Detection of VHE gamma-ray emission from the distant blazar 1ES 1101-232 with HESS and broadband characterisation

Abstract

Context: The blazar 1ES 1101-232 was observed with the High Energy Stereoscopic System (HESS) of Atmospheric Cherenkov Telescopes (ACT) in 2004 and 2005, for a live time of 43 h. VHE (E > 1011 eV) γ-rays were detected for the first time from this object.

Aims: VHE observations of blazars are used to investigate the inner parts of the blazar jets, and also to study the extragalactic background light (EBL) in the near-infrared band.

Methods: Observations in 2005 were conducted in a multiwavelength campaign, together with the RXTE satellite and optical observations. In 2004, simultaneous observations with XMM-Newton were obtained.

Results: 1ES 1101-232 was detected with HESS with an excess of 649 photons, at a significance of 10σ. The measured VHE γ-ray flux amounts to dN/dE = (5.63 ± 0.89) × 10-13 (E/TeV)-(2.94±0.20) cm-2 s-1 TeV-1, above a spectral energy threshold of 225 GeV. No significant variation of the VHE γ-ray flux on any time scale was found. 1ES 1101-232 exhibits a very hard spectrum, and at a redshift of z = 0.186, is the blazar with the highest confirmed redshift detected in VHE γ-rays so far.

Conclusions: The data allow the construction of truly simultaneous spectral energy distributions of the source, from the optical to the VHE band. Using an EBL model with ν Fν = 14 nW m-2 sr-1 at 1.5 μm as presented in Aharonian et al. (2006a) suggests an intrinsic VHE power output peak of the source at above 3 TeV.

Astronomy & Astrophysics 470, 475-489 (2007)
ArXiv pre-print

Auxiliary informations

H.E.S.S. spectra shown in Figure 4:

H.E.S.S. photon spectrum obtained using the total data set (March 2005 and June 2004 data)

Bin energy	energy error    mean energy     low energy	high energy     flux*            flux error	99% upper	deabs. flux*	deabs. flux	deabs. 99%
						boundary	boundary					limit				error		upper limit
[TeV]		[TeV]		[TeV]		[TeV]		[TeV]		[ph/cm^2/s/TeV]	[ph/cm^2/s/TeV]	[ph/cm^2/s/TeV]	[ph/cm^2/s/TeV]	[ph/cm^2/s/TeV]	[ph/cm^2/s/TeV]

0.262500	0.0375000	0.257254	0.0322540	0.0427460	0.211927E-10	0.108508E-10	---		0.368126E-10	0.188483E-10	---
0.350000	0.0500000	0.343005	0.0430050	0.0569950	0.120307E-10	0.374210E-11	---		0.278940E-10	0.867631E-11	---
0.467000	0.0670000	0.457587	0.0575870	0.0764130	0.697169E-11	0.163461E-11	---		0.239576E-10	0.561720E-11	---
0.623000	0.0890000	0.610549	0.0765490	0.101451	0.311513E-11	0.679648E-12	---		0.171182E-10	0.373478E-11	---
0.830500	0.118500	0.813942	0.101942	0.135058	0.882365E-12	0.333901E-12	---		0.790646E-11	0.299193E-11	---
1.10700		0.158000	1.08492		0.135920	0.180080	0.339341E-12	0.164412E-12	---		0.477126E-11	0.231169E-11	---
1.47600		0.211000	1.44646		0.181460	0.240540	0.984456E-13	0.851139E-13	---		0.199601E-11	0.172570E-11	---
1.96850		0.281500	1.92908		0.242080	0.320920	0.628221E-13	0.505260E-13	---		0.161559E-11	0.129937E-11	---
2.62500		0.375000	2.57254		0.322540	0.427460	0.537810E-13	0.350463E-13	---		0.159679E-11	0.104055E-11	---
3.50050		0.500500	3.43042		0.430420	0.570580	0.429470E-13	0.209872E-13	---		0.139868E-11	0.683504E-12	---
4.66850		0.667500	4.57504		0.574040	0.760960      (-0.944972E-14)  (0.100334E-13)	0.198815E-13  (-0.342878E-12)   (0.364056E-12)	0.721390E-12
6.22550		0.889500	6.10104		0.765040	1.01396	      (-0.245659E-15)  (0.578491E-14)	0.147241E-13  (-0.115537E-13)   (0.272074E-12)	0.692498E-12
8.30150		1.18650		8.13543		1.02043		1.35257	      (-0.391084E-15)  (0.311891E-14)	0.775542E-14  (-0.334422E-13)   (0.266702E-12)	0.663177E-12
11.0705		1.58250		10.8490		1.36100		1.80400	      (-0.418679E-14)  (0.173757E-14)	0.237333E-14  (-0.116821E-11)   (0.484820E-12)	0.662211E-12
14.7630		2.11000		14.4677		1.81470		2.40530	      (-0.925835E-15)  (0.866643E-15)	0.165941E-14  (-0.206821E-11)   (0.193599E-11)	0.370694E-11
19.6865		2.81350		19.2927		2.41970		3.20730	      ( 0.191400E-14)  (0.741210E-15)	0.363968E-14	---		---		---
26.2520		3.75200		25.7269		3.22690		4.27710	      (-0.137607E-15)  (0.211467E-15)	0.453942E-15	---		---		---
35.0075		5.00350		34.3072		4.30320		5.70380	      ( 0.407133E-15)  (0.227542E-15)	0.939667E-15	---		---		---
46.6835		6.67250		45.7495		5.73850		7.60650	      ( 0.173727E-15)  (0.987878E-16)	0.405024E-15	---		---		---
62.2535		8.89750		61.0082		7.65220		10.1428	      (-0.268941E-16)  (0.626697E-16)	0.143096E-15	---		---		---

