UVOT Thumbnails

This directory and its subdirectories contain thumbnails of UVOT images and DSS images of interest for Swift tiling observations. Such observations are carried out to search for counterparts to GW events and for afterglows for GRBs discovered by instruments other than BAT.

A processing pipeline is alerted when a new tiling observation has been processed at the SDC and is now available at the SDC Quick Look web site. Data from that observation (a sequence) is downloaded, the "best" UVOT exposure is chosen (most likely to have a counterpart based on filter, exposure time, and time since the trigger), and uvotdetect is run for that exposure. All the sources found are run through a series of checks to determine if they are likely to be the counterpart to the GW event (or GRB). The checks include:

comparing the position to that of sources in the USNO, HST Guide Star, and GAIA catalogs
size of the major and minor axes
nearness to other bright UVOT sources
alignment with readout streaks
nearness to smoke rings
nearness to known minor planets

Each source is given a quality rating, with a quality of 0 being the highest. For "sources of interest", thumbnails are produced and posted to this website. The types of thumbnails are:

Q0 -- quality 0 UVOT sources with images from UVOT and DSS
2uvot -- quality 0 UVOT sources with images of current and archival UVOT exposures if available
gal -- GLADE galaxies detected in UVOT image with images from UVOT and DSS
xrt -- likely XRT counterparts with images from UVOT and DSS

The pipeline reliably finds new sources if they are isolated from existing sources and not affected by defects in the UVOT images caused by very bright sources. It also produces some false alarms because of the large number of UVOT sources that have to be evaluated. The thumbnails allow scientists to quickly evaluate the reliability of possible UVOT counterparts. In addition, the source-finding software (uvotdetect) has trouble finding new sources within extended sources such as nearby galaxies. Consequently, thumbnails are also produced for nearby galaxies detected with UVOT. Finally, thumbnails are produced for suggested XRT counterparts.

Directory Structure

Initially files are placed in subdirectories with the name of the processed sequence and the creation time (e.g., 00030828001_190403d15h34m45s). These subdirectories are then moved into other subdirectories named after the GRB (e.g., GRB190305A) or the GW event (e.g., GW100011).

File Types

The 3 types of files are described below.

Blink Files

When clicked, these file will blink aligned thumbnail images, typically of a UVOT image and the corresponding sky region from the DSS. A sample file name is blink_gal_00030828001_uu184604793I_G3_NGC1316.html.

"gal" indicates that this is an interesting (GLADE) galaxy; other values are "2uvot", which blink 2 UVOT images, "Q0", which blink a Quality=0 UVOT source, and "xrt", which blink a UVOT thumbnail centered on an XRT position. A Quality=0 source is the highest quality rating for a UVOT source indicating that is likely a real astrophysical source, not a minor planet, and not in the USNO catalog.
"00030828001" indicates the UVOT sequence number
"uu184604793I" indicates the UVOT extension name
"G3" indicates the internal index to the list of galaxies; other values are "srcXX" or "sx", which indicates the internal source ID
"NGC1316" is the galaxy name in the GLADE catalog

jpg Files

These are the thumbnail image files. A sample file name is dss_00030828001_uu184604793I_G3_NGC1316.jpg.

"dss" indicates it is from the DSS; other possible values are "uvot", which means from a UVOT image or "combo_gal" (see example here), which means an image with both UVOT and DSS thumbnails
The other parts of the name have the same meaning as for the blink files.

Report Files

These are text files with a table summarizing the results for a particular sequence. The table contains information about the source that caused a thumbnail to be created (a GLADE galaxy, an XRT source, or a Quality=0 UVOT source), the name of the combination thumbnail image, and (where appropriate) information about the nearest UVOT source. A sample file name is thumb_report_190322d15h22m21s766071usUT.txt. The string "190322d15h22m21s766071usUT" indicates the time when the file was created. An example of the file is here.

The columns in the table have the following information:

Column	Contents
1	internal ID
2	RA of the source of interest (J2000)
3	Dec of the source of interest (J2000)
4	distance from the edge of the UVOT image in arc seconds Negative values are inside the image.
5	distance (Mpc) to galaxy as reported in the GLADE catalog
6	source magnitude (or count rate for XRT sources)
7	Start time of the UVOT exposure
8	file name of combination image
	*(The following columns are not present if the source of interest is a UVOT source.)*
9	RA of the nearest UVOT source
10	Dec of the nearest UVOT source
11	UVOT magnitude
12	Separation (in arc seconds) of the UVOT source position and the galaxy position