1. The spectral properties of Galactic X-ray sources at faint fluxes
Kristiina Byckling
Bob Warwick
Dolores Perez-Ramirez
University of Leicester, UK
X-ray Universe 2008
Granada,

2. Contents Introduction XMM observations in the Galactic Plane
Spectra of sources at intermediate fluxes
Conclusions and future work

3. Introduction
The brightest and most luminous X-ray sources in the Galaxy are high-mass and low-mass binaries (L_x = 10^36 – 10^39 erg s^-1).
At intermediate to faint fluxes, other classes of source such as SNRs, active binaries and CVs are also detected, although we don’t yet have detailed knowledge of the underlying populations.
By studying the latter sources detected serendipitously in XMM observations we hope to
Widen our knowledge of the Galactic source populations at intermediate to faint fluxes
Better understand the contribution to the unresolved X-ray emission from the Galactic Plane (GP)
-the brightest and the most luminous X-ray sources in the Galaxy are high-mass and low-mass binaries
-luminosities
-also sources at intermediate to faint fluxes, such as SNRs, CVs and active binaries.
-good knowledge on the source populations at bright fluxes whereas the knowledge at intermediate to faint fluxes lacking
-the reason we want to study the sources at these faint fluxes is that we want to widen our knowledge of these populations, and also understand how they contribute to the X-ray emission, which is still unresolved, from the GP

4. Soft Galactic emission Hard Galactic Ridge
-Suzaku data from 2007 by Ebisawa et al. 2007
Black one shows the Galactic Ridge X-ray spectrum, the red one the particle bg spectrum.
- the spectrum can be divided into two components: hard Galactic Ridge and soft Galactic emission. The feature which is clearly resolved for the first time are the iron K lines. Ebisawa et al fitted the Galactic Ridge X-ray spectrum with a powerlaw and 3 gaussians. The spectral fit image shows nicely the fit to the three iron lines at 6.4, 6,7 and 6.96 keV
Ebisawa et al. 2007

5. XMM observations in the Galactic Plane
XMM has observed a number of fields in the GP
-The XMM has made many observations along the GP, with shorter and longer exposure times. The images show how the observations have scattered around the GP. Also an image of the other side of the GP.

6. XMM observations in the Galactic Plane
Immediate tasks of the survey are to...
Identify a “clean” sample of sources
Study the spectral properties of the sample
Study the variation of spatial density with (l,b)
Correlate with 2MASS and other multiwavelength data sets
Pick out other interesting features in the observations
-Our survey consists of several tasks, which will be done soon. We want to identify a clean sample of sources and study the spectral features of this sample. We will also study the how the spatial density of the sources varies with Galactic coordinates, and see how the sources are correlated with 2MASS sources and other multiwavelength data. And also, if something interesting appears in the observations, we will look at these features more closely.

7. XMM observations in the Galactic Plane
We used the 2XMM catalogue for source identification
We selected fields in the region l = ±45, b = ±2.5 deg, i.e. the first galactic quadrant
In the XMM archive, we found ~100 data sets with suitable characteristics
We have rejected observations which are dominated by the target source or which show complex structure.
The typical fluxes for the sources studies range from ~10^-14 erg/s/cm^2 – 10^-12 erg/s/cm^2
-We have used the 2XMM catalogue sources to carry out the survey. The fields which we have used are located along the Galactic plane from -45 to +45 degrees, extending degrees in latitude.
-We have found ~100 observations, which are suitable for our survey, from the archive, and rejected those observations which are dominated by the target source in the field of view, or which show complex structure, such as some SNRs.
-Typical flux range for these sources vary between 10^-14 and 10^-12 erg/s/cm^2

8. XMM observations in the Galactic Plane: source sample
The “good” sources were chosen by using suitable selection criteria applied to the 2XMM catalogue, e.g. sources with detection maximum likelihood > 15 and by visual checking of the observations
Sources were flagged as “bad”, if confused by the target source etc. These were excluded from the analysis.
After final screening the total number of “good” sources was ~1600
-We used a selection criteria to choose the good sources, for example, we are using only sources with maximum likelihood > 15. And we have also visually checked each observation.
-If the sources were confursed by the target sources, those sources were flagged as bad and excluded from the analysis. After the final screening, the number of good sources was around For our survey, we will use only sources with at least 200 pn counts, otherwise they will be too faint.

