1.3 SITUACION ACTUAL DE LA METROETHERNET DE LA EMPRESA
2.1.2 Componentes del sistema
2.1.2.4 Tabla de características técnicas de la interfaz aire
2.1.2.5.1 Servicios Ethernet
In this section I compare the number of sources found from the log N-log S study (see Chap. 8) to the number of identified and classified XRBs (including sources in GlCs). The classified sources were taken
5.38×100 4 5.39×104 5.4×104 5.41×104 5.42×104 50 100 150 Flux (10 −14 erg cm −2 s −1)
Modified Julian Day XMMM31 J004317.5+412745 c9 c7 c8 c6 c5 7283 7284 7285 7286
(a) Light curve
0.01 0.02 0.05 Counts s −1 keV −1 1 0.5 2 −5×10 −3 5×10 −3 Residials
Channel Energy (keV)
pn FF thin
mos1 FF medium mos2 FF medium XMMM31 J004317.5+412745 c9 XMM−Newton, EPIC
(b) EPIC spectrum
Figure 9.32: Long-term light curve (a) and combined EPIC spectrum (b) of XMMM31 J004317.5+412745. The light curve contains data fromXMM-Newton(black crosses) and
Chandra(green circles) observations. 3σ upper limits of non detections are indicated by red arrows. The spectrum was fitted with an absorbed power-law model.
5 10 15 −1 −0.5 0 0.5 1 HR5 Flux (10−13 erg cm−2 s−1) c9 c7 c8
(a) Hardness flux
−1 −0.5 0 0.5 1 −1 −0.5 0 0.5 1 HR5 HR2 c9 c7 c8 (b) Colour colour
Figure 9.33: Hardness flux (a) and colour-colour (b) diagrams of XMMM31 J004317.5+412745. The sizes of the data points reflect the times of the observations. Larger data points represent later observa- tions.
Table 9.23:Spectral parameters of XMMM31 J004317.5+412745. M 31 field Model NH kBT Rin
√
cosi∗ Photon χ2 L†
X Instrument
(×1021cm−2) (keV) (km) Index (d.o.f)
XMMM31 J004317.5+412745 c7 DISCBB 0.15+0−0..4515 1.242+0−0..281213 6±2 26.02(22) 0.20 PN+M1+M2 c7 BREMSS 0.93+0.55 −0.45 6.886+7−2..926762 20.24(22) 0.27 PN+M1+M2 c7 PL 1.49+0−0..7076 1.70±0.23 19.29(22) 0.32 PN+M1+M2 c9 DISCBB 0.31+0−0..1614 1.423+0−0..138121 11±2 50.82(25) 1.19 PN+M1+M2 c9 BREMSS 0.95+0−0..2219 9.494+4−2..398376 29.47(25) 1.53 PN+M1+M2 c9 PL 1.29+0−0..3027 1.58+0−0..1009 28.57(25) 1.45 PN+M1+M2 TP PL 1.1±0.4 1.54+0−0..1413 30.9(23) 1.057 ACIS-S Notes:
∗: effective inner disc radius, whereiis the inclination angle of the disc
from Table 9.4.
The examination was carried out for the five regions, which were defined to study the radial dependence
of the log N-log S relations (cf. Fig. 8.3). The number of “missing” XRBs is the difference between the
number of expected XRBs, which was derived from the log N-log S relations, and the number of identi- fied/classified XRBs listed in Table 9.4.
Table 9.24 shows the number of sources obtained from the log N-log S relations (Cols. 3, 6), from corre- lations with the XMM LP-total catalogue (4, 7), and the differences between these numbers (number of miss-
ing XRBs: Cols. 5, 8) for two different limiting fluxes of 3.2×10−14erg cm−2s−1and10−13erg cm−2s−1
in the 2.0 – 10.0 keV band. We see that∼50% of the brighter (10−13erg cm−2s−1) XRBs from the XMM
LP-hard catalogue that are expected to be located in the dust ring region or outer disc region, and that
∼100% of the brighter XRBs from the XMM LP-hard catalogue that are expected to be located in the re-
gion beyond the D25ellipse, are classified as XRBs in the XMM LP-total catalogue. For a limiting flux of
3.2×10−14erg cm−2 s−1about one third of the XRBs from the XMM LP-hard catalogue that are expected
to be located in the dust ring region or outer disc region are classified as XRBs in the XMM LP-total cat- alogue. In other words, many faint XRBs from the XMM LP-hard catalogue with fluxes in the range of
3.2×10−14 erg cm−2s−1 to10−13erg cm−2 s−1 are only classified as<hard>sources in the XMM LP-
total catalogue. This is not surprising, as it is more complicated to detect variability in fainter sources than
in bright sources (cf.Sect. 7.4). This finding is also reflected in the lower flux limits of the detected XRBs
and GlCs (cf.Sects. 9.4.3 and 9.4.4), as the classification of XRBs is based on variability (cf.Sect. 9.4.3).
