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2SXPS Catalogue: About the web pages

Search catalogue | Catalogue paper | Table descriptions | Download catalogue files | Upper limit server.

On this page:

  1. Overview.
  2. Searching the catalogue.
  3. Source pages.
  4. Dataset pages.

Other documentation:


There are four basic groups of web pages available in this online interface to 2SXPS, as described below. These all make use of javascript and should work on any modern, standards-compliant browser. Some features (such as the light curve cross-hairs) may not work on mobile devices since they rely on the cursor location, but these are enhancements and do not affect the basic functionality of the site.

A common feature to all of the web pages is the glossary feature. Many of the terms, labels or headings on the web pages have an accompanying glossary entry giving more details. Such items are identified by a dashed green underline, and the cursor will change to the browser's ‘help’ cursor when it is over the entry. Clicking on the item will open a panel giving the glossary entry. This can be closed by clicking the ‘close’ link in the glossary panel, clicking anywhere outside of the panel, or pressing the escape key.

The four groups of web pages are documented below (unless otherwise stated). They are:

Search pages
Pages used for searching the 2SXPS catalogue.
Source pages
Pages giving details or products related to the individual 2SXPS sources.
Dataset pages
Pages giving details or products related to the 2SXPS dataset.
Upper limit server
Tools to calculate upper limits or flux estimates for sources not detected in 2SXPS. These are documented separately.

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There are two ways to search the catalogue, a simple cone search or a more complex ‘advanced’ query in which you can filter on individual parameters. There are several features common to both searches:

Which catalogue to search
You can select either to search for sources, or for datasets. The default search radius of the cone search is different for the two catalogues.
Cone Search

You can enter either an object name (which will be resolved via SIMBAD) or coordinates. Coordinates should be equatorial in epoch J2000 (FK5), the format is free-form; most common ways of entering coordinates should be supported. The default search radius is a generous 20″ for sources and 750″=12.5′ for datasets: this is approximately the radius of the XRT field of view.

For the simple search, a cone search is mandatory and so these fields must be completed. For the advanced search it is optional. If no details are entered then any sources/datasets matching the other query parameters will be retrieved; if a cone search is requested then only sources/datasets matching the cone search and the other specified parameters will be retrieved.

Which columns to retrieve
There are three pre-defined sets of columns you can retrieve: the basic (default) columns, a minimal set giving the bare details, or all columns. In addition you can select whether the columns giving parameter errors are retrieved. Note: for the advanced search, when you change the settings of these controls this will change which columns' checkboxes are set/unset on the query form, so you can still refine this. The definitions of the samples are listed below.
Output coordinate format
Coordinate fields can be returned either in sexagesimal or decimal formats.
Output format
By default an interactive HTML table containing search results is returned, but you can instead return ASCII data, with either commas or tabs as the field delimiter. In the ASCII case the sexagesimal-format columns will use spaces to separate degrees/hours/minutes/second, whereas in the HTML version context-dependent delimiters (°,′,″) are used.

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Simple (cone) search

The simple search requires a source name or position to be entered, and then simply carries out a cone search around this. Results are always ordered in increasing angular distance from the cone centre. Which columns are retrieved must be selected from one of the predefined samples. There is one option in addition to the common controls listed above: you can choose from some predefined samples of sources/datasets to return. The options are:

All All sources. All datasets.
Clean Sources with a detection flag of 0 or 1, a field flag of 0 or 1, and none of the ‘OpticalLoadingWarning,’ ‘StrayLightWarning’ and ‘NearBrightSourceWarning’ warnings set. Datasets with a field flag of 0 or 1.
Ultra-clean A subset of clean sources with detection and field flags of 0. Datasets with detection flag of 0.

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The advanced search gives you full control over what filters you apply to your search, which data are returned, and how the results are sorted. This is done via the table below the ‘Search’ button. This lists the columns in the database, and provides (in this order):

For any row in this table with data entered in the text box, the specified filter will be added. A cone search will also be applied if a name or position is supplied.

Since the sources table in particular contains a large number of columns, they do not, by default, all appear on the search page as it renders it unwieldy. Above the cone search box is a control, ‘Show filters for which columns?’. From this you can select which columns are listed in the filter table. The option ‘Custom’ allows you to show only controls relating to a certain characteristic such as position or spectral information, making it easy to find the specific controls you want.

As in the simple search there is a drop-down menu allowing you to return only a predefined list of columns, however for the advanced search this behaves in a slightly different way. When you change the setting in this box, the checkboxes in the filter table are modified according to your selection (e.g. if you select to retrieve only basic columns, then the checkbox will be selected for all columns in the basic list, and unset for everything else). However, you can still then select/unselect fields on the filter table. The list of columns that will retrieved is based on which columns are selected in the filter table when you submit the form, not on the value in this dropdown menu. The same is true of the ‘Retrieve error columns?’ control.

