1ES 0229+200: An extreme blazar with a very high minimum Lorentz factor
aa r X i v : . [ a s t r o - ph . H E ] S e p Astronomy&Astrophysicsmanuscript no. 17215 c (cid:13)
ESO 2018October 16, 2018
S. Kaufmann , S.J. Wagner , O. Tibolla , and M. Hauser Landessternwarte, Universit¨at Heidelberg, K¨onigstuhl, D-69117 Heidelberg, Germany Universit¨at W¨urzburg, 97074 W¨urzburg, GermanyReceived 9 May 2011; accepted 18 August 2011
ABSTRACT
The blazar 1ES 0229 +
200 is a high frequency peaked BL Lac object with a hard TeV spectrum extending to 10 TeV. Its unusualspectral characteristics make it a frequently used probe for intergalactic radiation and magnetic fields. With new, simultaneous ob-servations in the optical, ultraviolet (UV) and X-rays, the synchrotron emission is probed in great detail. The X-ray emission variesby a factor of ≈ Γ ≈ .
8) and it shows an indicationof excess absorption above the Galactic value. The X-ray emission is detected up to ∼
100 keV without any significant cut-o ff , thus1ES 0229 +
200 belongs to the class of extreme blazars. The simultaneous measured, host galaxy- and extinction-corrected optical andUV fluxes illustrate that the cut-o ff of the low energy part of the synchrotron emission is located in the UV regime. The minimumenergy of the electron distribution has to be rather high to account for this cut-o ff . This implies that there is a narrow-band energydistribution function of radiating electrons, which is responsible for the unusually hard TeV spectrum. Other extreme blazars havesimilar synchrotron peak frequencies but much softer TeV spectra, hence 1ES 0229 +
200 has one of the highest inverse Compton (IC)peak frequency and the narrowest electron distribution among the extreme blazars known to date.
Key words.
Galaxies: active - BL Lacertae objects: Individual: 1ES0229 +
200 - X-rays, UV, optical: observations
1. Introduction
The high-frequency peaked BL Lac object 1ES 0229 +
200 islocated at α J2000 = h m . s , δ J2000 = + ◦ ′ . ′′ (Rector et al. 2003) and has a redshift of z = .
14 (Woo et al.2005).High frequency peaked BL Lac objects (HBL) are charac-terized by two peaks in their spectral energy distribution (SED)which are located in the UV-X-ray and the GeV-TeV band, re-spectively. These are commonly interpreted in terms of leptonicmodels (e.g. Marscher & Gear 1985) as synchrotron and inverseCompton (IC) emission from a population of relativistic elec-trons upscattering their self-produced synchrotron photons (syn-chrotron self-Compton (SSC) models).1ES 0229 +
200 was discovered in the
Einstein
IPC SlewSurvey (Elvis et al. 1992), and classified as a high-frequencypeaked BL Lac object based on its X-ray to radio flux ratio(Giommi et al. 1995).The VLA observations of 1ES 0229 +
200 reveal a core fluxof 51 . ∼ ′′ at1.4 GHz and jet position angles of P.A. = − ◦ and P.A. = ◦ (Rector et al. 2003).1ES 0229 +
200 is not detected in the high energy γ -ray range(100 MeV < E <
100 GeV) by
Fermi / LAT in two years of obser-vations and hence it is not mentioned in the second
Fermi catalog(Abdo et al. 2011).In 1996, it was originally predicted to be a potential VHE γ -ray source based on its SED (Stecker et al. 1996), however,Whipple, HEGRA, and Milagro have only reported upper limits(Horan et al. (2004), Aharonian et al. (2004),Williams (2005)).Very high-energy (VHE, E >
100 GeV) emission up to 10 TeVwas first detected with the High Energy Stereoscopic System(H.E.S.S.) in 2006 (Aharonian et al. 2007). In this study, a hard spectrum with a photon index of
Γ = . ± . stat ± . sys wasreported. Besides 1ES 1426 +
428 (Aharonian et al. (2003)), 1ES0229 +
200 is the only source at redshift z > . +
200 has avery hard intrinsic VHE spectrum, hence it is well-suited to EBLstudies (e.g. Aharonian et al. (2007), Kneiske & Dole (2010)).Its spectral characteristics have been used to probe intergalacticmagnetic fields (e.g. Neronov & Vovk (2010), Tavecchio et al.(2010)). At the same time, these hard spectra are challengingfor blazar models. We have launched dedicated, simultaneousmulti-wavelength observations with XMM-Newton (X-ray, UV)and ATOM (optical) to determine the broad-band spectra in moredetail.
2. Multi-wavelength observations and data analysis
XMM-Newton , Swift , and
RXTEXMM-Newton observations of 1ES 0229 +
200 were carried outon August 21 and 23, 2009 for 23 and 28 ks, respectively. Theobservations were conducted with MOS1 and PN in full imag-ing mode and MOS2 in timing mode, all with a thin filter. Thetwo grating spectrometers onboard
XMM-Newton
RGS 1, 2 werealso used to acquire. The data analysis of the
XMM-Newton ob-servations was performed with SAS v.9.0. The data from theX-ray instruments were reprocessed as described in the SASuser-guide . Both observations are influenced by short soft pro-ton flares at the end of each observation, detected in the high >
12 keV emission for the PN ( >
10 keV for MOS) detector.Therefore, the good time intervals were determined using a cut http: // xmm.esac.esa.int / external / xmm user support / documentation / sas usg / USG / S. Kaufmann et al.: 1ES 0229 + F − , deabs (erg cm − s − ) XMM-Newton . ± .
