New INTEGRAL Galactic Plane Survey in SkyView

A new INTEGRAL Galactic plane survey has been added using data provided by R. Krivonos and colleagues.  (See paper and web site).   This survey combines 9 years of INTEGRAL IBIS observations from December 2002 through January 2011 into a single Galactic Plane image. A total of 135 megaseconds of exposure is included in the observations used. Survey data is generated for the Galactic plane in the region |b| <= 17.5. This survey is sensitive to about 1 millicrab in the hard X-ray range from 17-80 keV.

INTEGRAL Galactic Plane Survey: The Galactic Center


These data are based on observations with INTEGRAL, an ESA project with instruments and science data centre funded by ESA member states (especially the PI countries: Denmark, France, Germany, Italy, Switzerland, Spain), Poland and with the participation of Russia and the USA.

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SkyView updates

We are releasing a new version of SkyView today (2012-06-25). We’ve a separate article on the new INTEGRAL Galactic Plane surveys, but we’ve made some changes that affect many of the survey datasets. For each survey that we support, SkyView uses a survey description file, a custom XML format which includes both metadata on the survey (all the documentation you see), and the information about where the original survey images are stored. Heretofore we’ve used a separate file for each survey, e.g., the SDSSi had a separate file from the SDSSg. In the new version we support parametrized survey description files where we substitute values for parameters in the file. E.g., the text in the raw file survey.xml might include a line like

<Frequency> ${F} EHz </Frequency>

When we tell SkyView to use this file we would use the name survey.xml?F=2.7 and the raw XML would be rendered as

<Frequency> 2.7 EHz </Frequency>

Many surveys (SDSS, BAT, Fermi, IRAS, … ) have multiple bands where where the differences in the survey descriptions are easy to parametrize. In this new release the number of survey description files has dropped from over 100 to a little over 50.

While this saves a little space in the SkyView JAR, the major advantage is that it means we don’t have to repeat the common information, so we should be able to keep the survey descriptions more accurate over the long run. However it’s possible we missed some element where we’ve left a survey specific item in and not parametrized it properly. Please let us know if you see any problems.

Another change in the latest version is that we’ve made much more extensive use of the ability that SkyView has always had of providing links to related SkyView images in the results for a primary image. If you look at the new INTEGRAL Galactic plane surveys, the BAT data or the PSPC pointed surveys, you will see links to additional imagery. From the web page you can directly request intensity/flux maps for the INTEGRAL, BAT, RASS and PSPC data, but the results have links to exposure and counts maps, that are not available from the web page directly. You can invoke these directly in the batch interface however.

This allows us to keep the Web form a little cleaner. We’ve tied together the RASS Count and Intensity maps where they had previously been presented as separate surveys. We’ve also now have space to bring back the PSPC 0.6 degree cutoff maps. This is a mosaic of the high resolution cores of the ROSAT PSPC pointed observations.

With about 130 total surveys making it possible to find all of the surveys is becoming a real driver in our development.

If you are using one of the surveys that is not directly available and find the new organization to be a problem please contact us.

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SkyView using Xamin

Recently the HEASARC released a new more powerful interface to its catalog and archive, Xamin. We have just updated SkyView so that
SkyView catalog queries of tables in the HEASARC databases are now being made through this new Xamin interface rather than our older Browse interface. If you click on the “Link to HEASARC catalogs” in the results page to query HEASARC database, you will now start an Xamin session rather than run a Browse query.

Although the rows returned should be identical, the user interfaces for the two systems are very different so expect some changes if you click through. With Xamin you will start the web interface and you’ll get a browser page which has two panes, the query pane and a resuls pane. The query pane shows the query parameters that were used and allows you to follow up with any further queries that you are interested in. You may see Xamin processing your query, if it takes a while to get the results.

If you queried one catalog, the results pane will be the table of matching rows. If you queried many catalogs, then the results pane will show the number of matches for each catalog that had at least one. You can click on any row to see the results for that catalog.

Note that for both Browse and Xamin, you can get more rows from the query run at the HEASARC site than you saw in the image overlay. The catalog queries search a circle inside which the SkyView image is enscribed. So for a typical square image the catalog search looks at π/2 more area.

Please let us know if you have any questions or encounter any problems.

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New Fermi Surveys

We’re pleased to be able to provide a new set of Fermi surveys. Fermi is the highest energy survey in SkyView and heretofore we had been providing two bands of Fermi data, from 100 to 5450 MHz and 5450 MHz to 300 GeV. Fermi’s resolution is a very strong function of energy. With the bands we’d originally chosen, low energy, low resolution photons blurred the images of most sources. While the top band had very reasonable resolution, it had relatively few photons. The new Fermi data is broken into 5 bands:

  1. 30-100 MeV
  2. 100-300 MeV
  3. 300-1000 MeV
  4. 1-3 GeV
  5. 3-300 GeV

This seems to give a cleaner separation of the low energy/resolution data while keeping enough photons in the higher energy bands to really show the sky. This all sky image shows data from bands 3-5.

Fermi RGB all sky image

RGB image using Fermi bands 3, 4 and 5. Click for high res version

Harder gamma-ray sources show as blue. A myriad Galactic and high-latitude sources show.

