This database table is derived from the Swift TDRSS messages sent on ground soon after a BAT trigger occurs on-board. For each trigger there are associated up to 14 messages, however not all are always generated and sent on ground. The messages are generated on board by the BAT, XRT and UVOT instruments and the Figure of Merit part of the observatory's autonomy. The BAT and XRT can each have five different message types. The UVOT and FOM can each have two different message types. These TDRSS messages are the results of the on-board data processing of the three instruments and some contain data products. They are first distributed via the GCN and later archived. The BAT messages are: alert, 'ack' containing the position, or 'nack' if the position could not be calculated, a lightcurve and scaled map. The XRT messages are: centroid containing the position, an image (if the position has been calculated), centroid error if the position could not be calculated, spectra in Low Rate Photodiode and Windowed Timing modes, a lightcurve. The UVOT messages are: finding chart containing star positions and a subimage centered on the XRT position. The FOM messages are used to indicate if the FOM will or will not observe the new target and if the spacecraft will (or will not) request a slew for the new target. The parameters in this database table are a collection of high level information taken from the following messages : the BAT alert, 'ack' or 'nack' message, the FOM messages, the XRT position and image. If the information is not available the fields are left blank. All messages are provided as data products within this database table. This database table is generated at the Swift processing site. During operation, it is updated on daily basis. This is a service provided by NASA HEASARC .
The Swift UVOT instrument is a 30 cm modified Ritchey-Chretien reflecting telescope launched on
board the Swift satellite on November 20, 2004.
The range of optical and UV filters can accomodate wavebands between 1700 and 6500 Angstroms.
A full field image covers 17x17 arcminutes and at maximum spatial sampling is imaged onto 2048x2048 0.5"
pixels. A 1000 second observation can detect point sources to m=22.3 when no filter is used.
The Swift Serendipitous Source Catalog (Page et al., 2015) detects sources down to m=23-26 for
the six filters in very deep observations, but the typical limits are substantially brighter (~20-23 magnitude).
<p>
These surveys are mosaics of all Swift UVOT observations released between the start of the mission and July 2017.
Data were extracted from the HEASARC archive from the UVOT products directory. Mosaics are provided
in six filters and also with no filter, i.e., WHITE. The table below gives the number of
observations and bandpasses for each of the filters. For each UVOT observation standard processing generates a
counts and exposure file as a single multi-extension FITS file with a separate extension for each filter. To aid
processing, these extensions were copied into separate files in directory trees for each filter.
Four observations in which the exposure and counts maps did not agree on the filters
used were omitted from the processing.
<p>
Some observations were recorded with 0.5" pixels while others were binned to 1". All 0.5" observations
(typically fewer than 10%) were rebinned to the larger pixels for the counts maps since the counts
data scales with the pixel size.
Since the exposure values are intensive and do not vary significantly based upon the resolution, these data were
not generally rebinned unless it was needed to ensure that Order 9 Hips data were produced.
<p>
The CDS Hipsgen software was used to generate Order 9 HiPS data (~0.8" pixels) for both the Counts and
Exposure images. The HiPS (Hierarchical Progressive Survey VO standard) supports multi-resolution mosaics.
Any quantitative use of these images should note that the rebinning increases the
total counts by a factor of ~(1.0/0.8)^2 ~ 1.56. This software uses a bilinear interpolation to generate HEALPix tiles of an appropriate
order (18 in this case). <i>SkyView</i> developed software was used to divide the level 9 counts maps
tiles by the corresponding exposure maps to create intensity tiles.
Pixels where the exposure was less than 5 seconds were left as NaNs.
The lower order (8 to 3) order intensity tiles were then generated by averaging
2x2 sets of the higher order maps treating any missing maps or pixels as NaNs.
A HiPS all-sky image was generated by averaged the Order 3 tiles.
<p>
Only the Intensity HIPS files are presented in the SkyView web page directly, but intensity, counts and
exposure maps are available for all seven filters. Note that unlike the XRT HiPS data, the exposure
and counts maps have not been clipped. I.e., the source FITS files have been aligned with the
coordinate system and thus contain large numbers of unexposed pixels with 0 values.
These 0's are simply propogated to HiPS tiles.
NaNs are returned in regions which lie outside any of the original source images. For the Intensity map,
any pixel for which the exposure was less than 5s is returned as a NaN.
