[FRBVOEvent] FRB localization contours

[Casey Law]

A ds9-like region definition would be easy to support. I suppose a full
spatial probability function is the most complete you would need for an
interferometric localization.
You could probably get away with a ds9 region definition with an annotation
for the confidence level associated with a contour. The baseline assumption
may be that a contour is a 50% confidence region, but someone could provide
multiple contours if they like.

    casey

On Fri, Oct 26, 2018 at 1:10 PM Shriharsh Tendulkar <shriharsh at gmail.com>
wrote:

> Hi Adam, Casey, all,
>
> When I wrote my email yesterday, I was imagining that LIGO sends ds9-like
> contour definitions in text coordinates. Those would have been easy to fit
> into the XML format.
>
> It turns out that LIGO sends entire healpix maps with the probability,
> distance modulus etc for different pixels on the sky. The example provided
> below by Charlie Kilpatrick (UCSC) is for GW170817. It is 1.5 MB in size.
>
> We could embed healpix maps as binary data in the XML or we could provide
> a link to a URL hosting that probability distribution file.
> I do worry a little bit about increasing the size of the VOEvent too much.
>
> Regards,
> -- Shriharsh
>
> McGill Space Institute
>
>
> On Fri, Oct 26, 2018 at 11:23 AM Adam Brazier <abrazier at astro.cornell.edu>
> wrote:
>
>> If it's an optional field, it wouldn't break backwards compatibility and
>> would be more like a version 1.1
>>
>> It sounds like a good idea to me, although I would also like to see an
>> example?
>>
>> Cheers
>>
>> Adam
>>
>>
>> On Oct 26, 2018 2:08 PM, Casey Law <claw at astro.berkeley.edu> wrote:
>>
>> This sounds like a good change. My impression was that Emily and Leon
>> intended this protocol to be actively maintained. I suppose this could be a
>> v2 format and the VOEvent software would know how to parse the field
>> appropriately.
>> Do you have an example of a LIGO-like position contour?
>>
>>
>> On Fri, Oct 26, 2018 at 1:29 AM Shriharsh Tendulkar <shriharsh at gmail.com>
>> wrote:
>>
>> Hi all,
>>
>> I have been discussing FRB followup with regards to Swift and other
>> follow up. For interferometers, the localization regions are complicated
>> and are hard to describe with a simple position ellipse. Multiple bananas
>> are common. One can often get positions distributions that are different
>> than the beam shape.
>>
>> I propose that we add a position contour field to the FRB VOEvent
>> standard were we can specify LIGO-like (but much smaller size) position
>> contours. This will help follow up telescopes with small fields of views in
>> tiling the FRB field to search for afterglows. This field should allow for
>> multiple disjoint contours since sidelobes are complicated. The advantage
>> of sticking to the LIGO pattern is that the machinery already exists to
>> ingest and utilize those patterns.
>>
>> In order to maintain backwards compatibility and to ensure that simple
>> position errors are easy to communicate, this field will be in addition to
>> the beam shape ellipse.
>>
>> This is not hard to implement, but I would like to hear thoughts from
>> everyone about improvements, potential downsides and pitfalls.
>>
>> Cheers,
>> -- Shriharsh
>>
>> McGill Space Institute
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