THE INTEGRAL LMXRB MONITORING PROGRAMME
6.6 First results
In the frame of the multiwavelength campains and to keep track of all the executed and planned GPS and GCDE pointings I created a web page40including all the relevant information.
Coverage maps such as the one in Fig.6.5 are given for all the executed and planned observations.
Figure 6.5: Coverage map provided for the currently planned GPS of revolution 226.
The page is regularly updated and is publicly available in the attempt to ease coordinated observations within our collaboration as well as for external groups.
6.6 First results
We have analysed one year of INTEGRAL core programme data with the Off-line Scientific Analysis, OSA 3.0. The first impression from this analysis is that these data constitute a huge data base of information that has to be methodically analysed and studied. Just to give a feeling of the amount of results that can be extracted, we give in Table 6.3 the list of sources of our sample that have been detected at least in five pointings at a significance level of at least 5σ in the 20-40 keV ISGRI energy band.
Each pointing (2000s) can contain interesting variability patterns. All these data have to be carefully checked and fluxes in physical units (or upper limits) have to be given per source and energy band. Automatising the analysis is the only way to be able to analyse such a large data set. Once the results are available, each source has to be closely looked at: in Table 6.3, it is unlikely that all the detections at 5σ in the 200-400 keV band are real. The analysis has been performed in a "forcing mode": the software was asked to extract the flux at the catalogue position. If the source happens to be on the rim of the detector where normally there is a
40http://isdc.unige.ch/∼paizis/CP.html
Name Det1 Det2 Det3 Det4 Det5 Det6 Det7
Table 6.3: Number of pointings per energy band in which each source has been detected by ISGRI with a detection significance higher than 5σ (Detx with x=1,...,7 correspond to 20-40, 40-60, 60-80, 80-100, 100-150, 150-200, 200-400 keV). These numbers do not give information about the relative brightness of the source: the Crab is not dimmer than GX 9+1 but it was covered less often due to its position relative to the dithering pattern. What we intend to show is the amount of data available (each pointing is about 2000s long). The presence of detections in more than one energy band of course denotes a harder source. For comparison, the Crab is included in the last line of the table.
6.6. First results 77
noise pattern, the flux and corresponding signal to noise will be extracted and attributed to the source. This way of extracting the data was chosen for the first analysis of all the available core programme data in order to be able to extract upper limits for each source per pointing. The drawback of the noisy false detections can be minimised by selecting only the pointings in which the source was within a certain off-axis angle from the pointing direction.
The interpretation of the data from the LMXRBs of the sample can be done at many levels.
The highest level is to have a fast glance at all the sources via their lightcurves and hardness ratios. These types of results are being put on the web and give the hard X-ray flux history. With more data being added it will be easier to have a glance at the usual behaviour of the source, spotting unusual fluxes i.e. states that need to be further investigated possibly with coordinated multiwavelength observations.
The infrastructure for this step is already existing. We have built tools to regularly analyse the data, extract the results and display them in an efficient way (an example of the final output for X 1822-371 has been shown in Figs. 6.2 and 6.3).
A second level of study will be to seek a synthetic view of all the data. This means selecting some common parameters to characterise the spectra and the lightcurves for each source and then to see how these parameters depend on the source classification. Properties already seen in the soft X-rays determining a class might be confirmed but different classifications might reveal themselves. Examples for such parameters are the long term variability (is there a systematic difference in the hard X-ray variability among the different classes?), the average spectral hard-ness (would we define black holes, Atolls and Z sources on the basis of the hard X-ray spectra?), and INTEGRALdefined colour-colour diagrams (how do these sources move in a hard CD on a long term?). Figure 6.6 shows the combined CD for different types of sources based on a large RXTE archive. This long term study shows that portions of the CD have never been covered by neutron star systems, possibly due to their boundary layer emission. This kind of comparison requires large sets of data to have better chances to catch the sources in all their possible states.
A similar work will be done with the INTEGRAL data base, in newly defined, harder energy bands to seek e.g. for the influence of the boundary layer (or event horizon) in the less studied hard X-ray domain.
Results of this kind of study will be collected mainly on the long run. Large amounts of data spanning over a long period have to be gathered. As it has already been shown by Muno et al.
(2002) and Gierliński and Done (2002) only after collecting several years ofRXTE data could it be possible to see that actually Atoll sources, if observed long enough, do display a Z in the CD.
Currently the raw material has been extracted for all the sources of our sample. A few examples of ISGRI sky maps are given in Figs. 6.7, 6.8, 6.9. Each map is the mosaic of one revolution. These sky maps are part of my contribution to the HEASARC archive web pages.