Another result, which can be drawn from Table 9.24, is that many of the XRBs that are located in the inner disc of M 31 were not classified/identified in the XMM LP-total catalogue. The inner disc region contains large parts of the S1 and N1 fields, where each field was only covered in a single observation. Therefore it was not possible to determine the variability of sources located in these parts. Hence, the number of classified XRBs is below the expected number from the log N-log S diagram, due to there being too few sources recognised as variable.
The XMM LP-hard catalogue contains 45 sources that are listed as GlCs or GlC candidates in the XMM LP-total catalogue. Figure 9.34 shows the cumulative luminosity function of these sources. The CLF breaks
at about 4.6×1037erg s−1(2.0–10.0 keV). Below that break it is well fitted by a power-law with a slope of
∼0.3, and above the break the slope is about 1.2. The slopes are in good agreement with the values derived
in Kong et al. (2003a) for the population of LMXBs in globular clusters of M 31. The break luminosity seems to be a bit higher in the present study.
Table 9.24: Number of XRBs and missing XRBs in different regions for two different limiting fluxes (2.0–10.0 keV)
flux>3.2×10−14erg cm−2s−1 flux>10−13erg cm−2s−1
Region slope XMMLPh XMMLPt ∆ XMMLPh XMMLPt ∆
area−1 area−1 area−1 area−1 area−1 area−1
(1) (2) (3) (4) (5) (6) (7) (8)
inner disc 0.68±0.09 42±6 13 29±6 24.3±4.7 11 13.5±4.5 dust ring 0.56±0.11 22±4 7 15±4 9.9±2.7 5 5±3 outer disc 0.82±0.36 10±3 3 7±3 3.8±1.7 2 2±2 beyond D25 1.69±0.65 13±3 1 12±3 0.3±1.0 1 0
36
36.5
37
37.5
38
0
0.5
1
log(N)
log(Luminosity)
Figure 9.34:Cumulative luminosity function for X-ray sources located in globular clusters and globular cluster candidates.
Conclusions and Outlook
10.1 Conclusions
The classification of individual sources of X-ray emission in a galaxy provides us with new insights into its structure, dynamical history and evolution. Hence, it is necessary to obtain large samples of classified X-ray sources in nearby galaxies and to establish relationships to the galactic properties. These findings then can be applied to more distant galaxies.
This dissertation presents the analysis of a large and deep XMM-Newton survey of the bright Local
Group SA(s)b galaxy M 31. The survey observations were taken between June 2006 and February 2008. Together with re-analysed archival observations from June 2000 to July 2004 a full coverage of the whole
D25ellipse of M 31 withXMM-Newton, down to luminosity of∼1035erg s−1 in the 0.2 – 4.5 keV band, is
provided, for the first time.
The analysis of combined and individual observations allowed the study of faint persistent sources as well as brighter variable sources.
Within the investigations of the long term time variability of sources in the central field of M 31 (Chap. 6), 39 sources were found in addition to the 265 reported by PFH2005 in that field. The identifi- cation and classification of these sources, which was based on properties in the X-ray wavelength regime (hardness ratios and temporal variability) and on cross correlations with source catalogues at other wave- lengths, provide three SSS candidates, one SNR and six SNR candidates, one GlC candidate, three XRBs and four XRB candidates. Additionally, one foreground star candidate was identified and fifteen sources
were classified as<hard>, which may either be XRBs or Crab-like SNRs in M 31, or background AGN.
Five sources remained unidentified and without classification. Two sources were found to be extended. One
of them was classified as<hard>. The other remain without classification. Six sources of PFH2005, which
were classified as<hard>, showed distinct time variability. Based on that variability, their hardness ratios
and the strong absorption in the centre of M 31, they were classified as XRB candidates. The SNR classifi- cation of the source [PFH2005] 295 was changed to foreground star due to its distinct time variability and its identification with a faint stellar object. Other SNR classifications (sources [PFH2005] 316, [PFH2005] 318) were rejected due to time variability of the sources.
The source catalogue of the LargeXMM-NewtonSurvey of M 31 (Chap. 7) contains 1 948 sources in
total, of which 961 sources were detected for the first time in X-rays. The XID source luminosities range
from∼4.4×1034erg s−1 to 2.7×1038erg s−1. The previously found differences in the spatial distribution
of bright (>∼1037 erg s−1) sources between the northern and southern disc could not be confirmed. The
identification and classification of the sources was based on properties in the X-ray wavelength regime: hardness ratios, extent and temporal variability. In addition, information obtained from cross correlations with M 31 catalogues in the radio, infra-red, optical and X-ray wavelength regimes were used.
