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This page summarize the main points of the analysis I did on HESS J1857+026 using to 2 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.

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We fitted the source using pointlike above 300GeV to prevent contamination at low energy.

We obtained the following SED and best fit using Pass 7 :

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Fig. 10 : SED obtained using gtlike above 300 MeV. The best fit is show in yellow.

Here are the summary of the Pass 6 analysis :

The best fit obtained using pointlike gave the following parameters :

Table. 5. Parameters of the best fit obtained using pointlike on Pass6.

Those gave the following SED :

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Fig. 10 SED obtained with pointlike using Pass 

Using Pass 7 with 31 months of data the The source is fitted by a hard power law. The parameters of the best fit are those of the next table :

Table. 56. Parameters of the best fit obtained using gtlike.

SED modeling

Section under construction

Adam constructed a time-dependent one-zone SED model with constant expansion velocity, and assuming a distance of 9 kpc. The modeling only need an IC component.
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Fig. 11 show the SED modeling constructed by Adam. Blue point are those obtained with HESS data and the green one using ASCA observation. IC components : stellar (dot), IR (medium-dashed) and scattering on
CMB (long-dashed)
Preliminary fit:

Final B = 1.5 ± 1.0 ?G
Electron slope = 2.2 ± 0.1
Electron cutoff = 120 ± 40 TeV
Initial spin period = 13 ± 8 ms
Braking index = 2.5 ± 0.4

Theses parameters predict an age of 25 kyrs (21 kyrs predicted in Hessels et al. 2008 for the pulsar).

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With more data

To compare our spectral points to those obtained with MAGIC (talk at the ICRC Klepser et al., Mapping the extended TeV source HESS J1857+026 down to
Fermi-LAT energies with the MAGIC telescopes) we reanalyzed the source to 300 MeV using more data (36 months instead of 31). Here are the results obtained : Image Added
Fig. 11 Residual TS map obtained between 10GeV and 300GeV. Here HESS J1857 is not included in the model. The green contours are those obtained using HESS data (Aharonian et al.,2008).

The position of the Fermi excess is consistent with those of HESS. The black circle represents the position of PSR J1856+0245.

Table 7: Best fit parameters for 36 month of data fitting between 300MeV and 300GeV.

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Fig. 12 : SED obtained using gtlike above 300 MeV. The best fit is show in yellow. Statistic and systematics error bars are respectively the black and blue lines.

We added one source of systematics using a template consistent with those of HESS data (Aharonian et al.,2008). The SED thus obtained is consistent with the one shown by Klepser et al. at the ICRC.

Assuming a distance of 9kpc we derived the luminosity of the PWN to compute its gamma efficiency. We obtained :

L ? (PWN) = 12.69 49 X 10^35 ergs/s.

Using the pulsar Edot =4.6 X 10^36 we computed an efficiency of 35.7%4%. To compare to the 3.1% obtained using HESS data.

This efficiency is consistent with what is expected from Ackerman et al. 2011 (the order of magnitude of the percent) as is shown in the following picture : Image Removed

Fig. 12 13 ?-ray Luminosity of the Pulsar Wind Nebulae as a function of the spin-down
luminosity of the associated pulsar. All the pulsar wind nebulae detected by Fermi are
associated with young and energetic pulsars. Pulsar wind nebulae detected by Fermi are
marked with red stars. Blue squares represent pulsars for which GeV ?-ray emission
seems to come from the neutron star magnetosphere, and not from the nebula.

Using our model we derived and upper limit on the DC emission of the pulsar :

F(100MeV-100GeV)< 1.04e-8 ph/cm2/s leading to a limit on the gamma-ray luminosity of 7.47e34 erg/s.

Supporting X-Ray measurement

To obtain a precise flux for any potential X-ray PWN associated with PSR J1856+0245, we analyzed a 39-ks Chandra ACISI
observation (Obs. ID 12557) using CIAO version 4.3.1 with CALDB 4.4.3. PSR J1856+0245 is clearly detected as a point
source, but there was no immediate evidence for extended emission surrounding this position. Given that the size of the potential
X-ray PWN is not known, we investigated two extraction regions to see whether they produce a statistically significant excess
of counts compared with the background. These two extraction regions were in the form of annuli extending from 2''- 7''
and 2''-15'' respectively from the position of the pulsar. The background regions were chosen from several other source free
regions in the vicinity of the pulsar. For the 2''- 7'' extraction region we find an upper limit on the unabsorbed flux of
2X10^14 erg/s/cm2 (1-10 keV, 3? confidence), corresponding to a luminosity of 2X10^32 erg/s. The background-subtracted counts
in this region show a 1.7? excess from zero. For the 2''-15'' extraction region we find an upper limit on the unabsorbed flux of
5 X 10^14 erg/s/cm2 (1 - 10 keV, 3? confidence), corresponding to a luminosity of 5X10^32 erg/s. The counts in this region show a
2? excess from zero counts. Given the marginal significance of the count excesses in both cases we cannot convincingly claim
the detection of a weak X-ray PWN. These luminosity limits are derived from the 3? upper bound on the net count rate and assume
a typical powerlaw spectrum of index 1.5 for the PWN, a distance of 9 kpc, and a column density NH = 4X10^22 cm^2. An
in-depth analysis of the X-ray properties of PSR J1856+0245 will be presented elsewhere.