02 (9 . ± . × − Swift / XRT 5.,7.,8. August 2008 31249001-31249003 0.2-10 keV 1 . ± .
05 (1 . ± . × − Swift / XRT 19.Oct. - 23. Nov. 2009 31249004-31249019 0.2-10 keV 1 . ± .
03 (1 . ± . × − RXTE / PCA 1.Jan. - 13. Oct. 2010 95387 3-60 keV 1 . ± .
05 (1 . ± . × − BeppoSAX
16. July 2001 51472001 0.1-50 keV 1 . ± .
05 1 . × − ROSAT . ± . × − at 1keV Einstein . ± . × − at 1keV Table 1.
X-ray observations of 1ES 0229 +
200 showing the results for the annual binning of
XMM-Newton , Swift , and
RXTE , as wellas historical observations from
Einstein (Elvis et al. 1992),
ROSAT (Brinkmann et al. 1995) and
BeppoSAX (Donato et al. 2005).The measured fluxes are given for the energy range between 2 and 10 keV. For the
ROSAT and
Einstein observations, the fluxes aredetermined at an energy of 1keV. The absorption derived from the high precision
XMM-Newton spectra of N H = . × cm wasused for the XMM-Newton , Swift , and
RXTE spectra to determine the unabsorbed flux. The absorption detected in the
BeppoSAX spectrum was N H = . × cm (Donato et al. 2005).at 0.4 cts / s for PN (0.35 cts / s for MOS) for the high-energy countrate resulting in an e ff ective exposure of 7.3 ks for PN (23.1 ksfor MOS) for the first and 12.1 ks for PN (24.4 ks for MOS) forthe second pointing. No significant variations were found in ei-ther observation using di ff erent binning down to a timescale of100 (10) seconds for the imaging mode (timing mode) duringthese pointings.For the imaging mode, spectra were extracted from a sourceregion of 30 ′′ radius for the PN (80 ′′ for MOS) around the po-sition of 1ES 0229 +
200 and background regions with the sameradii, on the same chip of the detectors that contained the sourceregion. No significant pileup was found in the spectra of thesource regions using the tool epatplot . The RMF (redistribu-tion matrix file) and ARF (ancillary response file) are calculatedfor each spectrum using the tools rmfgen and arfgen .The grating spectrometers RGS 1, 2 onboard
XMM-Newton measure in the energy range 0.35 to 2.5 keV. The data are anal-ysed using the tool rgsproc .From October 19 to November 23, 2009, 16
Swift obser-vations were targeting on 1ES 0229 + . − . −
10 keV. In 2008, 1ES 0229 + ffi cient amount of counts. For the Swift spectral analysis, XRT exposure maps were generated withthe xrtpipeline to account for some bad CCD columns thatare masked out on-board. The masked hot columns appearedwhen the XRT CCD was hit by a micrometeoroid. Spectra ofthe
Swift data in PC-mode have been extracted with xselect from an annulus region with a radius of 0 . ′ at the position of1ES 0229 + ′ near the source. For the WT-mode, boxes ( ∼ . ′ × . ′ ) cov-ering the region with source photons and a background regionof similar size were used to extract the spectra. The auxiliaryresponse files were created with xrtmkarf and the responsematrices were taken from the Swift package of the calibrationdatabase caldb 4.1.3 .X-ray observations with the Proportional Counter Array(PCA) detector onboard RXTE (Bradt et al. 1993) were obtainedin the energy range 2 −
60 keV from January 1 to October 132010 with exposures of 1 − RXTE / PCAdata of PCU2 and the top layer 1 were considered to ensure the http: // heasarc.gsfc.nasa.gov / docs / heasarc / caldb / caldb intro.html highest signal-to-noise ratio. The data were filtered to accountfor the influence of the South Atlantic Anomaly, tracking o ff -sets, and electron contamination using the standard criteria rec-ommended by the RXTE
Guest Observer Facility (GOF). Forthe count rate of ∼ / s for this observations, the faint back-ground model, provided by the RXTE
GOF was used to gener-ate the background spectrum with pcabackest and the responsematrices were created with pcarsp .The second instrument onboard
RXTE , the HEXTE (HighEnergy X-ray Timing Experiment) onboard
RXTE takes data inthe energy range 15 to 250 keV. Since 2006, the HEXTE clusterA has been operating only in ON-source mode and since the endof 2009 the cluster B is permanently operating in OFF-sourcemode. For the spectral analysis, the cluster B data are used asbackground information for the cluster A data. The sum of allobservations from January 1 until October 13, 2010 show nosignificant signal from 1ES 0229 +
200 in this energy range.