The source catalogue contains 12 sources, with spatial extent between 600.20 and 2300.03. From spectral
investigation and comparison to optical images, five sources were classified as galaxy cluster candidates.
317 from 1 443 examined sources showed long term variability with a significance>3σbetween theXMM-
Newtonobservations. These include 173 sources in the disc, that were not covered in the study of the central field (Chap. 6). Three sources located in the outskirts of the central field could not have been detected as
variable in the study presented in Chap. 6, as they only showed variability with a significance>3σbetween
the archival and the “Large Project” observations. For 69 sources the flux varied by more than a factor of
five, and for ten by even more than a factor of 100 within theXMM-Newtonobservations.
To investigate the log N-log S relations of “hard” sources in the field of M 31 (Chap. 8) a catalogue of sources detected in the 2.0 – 10.0 keV energy range was created. Softer energies were excluded form this study to minimise the effects of absorption due to the interstellar medium of M 31. This catalogue
contains 1 254 sources, of which seven were found to be extended. A correlation with the Large XMM-
NewtonSurvey catalogue showed that, apart from 24 sources identified with foreground stars and foreground star candidates, and eight SNRs and SNR candidates, only sources identified / classified as XRBs, GlCs,
background sources, <hard> sources or those without classification were included in the 2.0 – 10.0 keV
catalogue. Hence, after background sources were subtracted, the log N-log S relations mainly probed the population of XRBs. The contribution of the background sources was estimated from the COSMOS field. This is an approximation, as the population of background sources in the field of M 31 has not to be the same as that observed in the COSMOS field.
The slope of the background corrected log N-log S relation for the whole galaxy is consistent with the expectation for spiral galaxies. To study the spatial dependence of the log N-log S relation the galaxy was di- vided on the one hand along the major axis (eastern and western part) as well as along the minor axis (north- ern and southern part), and on the other hand in five regions, which roughly correspond to the bulge, inner
disk, dust ring, outer disk, and the area beyond the D25ellipse of M 31. For the western and northern part,
the slopes are flatter than for the southern and eastern part. The “bump” in the∼3.2–8×10−13erg cm−2s−1
flux range that was detected in the CNC of the whole galaxy was also present in the CNCs of the eastern and northern part, while it was not visible in the western and southern parts. It was detected in the log N-log S relation of the dust ring region, too. The slopes of the CNCs of the inner disc and dust ring regions are in the value range expected from the universal log N-log S relation of HMXBs. Furthermore, the relation between the number of sources and star formation rate for these two regions is consistent with the one presented in Grimm et al. (2003), although the number of sources is rather low. Comparing the number of sources ex- pected for an HMXB population with the background corrected CNCs of the inner disc and dust ring region showed that the CNCs of the dust ring region only were in agreement with the expectation. However, addi- tional refinement in the theoretical prediction of the log N-log S relation (luminosity function) for HMXBs at low star forming rates is needed to confirm this finding.
The radial dependence of the source distribution in M 31’s disc could be well fitted with an exponential
profile, for limiting fluxes of∼3.2×10−14erg cm−2s−1and10−13erg cm−2s−1(=ˆ2.3×1036erg s−1 and
7.3×1036 erg s−1), respectively. The region beyond the D
25 ellipse still contains about 13 sources/deg2
of M 31 with fluxes above the completeness limit of ∼3.2×10−14 erg cm−2s−1 (=ˆ2.3×1036 erg s−1).
About 60% of all sources in the XMM LP-hard catalogue with fluxes above 3.2×10−14 erg cm−2s−1
(=ˆ2.3×1036erg s−1) were background sources. An investigation into the spatial dependence of the amount
of background sources showed that in the inner disc region∼20% of the sources were background objects,
while this fraction increased to>∼80% in the outer areas of M 31.
Discrepancies in source detection between the Large XMM-Newton Survey catalogue and previous
XMM-Newtoncatalogues could be explained by different search strategies, and differences in the processing of the data, in the parameter settings of the detection runs and in the software versions used. Correlations
able, transient, or unresolved. This is specifically true for sources located close to the centre of M 31, where
Chandra’s higher spatial resolution allows us to resolve more sources. Some of the undetected sources from
previousROSATstudies were located outside the field covered withXMM-Newton. However there were sev-
eral sources detected byROSATthat had aROSATdetection likelihood larger than 15. If these sources were
still in a bright state they should have been detected withXMM-Newton. Thus the fact that these sources are
not detected withXMM-Newtonimplies that they are transient or at least highly variable sources. On the
other hand 242<hard>XMM-Newtonsources were found with XID fluxes larger than10−14erg cm−2s−1,
however not detected withROSAT.
