Searching for Transients with LOFAR/CS1Casey Law (Amsterdam)

You know LOFAR...                What is CS1?

Possible layout of LOFAR stations

Low-band antenna in CS1

• Core Station 1 is a prototype LOFAR station• Located in LOFAR core • 96 LBAs and HBAs 

Good for commissioning, good for science!   Early LBA observations: • Frequencies from 10 - 90 MHz• Resolutions from 2 - 0.2 deg• Bandwidth ~  4 MHz• Correlating 16 dipoles        Aeff ~ 128 m2

dipoles have all-sky sensitivity...

... produce all-sky maps

Ultimate goal:  The Radio Sky Monitor

• Imaging survey at 30, 120 MHz

• 1 sec sensitivity:  500, 50 mJy

• Covers 1/4 of sky daily

The RSM in action

Sky coverage of the RSM

What will this produce?  •  Image ~300 deg2/s

  • Studies sky on range of

timescales

• Lightcurves of all sources

• Public access to databaseQuickTime™ and a

decompressorare needed to see this picture.

Image

srcdet

db

class

alert

Transient Detection Pipeline  (Posters by J. Swinbank and B. Scheers)   

• Real-time pipeline in Python

• Starts with image cubes, produces source lists, alerts.

The Search Data:• LBA, near 45 MHz• Bandwidth = 4 MHz• 24 hours

  Method:• Image for times of 4, 8 min, ..., 4, 8 hrs • Area of ~1200 deg2 • Run source detection• Search for good candidates

Image of North Celestial Pole at 45 MHz.  All 3C sources visible, some SNRs, M82.Search area shown in green. 

Example lightcurves:  

3C 390.3:

1 hour integrations

30 min integrations

Results

For 10 threshold, no transients.

Nondetection limits transient rate, f.

For Poisson statistics,P(Ndet=0) = e-fN

For 95% confidence,P(Ndet=0) = 0.05.

Constraint on transinents in LOFAR CS1 survey.

Comparison to Previous Results

  

    STARE (Katz et al. 2003)MOTER (Amy et al. 1989Green Bank 300ft (Gregory & Taylor 1986) FIRST/NVSS (Levinson et al. 2002)

ST

AR

EGreen Bank

MOTER

FIRST/NVSS

Summary

1. The TKP is actively developing tools to exploit LOFAR.

2. LOFAR/CS1 is able to do science today!

3. A 24 hour study of a 1200 deg^2 field found no transients.

4. Upper limits starting to constrain transient sky.