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Around Gaia (Alerts) in 30 questions

How many

Asteroids

will Gaia see?

250,000 asteroids

(mostly known)

alerts on new asteroids

candidates from

unsuccessful star matches

Will Gaia alert

on GRB optical

counterparts?

Gaia sampling and alerts delay

is not designed for catching GRBs.

Still, we expect to see:

1-2 on axis afterglows

5-15 orphan afterglows

What about known anomalous objects?

How many

Microlensing Events

will Gaia detect?

1000+ events expected to be detected photometrically.

Mainly in Galactic Bulge and Plane.

Mostly long time-scale events (tE>30d)

Such objects can be added to the Watch List. Every time Gaia observes them their data become publically available for inspection.

How many

Supernovae

will Gaia detect

over 5 years?

What about astrometric microlensing?

With precision of a few micro-arcseconds astrometric microlensing due to centroid motion will be easy to measure. But photometry is also needed - only Bulge is surveyed densely from the ground.

Larger deviations, of 0.1 mas will be possible to detect while on-going and alerts will be triggered to obtain complementary photometry.

6000 SNe expected down to 19 mag

~2000 before the maximum

but only after about 2yrs as we need time to build accurate astrometric model

How BP/RP spectra will be used for SNe?

What will be the main

triggers of Gaia alerts?

With Self-Organizing Maps we should be able to:

- confirm of non-stellar nature of the object

- classify the type of the supernova

- get the "age" of the supernova

- possibly even get the red-shift

SOM mapping

input spectra

  • Supernovae
  • Classical novae
  • Microlensing events
  • Be stars
  • GRB counterparts
  • R CrB-type stars
  • FU Ori-type stars
  • Asteroids
  • New things?

for ~15 mag object

How the alerts will be detected?

Simplest possible recipe:

1. compare

the most recent observation

with the historic data

2. inspect for unexpected changes

and using low-resolution BP/RP spectroscopy

template matching and using Self-Organzing Maps (SOMs) to obtain

e.g. spectral type of an object or supernova type.

New/rare objects will be immediately recognized with SOMs.

How the alerts will be classified?

On a light-curve level

exploiting characteristic features of the anomaly,

using Bayesian Classifiers (e.g. Gaussian Mixture)

What instruments Gaia will have?

Low-dispersion spectro-photometry: 640-1000 nm in 60 samples.

Low-dispersion spectro-photometry: 330-680 nm in 60 samples.

High-resolution spectrometry 847-874 nm at R~11,500, around Calcium triplet. Only for stars V<17 mag.

  • Skyalert.org

Stars from both telescopes are detected and have windows assigned.

Positions and G-band magnitudes

measured in windows.

How alerts will be disseminated?

  • email
  • www server
  • Twitter
  • iPhone app
  • ...?

What is windowing?

Most of the sky is empty.

Gaia will only transmit small windows around stars detected by Star Mapper.

What telescopes Gaia will have?

Gaia will be equipped with two 1.45x0.5m telescopes, pointing at 106.5 deg angle.

The light from both telescopes will then be gathered on a single

focal plane.

They will reach about V=20 mag.

  • coordinates
  • small footprint from SM window around an object
  • light curve
  • low-resolution spectrum at the trigger
  • classification result
  • cross-matching results

What will be in an alert?

author: Lukasz Wyrzykowski

Institute of Astronomy

University of Cambridge

wyrzykow@ast.cam.ac.uk

What is the precision of the

instantaneous astrometry?

0.1 mas at 15.5 mag in a single transit

selected areas

3 months

(not public,

for alerts verification)

What is

the precision of the

instantaneous photometry?

milli-mag in a single transit at 14 mag

Total number of data points collected over 5 years.

Areas at the nodes will be the first to get enough accumulated observations to start alerts early.

plot credit Jordi/Varadi

after accumulating enough historic observations

When will the first alerts be produced?

most of the sky

6-9 months

How does scanning law allow for fast full sky coverage?

the exact location depends on the starting conditions of the spacecraft and the time of launch

Example fraction of the sky observed

during the alerts verification.

Start: after first 3 months of data accumulation

Duration: around 3 months (90 days)

Access to alerts restricted to Gaia-FUN partners only.

Verification of detection and classification procedures.

Alerts will the first Gaia data made public - have to be realiable!

What is the Alerts Verification Phase?

two observations separated by ~2h

next pair after ~30 days

on the nodes: 2h, 4h, 2h, 4h

What is

the typical sampling?

  • investigate scientific potential of Gaia Alerts
  • suggest what else would be worth detecting and alerting
  • suggest dedicated detection algorithms and classification

techniques tailored on your

favourite type of objects

with my scientific interests

prepare your telescope for Gaia Alerts:

  • register at Skyalert.org
  • set-up your alerts on CRTS stream

(SNe, CVs, blazars, etc.)

  • follow-up the alerts
  • contact us if you have some data!

How to get involved now?

with my telescope time

  • on average, each object will be observed 80 times
  • some areas up to 240
  • Galactic Bulge and plane less often (~50)

How many data points will be collected?

Gaia @ ESA: http://gaia.esa.int

Gaia @ ESA-RSSD: http://www.rssd.esa.int/index.php?project=GAIA

Gaia Science Alerts Working Group: http://www.ast.cam.ac.uk/ioa/research/gsawg

Gaia Research Training (GREAT): http://great.ast.cam.ac.uk

Therefore alerts will be issued between couple and 24 hours

after the observation.

Gaia will be visible from Earth only for 8h a day.

All data from last 24h will be downlinked then.

Where can I find out more?

What is the data latency?

launch: mid 2013

first data: early 2014

first internal alerts: 3 months later

first public alerts: mid 2014

end of the mission: 2018-2019

What is the mission timeline?

from: ESA/Kourou

in: Soyuz-Fregat rocket

to: L2 Lagrange point

(1.5 million km from Earth)

Where from, where to, how?

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