of 960 photomultiplier tubes (PMT)
the system is well reproduced by simulations for cosmic
◦
(Vincent et al. 2003).Thesystemhasafieldofviewof5 .
rays, and the shape of simulated γ-ray images is consis-
In stereoscopic observation mode, it allows one to recon-
tentwiththe resultofCrabobservations.Dataanalysisis
structthe directionofindividual showerswith a precision
performed with two completely independent chains with
better than 0.1◦.
differentcalibrations,with independentMonte Carlosim-
ulations and with different analysis techniques.
The selected data have a total live time of 14.3 hours.
2. Observations and data analysis
The energy threshold estimated from Monte Carlo sim-
PSRB1706–44wasobservedwithtwoH.E.S.S.telescopes ulations at the average observation zenith angle (∼26◦)
between April and July 2003. During this commission- is about 350GeV. This threshold is higher than for
the four-telescope system since the telescopes were op-
Send offprint requests to: Bruno.Khelifi@mpi-hd.mpg.de
erated with higher trigger thresholds in the commission-
⋆
Universit´e Libre de Bruxelles, Facult´e des Sciences,
ing phase. Data were analysed using standard shower
Campus de la Plaine, CP230, Boulevard du Triomphe, 1050
reconstruction and standard background rejection meth-
Bruxelles, Belgium
⋆⋆ ods (Aharonian et al. 2004). Standard cuts, optimised on
now at Washington Univ., Department of Physics, 1
Monte Carlo simulations, have been applied on mean
Brookings Dr., CB 1105, St.Louis, MO 63130, USA
⋆⋆⋆ now at Department of Physics and Astronomy, Univ. of scaled Hillas parameters in order to increase the signal-
Sheffield, The Hicks Building, Hounsfield Road, Sheffield S3 to-backgroundratio.Showerswereclassifiedusingthe an-
7RH,U.K. gulardistanceθbetweentheirreconstructeddirectionand
F. Aharonian et al.: Observation of PSR B1706–44 with H.E.S.S. 3
the direction of possible source. For this standard analy-
sOisN,srheogwioenrs)wwehreenacthceepirteθd2awsacsomsminagllefrromthatnhe0s.o0u2rdceeg(rtehee2 eg) −1.5 4
d 3
(i.e. angular distance smaller than 8.5′). The background at. ( −2
was determined by counting events in a ring (the OFF L 2
region)centeredat the investigateddirection whose inner al.
G
radius is larger(>0.4◦) than the θ2 cut andwhose areais −2.5 1
7 times larger than the ON region. A normalization fac- 0
tor α is applied to these estimated background counts to
correct for the different size of ON and OFF regions and −3 −1
the different radial acceptance in the field of view.
−2
−3.5 −3
3. Results
−4
A plot of θ2 relative to the PWN position is shown
342 342.5 343 343.5 344
in Figure 1. The significance, calculated according to
Gal. Long. (deg)
Li & Ma (1983), is 0.1σ. Table 1 provides an overview of Fig.2. Significance map centered on PSR B1706–44.
the event statistics in the column labelled Standard. The The cross marks the pulsar position. The contour
analysisdescribedabovewasrepeatedwiththe same cuts lines correspond to the 2.2GHz image of G343–2.3
for every point in the field of view. The resulting signifi- (Duncan et al. 1995). The solid circle indicates the inte-
cancemapis presentedinFig.2.Itexhibits no significant gration region of the Standard cuts, the dashed circle the
point source excess in the vicinity of the pulsar or on the CANGAROOcutsandthedot-dashedcircletheRadioarc
radio emission arc. cuts. The significance distribution for the entire H.E.S.S.
In order to roughly reproduce the conditions of the fieldofviewiscompatiblewithaGaussianofmean−0.06
PSR B1706–44 detection by CANGAROO, the analysis and of sigma 1.09.
at the pulsar position was repeated using a looser θ2
cut of 0.05degree2 and selecting events above an energy
of 1TeV. The results are shown in the column labelled culates the integrated flux F directly as the difference of
CANGAROO of Table 1 and give no indication for a sig- the measured flux from the ON region and the flux of
nificant excess. For the analysis of the radio arc, a θ2 cosmic-rays from the OFF region:
cut of 0.36degree2 has been applied around the position
(17h08m,−44◦17’) and no significant excess is measured 1 Non 1 Noff 1
(column labelled Radio arc of Table 1). F(>ET)= −α .
T i=1 Ai i=1 Ai!
