Source, HESS J1303−631
PSR B1259-63Galactic Plane
5.3 XMM-Newton X-ray Observations
5.3.3 X-ray Spectrum
For the spectrum a small elliptical region covering the extension was taken as shown in Figure 5.21.. The on-region for spectral extraction was centered at α = 13h02m00s, δ = −63◦0505400 (where α is the right ascension coordinate and δ is the declination), with radii 1.09 and 00.9 with the major axis oriented along the position angle 101.5◦. The background region was taken with the same dimensions but centered onα = 13h01m52s, δ = −63◦0805500. The obtained spectrum was fitted using the spectral fitting software XSPEC.
The spectrum was fitted to an absorbed power-law model which yielded the following parameters: NH = (3.6 ±1.4)× 1022 cm−2, Γ = 2.7± 0.6, norm = (1.4 ±2.4)× 10−4 keV−1cm−2s−1,NH is the fitted column density which manifests itself as absorption
5 The Unidentified VHE Gamma-ray Source, HESS J1303−631
30.0 04:00.0 30.0 13:03:00.0 30.0 02:00.0 01:30.0
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IRAS 13010-6254
PSR
Figure 5.18: Smoothed XMM-Newton X-ray flux map. An extended X-ray source ap-pears from the position of the pulsar, PSR J1301−6305 (magenta dot), and extends roughly in the direction of the H.E.S.S. peak (green contours show 8, 14 and 20σ Gamma-ray significance) and in the direction of the star formation region, IRAS 13010−6254 (magenta circle). The green box shows the slice on excess events in the 2 −8 keV energy band. A presumably unrelated soft point source, 2XMM J130141.3-630535, is shown as a green dot.
72
Distance from Pulsar [arc sec]
-180 -160 -140 -120 -100 -80 -60 -40 -20 0 20 40
Counts
0 10 20 30 40 50 60 70 80 90
Slice Axis [arc sec]
-180 -160 -140 -120 -100 -80 -60 -40 -20 0 20 40
BG Counts
0 10 20 30 40 50 60 70 80 90
Figure 5.19: Top: the slice used for determination of X-ray extension. The presumably unrelated soft source, 2XMM J130141.3-630535, is fit with a King profile on the right. The compact region near the pulsar is fit with a Gaussian and a King profile is shown for comparison as a blue dashed line. The extended emission is fit with a Gaussian on the left.
Bottom: the slice used for background determination. The red dotted bin lies directly on a chip edge in the PN camera and is excluded from the analysis. The black horizontal dashed line indicates the fitted background level from a simultaneous fit of the sources and background slices. The vertical dashed line indicates the pulsar position.
5 The Unidentified VHE Gamma-ray Source, HESS J1303−631
Band Mean Width Int. Width P
E1 0.001◦±0.012◦ 0.214◦±0.011◦ 0.203◦±0.012◦ 0.43 E2 0.010◦±0.013◦ 0.172◦±0.013◦ 0.168◦±0.013◦ 0.15 E3 0.098◦±0.022◦ 0.080◦±0.020◦ 0.075◦±0.021◦ 0.97
Table 5.2: Results of the Gaussian fit to the slices on the excess maps in the energy bands E1 = (0.84 - 2) TeV, E2 =(2 - 10) TeV and E3 >10 TeV. “Mean” is the mean of the Gaussian, “Width” is the Gaussian width and “Int. Width”
is the intrinsic Gaussian width of the source after correcting for the PSF, P is the p-value of the fit.
Constant Fit χ2/N DF p-value Intrinsic Width 44.9 / 2 1.8×10−10 Gaussian Mean 18.3 / 2 1.1×10−4
Linear fit
Intrinsic Width 0.4 / 1 0.55 Gaussian Mean 2.4 / 1 0.12
Table 5.3: Quality of fit of a constant to the source intrinsic Gaussian extension and mean, measured from pulsar position, as a function of energy. The bad p-values indicate the presence of significant energy-dependent morphology.
°]
Figure 5.20: Zoom in of the slice on the X-ray extension near the pulsar after subtracting the fitted background, unrelated point source and extended emission region.
A fit to a Gaussian (left), center −11.9±4.2, Gaussian width 14.7±3.2, yielded an equally good fit as a fit to two point source (right) with fit qualitiesχ2/N DF of 13.42/10 and 10.16/9 respectively.
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PSR J1301-6305
Figure 5.21: The regions used for X-ray spectral extraction. The green ellipse shows the region used for signal extraction and the red ellipse shows the region used for background extraction. The regions were chosen to avoid other known sources and have roughly equal distance from the center of the field of view.
of the photons especially at lower energies.
Fixing the column density to this value in the spectral fit decreased the errors on the fit and yielded the following fit parameters: Γ = 2.7 ±0.2, norm = (1.3 ±0.7)× 10−4 keV−1cm−2s−1. This has, however, negligible effect on the integrated unabsorbed flux which is found to be
F2-10 keV = 1.2×10−13 erg cm−2s−1. 5.3.4 PMN Radio Observation
The region of HESS J1303−631 was covered by a survey of the southern sky by the Parkes, MIT and NRAO (PMN) radio telescopes at 4.85 GHz [Condon et al., 1993].
Calibrated maps were obtained from the NASA SkyView online tool, shown in Figure 5.22. There appears to be a radio source just East of the X-ray nebula and near the peak of the VHE source. The feature is found to have a peak flux of 0.030 Jy/beam, where one beam defines the resolution of the radio observation, in this case, 70 FWHM. This flux is at the detection limit of the survey, so this feature is not significant (and thus not reported in the catalog) and the flux is taken as an upper limit. This feature is consistent with the size of the PSF of the survey in the North-East to South-West direction, but may be slightly elongated in the North-West to South-East direction. Since the feature is not significant, no definitive conclusions can be made.
5 The Unidentified VHE Gamma-ray Source, HESS J1303−631
Figure 5.22: 4.85 GHz radio image from the PMN Survey in the HESS J1303−631 region.
H.E.S.S. contours are shown in green, XMM Newton X-ray contours are shown in black and the radio contours are shown in white. A radio source peaks about 3’ East of the pulsar position, just beyond the extended XMM X-ray source and near the center of the H.E.S.S. Gamma-ray source at a peak value of 0.03 Jy/beam.
Although it is unclear whether this radio feature does indeed represent a counterpart to the Gamma-ray and X-ray sources, since this lies in a rather complicated region of the radio sky, the location is promising due to its similarities with other known pulsar wind nebulae having a radio peak just beyond the X-ray nebula, as in, for example, PSR B1929+10 [Becker et al., 2006] and the much smaller scale example of the “Mouse” pulsar wind nebula [Gaensler et al., 2004b]. It is, however, difficult to determine an association with confidence, because the observed feature is roughly the size of the PSF, though there may be a slight elongation. The radio feature seen here is not resolved, as shown in Figure 5.22. Further observations at radio wavelengths may be able to determine more precise morphology and polarization in order to strengthen the association.