Remarks: *numbers in brackets are flux values compatible with zero flux, in the figure the corresponding upper limits were shown.

H.E.S.S. photon spectrum obtained using the March 2005 data

Bin energy	energy error    mean energy     low energy	high energy     flux*            flux error	99% upper	deabs. flux*	deabs. flux	deabs. 99%
						boundary	boundary					limit				error		upper limit
[TeV]		[TeV]		[TeV]		[TeV]		[TeV]		[ph/cm^2/s/TeV]	[ph/cm^2/s/TeV]	[ph/cm^2/s/TeV]	[ph/cm^2/s/TeV]	[ph/cm^2/s/TeV]	[ph/cm^2/s/TeV]

0.262500	0.0375000	0.257252	0.0322520	0.0427480	0.273374E-10	0.103372E-10	---		0.474858E-10	0.179560E-10	---
0.350000	0.0500000	0.343002	0.0430020	0.0569980	0.110247E-10	0.405194E-11	---		0.255613E-10	0.939461E-11	---
0.467000	0.0670000	0.457583	0.0575830	0.0764170	0.914223E-11	0.193630E-11	---		0.314153E-10	0.665367E-11	---
0.623000	0.0890000	0.610544	0.0765440	0.101456	0.239554E-11	0.774054E-12	---		0.131643E-10	0.425369E-11	---
0.830500	0.118500	0.813935	0.101935	0.135065	0.100919E-11	0.373049E-12	---		0.904288E-11	0.334272E-11	---
1.10700		0.158000	1.08491		0.135910	0.180090	0.401374E-12	0.190502E-12	---		0.564307E-11	0.267834E-11	---
1.47600		0.211000	1.44645		0.181450	0.240550	0.867792E-13	0.987613E-13	---		0.175922E-11	0.200213E-11	---
1.96850		0.281500	1.92906		0.242060	0.320940	0.427680E-13	0.585150E-13	---		0.109993E-11	0.150492E-11	---
2.62500		0.375000	2.57252		0.322520	0.427480	0.775860E-13	0.406178E-13	---		0.230360E-11	0.120598E-11	---
3.50050		0.500500	3.43039		0.430390	0.570610	0.543816E-13	0.250370E-13	---		0.177110E-11	0.815405E-12	---
4.66850		0.667500	4.57500		0.574000	0.761000      (-0.363529E-14)  (0.118140E-13)	0.279092E-13  (-0.131903E-12)  (0.428661E-12)	0.101266E-11
6.22550		0.889500	6.10099		0.764990	1.01401	      ( 0.200239E-14)  (0.677403E-14)	0.189559E-13  ( 0.941749E-13)  (0.318590E-12)	0.891518E-12
8.30150		1.18650		8.13536		1.02036		1.35264	      (-0.365540E-14)  (0.369783E-14)	0.723492E-14  (-0.312569E-12)  (0.316197E-12)	0.618650E-12
11.0705		1.58250		10.8489		1.36090		1.80410	      (-0.355073E-14)  (0.187143E-14)	0.289037E-14  (-0.990692E-12)  (0.522148E-12)	0.806444E-12
14.7630		2.11000		14.4676		1.81460		2.40540	      (-0.860880E-15)  (0.106315E-14)	0.218418E-14  (-0.192300E-11)  (0.237482E-11)	0.487893E-11
19.6865		2.81350		19.2926		2.41960		3.20740	      ( 0.296845E-14)  (0.958382E-15)	0.519833E-14	---		---		---
26.2520		3.75200		25.7267		3.22670		4.27730	      (-0.109541E-15)  (0.223934E-15)	0.502808E-15	---		---		---
35.0075		5.00350		34.3069		4.30290		5.70410	      (-0.206512E-16)  (0.844348E-16)	0.203035E-15	---		---		---
46.6835		6.67250		45.7492		5.73820		7.60680	      ( 0.245714E-15)  (0.139722E-15)	0.572853E-15	---		---		---

