Page under construction.

This page summarize the main points of the analysis I did on HESS J1857+026 using to sample of data.

The first analysis used 31 months of data collected from August 4, 2008, until March 2011. Only gamma-rays in the Diffuse class events were selected and we excluded those coming from a zenith angle larger than 100°.We have used the P6_V11_Diffuse instrument response functions (IRFs). We included in the model all the sources of the 18 month catalog and assiociated diffuse files.

The second analysis used the same amount of data. Only gamma-rays in the source class events were selected and we excluded those coming from a zenith angle larger than 100°. We have used the P7_V6_SOURCE IRFs. We included in the model all the sources of the 2FGL catalog and assiociated diffuse files.

The Region of Interest.

HESS J1857+026 is in the same region than the SNR W44 which is the brightest source of the region.

Fig 1. Counts map of the region above 6 GeV. Left Pass 6 analysis with 18 months catalog sources in green. Right : Same picture corresponding to the Pass 7 analysis with 2FGL sources represented in blue.

W44

The shape of W44 was fitted by an Elliptical Ring (ref. 1) and it spectra by a broken power law.

We saw an excess close to W44 and tried to refit the source to take into account this excess.

We refitted again the spectra of W44 by a Log-Parabola and studied the shape of W44.

The main point is that the results are consistent with previous work and with 2FGL cat.

 
Fig. 2. Comparison between the result of ref. 1 (red contours) and our results using pass 6 (white ring) . There is no error taken into account in this templates. Figure to be updated with Pass 7

Table 1.  Parameters obtained by fiting the shape of W44. The main point is that all of these values are consistent with the work of Tanaka et al. 2010.

Fig. 3 SED of W44 given by pointlike.

Adding a new source to Pass 7 Analysis

section under construction

Using 2FGL sources, Pass 7 IRFS and associated diffuses, we found a low energy excess quickly decreasing with energy.

To prevent contamination from this source on HESS J1857 we analysed it. The best fit we obtained is a point source located at 

RA=283.58 DEC=2.98

Fig. 4. Residual TS map between 100MeV and 1.3GeV using pointlike. Green crosses represents 2FGL sources

 
Fig. 5. SED of the source using pointlike.

The best fit using gtlike provided the following parameters alpha = 3.5 +/- 0.2, beta = 0.6 +/- 0.1, Eb ? 1.2 GeV, and N_0 = (3.1 +/- 0.5) X 10^{-12} photons/MeV/cm^2/s.

HESS 1857+026 Morphology above 10GeV

We made an analysis of the morphology of HESS 1857+026 above 10GeV. Three hypotheses were tested : point source, gaussian and disk.

No significant extension was found as can be seen in the following table. The delta show that we do not detect any extension of the source.

Table 2. TS and Loglike found above 10GeV for a point source, a gaussian and a Disk.

Fig. 4. Excess TSMap of a 10° * 10° roi around HESS 1856+026.

Fig. 5 Zoom of the previous TS map with a factor of 5. The green square represent an 2° * 2° roi and the green contours are those of HESS source.

Bibliography :

(1) Abdo et al., Science, 327, 1103-1106, 2010