XMM-Newton fieldofview
The source detection tool edetect chain revealed 20 pointsources in the field of view of the PN detector and one sourcethat is extended beyond the PSF of the instrument. Two pointsources are coincident with IRAS sources, four point sourcesare coincident with NVSS sources, and 15 with stars from theGuide Star Catalogue (GSC, Lasker et al. (2008)) (see table inonline supplement). The remaining point sources do not have acounterpart in these catalogues and remain unidentified.The extended source XMMU 023318.0 + α J2000 = h m . s , δ J2000 = + ◦ ′ . ′′ and is veryclose (58 ′′ o ff set) and likely connected to a point-like sourceXMMU 023315.5 + + α J2000 = h m . s , δ J2000 = + ◦ ′ ′′ and a flux of 0.4 Jy at 60 µ m (Moshir 1990). This infrared (IR) source has a radio counterpartNVSS023314 + . ± . ′′ separa-tion) point sources of which the brighter one can be identifiedwith USNO-B1.0 1102-0028956. . Kaufmann et al.: 1ES 0229 + XMM-Newton /OMand
Swift /UVOT
The optical monitor (OM) (Mason et al. 2001) onboard
XMM-Newton observed 1ES 0229 +
200 in the filters UVM2 (231 nm),UVW1 (291 nm), and U (344 nm) simultaneously with the X-ray telescope. The analysis of these data was performed with theanalysis described in the webpage .The UVOT instrument (Roming et al. 2005) onboard Swift measures the UV and optical emission in the bands UVW2 (188nm), UVM2 (217 nm), UVW1 (251 nm), U (345 nm), B (439nm), and V (544 nm) simultaneously with the X-ray telescopewith an exposure of 0 . − uvotmaghist taking into ac-count all photons from a circular region of radius 5 ′′ (standardaperture for all filters). An appropriate background was deter-mined from a circular region of radius 5 ′′ near the source regionwithout contamination of sources. The 75-cm telescope ATOM (Hauser et al. 2004), located at theH.E.S.S. site in Namibia, monitored the flux in the di ff erent fil-ters B (440 nm), V (550 nm), R (640 nm), and I (790 nm) accord-ing to Bessell (1990). The obtained data were analysed using anaperture of 4 ′′ radius. Photometric calibration was done usingthe standard fields SA 113 and SA 95 from Landolt (1992).
3. Spectral data in the synchrotron range
All
XMM-Newton , Swift , and
RXTE spectra are binned with atleast 25 counts and xspec v12.5 was used for the spectral anal-ysis. For the
XMM-Newton spectra, the energy ranges were re-stricted to 0 . −
10 keV for MOS and 0 . −
15 keV for PNfollowing the suggestion of the calibration information . TheMOS1 and PN spectra are fitted simultaneously using a con-stant parameter to account for the di ff erent normalizations. Apower-law model of the form F ( E ) = N ( E / E ) − Γ was used tofit the X-ray spectra taking into account the Galactic absorptionof N H = . × cm (LAB Survey, Kalberla et al. (2005)). Ascan be seen in Fig. 1a, the residuals of the fit to the X-ray spectradeviate from the expected form, which implies that their is eitheradditional absorption or di ff erent spectral characteristics.Fitting a power-law model with unconstrained absorption re-sults in a much better description of the data with χ / do f = . / = .
08. The fit parameter and the goodness of eachmodel is given in table 2. Residuals are shown in panel b of Fig.1. Alternatively, the deviations shown in Fig. 1 could beavoided by taking into account the Galactic absoption and fit-ting a broken power-law. This fit results in photon indices of Γ = . ± . Γ = . ± .
01, and a break at 0 . ± .
09 keV( χ / do f = / N H is located at red-shift z = = ff erent redshifts are in-distinguishable and have similar goodnesses of fit (at z = http: // xmm.esac.esa.int / sas / current / documentation / threads / omi stepbystep.shtml XMM-SOC-CAL-TN-0018:http: // xmm.vilspa.esa.es / docs / documents / CAL-TN-0018.pdf χ / do f = . / = χ / do f = . / +
200 or in the line of sight to the observer or in theMilky Way. We note that both a local enhancement of Galactic N H by 25% along the line of sight to 1ES 0229 + . × cm , areplausible. . . r m a li ze d c oun t s s − k e V − − − R e s i du a l s ( σ ) − − R e s i du a l s ( σ ) Energy (keV) a)b)
Fig. 1.
XMM-Newton
MOS1 (black) and PN (red) spectrum of1ES 0229 +
200 from August 21, 2009. The spectra can be wellfit with a power-law model taking into account an absorptionlarger than the Galactic absorption. In panel a , we plot the resid-uals for a power law considering the Galactic absorption as fixedparameter, and in panel b residuals for a power law with a freeabsorption.The XMM-Newton / RGS spectra show no significant lineemission and the continuum spectra are well-described by apower law with additional absorption comparable to the PN andMOS spectra.The spectrum of the extended source detected in the PN andMOS observations close to 1ES 0229 + . ′ for the PN detector (1 ′ for the MOS detectordue to the CCD gaps) and reveals 90% and 30%a faint sourcewith a flux of ≈ × − erg cm − s − . We were able to fitthe spectrum with a binning of at least 15 photons per bin witha fixed Galactic absorption and a power law model with Γ = . ± . χ / do f = /
96) and slightly better by a thermalmodel ( mekal ) with kT = ± χ / do f = / S. Kaufmann et al.: 1ES 0229 + N H Γ Norm. Norm. factor χ / do f F −
10 keV (cm ) (ph cm − s − keV − ) (PN) (erg cm − s − )21. August 2009 7 . × . ± .
01 (2 . ± . × − .
990 1125 . /
889 (9 . ± . × − (1 . ± . × . ± .
02 (2 . ± . × − .
004 959 . /
888 (8 . ± . × −
23. August 2009 7 . × . ± .
01 (2 . ± . × − .
974 1376 . / . ± . × − (1 . ± . × . ± .
02 (2 . ± . × − .
989 1133 . / . ± . × − Table 2.