Remarks: *numbers in brackets are flux values compatible with zero flux, in the figure the corresponding upper limits were shown.

H.E.S.S. photon spectrum obtained using the June 2004 data

Bin energy	energy error    mean energy     low energy	high energy     flux*            flux error	99% upper	deabs. flux*	deabs. flux	deabs. 99%
						boundary	boundary					limit				error		upper limit
[TeV]		[TeV]		[TeV]		[TeV]		[TeV]		[ph/cm^2/s/TeV]	[ph/cm^2/s/TeV]	[ph/cm^2/s/TeV]	[ph/cm^2/s/TeV]	[ph/cm^2/s/TeV]	[ph/cm^2/s/TeV]

0.338000	0.0760000	0.320062	0.0580620	0.0939380	0.184496E-10	0.792039E-11	---		0.398112E-10	0.170909E-10	---
0.535500	0.121500	0.506564	0.0925640	0.150436	0.655045E-11	0.204798E-11	---		0.255369E-10	0.798404E-11	---
0.849000	0.192000	0.803423	0.146423	0.237577	0.558272E-12	0.843190E-12	---		0.461804E-11	0.697489E-11	---
1.34550		0.304500	1.27317		0.232170	0.376830	0.212049E-12	0.247203E-12	---		0.365046E-11	0.425564E-11	---
2.13250		0.482500	2.01791		0.367910	0.597090	0.100742E-12	0.109175E-12	---		0.257479E-11	0.279032E-11	---
3.38000		0.765000	3.19826		0.583260	0.946740      (-0.254393E-13)  (0.322368E-13)	0.666048E-13  (-0.795790E-12)  (0.100843E-11)	0.208353E-11
5.35700		1.21200		5.06917		0.924170	1.49983	      (-0.100248E-13)  (0.141491E-13)	0.298909E-13  (-0.414766E-12)  (0.585404E-12)	0.123670E-11
8.49000		1.92100		8.03376		1.46476		2.37724	      ( 0.414467E-14)  (0.547406E-14)	0.173932E-13  ( 0.383275E-12)  (0.506210E-12)	0.160842E-11
13.4555		3.04450		12.7324		2.32140		3.76760	      (-0.288107E-14)  (0.217263E-14)	0.388365E-14  (-0.219161E-09)  (0.165270E-09)	0.295426E-09
21.3255		4.82550		20.1794		3.67940		5.97160	      (-0.766194E-15)  (0.890433E-15)	0.180406E-14	---		---		---
33.7985		7.64750		31.9822		5.83120		9.46380	      ( 0.110813E-14)  (0.578050E-15)	0.245895E-14	---		---		---
53.5670		12.1210		50.6881		9.24210		14.9999	      (-0.747960E-16)  (0.173848E-15)	0.396832E-15	---		---		---

Remarks: *numbers in brackets are flux values compatible with zero flux, in the figure the corresponding upper limits were shown.

X-ray spectra shown in Figure 5:

XMM-Newton spectrum (fit with broken powerlaw and taking into account galactic absorption)

	bin center	low energy	high energy	flux		flux error
	energy		boundary	boundary
	[keV]		[keV]		[keV]		[erg/cm^2/s]	[erg/cm^2/s]
	