9. Spectra of sources at intermediate fluxes
Our plan is to study the spectra of the brightest sources in the sample by summing the spectra of groups of sources
For this purpose we defined a sub-sample of sources each with a minimum of 200 pn counts (net of background)
A sub-sample of 184 sources met our criteria
-The idea in studying the spectra of the sources is to sum the spectra of the brightest sources. We will divide the sources into group according to the hardness ratio, and sum the spectra according to the hardness ratio. This is why we defined a sub-sample of sources with minimum of 200 net pn counts. With this method, we obtained a sub-sample of 184 sources which we will use for further analysis, but there are more sources to come....

10. Spectra of sources at intermediate fluxes
-An example field: (l=7.6 deg, b=1.4 deg)
- A combined PN/M1/M2 image in bands 1, 2, 3, 4 and 5
pn T_exp ~ s
-The field an example of one of the fields studied. The field is located at longitude of 7.6 degrees and latituded of 1.4 degrees. A combined PN/MOS1/MOS2 image in energy bands 1, 2, 3, 4 and 5.
-The arrow shows an example source which we included in the analysis. The pn count rate is ..??. We also show the spectrum of this source.

11. 184 pn sources divided into soft and hard
-The 184 pn sources which are used in the analysis are divided into soft and hard group. We can see a wide variety of hardness ratios.
184 pn sources divided into soft and hard

12. 184 pn sources divided into soft and hard
-and these groups are still divided into soft, soft-medium, medium-hard and hard source groups.
soft
soft-
medium
medium-
hard
hard
184 pn sources divided into soft and hard

13. Spectra of sources at intermediate fluxes: preliminary results
-The images show the preliminary results. We have summed the individual spectra of the sources belonging to the groups shown previously. The black spectrum shows the summed source spectrum and the red one the summed and scaled background spectrum.
-After dividing the sources into four groups according to the hardness ratio, we have 33 soft sources and 12 soft-medium sources.
The summed spectrum of soft sources
The summed spectrum of soft-medium sources
Red: summed and scaled background spectrum
Black: summed source spectrum

14. Spectra of sources at intermediate fluxes: preliminary results
-And the same for the medium-hard and hard sources. 16 medium-hard sources and 37 hard sources.
The summed spectrum of medium-hard sources
The summed spectrum of hard sources

15. Spectra of sources at intermediate fluxes: preliminary results
SOFT-
MEDIUM
SOFT
wabs (powerlaw+2 mekals)
n_H = 0.19 x 10^22 cm^-2
kT_1 = 0.46 keV
kT_2 = 0.95 keV
Photon index = 2.9
wabs(powerlaw+2 gaussians)
n_H=0.69 x 10^22 cm^-2
kT=2.8 keV
Photon index = 2.9
Work in progress....
MEDIUM-
HARD
- More preliminary results: we have fitted the four summed spectra in Xspec. Interestingly, we can see the iron lines in the soft-medium, medium-hard and hard spectra. Although, these results and fits still require more work.
HARD
wabs(powerlaw+3 gaussians)
n_H=0.98 x 10^22 cm^-2
kT=4.6 keV
Photon index = 2.18
wabs*pcfabs(bremss+3 gaussians)
n_H=3.07 x 10^22 cm^-2
kT=2.97 keV

16. Conclusions & future work
The average spectral properties of resolved sources at intermediate fluxes show some of features apparent in the “diffuse” spectrum of the GP
In future work, we will hope to investigate:
Spectral properties of the sources in more detail with a view investigating the contribution of faint galactic source populations to the GP emission.
Study the source density as a function of galactic latitude and longitude, and investigate the nature of the population through multiwavelength follow-up
-As a conclusion, we are able to see that our spectra show some of the features which are apparent in the diffuse GP spectrum.
-In the future, there still remains things to do, such as study the spectral feature of the sources in more detail and with a view investigating how these faint galactic source populations contribure to the GP emission.
-We will also study the source density as a function of Galactic coordinates, and investigate the nature of the population in multiwavelength.