X X
Standard CANGAROO Radio arc
Here, T is the live time, and both sums on the ON
Non 352 112 4746 and OFF regions run over all showers with reconstructed
Noff 2243 512 13688 energiesgreaterthanET.The effective areas(Ai)depend
α 0.15620 0.19258 0.34592
on the zenith angle and energy of each event, and α is
Excess 1.6±20.2 13.4±11.1 11.0±79.9
the normalization factor. As Ai is determined using the
Significance 0.1σ 1.2σ 0.1σ
reconstructed energy, the energy threshold should be in-
Table 1. Analysis results: Non and Noff are the event creased such that the bias of the reconstructed energy is
numbers in the ON and OFF regions, α is the normal- less than 10%. The upper limits derivedwith both meth-
isation factor. The results are reported for the standard odswerecalculatedusingtheunifiedapproachofFeldman
θ2 cut (column labelled Standard), for the cuts reproduc- & Cousins (1998) and a confidence level of 99%. To com-
ingthe conditionsofthe CANGAROO detection(column pare the upper limits from Method B with a prediction,
CANGAROO) and for the analysis of the radio arc (col- the investigated model spectrum must be integrated over
umn Radio arc). all energies starting at ET.
Table 2 gives the values of flux upper limits at 99%
Limits on the integral flux above certain energies ET confidencelevelforvariouscutsandmethods;bothmeth-
were obtained using two different methods. The first ods give similar results. With method A, the upper limit
method (Method A) tests the hypothesis that the num- atthePWNpositioncorrespondsto∼1%ofthefluxfrom
ber of excess events with energies above ET result from a the Crab Nebula (at the same energy threshold) and the
source with a power law spectrum with a (positive) pho- upper limit for the radio arc corresponds to ∼5% of the
ton index Γ. The photon index was varied between 2 and flux from the Crab Nebula. The upper limit which repro-
3. This rangeincludes the value of Γ=2.5from the earlier duces the experimental conditions of the CANGAROO
CANGAROO detection. The second method (Method B) experiment corresponds to ∼8% of the flux reported by
makes no assumption about the source spectrum and cal- that collaboration.
4 F. Aharonian et al.: Observation of PSR B1706–44 with H.E.S.S.
−1−2 sm10−10 UUppppeerr lliimmiittss ((MMeetthh.. AA)):: GG == 32 Esuqr.em6eonftAofhatrhoeniflaunxeitnatl.he(1X99-r7a)y. Tbhanisdrefrqoumiretshea smaemae-
c electron population that emits the hypothetical TeV ra-
E) Upper limits: Meth. B
> CANGAROO (95) diation. Measurements by Chandra (Gotthelf et al. 2002)
F(
−11 CANGAROO (00/01) provide a flux from the PWN, excluding the point-like
10
Durham Mark 6 (98)
emissionofthe centralsource;however,theirchosenanal-
BIGRAT (98) ′′
ysis region (radius less than 10 ) is smaller than the full
−12 extent of the PWN, for which Finley et al. (1998) found
10
′′
a best-fit exponential scale length of 27 . The flux mea-
sured by ASCA (Finley et al. 1998) encompasses the en-
10−13 tire PWN, but also includes the pulsar emission. To esti-
mate the PWN flux, we used the ASCA spectrum but
subtracted a point source contribution estimated from
10−14 ROSAT HRI to be (43±12)% (Finley et al. 1998), yield-
1 Energy (TeV) ing an unabsorbed flux of 5.5 × 10−13erg s−1 cm−2 in
Fig.3. Integralupper limits at 99% CL for the flux from the 2–10keV band for the PWN. The lack of observable
thePWNposition(solid,dottedanddot-dashedline).The X-ray emission below about 0.5keV due to interstellar
filled circle corresponds to the CANGAROO detection absorption means that the electrons producing the ob-
served X-rays have somewhat higher energy than those
of Kifune et al. (1995) and the CANGAROO integrated
producing TeV γ-rays,and an extrapolation of the X-ray
flux (grey area) is calculated from the result of a broken
power law fit to the 2000 and 2001 differential spectrum spectrum to lower energies is necessary. The spectral in-
(Kushida et al. 2003).Theopendiamondandthetriangle dex measured with ASCA, Γ=1.7+−00..54, is fully compati-
are from Rowell et al. (1998) and Chadwick et al. (1998), blewiththemoreprecisedeterminationfromBeppoSAX,
respectively. Γ=1.69±0.29(Mineo et al. 2002).Thederivedlowerlimit
on the magnetic field strength is then about 1µG when
oneassumesthatthe inverseComptonscatteringinvolves
Method A Method B
only the photons of the microwave background radiation
Standard 1.4×10−12 (0.35) 1.3×10−12 (0.50) andassumingthesamephotonindexintheX-rayandTeV
CANGAROO 6.4×10−13 (1.00) 7.7×10−13 (1.00) band. This value is however not very constraining given
Radio arc 5.8×10−12 (0.35) 3.5×10−12 (0.50) thatthemeanGalacticmagneticfieldisofthesameorder
of magnitude.