	0.21950		0.21200		0.22700		0.29000E-10	0.98507E-12
	0.23550		0.22700		0.24400		0.27037E-10	0.94868E-12
	0.25250		0.24400		0.26100		0.28134E-10	0.96954E-12
	0.27050		0.26100		0.28000		0.26293E-10	0.65995E-12
	0.29000		0.28000		0.30000		0.28799E-10	0.98100E-12
	0.31150		0.30000		0.32300		0.27650E-10	0.67547E-12
	0.33500		0.32300		0.34700		0.30781E-10	0.98499E-12
	0.35900		0.34700		0.37100		0.28168E-10	0.64063E-12
	0.38450		0.37100		0.39800		0.27994E-10	0.59567E-12
	0.41200		0.39800		0.42600		0.26170E-10	0.77794E-12
	0.44150		0.42600		0.45700		0.25963E-10	0.52245E-12
	0.47350		0.45700		0.49000		0.26345E-10	0.41103E-12
	0.50750		0.49000		0.52500		0.27083E-10	0.52227E-12
	0.54350		0.52500		0.56200		0.29332E-10	0.60597E-12
	0.58200		0.56200		0.60200		0.26063E-10	0.48551E-12
	0.62400		0.60200		0.64600		0.27596E-10	0.48328E-12
	0.66900		0.64600		0.69200		0.27289E-10	0.47008E-12
	0.71650		0.69200		0.74100		0.28274E-10	0.47280E-12
	0.76750		0.74100		0.79400		0.28598E-10	0.40735E-12
	0.82250		0.79400		0.85100		0.29315E-10	0.40731E-12
	0.88150		0.85100		0.91200		0.30011E-10	0.41457E-12
	0.94450		0.91200		0.97700		0.28730E-10	0.40903E-12
	1.01200		0.97700		1.04700		0.29242E-10	0.37464E-12
	1.08450		1.04700		1.12200		0.29317E-10	0.38522E-12
	1.16200		1.12200		1.20200		0.29980E-10	0.40291E-12
	1.24500		1.20200		1.28800		0.29833E-10	0.38142E-12
	1.33400		1.28800		1.38000		0.30008E-10	0.40094E-12
	1.42950		1.38000		1.47900		0.29971E-10	0.39162E-12
	1.53200		1.47900		1.58500		0.30279E-10	0.42378E-12
	1.64150		1.58500		1.69800		0.30138E-10	0.46121E-12
	1.75900		1.69800		1.82000		0.28748E-10	0.45084E-12
	1.88500		1.82000		1.95000		0.27256E-10	0.47038E-12
	2.01950		1.95000		2.08900		0.28659E-10	0.50931E-12
	2.16400		2.08900		2.23900		0.27623E-10	0.51064E-12
	2.31900		2.23900		2.39900		0.27543E-10	0.61400E-12
	2.48450		2.39900		2.57000		0.28061E-10	0.65422E-12
	2.66200		2.57000		2.75400		0.25734E-10	0.59745E-12
	2.85250		2.75400		2.95100		0.24761E-10	0.62283E-12
	3.05650		2.95100		3.16200		0.24951E-10	0.63367E-12
	3.27500		3.16200		3.38800		0.24762E-10	0.65957E-12
	3.50950		3.38800		3.63100		0.25806E-10	0.70111E-12
	3.76050		3.63100		3.89000		0.25469E-10	0.70688E-12
	4.02950		3.89000		4.16900		0.25021E-10	0.75900E-12
	4.31800		4.16900		4.46700		0.24651E-10	0.78286E-12
	4.62650		4.46700		4.78600		0.24298E-10	0.84360E-12
	4.95750		4.78600		5.12900		0.25269E-10	0.95718E-12
	5.31200		5.12900		5.49500		0.23595E-10	0.92711E-12
	5.69150		5.49500		5.88800		0.23258E-10	0.11168E-11
	6.09850		5.88800		6.30900		0.22060E-10	0.10812E-11
	6.53500		6.30900		6.76100		0.23039E-10	0.16228E-11
	7.00250		6.76100		7.24400		0.20318E-10	0.14463E-11
	7.50300		7.24400		7.76200		0.19848E-10	0.19902E-11
	8.04000		7.76200		8.31800		0.21832E-10	0.22201E-11
	8.61500		8.31800		8.91200		0.21352E-10	0.21706E-11
	9.23100		8.91200		9.55000		0.18307E-10	0.27253E-11

XTE spectrum shown in Figure 5

           
	mean energy	low energy	high energy	flux		flux error
			boundary	boundary
	[keV]		[keV]		[keV]		[erg/cm^2/s]	[erg/cm^2/s]
	
