On-demand source detection — Online Documentation

Overview.
Source table.
Image panel.
File downloads.

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Overview

The results of the source detection will give you a list of sources detected, along with an image of the field. If sources are detected, they are marked in that image.

This web page and this system is heavily based on the 2SXPS catalogue analysis. We advise you read the documentation supporting that catalogue, and the supporting paper to understand all of the details.

Not all aspects of the catalogue tools can be used in the on-demand analysis presented here. Specifically:

Times with bad astrometric solutions are not identified or removed before source detection.
The detections in the various bands are not combined into a unique source list for the dataset.
The XRT do not manually screen these results (obviously), so it is your responsibilty to check for artifacts such as diffuse emission.
No summary analysis of the field (e.g. average background, quality checks) are reported.

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Source table

On the left-hand side of the page is given a table, listing the sources found for the currently selected energy band. Above the table a control lets you select whether the coordinates are sexagesimal or decimal, and a link to download the the raw detection file for the sources.

The table itself lists the source number, RA, Dec, and the detection flag for each source. As you hover the mouse pointer over a given table row, the source region in the image will turn yellow, to help identify the source. Clicking on the source number will open an extra panel in the table, giving more details about the source.

Detection flags

Each source is assigned a detection flag, indicating the likelihood that it is real. These flags are based on the cumulative false positive rate, thus:

Good: Source has a ≤0.3% probability of being spurious (i.e. ≥3-σ detection).
Good+Reasonable: Source has a ≤1% probability of being spurious.
Good+Reasonable+Poor: Source has a 10% probability of being spurious.

Note that, as these are cumulative, the probability of a reasonable or poor source being false are higher than the values above. Very approximately, the false positive rate among reasonable and poor sources is about 7% and 35% respectively.

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Image panel

The image panel to the right uses JS9 to present the image.

At the top of this panel is a link to each of the energy bands for which you requested source detection, and the exposure map. Clicking on this label will change the image being displayed, and update the source table to show the sources from this band as well.

Next follow a few controls. First a simple checkbox which shows whether the sources identified with regions. The second control is only present for images larger than 1000×1000 pixels in size. These images can be slow to load and so we provide binned-up versions as well which are given by default; this control lets you select which is shown. The final control allows whether to view the source image in the selected band, or the background map. For the latter you can select whether the models of the detected sources are shown or not.

The final line above the image allows you to download the FITS files. Note that these are always the full-resolution files, not the binned up version.

The final part of this panel is the image itself. This is rendered with JS9 and you can interact with it accordingly. By default the zoom is such as to fit the entire image in the field. The sources are shown, colour coded according to their detection flag: good=green, reasonable=cyan and poor=orange. Regions marked with a box or diamond have been automatically flagged as potentially unreliable, for example they may lie on or close to modelled stray light emission.

In order to help associate sources in the image with the source table if you click on a source region in the image the corresponding source in the table will be highlighted.

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File downloads

At the very top of the page are links to download all files associated with this source detection run, in a variety of formats. This download can contain many files, depending on the parameters of your job. The most important files are those which begin: detect_job - these are the summary files. These files are described below, where $band refers to the energy band the file is for, total, band1 (soft), band2 (medium), band3 (hard). The numbers XXXX are unique to your job.

detect_job_xxx_$band.img.gz: The image in the specified band.
detect_job_xxx_$band_final_BGmap.img.gz: The background map in the specified band, after all sources had been detected and localised.
detect_job_xxx_$band_final_BGmap_w_source.img.gz: The background map in the specified band, with the PSF models of the detected sources added back in.
detect_job_xxx_$band_ex.img.gz: The exposure map.

File names with _binned are the binned-up versions of the above. The other files are largely log files or contain relatively esoteric information you should not need. The only exception to this are the files giving the raw details of the source detection, described next.

The raw detection files

The files sources_total.list and sources_band{1,2,3}.list (if all bands were searched) will exist for every band in which sources were detected. These can also be downloaded from the link above the source table. These contain a space-separated line for each source, with the format defined below.

If you are using the API then you can also retrieve these files as a Python dict (or the raw JSON string if querying the API directly). In that case the dictionary index labels are also listed below.

All errors are 1-σ unless stated.

Position in line	Name in Python dict	Value
0	sno	Source no
1	x	Source x position (image coordinates).
2	y	Source y position (image coordinates).
3	ra	Source RA (J2000, degrees).
4	ra_pos	RA positive error (degrees).
5	ra_neg	RA negative error (degrees).
6	dec	Source delinration (J2000, degrees).
7	dec_pos	Dec positive error (degrees).
8	dec_neg	Dec negative error (degrees).
9	err90	Err₉₀ (i.e. 90% confidence radial position error, includes systematics).
10	l	Galactic longitude, l.
11	b	Galactic latitude, b.
12	C	Number of counts found in the count-rate measurement region.
13	rawrate	Raw count-rate - produced by the PSF fit.
14	rate	Refined count-rate, producted after fitting was complete.
15	rate_pos	Positive error on the refined count rate.
16	rate_neg	Negative error on the refined count rate.
17	rateCF	Correction factor for the count-rate (for vignetting, bad columns, pile up etc).
18	bgInFit	Background count-rate at the source location used in source position fitting.
19	B	Number of background counts used in the count-rate assessment.
20	Cstat	Cstat from the PSF fit,
21	Cbg	Cstat if we assume no source is present.
22	Lbg	Likelihood that the source is not a background fluctuation.
23	SNR	Source S/N
24	PSFRad	Radius of source fitting region (pixels)
25	MergeRad	Deprecated value
26	FlagName	The detection flag, as a string.
27	ImOntime	Peak exposure time in the image.
28	FracExp	Exposure at the source location as a fraction of the above.
29	offaxis	Mean source offaxis angle in the dataset(s) analysed (arcminutes).
30	NNDist	Distance to the nearest neighbouring detection in this band (arcseconds).
31	OKNNDist	Distance to the nearest neighbouring good or reasonable detection in this band (arcseconds).
32	OLwarn	Whether optical loading may affect this source. Value is magnitudes above the optical loading warning level.
33	SLwarn	Whether this source may be affected by, or an artifact of, stray light.
34	CtsInFit	Counts include in the PSF fit
35	detFlag	Numerical value of the detection flag.
36	shortFF	Deprecated
37	usedPup	Whether the best position fit included pileup
38	pupS	Pileup S parameter
39	pupl	Pileup l parameter
40	pupc	Pileup c parameter
41	puptau	Pileup τ parameter
42	bgRateAtSrc	The background rate at the source position, in (ct/sec/pix)

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On-demand source detection — Online Documentation

Contents

Overview

Source table

Detection flags

Image panel

File downloads

The raw detection files