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Gamma Ray Burst and Transient Rapid Follow-up

#### Introduction

This demo will provide astronomers with a coherent view of what is known
about a given region of the sky. It is inspired by the need to respond
rapidly to transient phenomena in the sky, especially gamma-ray bursts
where there is an enormous premium on data taken within the first few
minutes after the burst. This memo describes the information to be
provided to the user including the potential sources for that
information and how the information will be organized. One of the key
issues for the VO that this demo must address, is how we can provide
large amounts of data to the user without overwhelming them.

Gamma Ray Bursts are transients observed as intense pulses in the
low-energy gamma-ray regime. Until a few years ago when the first
optical counterparts were discovered using the SAX satellite the nature
of GRB\'s was unknown. It now appears that many if not all GRB\'s are
the results of processes in distant galaxies, presumably collisions of
highly condensed objects.

Since GRB\'s are primarily detected in the low-energy gamma ray regime,
where no high-resolution imaging technologies have been available, the
positions of most bursts have been very poorly constrained. Only in a
very few cases where a corresponding object has been detected near the
position of the burst in some other waveband, or where a burst has been
detected by multiple spacecraft, has an accurate position been
determined. Heretofore the gamma-ray locations have typically had
several degree diameter error circles. The next generation of GRB
satellites, notably Swift, will provide position errors of a few
arc-minutes within a few seconds and in some cases will improve the
accuracy using other telescopes on-board to arc-second precision within
several minutes. Note that even if the position of the gamma-ray burst
is precisely known, information about the region may be extremely
helpful to planning rapid followups: Is there substantial HI column? Are
there nearby bright objects? What observatories can view the source? Is
there a substantial IR background? Are there pre-burst comparison data?
...

The demo will support regions of interest ranging from a few arc-minutes
to roughly a degree. In the context of our demo the 'field of view' will
usually be specified by the astronomer performing the demo. We'll also
likely wish several 'prepackaged' fields. The GRB demo will provide with
the following information astronomers within seconds after the initial
declaration of the burst or other transient event:

-   Known characteristics of the GRB or other transient

-   Images of the sky in all available wavebands at all the best
    available resolution

-   Descriptions of solar system objects in the field of view at the
    epoch of the event

-   Descriptions of Galactic sources in the field of view, with
    potential variable sources clearly identified.

-   Descriptions of known extra-galactic sources in the field of view

-   Fields of view of observations that overlap the region of interest
    that are available from on-line archives.

-   Descriptions of observatories that may be able to observe the event
    immediately

-   Bibiliographic references for any object in the region of interest.

While this demo is driven by the response to transient events, much of
the information would be useful to astronomers who are interested in a
given region for other reasons. This demo provides users with a coherent
summary what is known about a region of the sky. NED and SIMBAD
currently provide information about objects in a given region while
Astrobrowse-style services enable users to query many services but do
not organize the results in a useful fashion. In the sense that the
information is collated and presented to the user in a consistent
fashion, this demo represents Astrobrowse done right. We anticipate that
this service will prove useful to astronomers regardless of the
connection with transient phenomena.

# Data presentation

The two user interfaces that we anticipate using in this demonstration
are the CDS' Aladin interface and the OASIS system developed at IRSA.
Both of these interfaces allow us to consider data as multiple planes of
information. The interfaces allow the user to select the planes to be
viewed. Interfaces may also allow planes to be combined, e.g., to use
three planes to generate a color image of the region.

Below we discuss the information to be made available on each plane.
Note that the actual display of the data is up to the user interface
which may organize data however its designers wish. However the
following is suggested as the preliminary choices for our demo.

Planes can be broken into three basic categories:

1.  Text planes provide information that is not conveniently given
    graphically. E.g., the position of the event, observatory, Sun and
    Moon are given in a text plane. These planes may include graphics,
    but the focus of these planes are the actual numbers. Text planes
    include the summary plane, the observatories plane, and planes
    giving the catalog data corresponding to the object planes.

2.  Image planes provide images of the region using existing survey
    data. Image planes will normally be available in the optical, X-ray,
    IR and radio.

3.  Overlay planes primarily give information about objects that may be
    in the field of view. For the demo the overlay planes are mostly
    organized according to distance from the Earth. Overlay planes are
    typically represented as graphical displays showing the positions of
    objects that in a fashion convenient for overlay on each other and
    the image planes. A text listing describing the objects/annotations
    is available in an associated text plane.

-   An Earth satellite plane gives the positions of satellites as seen
    from the site that initiated the alert. \[This plane is optional and
    likely not included in early iterations of the demo.\]

-   The Solar System plane gives information about solar system objects.

-   The Galaxy plane gives information about stars and other objects
    within our Galaxy.

-   The Extragalactic plane gives information about objects outside the
    Galaxy.

-   One special 'overlay' plane is the Observation plane, which provides
    the footprints of available on-line observations within the region
    of interest.

##### Plane Descriptions

## Summary Plane

  ----------------- --------------------------- -----------------------------
  **Information**   **Description**             **Source**

                                                

  ID                Unique identification of    Notification service
                    event                       

  Position          RA/Dec of event             Notification service

  Position error    Error radius or ellipse of  Notification service
                    event                       

  Event type        What kind of event trigger  Notification service
                    is this?                    