Table 2. Flux upper limits at 99% confidence level for
the pulsar position in s−1cm−2. The upper limits from Acknowledgements. The support of the Namibian authorities
Method A were calculated assuming a photon index of and of the University of Namibia in facilitating the construc-
Γ=2.5.Thenumbersinparenthesesaretheenergythresh- tion and operation of H.E.S.S. is gratefully acknowledged,
olds(inTeV)forwhichtheupper limitsweredetermined. as is the support by the German Ministry for Education
and Research (BMBF), the Max Planck Society, the French
4. Discussion and Conclusions MinistryforResearch,theCNRS-IN2P3andtheAstroparticle
Interdisciplinary Programme of the CNRS, the U.K. Particle
The reported upper limits on the flux of TeV γ-rays are PhysicsandAstronomyResearchCouncil(PPARC),theIPNP
roughly one order of magnitude lower than the reported of the Charles University, the South African Department of
CANGAROO flux and a factor of 55 lower than earlier Science and Technology and National Research Foundation,
and by the University of Namibia. We appreciate the excel-
limits(Rowelletal.1998).TheCANGAROOobservations
lent work of the technical support staff in Berlin, Durham,
werenotcontemporaneouswiththeH.E.S.S.observations,
Hamburg,Heidelberg,Palaiseau,Paris,Saclay,andinNamibia
which raises the question of whether the TeV emission
intheconstructionandoperationoftheequipment.Wewould
could be variable on a time scale of years. Such a vari-
also like to thank the Australia Telescope National Facility
ability seems unlikely given our current understanding of
(ATNF) for provision of 2.2GHzradio data.
PWN (Blondin et al. 2001). Another potential reason for
the discrepancy could be an object confusion along the
References
line of sight. There are, however, no BL Lac objects or
variable galactic TeV γ-ray emitters known around the Aharonian, F., Atoyan A.M. and Kifune T., 1997, MNRAS,
pulsar. It has been pointed out (Aharonian et al. 1997; 291, 162
Kushida et al. 2003) that the high flux level reported by Aharonian, F., Akhperjanian, A.G., Aye, K.-M., et al., 2004,
accepted by Astron. & Astrophys.(astro-ph/0411582)
CANGAROO is surprising. Since the X-ray luminosity is
Becker, W., Brazier, K.T.S., Tru¨mper, J., 1995, Astron. &
about 0.01% of that of the Crab PWN, the TeV γ-rays
Astrophys.,298, 528
should be emitted from a much larger volume than the
Bernl¨ohr, K., Carrol, O., Cornils, R., et al., 2003, APh., 20,
X-rays, according to the inverse Compton (IC) scenario.
111
Using the H.E.S.S. flux upper limit above 1TeV, a Blondin,J.M.,Chevalier,R.A.,Frierson,D.M.,2001,ApJ,563,
lower limit on the magnetic field can be derived from 80
F. Aharonian et al.: Observation of PSR B1706–44 with H.E.S.S. 5
Bock, D.C.-J. & Gvaramadze, V.V., 2002, Astron. &
Astrophys., 394, 533
Chadwick, P.M., Dickinson, M.R., Dipper, N.A., et al., 1998,
APh, 9, 131
Duncan,A.R.,Steward,R.T.,Haynes,R.F.,Jones,K.L.,1995,
MNRAS,277, 36
Feldman, G.J. & Cousins, R.D., 1998, Phys. Rev.D, 57, 7
Finley, J.P., Srinivasan, R., Saito, Y., et al., 1998, ApJ, 493,
884
Giacani,E.B.,Frail,D.A.,Goss,W.M.,Vieytes,M.,2001,AJ,
121, 313
Gotthelf,E.V.,Halpern,J.P.,Dodson,R.,2002,ApJ,567,L125
Hofmann, W., 2003, Proc. 28th ICRC, Tsukuba, Univ.
Academy Press, Tokyo, p. 2811
Kifune, T., Tanimori, T., Ogio, S., et al., 1995, ApJ, 438, L91
Kushida, J., Tanimori, T., Kubo, H., et al., Proc. 28th Int.
CosmicRayConf.,Tsukuba(2003),Univ.AcademyPress,
Tokyo, p. 2493
Li, T.-P. & Ma, Y.-Q., 1983, ApJ, 272, 317
McAdam,W.B.,Osborne,J.L.,Parkinson,M.L.,1993,Nature,
361, L516
Mineo, T., Massaro, E., Cusumano, G.,Becker, W., 2002,
Astron. & Astrophys.,392, 181
Rowell, G.P., Dazeley, S.A., Edwards, P.G., Patterson, J.R.,
Thornton, G.J., 1998, APh, 194, 332
Vincent,P.,Denance,J.-P.,Huppert,J.-F.,etal.,2003,Proc.
28thICRC,Tsukuba,Univ.AcademyPress,Tokyo,p.2887