XMM-Newton fit parameter, goodness of fit, and unabsorbed flux resulting from a simultaneous fit of the MOS1 and PNX-ray spectra. The absorption was fixed to the Galactic absorption of the LAB survey (Kalberla et al. 2005) in the first model andlet free to vary for the second resulting in additional amount of absorption.The annual averages of the
Swift spectra in 2008 and 2009are shown in table 1. The consecutive pointings of the 2009 dataobtained between October and November were binned in threeten-day intervals each to increase the statistics and are shownin Fig. 2. Initially, a simple power law and a free absorptionwas used to fit these spectra and result in the best descriptionof the spectral shape. No significant change in absorption wasdetected with values of N H = (1 . ± . × cm in 2008and N H = (1 . ± . × cm , N H = (0 . ± . × cm and N H = (1 . ± . × cm for the spectra of 2009 binnedin ten-day intervals. These values are comparable to the one ob-tained from the XMM-Newton spectra, which provide the mostprecise determination of the additional absorption. A total col-umn of N H = . × cm was assumed to obtain the pho-ton indices and the fluxes (see table 1 and Fig. 2). The Swift data from August 2008 were analysed and are shown in the leftpanel in Fig. 2 (2454685 JD). It should be noted here that thesedata were already presented in Tavecchio et al. (2009). Our re-analysis reveals that the integrated flux between 2 and 10 keV islower by a factor of ∼
7, but confirms the spectral indices. Thisis independent of the choice of a higher value of N H .The RXTE spectra have been summed covering about 30days to achieve higher statistics. The energy range from 2-3keV and 20-30 keV were excluded from the spectral analysis,because of instrumental features (e.g. spikes in the backgroundfiles, see website ). A simple power-law was used to fit thesespectra. The resulting photon indices and fluxes can be seen inFig. 2.The historical spectrum of BeppoSAX was fitted with a powerlaw of photon index
Γ = . ± .
05 and a free absorption of N H = (10 ± × cm − in the energy range 0 . −
50 keVwithout any indication for a cut-o ff at the high energy end(Donato et al. 2005).The Swift / BAT spectrum taken from the 58 month catalog (Baumgartner (2010)) is well fit by a power law with photonindex of Γ = . ± . χ = .
02) and result in a flux between14 and 195 keV of F = (28 . ± . × − erg cm − s − . The BeppoSAX
PDS spectrum of 2001 (Donato et al. 2005) is in goodagreement with this high energy spectrum of
Swift / BAT.
4. Temporal study
Regular monitoring observations with ATOM starting in 2006with 7 observations in 2006, 47 in 2007, 86 in 2008, 61 in 2009,and 24 in 2010 show no significant variations ( < m R = . ± .
01 mag and m B = . ± .
02 mag.The UV results from
XMM-Newton and
Swift of 2008 and2009 are shown in Fig. 3. The U and UVW2 band emission was http: // / xrays / programs / RXTE / pca / doc / bkg / bkg-2009-spikes / http: // heasarc.gsfc.nasa.gov / docs / Swift / results / bs58mon / time / JD pho t on i nd e x XMM-NewtonSWIFTRXTE2454685 time / JD pho t on i nd e x Swift8e-121e-111.2e-111.4e-111.6e-111.8e-11 F - k e V / e r g c m - s - XMM-NewtonSWIFTRXTE8e-121e-111.2e-111.4e-111.6e-111.8e-11 F - k e V / e r g c m - s - Swift
Fig. 2.
The X-ray flux of 1ES 0229 +
200 varied by a factor of ∼ XMM-Newton (red cirlces),
Swift (black opensquares), and
RXTE (blue crosses) in the energy range 2-10 keV.For comparison, the
Swift observation of 2008 is also shown.The lower panel displays the spectral indices derived by fittingpower-law models to the spectra. m a g UUVW1UVW2UVM22454685time / JD17.417.617.81818.218.418.6 m a g Fig. 3.
Ultraviolet fluxes measured by
XMM-Newton and
Swift for 1ES 0229 +
200 in 2008 (average over 3 days) and 2009(U: black circles, UVW1: blue open squares, UVW2: redcrosses, UVM2: brown open diamonds). The flux points at JD2455064.6, 2455066.6, 2455117.8, and 2455118.9 are shifted by ± . p χ =
70% and p χ = ∼
30% and ∼ +
200 instead shows an increaseby a factor of around two starting at JD 2455120, as can beseen in Fig. 2. For all of 2010, only a marginal variation couldbe detected. During 2008-2010, marginally significant spectralchanges could be detected as variations in the photon index( p χ =
1% for a constant) that were uncorrelated with the flux . Kaufmann et al.: 1ES 0229 + variation (see Fig. 2). During all epochs, the source can be well-described with a power-law model and an absorption in excessof the Galactic absorption, as described in section 3. At ener-gies above 14keV, measured by Swift / BAT, marginally signifi-cant variation is detected in the monthly lightcurve with a prob-ability for the fit of a constant of p χ ≈
1% over the 58 monthsof observation (Baumgartner (2010)). However, since a long in-tegration time is needed, a behaviour similar to that in the 2-10keV range would be di ffi cult to detect.
5. Spectral energy distribution −3 − − × − × − × − × − ν F ν [ e r g c m − s − ] energy [keV] Fig. 4.
Synchrotron emission of 1ES 0229 +
200 with simulta-neously measured optical, UV, and X-ray emission by ATOMand
XMM-Newton of August 21, 2009 (black dots). The opti-cal and UV emission is corrected for both the host galaxy andGalactic extinction, and the X-ray emission observed by
XMM-Newton / MOS is corrected for the absorption. The bars in theUVW1 and UVM2 bands are explained in section 5.1. The greyopen squares represent the non-simultaneous
Swift / XRT spec-trum (corrected for detected absorption) with the highest flux in2009. The
Swift / BAT 58 month (Dec. 2004 - Oct. 2009) spec-trum is shown in the energy band >
10 keV (black crosses).The dashed line (butterfly) represents the
BeppoSAX spectrumfrom 2001 (Donato et al. 2005). The grey upper limits representhistorical UV observations with
GALEX that are extinction cor-rected and of origin discussed in the text.The simultaneous observations in the optical by ATOM, theUV, and X-rays by
XMM-Newton are considered to study thesynchrotron spectrum (see Fig. 4, simultaneous data of August,21 2009).