Once a search has been submitted the controls will be hidden, however a ‘Modify query’ link will show it again so that the query can be edited.

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Definitions of the predetermined samples

You can select to retrieve only a pre-defined set of columns from the search. Which columns are retrieved for each set are given here. The lists show the columns in the ‘Basic’ sample; those marked with asterisks are in the ‘Minimal’ sample.



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Source pages

The per-source web pages are split into the following series of sections. A navigation bar at the top of the page gives quick access to these.

Summary information

The first section of the page gives an overview of the source details, and a series of thumbnail images. The left-hand side of the pages lists various details, such as the flag, total exposure at the source location, position etc. Links are also provided to search the dynamic Vizier and SIMBAD catalogues, and to build customised products for the source using the online point-source analysis tools provided by the UKSSDC. This latter link will automatically fill out the form, but only selecting data contained within 2SXPS, therefore you may wish to modify the settings if you want to include newer data.

To the right of this section is a panel containing a thumbnail image of the source, 160 pixels (6.3′) to a side, with the source in the centre. A cross-hair marks the source position, and information about the detection flag (given textually in the left-hand summary panel) is also encoded into the cross-hair colours, as described in the next paragraph. By default the image shown is the total-band image. Above the image are links to all of the energy bands and the exposure map. Moving the mouse over one of these updates the displayed image; clicking the link opens the image.

The cross-hairs contain information about the source flag and any warnings. All source thumbnails contain a set of cross-hairs aligned vertically and horizontally: these are coloured according to the source detection flag. Good sources are green, Reasonable are cyan and Poor sources are orange.

If other warnings were present, a second set of cross-hairs will be present, bisecting those just described. These are also coloured according to the warnings, and in the event that multiple warnings exist, the arms of the cross-hairs will have different colours. A red cross-hair indicates that at least one of the warning bits in the detection flag was set. A blue cross-hair means that the source was in a region affected by stray light, and a white cross-hair (black on the exposure map image) means that there is a warning of possible optical loading.

If the field flag associated with this source was set in any way, a warning appears immediately after the summary section. This is because the presence of artifacts or diffuse emission producing structure in the background may result in inaccurate background subtraction which can affect the temporal and spectral parameters presented in the subsequent sections.

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Spectral/flux information

This section consists of a table, giving the details of the source flux and spectral parameters. By default the deduced flux (from both power-law and APEC spectral models) is presented, along with its provenance. If there was a custom-built spectrum created for this source a second table section show the fluxes deduced from this, along with thumbnail images of the spectrum and fit. These images are also links to the spectrum page for the source.

Above the table is a link to show some controls. Using these you can select whether to show both power-law and APEC spectra or just one; which methods of deriving the fluxes should be shown, and whether the spectral details (i.e. photon index / plasma temperature, absorption) are shown, if available.

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Temporal information

This section gives details of the source brightness and variability. First a table shows, for each energy band, the mean and peak count-rates; whether the source was detected in the band and if not, an upper limit on its count-rate, and then the details of measured counts, background level and PSF correction used to determine the mean rate. Finally, this table gives variability information for both per-snapshot and per-obsid binning. This is in the form of the probability that the source is constant based on the Pearson's χ2, thus low values indicate a variable source.

Below this come two panels showing light curves of the source, the first shows one bin per obsID, the second one bin per snapshot. These are interactive plots. At the top of each section are a series of links, one for each band and hardness ratio, which control which light curve is displayed. This is followed by controls to change how the data are shown, controls of the data axes and then a series of links before the actual (interactive) light curve, all described below.

Light curve interactive controls

X-axis time system

After the links to select which energy band or HR is shown, there are two drop-down menus. The first of these selects what time system is used for the x-axis. Three systems are supported:

Swift Mission Elapsed Time. This is seconds in Terrestrial Time (TT) since 2001 January 01.
Modified Julian Date
Barycentric Dynamical Time.
Note that the barycentric correction was carried out for the mid-point of the observation.

(For more details about time systems, we recommend this excellent tutorial on the XTE web pages).

Plotting of non-detections

The next drop-down menu controls how datapoints are shown for observations / snapshots in which the source was not detected in the blind search. The options are to always show 3-σ upper limit arrows in such cases; to show datapoints with 1-σ error-bars, or to automatically choose between these. In this latter case, which is the default option, if the source is detected in the retrospective analysis a datapoint is shown, otherwise an upper limit is given.

