Optical TDE hunting with Gaia Jerusalem TDE workshop, 2nd November 2015 Nadejda Blagorodnova ( ) & Gaia Science Alerts DPAC team
TDE are nuclear transients In/close to the nucleus
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
Gaia?
Earth L2
What is Gaia? 109 stars in the Milky Way, 1.5x106 galaxies, 4x105 quasars and 6000-10000 SN! Launched 19 December 2013 Nominal start of the mission: 25th September 2014
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
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 RVS3 0.42 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
)
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
Gaia parameter space Original diagram in Kasliwal et. al, 2011
Hunting?
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
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
Simulated Real 1 4 (arcsec) ~25% galaxies detected from 1.3M from SDSS mag< 20
What galaxies are detected? Blue cloud Red sequence Blue cloud Red sequence Redshift rmodel u-r
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
GIBIS: Gaia Instrument and Basic Image Simulator
% resolved in function of magnitude difference bulge-sn Blagorodnova et. al. 2015 Simulation for bulges with Re=1 arcsec
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
Fainter bulges SN brightness Galaxy + SN Brighter bulges Brighter bulges SN only Fainter bulges
Expected detection efficiencies from simulations
Transient Characterisation Li et. al. 2011 - SN rates per galaxy - Absolute magnitude distribution - Rates per galaxy type Gezari et. al. 2012, Chornock et. al. 2014 - TDE Lightcurves from PS1 Lodato and Rossi, 2011 - Theoretical TDE Lightcurves Van Velzen and Farrar, 2014 - TDE rate per galaxy
Detection efficiency Full sky detection efficiency Limiting magnitude for candidates G = 19 Efficiency vs. Redshift
TDE vs. SN - nuclear case mlim = 19mag, Δm=0.5mag Detected TDE ~ Detected unresolved SN -> Low contamination!
What is the current status of Gaia Science Alerts?
Gaia14aaa
Gaia Alerts (so far) - 275 published alerts until June 2015-98 spectroscopically confirmed SN - apparent lack of nuclear SN/TDE? <1 arcsec?
New parameters On-board parameters Old parameters De Bruijne et. al, 2015 0.5 http://www.cosmos.esa.int/web/gaia/iow_20150409 http://www.cosmos.esa.int/web/gaia/iow_20141205
Validation phase and improvements
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!
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!