The host galaxy of 1ES 0229 +
200 is an elliptical galaxy witha brightness of m host , R = . ± .
01 mag and a half-lightradius of r e = . ± . ′′ (Urry et al. 2000). Other observa-tions in the Bessel R-band with the Nordic Optical Telescope(NOT) (Falomo & Kotilainen 1999) show results with m host , R = .
76 mag and r e , R = ′′ . The host galaxy profile of 1ES available on http: // heasarc.gsfc.nasa.gov / docs / Swift / results / bs58mon /
10 15 20 25 − − − − − − ν F ν [ e r g c m − s − ] frequency [Hz] Fig. 5.
Spectral energy distribution of 1ES 0229 +
200 withsimultaneous measured optical, UV, and X-ray fluxes, allcorrected for host galaxy emission, Galactic extinction, andGalactic absorption is shown as black data points. The 58 months
Swift / BAT spectrum is shown >
10 keV (black crosses). In grey(filled and open circles), historical radio and UV data are shownand their origin is discussed in the text. The grey upper limitsin the GeV energy range are taken from Dermer et al. (2010)and represent the upper limit in the energy bins 0 . − −
10 GeV, and 10 −
100 GeV by
Fermi observations (Aug.2008 to Sep. 2010). The VHE γ -ray spectrum measured byH.E.S.S. (black circles, taken from Aharonian et al. (2007)), aswell as the EBL corrected, intrinsic source spectrum (grey opendiamonds) with a hard photon index, which implies an inverseCompton emission peaking at very high frequency ( > Hz),is shown. The solid line represents an SSC model that can de-scribe the intrinsic synchrotron and inverse Compton emissionof 1ES 0229 + +
200 was also studied in the Bessel U, B, and V-bands withthe Nordic Optical Telescope (NOT) by Hyv¨onen et al. (2007).The results are m host , B = .
75 mag, m host , U = .
83 mag,and m host , V = .
58 mag with half light radii r e , B = . ′′ , r e , U = . ′′ , and r e , V = . ′′ . In order to correct for the hostgalaxy light, a de Vaucouleurs profile of the galaxy was assumedand the measured brightness was transformed to that of an aper-ture of 4 ′′ using equation (4) of Young (1976). ATOM photome-try was performed with a 4 ′′ aperture. The resulting host-galaxycorrected fluxes would result in an unphysical bump in the Vband in the SED (in ν F ν ) since the calculated influence of thehost galaxy in the V band is only 30%, while in the R and B bandit is 90% and 30%, respectively. Hence, the influence of the hostgalaxy in the R, B, V, and U filters were also calculated using aspectral template for a nearby elliptical galaxy by Fukugita et al.(1995). Here, the R-band magnitudes and the half-light radiusdetected by Falomo & Kotilainen (1999) were used. The influ-ence of the host galaxy is then ∼ ∼ ∼
57% for R,V, and B, respectively, which are the values that we used to cor-rect the measured fluxes (shown in Fig. 4). The host-galaxy cor-rected flux in the R-band is compatible with the detected nucleusmagnitude of Falomo & Kotilainen (1999) and Urry et al. (2000)as expected from the absence of variability. The host galaxy in-fluence in the UVW1 and UVM2 bands is unknown. Figure 4therefore shows two values, connected by a bar. The upper ones
S. Kaufmann et al.: 1ES 0229 + correspond to the measured values corrected only for extinction,the lower ones also assume a correction for the host galaxy of30% (the value derived in the adjacent U band).In an independent check, the spectral slope was extractedusing the Sloan Digital Sky Survey (SDSS) observations (fivebands taken simultaneously). The resulting slope is identical tothe one measured by ATOM. Since the data do not match theepoch of the ATOM observations, the absolute fluxes were notconsidered. Since the host galaxy magnitudes were not extinction corrected,the influence of the host galaxy was first subtracted. The extinc-tion correction was thereafter applied to the AGN light.The measured UV fluxes were corrected for dust absorp-tion using E(B-V) = A λ / E ( B − V ) ratios given in Seaton (1979), resulting in a cor-rection of 70% , ,
48% for the UVM2, UVW1 and U-band,respectively. For the optical filters, the values for the extinc-tion were derived from the interstellar reddening curve and tablegiven by Zombeck (1990) . The correction of N H absorption wasapplied as described in Section 3. GALEX observed 1ES 0229 +
200 at October 29, 2007 in thefar UV (152 . . . µ Jy and 50 . µ Jy, respectively,taken from GalexView . The measured near and far UV fluxeswere corrected for dust absorption using E(B-V) = A λ / E ( B − V ) ratios given in Seaton(1979). A correction of 64% and 68% resulted for the far andnear UV bands, respectively. Owing to a lack of informationabout the host galaxy influence in these wavebands (this influ-ence should be very small compared to the extinction correc-tion), the measured fluxes are shown as upper limits for the in-trinsic synchrotron spectrum of 1ES 0229 +
200 (shown as greyarrows in Fig. 4).In 2006, 2008, and 2009
Integral also observed 1ES0229 +
200 several times for approximately 66 ks with ISGRI(17 −
80 keV) and 61 ks with JEM-X (3 −
10 keV), but thesource appears faint and too few photons were detected so thatno reasonable light curve or spectrum could be extracted .In historical snapshot observations of VLA at 6 cm in 1992fluxes of 41 . .
