Keep an eye on the EWG discussions

smyers
Posts: 29
Joined: Mon Sep 09, 2013 4:43 pm

Keep an eye on the EWG discussions

Postby smyers » Mon Mar 10, 2014 12:25 pm

The Extragalactic Working Group viewforum.php?f=61 is discussing the pros and cons of all-sky vs. (medium) wide vs. deep as well as multi-epoch components for each. Be sure to join in that discussion where you can!

-Steve

jlazio
Posts: 8
Joined: Thu Mar 20, 2014 11:13 pm

Re: Keep an eye on the EWG discussions

Postby jlazio » Thu Mar 20, 2014 11:18 pm

Following up on Steve's suggestion, here's what's currently being discussed in the Extragalactic WG: a three tiered survey with the following structure

DEEP to a depth of ~ 1.5 microJy/beam over 10 deg^2
WIDE to ~30uJy over 3600 sq. deg.
ALL-SKY to ~100uJy over ~30k sq deg. (excluding the WIDE area)

From the transient sky perspective, I think that we could live with these. The ALL-SKY and WIDE would produce a "baseline" image for all future transient searches (at least in the northern sky), and both WIDE and DEEP would require multiple visits to a field in order to obtain the required depth so that they could be searched for transients themselves.

jlazio
Posts: 8
Joined: Thu Mar 20, 2014 11:13 pm

Re: Keep an eye on the EWG discussions

Postby jlazio » Thu Mar 20, 2014 11:47 pm

From a recent discussion in the Extragalactic WG:

> On another point, for cadence are we just going to see what the
> transients/variables people suggest, or do we have some preference
> of our own? Could consider a starting approach of a logarithmic
> cadence to sample as much "discovery space" as possible.

A good question. The Transient & Variability WG has been a bit quiet, so I'll toss in the following few thoughts:

I attach a slide from a recent talk. The sequence of light curves shows the evolution of a radio supernova at different wavelengths. The blue vertical lines are intended to guide the eye and are at 100 days post-explosion. These curves are for radio supernovae, but a similar behavior is seen for gamma-ray bursts and tidal disruption events.

While a wavelength of 13 cm isn't shown, it's fairly easy to interpolate between 6 and 20 cm. You can see that the peak flux density appears about 100 days after the explosion at 6 cm and several hundred days at 20 cm. Thus, if one wanted to "blink" two images and search for this kind of source, one would probably want the cadence to be, say, several tens of days. I suspect that's a bit longer than we could tolerate for conducting the kinds of extragalactic surveys being discussed.

Another kind of variable that might show up at S band are extreme scattering events. These have time scales of months, but they show structure on time scales of days to several days, which is crucial to identifying them as extreme scattering events.

Thus, to the extent possible, on a given pointing, an initial target might be a cadence of a few to several days, with the objective of getting to the required depth in no longer than, say, 50 days, per pointing. Presumably this consideration would apply only to DEEP and WIDE, as ALL-SKY requires that each pointing position be visited once in order to complete the survey in a timely fashion.
Attachments
Lazio-RadioTransientSky.jpg
PPT slide showing light curves of a radio supernova as an example of an expanding incoherent synchrotron source.


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