	3.42499		3.21897		3.63101		0.36051E-10	0.25798E-12
	3.83719		3.63101		4.04337		0.33516E-10	0.24792E-12
	4.24965		4.04337		4.45593		0.31223E-10	0.25452E-12
	4.66236		4.45593		4.86880		0.30082E-10	0.27035E-12
	5.07537		4.86880		5.28193		0.28865E-10	0.29251E-12
	5.48863		5.28193		5.69532		0.28033E-10	0.31833E-12
	5.90214		5.69532		6.10896		0.27521E-10	0.34165E-12
	6.31591		6.10896		6.52286		0.26595E-10	0.36029E-12
	6.72994		6.52286		6.93702		0.26076E-10	0.38124E-12
	7.14426		6.93702		7.35150		0.24980E-10	0.40645E-12
	7.55883		7.35150		7.76616		0.23662E-10	0.44196E-12
	7.97366		7.76616		8.18115		0.23623E-10	0.48072E-12
	8.38878		8.18115		8.59640		0.22762E-10	0.50818E-12
	8.80415		8.59640		9.01190		0.21209E-10	0.53532E-12
	9.21978		9.01190		9.42766		0.20935E-10	0.57856E-12
	9.63567		9.42766		9.84368		0.20230E-10	0.63106E-12
	10.05184	9.84368		10.26001	0.19736E-10	0.69271E-12
	10.46831	10.26001	10.67660	0.18385E-10	0.76472E-12
	10.88503	10.67660	11.09345	0.18226E-10	0.84592E-12
	11.30200	11.09345	11.51055	0.18062E-10	0.92829E-12
	11.71923	11.51055	11.92792	0.16436E-10	0.10223E-11
	12.13676	11.92792	12.34560	0.18230E-10	0.11568E-11
	12.55453	12.34560	12.76347	0.17767E-10	0.13048E-11
	12.97257	12.76347	13.18166	0.15563E-10	0.14564E-11
	13.39092	13.18166	13.60018	0.14141E-10	0.16015E-11
	13.80953	13.60018	14.01888	0.15436E-10	0.17509E-11
	14.22840	14.01888	14.43791	0.15898E-10	0.19124E-11
	14.64755	14.43791	14.85719	0.13380E-10	0.20917E-11

XTE lightcurve shown in Figure 3:

	time		low time	high time	flux			flux lower limit	flux upper limit
			boundary	boundary	
	[MJD-53400]	[MJD-53400]	[MJD-53400]	[10^-11 erg/cm^2/s]	[10^-11 erg/cm^2/s]	[10^-11 erg/cm^2/s]
	
	34.8960		34.8130		34.9791		4.8984			0.46400E-01		0.48400E-01
	35.9646		35.8594		36.0698		4.7351			0.36800E-01		0.43100E-01
	36.9473		36.8430		37.0517		4.7922			0.39100E-01		0.37400E-01
	37.9664		37.8324		38.1004		4.9457			0.48300E-01		0.45600E-01
	38.8938		38.8098		38.9778		5.0004			0.45100E-01		0.49500E-01
	39.9289		39.7930		40.0648		4.9700			0.45600E-01		0.35200E-01
	40.9121		40.7769		41.0474		5.2374			0.53500E-01		0.50900E-01
	41.9275		41.8256		42.0295		5.2984			0.52900E-01		0.54400E-01
	42.9116		42.8109		43.0122		5.4686			0.50800E-01		0.64600E-01
	43.9594		43.8576		44.0613		5.3556			0.65400E-01		0.72600E-01
	44.9251		44.8411		45.0091		5.2370			0.58600E-01		0.70500E-01

Optical spectrum shown in the SED in Figure 6:

XMM-Newton optical monitor (OM) deabsorbed spectrum

	central wavelength	aperture	inner bckgr	outer Bckgr	magnitude	magnitude error		flux		flux error
	[Angstroem]		[pixel]		[pixel]		[pixel]		[mag]		[mag]			[mJy]		[mJy]
	
	5430			12		14		25		16.75		0.03			0.78795		0.02147
	4500			12		14		25		17.36		0.02			0.55099		0.01006
	3440			12		14		25		16.55		0.01			0.40959		0.00376
	2910			12		14		25		16.29		0.20			0.45876		0.07718
	2310			12		14		25		15.99		0.20			0.53886		0.09066

XMM-Newton optical monitor (OM) deabsorbed and host-galaxy subtracted spectrum

	central wavelength	aperture	inner bckgr	outer Bckgr	magnitude	magnitude error		flux		flux error
	[Angstroem]		[pixel]		[pixel]		[pixel]		[mag]		[mag]			[mJy]		[mJy]
	
	5430			12		14		25		16.75		0.03			0.55068		0.02148
	4500			12		14		25		17.36		0.02			0.48371		0.01005
	3440			12		14		25		16.55		0.01			0.39420		0.00376
	2910			12		14		25		16.29		0.20			0.45876		0.07718
	2310			12		14		25		15.99		0.20			0.53886		0.09066

Table of Contents