09 mJy(Perlman et al. 1996) were detected (shown as grey open circlesin Fig. 5). With 6 cm VLBA observations this flux was resolvedinto a core of 22 . . . +
200 was found tohave curved jets to the north and south with extensions of 30 ′′ .The core fluxes are shown as grey filled circles in Fig. 5. Katarzy´nski et al. (2006) demonstrated that synchrotron spectrawith a high minimum Lorentz factor can explain a very hardinverse Compton spectra. The simultaneously obtained data inthe optical, UV, and X-ray bands cover the whole synchrotron online version http: // ads.harvard.edu / books / hsaa / toc.html http: // galex.stsci.edu / GR6 see e.g. http: // / heavens webapp / integral emission. This allows an empirical determination of the mini-mum Lorentz factor in 1ES 0229 + XMM-Newton measurements constrains the synchrotron spec-trum very e ffi ciently.The photon index Γ = α + n of the electron distribution N ( E ) dE ∝ E − n dE with the relation n = − − α . A broken powerlaw with a canonical cooling break of ∆ n = +
200 detectedin the X-ray emission places constraints on the maximum sizeof the emission volume considered in the SSC model which isinferred to be R < ( ∆ t / sec) × D × c ≈ D × . × m.The peaks in the SED are commonly explained by lep-tonic models, such as those of Marscher & Gear (1985), as syn-chrotron and inverse Compton (IC) emission from a popula-tion of relativistic electrons up-scattering their self-producedsynchrotron photons (synchrotron self-Compton models (SSC)).The code of Krawczynski et al. (2004) for a one-zone SSCmodel was used to describe the intrinsic emission of 1ES0229 + . −
100 keV. The absorption and host galaxy corrected UV-optical emission below this range is significantly steeper andstrongly constrains the minimum energy of the electron distri-bution function, yielding a very high value. The well-determinedspectral index in the X-ray regime has to describe the low-energyspectral index of the electron distribution n = − .
6. The un-cooled electron spectral slope hence has n = − . R = × m).This radius is an upper limit and is fixed independently of theSED modelling. Smaller values of radii would also be consis-tent with the variability constraint. Tavecchio et al. (2009) useda smaller value in their attempts to describe the SED compiledin their study. The SED shown in Fig. 5 cannot be reproducedwith a radius ( R < × m) (see below). To account forthe high energy peak of the IC emission, the underlying elec-tron distribution must be very narrow. Together these constraintsare best met with the model parameters E min = × eV( γ min = . × ), E break = . × eV ( γ break = . × ), E max = × eV ( γ max = . × ), and a magneticfield of B = . × − G. The Doppler factor of D =
40 waschosen as the smallest one possible to reproduce the spectra.This model can describe the simultaneously obtained spectrain the synchrotron regime, the long-term hard X-ray spectrumby
Swift / BAT, and the non-simultaneous, intrinsic TeV spec-trum. The peak frequency of the synchrotron and IC emissionbased on the described model are ν sy , peak = . × Hz and ν IC , peak = . × Hz. The peak fluxes show a slight Comptondominance with ν sy , peak F ν sy , peak = . × − erg cm − s − and ν IC , peak F ν IC , peak = . × − erg cm − s − . This model is shownin Fig. 5 as a solid line, while the dashed line represents theabsorption by the EBL using the model of Franceschini et al.(2008). This model is in good agreement with the EBL absorp-tion model used in Aharonian et al. (2007) to correct the ob-served TeV spectrum (shown in Fig. 5). . Kaufmann et al.: 1ES 0229 + The cooling break is at very high energies such that a singlepower-law model for the electron distribution with n = − . γ min is given by F sy ∼ ν / , leading to a slopefor the IC part that is similar to that is required to fit theTeV spectrum. Attempting to fit the overestimated X-ray flux,Tavecchio et al. (2009) derived a di ff erent set of parameters,including a higher (factor 10) magnetic field and a smallerradius. The initial model presented above used an upper limitto the radius, which was not optimized in the SED fitting. Inan attempt to explore models with smaller radii, attempts weremade to reproduce the SED with smaller radii. The precisedetermination of the low energy cuto ff in the UV range and thewell-determined spectral shape in the X-ray range can only bereproduced by invoking a very high Doppler factor (D > ff of the synchrotron emission above 100 keV rep-resents the maximum energy of the electron distribution. Nochange in spectral shape could be detected in the Swift / BATspectrum. Therefore only a lower limit to the maximum cut-o ff energy could be determined empirically. The precise measure-ment of the maximum energy would require a soft γ -ray de-tection. In the IC part of the spectrum, the maximum energycannot be determined emprically either because any increase in E max does not result in a change in the IC spectrum because ofKlein-Nishina suppression. Assuming that the high energy cut-o ff of the synchrotron emission is at the high energy end of the Swift / BAT spectrum ( ∼
100 keV), this results in an electron dis-tribution that extends only over five orders of energy.Changes in the peak fluxes of the synchrotron emission (suchas the di ff erence between the XMM-Newton and the Swift / XRTspectrum, as shown in Fig. 4) were also tested. Any changes inthe parameters of the emission volume corresponding to an in-crease in flux by a factor of ∼ ∼ + n = − . n = − .
6, a separate modelcan be constructed. This scenario cannot be excluded by our si-multaneously measured SED above 10 Hz, but would requirea large Doppler factor of about D =
100 in order to account forthe high energy peak of the IC emission. This alternative modelalso underpredicts the radio flux of the resolved core by a largefactor, e.g. around 70%. Interestingly, the radio flux of the jet, asmeasured by Rector et al. (2003), could be represented by suchmodel, indicating that the whole synchrotron emission originatesfrom the resolved jet. Another possible way of explaining thehigh IC peak using such an electron distribution function, butwith a lower Doppler factor, would be to invoke an additionalexternal Compton contribution resulting from the scattering ofthe CMB as discussed in B¨ottcher et al. (2008) for 1ES 1101-232, a distant TeV blazar with a hard TeV spectrum. This model would decouple the X-ray and TeV emission because most of theTeV emission would result from the interaction with the CMBfurther away from the synchrotron emission region of the jet.This model would imply no VHE variability on short timescales.The e ff ect of the CMB scattering depends on the distance to thesource, so that it is more likely to be detectable in distant sourcessuch as 1ES 0229 +
200 and 1ES 1101-232.