The mosaic of all the revolutions with GPS and GCDE data of the AO1 (about 5.7 Msec) was already given in Fig. 5.7.
A few examples of the lightcurves that are automatically extracted by the existing infrastruc-ture are given in Figs. 6.10 to 6.16. The time covered is IJD∼[1100-1300] which corresponds to the period between January 2003 and July 2003. The source coverage depends on the position of the source with respect to the GPS and GCDE scans (Cyg X-2 and Sco X-1 are less thoroughly covered).
The scientific analysis package used to extract these lightcurves is OSA 3.0, with which 1Crab gives ∼100,∼45 and∼20 counts per second in the 20–40, 40–60, 60–80 keV bands respectively.
In the lightcurves each bin corresponds to one pointing (about 2000 sec). The different size
Figure 6.6: Combined colour-colour diagrams for differnt source types. Hard colour is the ratio of fluxes in 9.7–16 and 6.4–9.7 keV bands and soft colour is the ratio of 4–6.4 and 3–4 keV. Open circles represent black hole candidates, red, cyan and blue filled circles neutron star systems i.e.
atolls, Z sources and the peculiar Cir X-1, respectively. The hatched region is inaccessible to neutron stars due to their boundary layer emission. Spectra with colours falling in this region are seen only in black hole candidates (taken from Done & Gierliński 2003).
Figure 6.7: ISGRI mosaic of the GPS performed in revolution 66 (about 25 ksec, 20-40 keV).
6.6. First results 79
Figure 6.8: ISGRI mosaic of the GPS performed in revolution 67 (about 20 ksec, 20-40 keV).
Figure 6.9: ISGRI mosaic of the GCDE performed in revolution 65 (about 200 ksec, 20-40 keV).
of the error bars within one source is also related to the position of the source with respect to the ISGRI FOV: a source in the FCFOV is detected with a better signal to noise than in the PCFOV (see Section 4.2.2).
The tools available to extract the data allow a certain degree of interaction: it is possible to choose the source to be displayed, the type of diagram (lightcurve, HID, CD etc), the number of energy bands, the axis ranges and the instrument. Other correlations can be also studied on the fly such as the countrate or detection significance as a function of the off-axis angle. In this way it is possible to browse our archive in an efficient and quick way.
We have started a more detailed study on the persistently bright sources for which we had sufficient data. The results are described in the two papers included in this chapter. The first one is the paper prepared for the A&A INTEGRALspecial issue (Paizis et al., 2003) while the second is the contribution to the 5thINTEGRALWorkshop held in Munich (Paizis et al., 2004b).
At the time of writing of the first one, many parts of the software had still to be validated and the results obtained to be cross-checked. The instrument calibrations were in a very raw state and this is reflected in the paper where mainly the potential of the monitoring programme is shown. Things evolved until the second paper, for which we had a better knowledge of the in-struments and software issues. We went further in the study, starting to look into the variations of the sources as a class, into the average spectra and into the behaviour of the sources in the traditional energy bands.
The third level of study is the most detailed one and consists of taking one source at a time and going through all the available data, in a systematic study of its temporal and spectral properties. In the next chapter such a study for GX 5-1 is given (Paizis et al., 2004a).
6.6. First results 81
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Lightcurve for Sco X-1 (isgri)
Figure 6.10: ISGRI lightcurves of Sco X-1 in the 20–40, 40–60, 60–80 keV bands. The error bars are at 1σ.
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Lightcurve for Cyg X-2 (isgri)
Figure 6.11: ISGRI lightcurves of Cyg X-2 in the 20–40, 40–60, 60–80 keV bands. The error bars are at 1σ.
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Lightcurve for GX 3+1 (isgri)
Figure 6.12: ISGRI lightcurves of GX 3+1 in the 20–40, 40–60, 60–80 keV bands. The error bars are at 1σ.
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Lightcurve for GX 9+1 (isgri)
Figure 6.13: ISGRI lightcurves of GX 9+1 in the 20–40, 40–60, 60–80 keV bands. The error bars are at 1σ.
6.6. First results 85
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Lightcurve for 1728-169 (isgri)
Figure 6.14: ISGRI lightcurves of GX 9+9 in the 20–40, 40–60, 60–80 keV bands. The error bars are at 1σ.
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Lightcurve for GX 17+2 (isgri)
Figure 6.15: ISGRI lightcurves of GX 17+2 in the 20–40, 40–60, 60–80 keV bands. The error bars are at 1σ.
6.6. First results 87
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Figure 6.16: ISGRI lightcurves of GX 5-1 in the 20–40, 40–60, 60–80 keV bands based. The error bars are at 1σ.
DOI: 10.1051/0004-6361:20031207
cESO 2003