Since the blind search was not carried out on individual snapshots, in the per-snapshot light curve, for the purposes of choosing what data points to show, a source was treated as being blindly-detected only for snapshots where the source was retrospectively detected and the snapshot is in an obsid in which the source was blindly detected.

Plotting of bin markers

The datapoints shown with 1-σ error-bars, by default the only marker for each point is the 1-σ error bar on the y-axis, and a line on the x-axis indicating the time covered by the bin. The intersection of these lines indicates the bin centre and y-value. For light curves covering a large time range, or where the count-rate / HR range is large compared to the error bars on the bins, these points may be hard to see. Therefore you can instead select to draw a bin marker in the form of a small circle at each bin position (except for upper limits), to help make the bins clearer. Note that the size of this marker is unrelated to any characteristics of the data point, and may well hide the error bars.

Plot axis controls

By default the controls to change the ranges of the light curve axes are hidden, except for checkboxes to select whether or not to use logarithmic scales. The ‘Show plot axis controls’ link will reveal a form enabling you to directly enter the values for the axis limits. Alternatively you can change these limits interactively with your mouse or pointing device. Note that you cannot scale an axis logarithmically if one of the limits is ≤0.

Data (and enlarge) links

The three links immediately above the plot give you access to the image or data. The first one will generate for download a postscript version of the plot, generated using qdp. The second link displays the data file corresponding to the plot. This is formatted for use in qdp but can easily be read into other plotting packages. The separate datasets (e.g. blind detections, upper limits) are grouped together. The final link grows the light curve panel to the full page width; as well as aiding visual inspection of the light curve, this also results in a larger png version of the file being produced by your browser when you right-click on the image and select to view or save it.

The postscript versions of the plots are designed to match the on-screen plots as closely as possible. However, qdp cannot plot large values on the axes, as are needed when plotting with the TDB or MET time systems. Therefore, the postscript plots generated with these axes have the time values divided by 106 or 108 for TDB and MET respectively.

The interactive light curve plot

The light curve plot itself can also be interacted with, for example, you can click and drag on the light curve to zoom in on the selected area. The full set of controls is:

The key presses and scroll functionality only work when the cursor is over the light curve. These functions may not work on mobile devices.

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External catalogue matches

This section consists of a table giving details of any source found in an external catalogue which is spatially coincident (at the 3-σ level) with the 2SXPS source. The table gives the distance from the 2SPXS source, originating catalogue, source identifier and position information. The table columns are links to sort the table on that column; a second click on the link inverts the sort order. The list of catalogues against which cross-correlation was carried out is given in Section 5 of the 2SXPS paper.

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This section contains up to two tables, giving details of all of the datasets in which the source was found in the blind detection. The first table shows the stacked images and the second the observations; if the source was never detected in a stacked image / observation, then the relevant table will not be shown. If the source is detected in any band (even if not all bands) in a given dataset, that dataset is given in this section.

The tables give the dataset identifier, which links to the web page for that dataset, and some summary details for the source in the dataset (best detection flag, exposure at the source position, HRs and field flag) and then details of the source detection in that dataset in the total band. The link, ‘Show table controls’ above the tables lets you select which details and energy bands are shown.

For each energy band shown there is a link, ‘details’, which expands the table row to show full details of all of the parameters from the blind detection in the dataset and band selected. For any energy band in which the source was not found in the blind search, an upper limit is given with a link to show more details. This link expands the panel and will report whether or not the retrospective analysis yielded a detection; if yes, the count-rate and 1-σ errors from that analysis will be shown.

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The final section of the per-source web pages lists all the datasets which covered the position of the source, but in which it was not detected in energy band. Up to two tables are shown: one for stacked images and one for individual observations.

The tables give the dataset identifier, which links to the web page for that dataset, and then for each energy band an upper limit, and the details (measured counts, expected background, PSF correction factor and exposure at the source position) from which it was produced. A link is given next to the upper limit which will expand the panel and reports whether or not the retrospective analysis yielded a detection; if yes, the count-rate and 1-σ errors from that analysis will be shown.

The link, ‘Show table controls’ above the tables lets you select which details and energy bands are shown.

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Spectrum pages

For sources with more than 50 net counts, a spectrum was automatically created using the tools that power our on-demand and automatic GRB analysis tools. Note: These spectra were created only using datasets in which the source was detected (blind or retrospectively) so as to give the most accurate source parameters (rather than adding datasets containing only background events). However this means that the flux given in the spectral fit will be biased towards higher values for sources which are not always detected. The source mean flux given in the catalogue and the summary and flux sections of this page are not taken directly from this spectrum. Instead, the energy conversion factor (to convert from count-rate to flux) is taken from the spectral fit, and then the source mean count-rate, which is averaged over all observations of the source regardless of whether it was detected, is multiplied by the ECF to give the mean flux.