6. Conclusions
The X-ray spectral information that have been presented herecover all available X-ray data up to October 2010. Together withthe simultaneous UV and optical observations, they yield a verygood coverage of the synchrotron emission. Our detailed studyof the high quality
XMM-Newton spectrum has inferred an ab-sorption higher than the nominal Galactic column density, whichcould be intrinsic to the source or caused by Galactic excess ab-sorption.The host-galaxy, extinction-corrected optical and UV fluxeshave been shown to provide strong evidence that the cut-o ff ofthe low energy part of the synchrotron emission is located be-tween the optical and X-ray regime. Therefore, the minimumenergy of the electron distribution has to be rather high to ac-count for this cut-o ff . As suggested by Katarzy´nski et al. (2006),an electron distribution with a high minimum Lorentz factoris needed to reproduce a hard TeV spectrum. A narrow elec-tron distribution, as indicated by the high minimum energy, re-sults in a hard intrinsic VHE γ -ray spectrum as deduced for1ES 0229 + > Hz), hencethe initial electrons are very energetic.An earlier attempt to utilize the suggestion byKatarzy´nski et al. (2006) was reported by Tavecchio et al.(2009), assuming a high minimum Lorentz factor. The maindi ff erences between the model presented here and their attemptsare caused by the new, precisely determined low-energy cut-o ff in the optical regime and the simultaneously determined X-rayspectrum.A broken power-law could be an alternative description tothe additional absorption found in the X-ray spectra. However,the low energy extrapolation of the X-ray spectrum would not fitthe optical range and is therefore disfavoured.The hard X-ray spectrum up to 15 keV together with thelong-term spectrum by Swift / BAT have been found to show thatthe synchrotron peak is extended up to ∼
100 keV without anysignificant cut-o ff in the X-ray spectrum.1ES 0229 +
200 is defined as a high-frequency peaked BLLac object, and the measured synchrotron emission peaks athigher frequencies ( >
100 keV) than usual for HBL and be-longs therefore to the class of extreme blazars. The exact peakfrequency cannot be determined, since the hard X-ray spectrumdoes not show any significant cut-o ff . Assuming that the high en-ergy cut-o ff of the synchrotron emission is at the high energy endof the Swift / BAT spectrum ( ∼
100 keV), the underlying electrondistribution extend only over five orders of magnitude in energy,which is a narrow range. For no other extreme blazar has thisrange been demonstrated to be so narrow.The low energy part of the synchrotron emission has not beenfound to show significant variation over four years in the opticalR band. Only minor variation has been detected in the ultravioletflux during 2008 and 2009. The 2-10 keV X-ray flux insteadvaried by a factor of ≈ S. Kaufmann et al.: 1ES 0229 + Swift / BAT, variations in this amplitude and timescale could notbe detected because of the longer integration time needed.Several blazars are known as so-called extreme blazarswith synchrotron emission extending to high energies(Costamante et al. 2001). It has been found that Mkn 501revealed a very high energy peak of synchrotron emissionaround 100 keV in a flare with a detected large shift in the peakfrequency compared to previous observations (Pian et al. 1998).The monitoring by
BeppoSAX of 1ES 2344 +
514 has identifiedhuge changes in the synchrotron peak frequency within one yearwith di ff erent spectral shapes (Giommi et al. 2000). INTEGRAL observations of 1ES 1426 +
428 display a synchrotron peakfrequency around 100 keV (Wolter et al. 2008). These extremeblazars have similar synchrotron peak frequencies to 1ES0229 + + + Acknowledgements.
The authors acknowledge the support by the
XMM-Newton team in arranging simultaneous observations. The execution and availability ofthe
RXTE and
Swift observations and the use of the public HEASARC soft-ware packages are acknowledged. S.K. and S.W. acknowledge support from theBMBF through grant DLR 50OR0906.
