Optical TDE hunting with Gaia

Transcription

1 Optical TDE hunting with Gaia Jerusalem TDE workshop, 2nd November 2015 Nadejda Blagorodnova ( ) & Gaia Science Alerts DPAC team

2 TDE are nuclear transients In/close to the nucleus

3 Tidal Disruption Events vs. SNe Strubbe and Quataert, 2012 Gezari et. al., 2012 Slower rise/decay Arcavi et. al., 2014 Need for high accuracy astrometry to constrain the position within the galaxy High contamination in ground-based surveys

4 Gaia?

5 Earth L2

6 What is Gaia? 109 stars in the Milky Way, 1.5x106 galaxies, 4x105 quasars and SN! Launched 19 December 2013 Nominal start of the mission: 25th September 2014

7 Single Gaia observation = Transit detection and FOV discrimination astrometric measurements photometry (dispersed images) radial velocity (dispersed images) SM1 SM2 AF1 AF2 AF3 AF4 AF5 AF6 AF7 AF8 AF9 BP RP RVS1 RVS2 RVS3 Camera: 0.75 deg 2 pixel: 10x30 µm (59x177 mas) 0.42 m WFS2 star <20 mag detected! Place window. WFS1 BAM2 AC Animation by Berry Holl, Geneva BAM1 windows observed: ~4.4 sec 0.93 m AL ~45 sec

8 detection and FOV discrimination astrometric measurements photometry (dispersed images) radial velocity (dispersed images) WFS2 WFS1 BAM2 BAM1 SM1 SM2 AF1 AF2 AF3 AF4 AF5 AF6 AF7 AF8 AF9 BP RP RVS1 RVS2 RVS m Scan motion AC AL 0.93 m Background estimation: - 5th lowest value of 16 samples Flux estimation: - Central 3x3 - background Source detection: - Flux - Geometry 3x3 window Details in De Bruijne et. al. 2015

9 )

10 The catalogue New Scans New transits Historic Scans Measurements for each transit Historic transits SM AF 1 AF 2 AF 3 AF 4 AF 5 AF 6 AF 7 AF 8 AF 9 50M day -1 SOURCE Match radius

11 Gaia parameter space Original diagram in Kasliwal et. al, 2011

12 Hunting?

13 Transient detection hunting process Candidate parameters: - mlim=19mag - Δlim=0.5mag Galaxy detected? no yes m T < m lim? New object? yes no no yes Orphan No detection Δ m > Δ lim? New source yes no Old source No detection

14 Candidate parameters: - mlim=19mag - Δlim=0.5mag Galaxy detected? no yes m T < m lim? New object? yes no no yes Orphan No detection Δ m > Δ lim? New source yes no Old source No detection

15 Simulated Real 1 4 (arcsec) ~25% galaxies detected from 1.3M from SDSS mag< 20

16 What galaxies are detected? Blue cloud Red sequence Blue cloud Red sequence Redshift rmodel u-r

17 Candidate parameters: - mlim=19mag - Δlim=0.5mag Galaxy detected? no yes m T < m lim? New object? yes no no yes Orphan No detection Δ m > Δ lim? New source yes no Old source No detection

18 GIBIS: Gaia Instrument and Basic Image Simulator

19 % resolved in function of magnitude difference bulge-sn Blagorodnova et. al Simulation for bulges with Re=1 arcsec

20 Transient detection process Galaxy detected? no yes m T < m lim? New object? yes no no yes Orphan No detection Δ m > Δ lim? New source yes no Old source No detection

21 Fainter bulges SN brightness Galaxy + SN Brighter bulges Brighter bulges SN only Fainter bulges

22 Expected detection efficiencies from simulations

23 Transient Characterisation Li et. al SN rates per galaxy - Absolute magnitude distribution - Rates per galaxy type Gezari et. al. 2012, Chornock et. al TDE Lightcurves from PS1 Lodato and Rossi, Theoretical TDE Lightcurves Van Velzen and Farrar, TDE rate per galaxy

24 Detection efficiency Full sky detection efficiency Limiting magnitude for candidates G = 19 Efficiency vs. Redshift

25 TDE vs. SN - nuclear case mlim = 19mag, Δm=0.5mag Detected TDE ~ Detected unresolved SN -> Low contamination!

26 What is the current status of Gaia Science Alerts?

27 Gaia14aaa

28 Gaia Alerts (so far) published alerts until June spectroscopically confirmed SN - apparent lack of nuclear SN/TDE? <1 arcsec?

29 New parameters On-board parameters Old parameters De Bruijne et. al,

30 Validation phase and improvements

31 Conclusions Gaia is TDE-friendly: is a suitable tool for highaccuracy measurements of slow-rising transients. Change in on-board detection parameters has increased the number of fake detections. Currently, changes in pipeline focus on cleaning the sample and approaching the nucleus! First candidates coming soon!

32 Gaia DPAC & Heather Campbell Morgan Fraser Gerry Gilmore Diana Harrison Simon Hodgkin Mike Irwin Seppo Mattila Sergey Koposov Rubina Kotak Guy Rixon Sjoert Van Velzen Lukasz Wyrzykowski Nicholas A. Walton Thank you!