We’ve imaginatively named these surveys Fermi 1, 2, 3, 4 and 5 in order of increasing energy. They contain all of the Fermi data available through the beginning of April 2012. The Fermi sky exposure is now considered to be sufficiently uniform that we are providing these surveys as counts maps rather than intensity maps. We’ll be adding exposure information soon.

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WISE All-Sky Data Available in SkyView

SkyView is now serving the data from the WISE All-Sky Data release. The main difference with the preliminary release is coverage on the ~40% of the sky that was missing in the earlier release. However the entire dataset has been reprocessed using updated calibrations and such.

We download WISE data from IRSA in large tiles, caching each tile so that we never have to download the same tile twice. It can take a while for WISE images to be generated if there has been no request in that region before, even when you are requesting only a very small region. It can easily take a minute or more to get the files we need to generate your image. As our cache grows you’ll be more likely to hit it and access should be much faster. Once data are in the cache it takes only a couple of seconds to generate a typical image.

The WISE data give us a view of the infrared sky comparable to the DSS optical images in the optical. We anticipate WISE being one of SkyView’s most popular surveys.

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SkyView Surveys Summary: I

Recently we’ve been updating and systematizing some of the metadata we have on SkyView surveys, trying to make sure that we have consistent, quantitative description of each one. Some of the key metadata are the resolution of the survey on the sky, sensitivity and sky coverage. It’s quite difficult to provide single numbers for these in a consistent way. E.g., for lots of surveys the resolution varies depending upon where you are. In some cases it even depends upon the spectrum of the source.

So take this with a grain (or maybe even a spoonful) of salt, but here’s a graph of the nominal resolution of SkyView’s surveys as a function of wavelength.

The resolution of SkyView surveys as a function of frequency

Resolution of Surveys Available in SkyView


The surveys span about 18 orders of magnitude in frequency. That’s pretty amazing. If you want to get a sense of how big that range is, consider the ratio of the distance to the nearest stars to your height… An immense difference — but only 1% of the range of SkyView‘s frequency coverage!

Looking at the graph we can split surveys into three categories based on their resolution: High resolution surveys have better than 10″ resolution. Most of these are concentrated near the optical, but there are a couple of outliers. Medium resolution surveys, with resolutions of about 1’ are the most common. These surveys have resolution comparable to our eyes. A fair number of surveys have resolutions of a degree or more. This doesn’t necessarily mean they are less valuable. Sometimes you want to look at the forest and not the trees.

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What are people interested in? (2)

A few years ago we posted an image of the sky which showed what people have been looking at. Here’s an update giving the distribution of pixel centers for the last 10,000,000 or so SkyView images (about the last 18 months). This doesn’t include images in Cartesian, TOAST, CobeCube or Aitoff projections, nor do we include data using Ecliptic coordinates. However these only account for about 0.5% of the images we generate, so they wouldn’t make much difference.
Density distribution for skyview images.
The image is an Aitoff projection in equatorial coordinates with a Galactic coordinate grid overlaid. The data were originally sampled into a Cartesian grid with 1 degree pixels and that was resampled into an Aitoff grid using the clip resampler.

The image is very different from what we saw a couple of years ago where there where lots of ‘tire tread’ patterns in the data as people retrieved data in very specific regions. This looks like it’s a fairer realization of what parts of the sky are interesting.

And what was the very top location? It’s not 0,0 — which is what I would have guessed — nor the Galactic center or pole. All of those have pretty high values too. But the single highest pixel count (with about 40,000 images generated) was for the pixel that includes the center of M31. A clear winner for the most popular object in the sky!

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WISE versus IRAS

Just to see the incredible improvement WISE makes over the IRAS data here are two images of the same region (0.2×0.2 degrees at RA=2h 40m, Dec=20). The IRAS image (from the IRIS 12 micron survey) is very pixelated… There’s almost nothing there.
IRAS 12 micron image (IRIS 12 survey)

The WISE 12 micron data shows vastly more detail. Even in this boring region dozens of objects are clearly detected.
WISE 12 micron image

Note that the WISE surveys have been set to use the loglog scaling by default. Many features will not show up using the log scaling that is the default for most surveys.

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SkyView links to WISE Preliminary Release Data

Data from the Wide-field Infrared Survey Explorer (WISE) Preliminary Release are now available in SkyView. WISE has made 4 all-sky surveys at 3.4, 4.6, 12 and 22 microns. The WISE surveys provide a remarkable picture of the sky in the infrared.

The two longest WISE wavelengths correspond closely to the two shorter IRAS bands but WISE has vastly higher resolution and sensitivity. The two shorter WISE wavelengths fill in the gap between the 2MASS K band (2.16 microns) and the 12 micron data.

The preliminary release covers a bit over half the sky as shown in this coverage map from the WISE archive at IPAC.WISE Preliminary Release coverage

Note that WISE data are distributed in large chunks. When SkyView first observes a region it will download the WISE data from the IPAC archive which may take a while. Subsequent images from the same region should run much faster.

As the title of the survey suggests, a full WISE release is forthcoming and should be available next month. We’ll switch over to that as soon as it’s available through the appropriate VO protocols.

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