Discussion

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Fig. 13 SED modeling

To investigate the global properties of the PWN, we apply a one zone time dependent SED model, as described in Grondin et al.
(2011b) and Abdo et al. (2010a). This model computes SEDs from evolving electron populations over the lifetime of the pulsar
in a series of time steps. During the free-expansion phase of the PWN (assumed to be ~ 104 years) we adopt an expansion
of R / t, following which the radius evolves as R / t^0.3, appropriate for a PWN expanding in pressure equilibrium with a
Sedov phase SNR. Over the pulsar lifetime the magnetic field evolves as B / t^1.5, following ~500 years of constancy. We fix
the pulsar braking index to the canonical value of 3.

We assume the existence of three primary photon fields (CMBR, far IR (dust), and starlight) and use the interstellar
radiation mapcube within the GALPROP suite (Porter et al. 2005) to estimate the photon fields at the Galactic radius of PSR
J1856+0245. A distance of 9 kpc in the direction of the pulsar corresponds to a Galactic radius of 5.4 kpc. At this radius, the
peak of the SED of dust IR photons corresponds to a black body temperature of T ~ 32 K with a density of ~ 1.1 eV cm^3, while
the SED of stellar photons peaks at T ~ 2500 K with a density of ~ 1.2 eV cm^3.

Spectral measurements consist of LAT, MAGIC (Klepser et al. 2011) and H.E.S.S. (Aharonian et al. 2008) data points, as
well as the 2'' - 15'' X-ray upper limit described above.

A simple exponentially cutoff power-law injection of electrons, evolved properly over the pulsar lifetime, often provides
an adequate match to PWNe SEDS. For this injectin spectrum we fit four variables: final magnetic field Bf = 0.8 +/ - 0.4 ?G,
electron high energy cuto Ecut = 66 -+/ 16 TeV, electron powerlaw index p = 2.25 +/- 0.03, and initial pulsar spin period P0 =
9.9 +/- 6.1 ms, which gives an age of 20 kyr. This model yields a 2=do f = 23/9=21 and poorly matches the low energy MAGIC
points, as shown in Figure 2 (Left).

Another option to fit the multi-wavelength data is to adopt the relativistic Maxwellian plus power-law tail electron spectrum
proposed by Spitkovsky (2008). We implement this spectrum as described in Grondin et al. (2011b). The best fit, presented in
Fig. 2 (Middle), is obtained with kT = 0.96 +/- 0.17 TeV corresponding to an upstream gamma-factor of 3.7 X 10^6, a magnetic
field of Bf = 1.0 +/- 0.9 ?G, a cutoff at Ecut = 92 +/- 26 TeV and a power-law index of p = 2.45 +/-  0.12, consistent with the value
of ~ 2.5 proposed by Spitkovsky (2008). The braking index of n = 3 and initial spin period of P0 = 48 +/- 4 ms give an age of
13 kyr. The relativistic Maxwellian plus power law model better matches the multi-wavelength data, with a 2=do f = 13.6=20.
A hadronic scenario is also possible, with  -rays arising from proton-proton interactions and subsequent pion decay. For this
model, corresponding to Fig. 2 (Right), we fix the ambient gas density at 50 cm^3 and age at 20 kyr. We find a best fit of

2=do f = 24/7=21 with a magnetic field of Bf = 10 +/- 20 ?G,proton cuto at Epcut = 73 +/- 27 TeV, a proton power-law index of

p = 1.83 +/- 0.03, and an energy content in protons of 6.9 +/- 0.6 X 10^49 erg.

The MAGIC and H.E.S.S. data combine to form a powerlaw spectra of index ~ 2.3 over nearly three decades in energy.
This VHE data, combined with the limits imposed by the steep LAT data, is diffcult to match with a simple power-law injection
of electrons (or protons), and we find a significantly better fit with a relativistic Maxwellian plus power-law spectrum. Yet
the exceedingly low magnetic field of the leptonic fits, due to the stringent X-ray upper limit, call into question these models.
Such a low magnetic field implies that if PWN leptons are indeed responsible for the
-ray flux, they must be dominated by relic electrons which have escaped the PWN core into very
weakly magnetized surroundings. The hadronic scenario relaxes this constraint, though the energy requirements are quite high
even for a dense ambient medium, and a very hard power-law index is required. At present the true nature of HESS J1857+026
remains a mystery, though the new LAT data and X-ray upper limit hint that this source is far from the typical TeV PWN.

In the paper

I'm now writting the draft of an A&A letter with M.-H. Grondin, M. Lemoine-Goumard, A.Van Etten, B. Stappers, A. Lyne, C. Espinoza.

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1. Search for pulsation. -> No pulsed emission
2. Spatial and spectral analysis

• Spatial
• Spectral

The fourth part summarize the X-Ray observations

The discussion begins with the SED modeling and present the gamma-ray luminosity and efficiency.

I would like to show 3 figures which are th Fig. 4, 8 and 1114 and 16(comming soon).

The draft is coming soon.

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