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 |