To study the properties of the different source populations of M 31, it was necessary to separate fore- ground stars (39 plus 227 candidates) and background sources (11 AGN and 49 candidates, 4 galaxies and 19 candidates, 1 galaxy cluster and 5 candidates) from the sources of M 31. 1 263 sources could only be
classified as<hard>, while 139 sources remained without identification or classification.
The catalogue of the LargeXMM-Newtonsurvey of M 31 contains 40 SSS candidates, with unabsorbed
0.2–1.0 keV luminosities between 1.8×1034 erg s−1 and 2.8×1037 erg s−1. SSSs are concentrated to the
centre of M 31, which can be explained by their correlation with optical novae, and by the overall spatial
distribution of M 31 late type stars (i. e.enhanced density towards the centre). Of the 14 identifications made
of optical novae, five were presented in more detail. Among them is the first nova/SSS detected in an M 31 globular cluster. Correlations with previous X-ray studies revealed that only three SSSs were visible for at least one decade. This is in agreement with the strong long term variability found for the class of SSSs. In
addition the correlations showed that previous SSS studies ofROSATandChandracontain a non-negligible
number of sources that were erroneously classified as SSSs. In particularChandrastudies had low selection
power. Two sources (No 1 034 and No 1 136) showed a transition from supersoft to hard state between the
ChandraandXMM-Newtonobservations. This behaviour is consistent with the behaviour known to occur
in BH XRBs. However, other source types likee. g.symbiotic stars cannot be excluded yet.
The 25 identified and 37 classified SNRs had XID luminosities between 1.1×1035erg s−1and 4.3×1036
erg s−1. Three of the 25 identified SNRs were detected for the first time in X-rays. For one SNR theROSAT
classification can be confirmed. Six of the SNR candidates were selected from correlations with sources in SNR catalogues from the literature. As these six sources had rather “hard” hardness ratios they are good candidates for “plerions”. An investigation of the spatial distribution showed that most SNRs and candidates are located in regions of enhanced star formation, especially along the 10 kpc dust ring in M 31. This connection between SNRs and star forming regions, implies that most of the remnants are from type II supernovae. Most of the SNR classifications from previous studies have been confirmed. However, in five cases these classifications are doubtful.
The population of “hard” M 31 sources mainly consists of XRBs. These rather bright sources (XID
luminosity range: 1.0×1036erg s−1to 2.7×1038erg s−1) were selected from their transient nature or strong
long term variability (variability factor>10; 10 identified, 26 classified sources). The spectral properties of
three transient sources were presented in more detail.
A sub-class of LMXBs is located in globular clusters. They were selected from correlations with optical sources included in globular cluster catalogues (36 identified, 17 classified sources). The XID luminosity
of GlCs ranges from 2.3×1035 erg s−1 to 1.0×1038 erg s−1. The spatial distribution of that source class
also showed an enhanced concentration to the centre of M 31. From detailed spectral and time variability studies of three GlC sources, one was identified as a black hole LMXB and an other one as a neutron star candidate. Changes in source classification from previous studies were nearly always due to changes in the classifications of the optical counterpart in newer papers.
From optical and X-ray colour-colour diagrams possible HMXB candidates were selected. If the sources were bright enough, an absorbed power-law model was fitted to the source spectra. Two of the candidates had a photon index consistent with the photon index range of NS HMXBs. Hence these two sources were
suggested as new HMXB candidates.
A comparison between the number of XRBs found in the log N-log S study with the number of identified and classified XRBs (including those located in GlCs) listed in the XMM LP-total catalogue showed that
many faint XRBs detected in the log N-log S study with 2.0–10.0 keV fluxes in the range of 3.2×10−14erg
cm−2s−1 to10−13 erg cm−2 s−1 (=ˆ2.3×1036 erg s−1 to 7.3×1036erg s−1) were not identified as XRBs
or XRB candidates in the XMM LP-total catalogue and thus were only classified as<hard>sources in the
XMM LP-total catalogue. This is not surprising, as variability was used to classify XRBs and it is more complicated to detect variability of fainter sources than of bright sources. Many XRBs that are located in the inner disc of M 31 were not classified/identified in the XMM LP-total catalogue. One reason is that large parts of the inner disc region are located in the S1 and N1 fields, for which no variability could have been determined, because each of them was covered in only one observation.
This work gave us deeper insights into the long-term variability, spatial and flux distribution, and log N- log S relation of the sources in the field of M 31 and thus helped us to improve our understanding of the X-ray source population of M 31.