<table border>
<tr><th align=center>Filter</th><th>Count</th><th>Central Wavelength (&#8491;;)</th><th>Bandpass (&#8491;;)</th><th>Central Frequency(THz)</th><th>Bandpass (THz)</th><th>Coverage</th></tr>
<tr><th align=center>WHITE</th><td align='center'>3,000</td><td align='center'>3600</td><td align='center'>1600-6000</td><td align='center'>832</td><td align='center'>500-1874</td> <td>0.0017</td></tr>
<tr><th align=center>V</th><td align='center'>30,557</td><td align='center'>5468</td><td align='center'>5083-5852</td>< <td align='center'>548</td><td align='center'>512-590</td> <td>0.0171</td></tr>
<tr><th align=center>B</th><td align='center'>28,347</td><td align='center'>4392</td><td align='center'>3904-4880</td> <td align='center'>683</td><td align='center'>614-768</td> <td>0.0112<td></tr>
<tr><th align=center>U</th><td align='center'>49,954</td><td align='center'>3465</td><td align='center'>3072-3875</td> <td align='center'>865</td><td align='center'>774-975</td> <td>0.0287</td></tr>
<tr><th align=center>UVW1</th><td align='center'>60,690</td><td align='center'>2600</td><td align='center'>2253-2946</td> <td align='center'>1154</td><td align='center'>1017-1330</td><td>0.0277</td></tr>
<tr><th align=center>UVM2</th><td align='center'>56,977</td><td align='center'>2246</td><td align='center'>1997-2495</td> <td align='center'>1334</td><td align='center'>1201-1501</td>>td>0.0314</td></tr>
<tr><th align=center>UVW2</th><td align='center'>54,590</td><td align='center'>1928</td><td align='center'>1600-2256</td> <td align='center'>1554</td><td align='center'>1328-1874</td><td>0.0260</td></tr>
</table>
<strong>Observation counts and bandpasses for UVOT Filters</strong>
<p> Provenance: Data generated from public images at HEASARC archive. This is a service of NASA HEASARC.
The UVOT runs only one type of configuration filter/mode/window in a given time interval. This database table, therefore, contains for a given time interval a single record that describes one configuration. This database table is generated by the Swift Data Center. During operation, it is updated on daily basis. This is a service provided by NASA HEASARC .
The Swift XRT (<a href="https://ads.harvard.edu/abs/2005SSRv..120..165B">Burrows et al 2005, SSRv, 120, 165</a>)
is a sensitive, broad-band (0.2 - 10 keV) X-ray imager
with an effective area of about 125 cm**2 at 1.5 keV.
The 600 x 600 pixel CCD at the focus provides
a 23.6' x 23.6' field of view with a pixel scale
of 2.36". The point spread function
is 18" (HPD) at 1.5 keV.
<p>
These XRT surveys represent the data from the first 12.5 years of Swift X-ray observations.
They include all data taken in photon counting mode. A total of just over 8% of the sky
has some non-zero exposure. The fraction of sky exposed as a function of the exposure is given
in the following table:
<table border>
<tr><th>Exposure</th><td>>0</td> <td>10</td> <td>30</td> <td>100</td> <td>300</td> <td>1000</td> <td>3000</td>
<td>1000</td> <td>30000</td> <td>100000</td><td>300000</td></tr>
<tr><th>Coverage</th>
<td> 8.42 </td><td> 8.37 </td><td> 8.29 </td><td> 7.67 </td><td> 7.29 </td><td> 5.68 </td>
<td> 3.40 </td><td> 1.26 </td><td> 0.35 </td><td> 0.044 </td><td> 0.00118</td></th>
</table>
The individual exposure and counts maps have been combined
into a Hierarchical Progressive Survey (HiPS) where the data are stored in tiles
in the HEALPix projection at a number of different resulutions. The highest resolution
pixels (HEALPix order 17) have a size of roughly 1.6". Data are also stored at lower
resolutions at factors of 1/2, 1/4, 1/8, 1/16, and 1/32, and in an all sky image with a resolution
1/256 of the higest resolution. An intensity map has been created as the ratio
of the counts and exposure maps.
<p>
These surveys combine the basic count and exposure maps provided as standard products
in the Swift XRT archive in obsid/xrt/products/*xpc_(sk|ex).img.gz. The surveys were created as follows:
<ul>
<li>All of the exposure maps available in the archive in mid-May 2017 were combined
using the CDS-developed Hipsgen tool. This includes 129,063 observations for which
both count and exposure files were found in PC mode. Three exposures where there was
a counts map but no exposure map were ignored. A few exposure files had more than
one exposure extension. 1,082 files had two extensions and 1 file had 3 extensions.
The 1084 HDUs in extensions were extracted as separate files and included in the total exposure.
The value of 0 was given to the Hipsgen software as the null value for the FITS files.
This caused the CDS software to treat such pixels as missing rather than 0 exposure.
<li>
The counts data was extracted from the counts maps for each observation using <i>SkyView</i>
developed software. For any pixel in which a count was recorded, the corresponding
exposure file was checked and if there was any exposure (in any of the associated
extensions), then the count was retained. If there was no exposure in any of the extensions
of the corresponding exposure file, the counts in the pixel were omitted. Once a count
was accepted, the overlap between the counts map pixel and the pixels of the corresponding
HiPS tile (or tiles) was computed. Each count was then assigned entirely to a single
pixel in the HiPS tile randomly but with the destination pixel probabilities weighted by area of
the overlap. Thus if several pixels were found in a given counts map pixel they
might be assigned to different pixels in the output image. The HiPS pixels (~1.6") used were
of substantially higher resolution than the XRT resolution of 18" and somewhat higher than
the counts map resolution of 2.36".
