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

1
Discovery of the X-ray emission from the darkest
TeV object HESS J1741-302
H. Matsumoto, H. Uchiyama, T. G. Tsuru, K. Koyama
(Kyoto University), O. Tibolla (Heidelberg
University)
Abstract HESSJ1741-302 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. Introduction
3. Suzaku Results (Region B)
HESS 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).
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.
A
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.
B
Figure 4 X-ray image of region B (a) 0.42 keV
band and (b) 210 keV band. The images were
obtained with the FI sensor (XIS0XIS3).
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)).
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(1.620.34)?1022
cm-2. G1.130.60 Observed F(2-10keV) 2.2?10-12
erg s-1 cm-2 Three lines 1. center6.390.03keV,
EW172 eV 2. center6.660.02keV, EW186 eV 3.
center6.950.03keV, EW172 eV
TeV (gray) 2-10keV (green)
Figure 5 X-ray spectrum (XIS0XIS3) of the new
object and the best-fit parameters.
Figure 2 X-ray image of region A (a) 0.42 keV
band and (b) 210 keV band. The images were
obtained with the FI sensor (XIS0XIS3). (c)
X-ray contours of the 2-10 keV band are overlaind
on the TeV gamma-ray image.
The power spectrum of the new object shows a
periodicity of 432.1?0.2 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 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 G1.130.60, NH(3.952.70)?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)3.2?10-13 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.
(a)
(b)
2.314Hz (P432.1s)
Figure 6 (a) Power spectrum of the new object.
(b) light curve of the new object folded with a
period of 432.1 s.
NH(3.952.70)?1022 cm-2 , G1.130.60 Observed
F(2-10keV) 3.2 ?10-13 erg s-1 cm-2 Absorption
corrected F(2-10keV) 3.9?10-13 erg s-1 cm-2
Reference
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 (XIS0XIS3) and BI (XIS1)
sensors, respectively.

1. 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