1. Takayasu Anada (E-mail: anada at astro.isas.jaxa.jp), Ken Ebisawa, Tadayasu Dotani, Aya Bamba (ISAS/JAXA)anada at astro.isas.jaxa.jp Gerd Puhlhofer, Stefan Wagner (Univ. of Heidelberg) Suzaku Observation of the Unidentified VHE Gamma-Ray Source HESS J1837-069 HESS J1837-069 is one of the very-high-energy (VHE) gamma-ray objects discovered by a Galactic plane survey with the H.E.S.S. Cerenkov telescope system. Although a point-like source, which was detected in the ASCA and the INTEGRAL Galactic plane survays, was suggested as a candidate counterpart to the HESS source, its position was offset by a few arc-minuite. We observed this source with Suzaku and studied the spectral and temporal characteristics of the source in order to reveal the origin of the VHE emission. As a result, we confirmed the positional offset of the candidate counterpart and found that the it has a non-thermal spectrum without any variability, which is characteristic to a pulsar wind nebula (PWN). Thus we consider that this source is a PWN. In order to test this hypothesis, we compared the nature of this source with that of other PWN candidate HESS sources in terms of the flux ratio and the positional offset between the X- ray and HESS sources. A Galactic plane survey with the H.E.S.S. Cerenkov telescope system revealed new VHE sources, many of which have not been identified so far in other energy bands. Understanding the origin of such VHE gamma-ray emission is one of the most intriguing problems in high energy astrophysics. HESS J1837-069 is one of the VHE sources discovered in the survey. Nature of the source and the origin of this VHE radiation are not known yet (PWN? SNR? Others?). Presence of an X-ray source, AX J1838.0-0655, within the VHE emission region was known from the ASCA (0.7-10 keV, Bamba et al. 2003) and INTEGRAL (20-100 keV, Malizia et al. 2005) observations. This is a candidate counterpart to the HESS source. We observed this source with Suzaku to identify its nature. Introduction: HESS J1837-069 Aharonian et al. 2006 Malizia et al. 2005 Bamba et al. 2003 ASCA GIS (0.7-7 keV) INTEGRAL IBIS (20-100 keV) (1997/10/14 12ks) (1999/09/28 37ks) AX J1838.0-0655 XIS image X-ray sources are found at the Galactic north and south to the HESS source. Offsets of bright and faint X-ray sources are 6’.6, 4’.7, respectively. Bright X-ray source seems to be a point-like source accompanied with a diffuse component. Suzaku (XIS 0+1+3) 0.4 - 10 keV count map Red cross: gaussian brightness peak of H.E.S.S. excess map Red ellipse: rms size of the gaussian brightness profile of VHE emission Chandra (ACIS 0-3) 0.4 - 10 keV count map archived on Aug. 19, 2007 XIS spectra SRC1 SRC2 BGD N H = 5.4 (±0.5) ×10 22 /cm 2, Γ = 1.3 (±0.1) F (2-10 keV) = 10.1 (±0.6) ×10 -12 erg/cm 2 /s Non-thermal spectra No significant variabilities from the spectra obtained by ASCA GIS are seen. N H = 4.0 ( ) ×10 22 /cm 2, Γ = 2.0 (±0.3) F (2-10 keV) = 1.7 (±0.3) ×10 -12 erg/cm 2 /s +1.2 -0.8 HXD timing If origin of the VHE emission is PWN, corresponding pulsar should be associated to it. Utilizing the high time resolution of HXD-PIN (61μs), we searched for pulsation from the region including HESS J1837-069. (Only 10-20 keV data was extracted for good S/N.) No significant periodic pulse is seen. Power spectrum (1bin=5ms, T=10ks) plotted the maximum (upper) and the mean (below) values per 1000 bin. H.E.S.S. (> 250 GeV) Significance map of the Galactic plane survey Smoothed excess map of the region surrounding HESS J1837-069 assuming 3% systematic error 6.6’ AX J1837.3-0652 AX J1838.0-0655 4.7’ 3 45 6 7 12 F TeV v.s. F X Crab Nebula = HESS J0534+220 Two X-ray sources are found at the Galactic north and south to HESS J1837- 069. They have non-thermal spectra without any variabilities. We observed HESS J1837-069 with Suzaku. These natures are consistent with other HESS sources identified as PWNe. No significant pulsation was detected. More observations are required to test the hypothesis that this HESS source is a PWN. Analysis and Results Comparison with other HESS sources Morphological analysis Conclusion X-ray flux is comparable to TeV flux for SRC1, which is consistent with other HESS sources identified as PWNe (except for the crab nebula). SRC2 is relatively faint in X-rays, but it can still be a candidate counterpart of the HESS source. 6’.6 AX J1837.3-0652 AX J1838.0-0655 4’.7 X-ray sources are found at the Galactic north and south to the HESS source. They have non-thermal spactra and without variabilities. No significant pulsation was detected. Some of the HESS sources identified as PWNe have obvious offset between the VHE emissions and the positions of the pulsar. HESS J1837-069 is also such an offset PWN !? We observed this source with Suzaku on 2007 March 5-6 for a net exposure of 42 ks. The origin of this VHE emission is PWN? In order to test this hypothesis, we compare the nature of this source with other HESS sources identified as PWNe in terms of the flux ratios and the positional offset between the X-ray and HESS sources. : X-ray emission from the candidate counterpart of the HESS J1837-069 shows non-thermal spectra without variabilities, which are characteristic to PWNe. Green contour: smoothed X-ray count map obtained by Suzaku XIS in the 0.4-10 keV band. HESS J1837-069 ASCA GIS INTEGRAL SRC1 SRC2 A table showing photon indexes and fluxes in the TeV gamma-ray range of HESS sources identified as PWNe and those of the X-ray candidate counterpart sources. The ratios of the TeV fluxes to the X-ray fluxes are also tabulated. We compared the best fit positions of the HESS sources identified as PWNe with the positions of the associated pulsars. white contour: X-ray count map by ROSAT white contour: 5σ, 7.5σ, 10σ significance levels (with the outermost being the 5σ contour) white contour: X-ray count map by ROSAT Using the LogN-LogS relation (Sugizaki et. al. 2001), we estimated chance probability of finding a source with the same flux as SRC2 in a few arc- minutes, and found that it is approximately a few percent. Thus we cannot exclude the possibility that the SRC2 is an unrelated source to HESS J1837- 069. Chance coincidence probability of SRC2 HESS J1514-591 PSR B1509-58 3’.13’.1 PSR J1420-6048 HESS J1418-609 HESS J1420-607 3’.13’.1 8’.28’.2 RabbitRabbit Vela Pulsar HESS J0835-456 26’26’ In these figures below, color shows the smoothed excess map of the VHE emission. The Suzaku conference in San Diego, CA (December 10th-12 th 2007)