Unraveling HESS J1745-303 with new results from the Fermi-LAT telescope

1. Unraveling HESS J1745-303 with new results from the Fermi-LAT telescope G.A. Caliandro1, L. Falletti2, J. Cohen-Tanugi2 and E. Nuss2 on behalf of the Fermi LAT Collaboration and the Pulsar Timing Consortium 1Institut de Ciències de l'Espai (IEEC-CSIC) 2LUPM – Université Montpellier 2 / CNRS-IN2P3 G.Andrea Caliandro – CRISM 2011

2. HESS J1745-303 F. Aharonian et al., A&A 483, 509–517 (2008) • HESS J1745-303 is classified as unidentified extended source • Very complex morphology, which presents 3 identified emission regions (A, B, and C) • Not well understood yet whether the emission is composed of different or a single source • Similar spectral indices have been found for the three peaks in the VHE range 3EG J1744-3011 • VHE counterpart candidates: • SNR G359.1-0.5 • SNR G359.0-0.9 • PSR J1747-2958 • PSR B1742-30 Full emission Region A G.Andrea Caliandro – CRISM 2011

3. Environment 12CO J=2–1 map 12CO J=2–1 map • HESS J1745-303 is at the edge of the overall 12CO distribution along the Galactic Center . • The northern part of the HESS source coincides with a local peak of the molecular cloud. • The HI gas wraps the CO molecular cloud. Indeed they are physically connected. But in the southern part of the HESS source the CO emission is absent. G359.1-0.5 HI emission Hayakawa et al. 2011arXiv1105.5207H Hayakawa et al. 2011, arXiv:1105.5207 G.Andrea Caliandro – CRISM 2011

4. Fermi-LAT data analysis E>1GeV • In the Fermi-LAT data a significant excess spatially coincident with HESS J1745-303 was claimed by Hui, et al., (2011, arXiv:1104.4836) • The morphology of the excess in the GeV energy range shows complex features, that jointly with the properties of the ISM, can help in the understanding of this source • At E>1GeV the emission come mainly from region A, and the morphology is quite similar to the VHE emission • At slightly higher energies (E>3GeV), the morphology changes significantly. Region A is not dominant anymore at these energy. On the contrary, the emission come from the southern part of the HESS source. • Modeling the excess at E>3GeV with point-like sources, two detections turn out. • src1 : TS~43, Flux(E>0.1GeV) = (6.±3.) 10-8 cm-2 s-1 • src2 : TS~70, Flux(E>0.1GeV) = (8.±3.) 10-8 cm-2 s-1 PRELIMINARY E>3GeV G.Andrea Caliandro – CRISM 2011

5. Summary • A significant excess observed by Fermi-LAT is spatially coincident with HESS J1745-303. We studied the morphology of this excess, discovering that at high energies (E>3GeV) the emission is near the regions B, and C, while at lower energy the emission is close to region A, where the VHE gamma rays are dominant. • The Fermi-LAT results, with the CO and HI maps, strongly point toward a different nature of the emission coming from region A, with respect to regions B and C. • Further in-depth analyses are on-going within the Fermi-LAT collaboration to fully characterize the GeV emission spatially coincident with HESS J1745-303, especially with respect to region A. G.Andrea Caliandro – CRISM 2011

6. Hui, et al., 2011, arXiv:1104.4836 • They claimed a detection at 18 and 6 sigma in 1-20GeV and 10-20 GeV, respectively • They found that a symple power-law with photon index ~-2.6 describe the spectrum for E>1GeV calculated with unbinned gtlike for a point source at the nominal position of the HESS source TS maps centered at the nominal position of HESS J1745-303 The blue circle represents the 1 positional error circle determined by gtfindsrc. G.Andrea Caliandro – CRISM 2011

7. MC and HI masses (Hayakawa et al. 2011, arXiv:1105.5207) • 12CO mass = 1.6 x 106 M⊙ • Within the 4 significance contours • Distance of 8.5kpc • Conversion factor N(H2)/W(12CO1-0) = 7.0 x 1019 cm-2 (K km s-1)-1 • HI mass • Optically thin hypothesis: ~1 x 104 M⊙ • Optically thik hypothesis: ~7 x 104 M⊙ G.Andrea Caliandro – CRISM 2011