References
Abdo, A. A., et al. (Fermi-LAT Collaboration) 2011, ArXiv: 1108.1435Aharonian, F., et al. (HEGRA Collaboration) 2003, A&A, 403, 523Aharonian, F., et al. (HEGRA Collaboration) 2004, A&A, 421, 529Aharonian, F., et al. (H.E.S.S. Collaboration) 2007, A&A, 475, L9Baumgartner, W. H. a. 2010, submitted to ApJSBessell, M. S. 1990, PASP, 102, 1181B¨ottcher, M., Dermer, C. D., & Finke, J. D. 2008, ApJ, 679, L9Bradt, H. V., Rothschild, R. E., & Swank, J. H. 1993, A&AS, 97, 355Brinkmann, W., Siebert, J., Reich, W., et al. 1995, A&AS, 109, 147Burrows, D. N., Hill, J. E., Nousek, J. A., et al. 2005, Space Science Reviews,120, 165Condon, J. J., Cotton, W. D., Greisen, E. W., et al. 1998, AJ, 115, 1693Costamante, L., Ghisellini, G., Giommi, P., et al. 2001, A&A, 371, 512Dermer, C. D., Cavadini, M., Razzaque, S., et al. 2010, arXiv:1011.6660Donato, D., Sambruna, R. M., & Gliozzi, M. 2005, A&A, 433, 1163Elvis, M., Plummer, D., Schachter, J., & Fabbiano, G. 1992, ApJS, 80, 257Falomo, R. & Kotilainen, J. K. 1999, A&A, 352, 85Franceschini, A., Rodighiero, G., & Vaccari, M. 2008, A&A, 487, 837Fukugita, M., Shimasaku, K., & Ichikawa, T. 1995, PASP, 107, 945Giommi, P., Ansari, S. G., & Micol, A. 1995, A&AS, 109, 267Giommi, P., Padovani, P., & Perlman, E. 2000, MNRAS, 317, 743Hauser, M., M¨ollenho ff , C., P¨uhlhofer, G., et al. 2004, AstronomischeNachrichten, 325, 659Horan, D., Badran, H. M., Bond, I. H., et al. 2004, ApJ, 603, 51Hyv¨onen, T., Kotilainen, J. K., Falomo, R., ¨Orndahl, E., & Pursimo, T. 2007,A&A, 476, 723Kalberla, P. M. W., Burton, W. B., Hartmann, D., et al. 2005, A&A, 440, 775Katarzy´nski, K., Ghisellini, G., Tavecchio, F., Gracia, J., & Maraschi, L. 2006,MNRAS, 368, L52Kneiske, T. M. & Dole, H. 2010, A&A, 515, A19Krawczynski, H., Hughes, S. B., Horan, D., et al. 2004, ApJ, 601, 151Landolt, A. U. 1992, AJ, 104, 340Lasker, B. M., Lattanzi, M. G., McLean, B. J., et al. 2008, AJ, 136, 735Marscher, A. P. & Gear, W. K. 1985, ApJ, 298, 114Mason, K. O., Breeveld, A., Much, R., et al. 2001, A&A, 365, L36Moshir, M. 1990, in IRAS Faint Source Catalogue, version 2.0 (1990)Neronov, A. & Vovk, I. 2010, Science, 328, 73Perlman, E. S., Stocke, J. T., Schachter, J. F., et al. 1996, ApJS, 104, 251Pian, E., Vacanti, G., Tagliaferri, G., et al. 1998, ApJ, 492, L17Poole, T. S., Breeveld, A. A., Page, M. J., et al. 2008, MNRAS, 383, 627Rector, T. A., Gabuzda, D. C., & Stocke, J. T. 2003, AJ, 125, 1060Roming, P. W. A., Kennedy, T. E., Mason, K. O., et al. 2005, Space ScienceReviews, 120, 95Schachter, J. F., Stocke, J. T., Perlman, E., et al. 1993, ApJ, 412, 541Schlegel, D. J., Finkbeiner, D. P., & Davis, M. 1998, ApJ, 500, 525Seaton, M. J. 1979, MNRAS, 187, 73P Stecker, F. W., de Jager, O. C., & Salamon, M. H. 1996, ApJ, 473, L75Tavecchio, F., Ghisellini, G., Foschini, L., et al. 2010, MNRAS, 406, L70Tavecchio, F., Ghisellini, G., Ghirlanda, G., Costamante, L., & Franceschini, A.2009, MNRAS, 399, L59Urry, C. M., Scarpa, R., O’Dowd, M., et al. 2000, ApJ, 532, 816Williams, D. A. 2005, in American Institute of Physics Conference Series, Vol.745, High Energy Gamma-Ray Astronomy, ed. F. A. Aharonian, H. J. V¨olk,& D. Horns, 499–504Wolter, A., Beckmann, V., Ghisellini, G., Tavecchio, F., & Maraschi, L.2008, in Astronomical Society of the Pacific Conference Series, Vol. 386,Extragalactic Jets: Theory and Observation from Radio to Gamma Ray, ed.T. A. Rector & D. S. De Young, 302Woo, J., Urry, C. M., van der Marel, R. P., Lira, P., & Maza, J. 2005, ApJ, 631,762Young, P. J. 1976, AJ, 81, 807Zombeck, M. V. 1990, Handbook of space astronomy and astrophysics, ed.Zombeck, M. V.
7. Supplement
For the online supplement: . Kaufmann et al.: 1ES 0229 + F − s − ) Possible counterpart (radio, IR, optical)1ES 0229 +
200 02:32:48.592, + . ± . × − NVSS 023248 + + + . ± . × − GSC2.2 N33123012274XMMU 023227.3 + + . ± . × − NVSS 023227 + + + ± × − GSC2.3 NC6R014254XMMU 023318.0 + + ± × − –XMMU 023212.7 + + ± × − –XMMU 023315.5 + + ± × − NVSS 023314 + + + + ± × − GSC2.2 N331230310392XMMU 023314.7 + + ± × − –XMMU 023248.2 + + ± × − –XMMU 023315.2 + + . ± . × − GSC2.3 NC6P013245XMMU 023230.4 + + . ± . × − –XMMU 023233.2 + + ± × − GSC2.3 NC6R010173XMMU 023219.6 + + . ± . × − NVSS 023219 + + + . ± . × − GSC2.3 NC6P013116XMMU 023321.4 + + . ± . × − GSC2.3 NC6P002203XMMU 023314.7 + + . ± × − GSC2.3 NC6R010904XMMU 023254.6 + + ± × − –XMMU 023307.2 + + ± × − GSC2.3 NC6R011298XMMU 023328.0 + + ± × − IRAS 02306 + + + ± × − GSC2.3 NC6P001373XMMU 023211.7 + + ± × − GSC2.2 N3312301924
Table 3.
X-ray sources detected in the
XMM-Newton observation on 1ES 0229 ++