  Originating Site  Who sent the trigger        Notification service

  Site position     Coordinates of site (may be Notification service
                    in orbit)                   

  Galactic                                      Calculated
  coordinates                                   

  Ecliptic                                      Calculated
  coordinates                                   

  Solar angle       Current angle between       Calculated
                    position and sun            

  Lunar angle       Current angle between       Calculated
                    position and moon           

  nH column         Neutral hydrogen column at  HEASARC nH service
                    position                    
  ----------------- --------------------------- -----------------------------

# Image planes

Image planes will be provided giving the 'best' image\[s\] available for
that region in the given wavelength regime. Within each regime we give
list of possible sources starting with the most 'best' resource.

*Optical*:

-   DSS2 Red and Blue images

> Potential sources:
>
> CalTech cutout service
>
> DSS2 service at ST
>
> The ST services do not provide for distribution of lower resolution
> images. This may be an issue for very large (\~1 degree) regions.

### SkyView

-   DSS image

Same sources as above

*Infrared:*

-   2MASS 3 color images

Potential sources:

IRSA mosaicking service: This is to be available on an alpha basis by
the end of the month.

SkyView. Unacceptably slow for large regions

-   IRAS 4 color images

The IRAS data are just barely high enough resolution to be useful. With
90" pixels the standard ISSA data may only be helpful in giving a sense
of the IR background in the region and showing whether there are any
nearby bright sources. There used to be a service that provided
specially produced higher resolution images on request. This took quite
a while though.

Potential sources:

IRSA cutout services

SkyView

*X-ray:*

The only even modest resolution all-sky X-ray survey is the ROSAT
all-sky survey. The PSPC pointed observations cover \~15% of the sky.
Howver the coverage in a PSPC pointed observations will tend to show
structure due to the framework of the detector. While the PSPC data may
be used in later iterations, it may be more appropriate to link to these
observations below in the observations layers rather than provide them
in the image layer.

ROSAT All-sky Survey

Source: SkyView

*Radio:*

No single high-resolution survey of the entire sky is available in the
radio. The combination the NVSS and SUMSS covers the great majority of
the sky and there is substantial coverage with the FIRST and WENSS
surveys at somewhat better resolution. The radio data is prone to having
small scale features in its coverage.

-   FIRST

Potential sources:

FIRST cutout service

SkyView

-   WENSS

SkyView

-   NVSS

SkyView

-   SUMSS

The SUMSS data is still fairly raw and it may not be appropriate.
However it is the only high resolution radio data at the South Pole.

Source: SkyView

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## Observation Plane\[s\]

The observation plane is intended to existence and specific footprint of
existing, on-line archival data in the region of interest.

Source: IMPRESS

Additional sources would be nice, especially for ground data.

## Satellite Plane

For transient phenomena observed from the Earth it may be useful to have
a plane which represents the positions of Earth satellites as seen from
the site of the original observation of the transient. Satellite flares
can easily reach --8 or better and may trigger alerts. This layer is
optional and would likely not be available in early versions of the
demo.

Source: Two-line satellite ephemerides seem to be available at a number
of sites on the Web, but I have not yet located a Web service that finds
satellites that are located at a given point and time. For the small
number of satellites this is a fairly straightforward calculation.
Unfortunately the two-line data gives no information about the
brightness of the satellite and some manual culling of the lists by
someone knowledgeable about the characteristics of artificial satellites
may be needed. The HeavensAbove Web site does provide a list of Iridium
flashes expected near a given point but in a fairly difficult format to
parse.

## Solar System Plane

While it seems unlikely that transient events of the kind that will
trigger an alert would originate within the solar system, asteroids or
comets fortuitously within the field of view might confuse observers.
Since we are not particularly concerned with NEO's, we probably do not
need to worry about the parallax between observers at different
locations on the Earth or with satellites in low Earth orbit.

Source: Horizons service, JPL

A listing of the solar system objects near a given point at a given
epoch is given in reasonably simple to parse format. Positions and
estimated magnitudes are given.

## GSC2 Plane

## The GSC2 data are represented in a plane of their own since they include both Galactic and extragalactic data. The user interface is expected to use both the extent flag and the magnitude information in representing the objects.

Sources: HST GSC2 server, VizieR

## Galaxy Plane

The Galaxy plane known Galactic objects presumably as a graphic overlay.
An associated table gives further details on each object. Bibliography
links to ADS references will be made, but bibliography information will
not be stored in the demo. This and the following plane are similar in
concept to the NED and SIMBAD graphics giving the objects in a given
region.

Information from the following catalogs will be provided: In some cases
where a given catalog provides a large number of hits, information from
that catalog may provided in its own plane (a la the GSC2). The VizieR
catalog service (at one of its several mirrors) is anticipated to be the
source of the data. The catalogs and categories here are just an initial
selection.

Variable Stars: Kholpev (II/214), Kazarovets (II/219)

X-ray binaries: Ritter (V/99), Liu (V/106)

## Extragalactic Plane

This plane shows known extragalactic objects in the field of view. This
plane differs from the Galactic plane primarily in the catalogs that are
queried.

Globular clusters: Arp (VII/13), Harris (VII/195)

Galaxies: De Vaucouleurs (VII/116), Corwin (VII/155)

Clusters: Abell and Zwicky (VII/4)

## Observatories Plane

This text plane lists observatories for which observations of the target
are immediately feasible -- at least subject to basic constraints of
darkness and visibility. If the VO develops coherent metadata to
describe observatories then it might be possible for the user to request
information on observatories capable of particle kinds of observations,
e.g., high resolution spectral imaging.

Source: Positions of ground optical observatories are available on-line
from JPL. The Astronomical Almanac should have listings of most
observatories but I have yet to get a machine readable version. Manual
editing of the list is probably needed. For the demo inclusion of space
observatories is probably not needed. In any case they are unlikely to
be able to respond to a request to observe a TOO within time-scales of
less than hours.