<p>
A total of 183,750,428 photons were extracted from the counts maps while 15,226 were rejected
as being from pixels with 0 exposure. There were 501 pixels which required special
treatment as straddling the boundaries of the HEALPix projection.
<li>
The resulting counts tiles were then clipped using the exposure tiles that had been
previously generated. Basically this transferred the coverage of the exposure tiles
to the counts tiles. Any counts pixel where the corresponding exposure pixel was a NaN
was changed to a NaN to indicate that there was no coverage in this region.
<p>
During the clipping process 137,730 HiPS level 8 were clipped (of 786,432 over the entire sky). There were
12,236 tiles for which there was some exposure but no counts found. During the clipping process
2 photons were found on pixels where there was no corresponding exposure in the exposure tiles.
This can happen when the pixel assignment process noted above shifts a photon just outside the
exposed region but should be -- as it was -- rare. These photons were deleted.
<li>
After creating the clipped level 8 counts maps, level 7 to 3 tiles and an all sky map
where generated by averaging pixels 2x2 to decrease each level.
When adding the four pixels in the level N map together
only pixels whose value was not NaN were considered.
<li>
Finally an intensity map was created by dividing the counts tiles by the exposure tiles.
To eliminate gross fluctuations due to rare counts in regions with very low exposure, only
regions with exposure > 1 second were retained. A total of 30 photons were deleted due to
this criterion.
</ul>
<p>
Note that while any sampler may in principle be used with these data, the Spline sampler may
give unexpected results. The spline computation propogates NaNs thought the image and
means that even occasional NaNs can corrupt the
output image completely. NaNs are very common in this dataset.
Also, if the region straddles a boundary in the HEALPix projection,
the size of the requested input region is likely to exceed memory limits since the HiPS
data are considered a single very large image. Provenance: Data generated from public images at HEASARC archive. This is a service of NASA HEASARC.
The XRT runs only one type of configuration mode/window in a given time interval. The table therefore contains for a given time interval a single record that describes one configuration. A new record is generated when the following is changing within an observation: new operating mode , new pointing mode, or new window configuration. This database table is generated by the Swift Data Center. During operation, it is updated on daily basis. This is a service provided by NASA HEASARC .
The Sydney University Molonglo Sky Survey (SUMSS) is a deep radio
survey at 843 MHz of the entire sky south of declination -30&#176;;, made using
the Molonglo Observatory Synthesis Telescope (<a href="https://www.physics.usyd.edu.au/astrop/most/"> MOST </a>), located near Canberra, Australia.
The images from the SUMSS are produced as 4 x 4 degree mosaics of up to
seventeen individual observations, to ensure even sensitivity across
the sky. The mosaics slightly overlap each other. Data were last updated on January 28, 2015.
<p>
Images can also be obtained from the <a href="https://www.astrop.physics.usyd.edu.au/cgi-bin/postage.pl">SUMSS Postage Stamp Server</a>.
<p>
The SUMSS is intended to complement the NRAO-VLA Sky Survey (NVSS) which
covered the sky between +90 and -40 deg declination, at a
frequency of 1400MHz.
<p> Provenance: The SUMSS project team, University of Sydney. This is a service of NASA HEASARC.
Sternberg Astronomical Institute Virtual Observatory Project
Description:
The Sloan Digital Sky Survey is a project to survey a 10000 square degree area
on the Northern sky over a 5 year period. A dedicated 2.5m telescope is
specially designed to take wide field (3 degrees in diameter) images using
a 5x6 mosaic of 2048x2048 CCD, in five wavelength bands, operating in drift
scan mode. The total raw data will exceed 40 TB. A processed subset, of
about 1 TB in size, will consist of 1 million spectra, positions and image
parameters for over 100 million objects, plus a mini-image centered on each
object in every color. The data will be made available to the public after
the completion of the survey
Sternberg Astronomical Institute Virtual Observatory Project
Description:
The Sloan Digital Sky Survey is a project to survey a 10000 square degree area
on the Northern sky over a 5 year period. A dedicated 2.5m telescope is
specially designed to take wide field (3 degrees in diameter) images using
a 5x6 mosaic of 2048x2048 CCD, in five wavelength bands, operating in drift
scan mode. The total raw data will exceed 40 TB. A processed subset, of
about 1 TB in size, will consist of 1 million spectra, positions and image
parameters for over 100 million objects, plus a mini-image centered on each
object in every color. The data will be made available to the public after
the completion of the survey
The Extended IRAS Galaxy Atlas (EIGA) is an extension of the original IRAS Galaxy Atlas (IGA) to b = 6.7 deg.. High resolution images at 60 microns and 100 microns have been produced to match the latitude coverage of radio continuum observations obtained as part of the Canadian Galactic Plane Survey (CGPS). Also associated with the EIGA and IGA is the Mid-Infrared Galaxy Atlas (MIGA).