Discovery of the X-ray emission from the darkest TeV object HESS J1741-302

H. MatsumotoH. Matsumoto, H. Uchiyama, T. G. Tsuru, K. Koyama (Kyoto University), O. Tibolla (Heidelberg University)

AbstractHESSJ1741-302 is one of the darkest TeV gamma-ray objects discovered along the Galactic plane. The object may be related to the diffuse TeV emission from the Galactic center ridge. We observed this object with the Suzaku XIS, and we discovered an X-ray object coincides with the TeV gamma-ray peak. Furthermore, we discovered a new X-ray object in the vicinity of HESSJ1741-302. Spectral and temporal analyses suggest that the object is a cataclysmic variable.

1. Introduction1. IntroductionHESS J1741-302 (hereafter HESSJ1741) is one of the “darkest” TeV gamma-ray objects discovered along the Galactic plane (Omar et al. 2008; Omar et al. 2009). The object may have some relations to the diffuse TeV gamma-ray emission from the Galactic center ridge (Aharonian et al. 2006). Then we observed HESSJ1741 with the Suzaku XIS. In this poster, we report the results of the two regions (Figure 1).

ReferenceReference1. Aharonian, F., et al.\ 2006, Nature, 439, 695 2. Tibolla, O., Komin, N., Kosack, K., & Naumann-Godo,

M. 2008, American Institute of Physics Conference Series, 1085, 249

3. Tibolla, O., Komin, N., Kosack, K., & Naumann-Godo, M. 2009, American Institute of Physics Conference Series, 1112, 233

A

B

Figure 1: TeV gamma-ray image of HESS J1741-302 obtained with the H.E.S.S. telescope. The blue and green boxes show the regions where we observed with the Suzaku XIS.

2. Suzaku Results (Region A)2. Suzaku Results (Region A)We observed region A on Feb. 24, 2009 for 45ks. Figures 2a and 2b show the XIS FI images in the 0.4-2 keV and 2-10 keV bands. There is an X-ray object in the hard-energy band. The X-ray object coincides with the peak of the TeV gamma-ray emission (fugure 2(c)).

Figure 2: X-ray image of region A : (a) 0.4—2 keV band and (b) 2—10 keV band. The images were obtained with the FI sensor (XIS0+XIS3). (c) X-ray contours of the 2-10 keV band are overlaind on the TeV gamma-ray image.

(a) 0.4-2keV (b) 2-10keV

Figure 3 shows the X-ray spectrum of the hard X-ray object. The spectrum can be described with an absorbed power-law model. The best-fit parameters are Γ=1.13±0.60, NH=(3.95±2.70)1022 cm-2. The heavy column density suggests that the object is in the Galactic center region. The observed X-ray flux is F(2-10keV)=3.210-13 erg s-1 cm-2. The preliminary analysis of the TeV data suggests that the TeV flux is F(1-10TeV)~2 10-12 erg s-1 cm-2. Thus the flux ratio is F(1-10TeV)/F(2-10keV)~6.

Figure 3: X-ray spectrum of the X-ray object in figure 2 (b). The black and red data show the spectrum of the FI (XIS0+XIS3) and BI (XIS1) sensors, respectively.

NH=(3.95±2.70)1022 cm-2 , Γ=1.13±0.60Observed F(2-10keV) = 3.2 10-13 erg s-1 cm-2

Absorption corrected F(2-10keV) = 3.910-13 erg s-1 cm-2

3. Suzaku Results (Region B)3. Suzaku Results (Region B)Region B was observed on Oct. 4, 2008 for 54ks. X-ray images of region B are shown in figure 4. We found a new object which is conspicuous in both the soft and hard energy bands. The other objects in the soft energy band are probably foreground stars.

(b) 2-10keV

(c)TeV (gray)2-10keV (green)

Figure 4: X-ray image of region B : (a) 0.4—2 keV band and (b) 2—10 keV band. The images were obtained with the FI sensor (XIS0+XIS3).

(a) 0.4-2keV

New object

Foreground star

The X-ray spectrum of the new object exhibits three iron lines clearly (figure 5). The spectrum can be described with an absorbed power-law model plus Gaussian lines.

The best-fit parameters:NH=(1.62±0.34)1022 cm-2.Γ=1.13±0.60Observed F(2-10keV)= 2.210-12 erg s-1 cm-2 Three lines:1. center=6.39±0.03keV, EW=172 eV2. center=6.66±0.02keV, EW=186 eV3. center=6.95±0.03keV, EW=172 eV

Figure 5: X-ray spectrum (XIS0+XIS3) of the new object and the best-fit parameters.

The power spectrum of the new object shows a periodicity of 432.10.2 s (figure 6a). We can see the clear periodicity in the folding light curve (figure 6b). Based on the iron lines and the periodicity, the new object is probably a cataclysmic variable.The column density is lower than the X-ray object in region A, and this may indicate that this object is not related to HESSJ1741.

Figure 6: (a) Power spectrum of the new object. (b) light curve of the new object folded with a period of 432.1 s.

(a) (b)2.314Hz (P=432.1s)