For sources where a spectrum was created, a dedicated web page exists for those spectra, accessed by clicking on the thumbnail image of the spectrum in the flux section of the source page. This page has a link to download the spectrum; this will yield a gzipped tar file containing all the files necessary to fit the spectrum yourself; they are configured for use in xspec but can be used in other X-ray spectral fitting programs. The main file to load into xspec is interval0pc.pi which contains links to the background spectra, RMF and ARFs in its FITS headers. Full details of the tar file are given in the on-demand spectra documentation.

After the download link, the page has two sections, one for the automatic power-law fit and one for the APEC model fit. Each section contains a plot showing the best-fitting model (with the data binned up for presentation purposes) and the ratio between the data and the model. This is followed by a table giving details of the spectral fit and parameters deduced from it.

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Dataset pages

The dataset pages consist of a self-explanatory summary section, giving basic details of the field, followed by a table of sources detected in the dataset and an interactive image of the dataset. These latter two sections interact with each other, as described below.

Source table

This table lists details of all of the sources deteted in this dataset. Note that not all sources may be detected in every band so, by default, sources may be listed in this table that cannot be seen in the image to the right of the table. Each source in the table has a simple numeric identifier (starting at 1) which identifies it within this dataset only, followed by the source position and detection flag. The table rows are also coloured according to the flag. Moving the cursor over a given source will cause the region associated with that source in the image to turn yellow (if it was detected in the displayed energy band), helping to associate the table entries with specific sources.

The source numbers in the table are links which, when followed, expand the table row to give more details of the source. First, the position error and off-axis angle in this dataset are shown, along with the 2SXPS source identifier. This latter serves as a link to the source results page for that source. Below this some details relating to the source's charateristics in the energy band currently displayed in the image are given; these details depend on whether or not the source was detected in the blind search in this energy band. If it was, a link is given to view the detection details in a new page.

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Interactive image

To the right of the table is a panel containing and controlling an interactive image of the dataset, displayed using js9 — an in-browser version of the popular ds9 astronomical image-viewing software. The top of this section contains links to each of the 2SXPS energy bands and the exposure map; following these links changes which image is displayed. This is followed by an option as to whether to show regions marking the positions of detected sources, and whether to include in this sources which are in 2SXPS and lie within the field of view of the current dataset, but were not detected in the dataset and band displayed.

The next line contains one or two drop-down menus. The first is only present for stacked images larger than 1000x1000 XRT pixels. For these datasets, by default a binned-up image (rebinned to be no bigger than 1000x1000) is presented, to reduce the amount of data (and hence load time) contained in the page. You can select instead to view the image at original resolution, but this may take some minutes to load and your browser may issue a warning about a stalled script while it loads and renders (you should dismiss this warning). For all datasets the second drop-down menu lets you select whether to view the actual XRT image requested, or the background map (with or without the PSF models of fitted sources).

Finally, directly above the js9 panel are links to download the FITS images corresponding to the selected energy band. This is always the full-resolution image, even when it is the binned-up version being displayed.

The js9 image panel itself is an interactive plotting and viewing system and you can zoom, pan, change the scaling etc. We do not document that system here and refer readers to the js9 website. Here we will simply note that the mouse-button use differs from ds9, in that the left button is used to change the colour scaling, and the right one used to pan. Note that we have not installed the server-side component on js9.

Regions in the js9 display and interaction with the source table

For each source found in the blind detection in the energy band shown, a js9 region is plotted in the image. For most sources the region is a circle which is coloured according to the detection flag (green for Good, cyan for Reasonable and orange for Poor). If the source has the stray light warning flag set (i.e. its position overlaps fitted stray light) the region is square instead of circular, and if any of the warning bits in the detection flag were set, the region is a diamond shape.

If you select one of the displayed regions, the corresponding entry in the sources table to the left of the image will be highlighted and (if necessary) the table scrolled to make it visible.

If the ‘Include sources not detected in the image?’ option is set, then other regions are also shown. Sources which are detected in the current dataset, but not the selected band, will appear as coloured regions like those displayed already, but with a colon before the source number. Sources not detected in this dataset appear as white regions with a label ‘G’, ‘R’ or ‘P’ indicating whether the source was a Good, Reasonable or Poor detection.

We wish to particularly thank js9 developer Eric Mandel for his support and responsiveness to our queries, bug reports and general pestering during the creation of these web pages.

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Individual detection details

The sources table provides a link to view full detection details of a source in the viewed dataset and energy band (if it was detected in the blind search on that band). This opens a new page listing all of the properties related to that detection. Each source property has a glossary entry describing it, and corresponds to an entry in the detections database table.

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