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Producing Science with the Palomar
Transient Factory
Branimir Sesar (MPIA, formerly Caltech)
Producing Science with the Palomar
Transient Factory
Branimir Sesar (MPIA, formerly Caltech)
Survey Goals & Key Projects(Law et al. 2009, Rau et al. 2009)
• Goal: to study the transient and variable sky
• Extragalactic
• Transients in nearby galaxies, CC SNe, TDE, Hα Sky Survey, search for eLIGO/EM counterparts
• Galactic
• AM CVn systems (H + He WD), CVs, RR Lyrae stars to map the Milky Way structure and dynamics
• Solar System: KBOs, small NEAs/PHAs (prospect for growth → asteroid retrieval mission)
P48 wide-field imager →Discovery engine P200
Spec. followup
P60Photo. followup
P48 wide-field imager →Discovery engine
P200Spec. followup
P60Photo. followup
Fast spectroscopic typing with SED Machine (R~100, PI: Nick Konidaris, Caltech)
R~100 spectra of various transients and variables→ important spectral features are still discernibleR~100 spectra of various transients and variables→ important spectral features are still discernible
P48 Overview
• 7.26 deg2 field-of-view → will be upgraded to 47 deg2 for ZTF (2015-2016)
• 1” / pixel resolution → barely sampled at median 2” seeing → PSF photometry possible
• Robotic telescope & scheduler → automatic selection of fields → time & money saver
• g', R, and 2 Hα filters
• ~250 images / night
CFHT12k camera(well-defined cosmetics)
PTF Image Differencing Engine (PTFIDE; Frank Masci, IPAC)
Real-time Pipeline (transients)
Real-time Pipeline (transients)
Time from exposure to alert: 20 – 40 min
0.3% contamination, 0.7% of real transients missed
IPAC Pipeline (variables & light curves)
• Repeatability of < 0.01 mag
• R-band 5σ limit @ 20.6 mag (aperture), 20.9 mag (PSF)
• 12,000 deg2 with >30 epochs
• 1st PTF/iPTF data release (M81, M44, M42, Cas A, Kepler) http://www.ptf.caltech.edu/page/first_data_release
• Public release of PTF, iPTF and ZTF data (w/ NSF funding)
coverage of the Galactic plane (|b| < 5 deg)
Science
• 2,254 spectroscopically confirmed SNe
• 88 publications (5 in Nature)
• Finding dSphs with PTF SN Ia in M101 (PTF11kly; Nugent et al. 2011, Li et al. 2011)
Hundreds of low-luminosity dSph galaxies orbiting the MW?
Low-luminositydSph
Tollerud et al. (2008)
Estimated number of observable faint MW satellites
• LSST should be able to observe ~300 low-luminosity dSphs
• About 50 low-luminosity dSphs in ~10,000 sq. deg and between 60 - 100 kpc
Segue I (MV = -1.5, D = 23 kpc, r
h = 30 pc)
MSTO
RR LyraeBHB
Only 6 RGB stars!
Seg RGB → orangeSeg MS → blue
“Segue I”-like dSph at 60 kpc (MV = -1.5)
dSph RGB → orangeforeground → white
Segue I (MV = -1.5, D = 23 kpc, r
h = 30 pc)
MSTO
RR LyraeBHB
Only 6 RGB stars!
Seg RGB → orangeSeg MS → blue
Table 4 of Boettcher, Willman et al. (2013)
Boo III 1 -2.0 (Sesar, submitted to ApJ)Boo II 1? ? (within 1.5' of Boo II @ 33 kpc)
Almost every dSph has at least one RR Lyrae star → use distant RR Lyrae stars as tracers of low-luminosity dSphs
~180 RRab stars between 60 and 100 kpc
Orange – Sgr?
“Segue I”-like dSph at 60 kpc
dSph is still invisible in the color-magnitude diagram
Pick a distant RR Lyrae star
D = 60 kpc
Select stars that may be at the distance of the RR Lyrae star
M92 isochrone at 60 kpc
Plot angular coordinates with respect to the coordinates of the RR Lyrae star
Convert angular to projected distances
Repeat for a different RR Lyrae star (i.e., sightline) and add onto the same plot
Repeat for a different RR Lyrae star (i.e., sightline) and add onto the same plot
Overdensity of sources when fdSph
= 1.0 ...
Note: This is just for visualization
...when fdSph
= 0.2
… when f = 0 (i.e., just the background)
Sensitivity of the detection method
Black pixels: parameter space where detection is possible at 3-sigma level
19
27
37
49
74
98
123
Minimum number of dSphs needed for a detection
What is observed in SDSS
Constraining the luminosity function of dSph galaxies
rh = 120 pc
rh = 30 pc
PanSTARRS1
S82 light curve PS1 light curve
PS1 is deeper than PTF, and covers more area → repeat search
RR Lyrae Stars
• Old, evolved stars (> 9 Gyr) → trace old populations of stars
• Standard candles → identify them → know their distance (with ~6% uncertainty)
• Bright (V ~ 21 at 110 kpc)
• Variable stars (P ~ 0.6 day) with distinct light curves ( ~1 mag amplitude) → easily identifiable
• Repeated observations (~30 or more) are needed
Light curve of an RR Lyrae type ab
Death throes - An outburst from a massive star 40 days before a supernova explosion (Ofek+ 2013)
No detection @ -60 & -50 days
Outburst!
Explosion!
Localization of an optical afterglow in 71 deg2 (Singer et al. 2013)
ZTF will cover this area with ~2 images
Optical afterglow
GRB 130702A to iPTF13bxl Timeline
• 00:05 Fermi GMB trigger (UT July 2nd)
• 01:05 position refined by human (GBM group)
• 03:08 Sun sets at Palomar
• 04:17 PTF starts observations (10 fields, 2x60-s per field; 72 square degrees)
• 4214 "candidates": 44 were known asteroids, 1744 were coincident with stars (r<21) → 43 viable candidates
• Human inspection reduced this to 6 excellent candidates
• iPTF13bxh core of a bright galaxy, iPTF13bxr known quasar, iPTF13bxt was close to a star in SDSS
• Remaining candidates: iPTFbxl(RB2=0.86), iPTFbxk (RB2=0.83) and iPTFbxj (RB2=0.49)
• Sunrise in California
GRB 130702A to iPTF13bxl Timeline
• 00:50 Swift observations for iPTF13bxl requested (UT July 3rd) → X-ray source detected
• 04:10 Robotic observations of these candidates at P60 → iPTFbxl showed decline relative to first P48 observation (!)
• 04:24 Spectral observations on the Palomar 200-inch → spectrum is featureless (!!)
• 08:24 Announced iPTF13bxl as afterglow (ATEL, GCN)
• 17:34 LAT localization (3.2 square degrees)
• 19:03 IPN announces annulus of width 0.9 degrees
• 23:17 Magellan observations led to z=0.145
Small, but potentially hazardous asteroids
Adam Waszczak (grad student @ Caltech)
NEA 2014 JG55 (diameter: 10 m, closest approach: ¼ Earth-Moon distance)
RR Lyrae stars in SDSS Stripe 82 (Sesar, Ivezić+ 2010)
“Smooth” inner halo ends at 30 kpc → only streams and dSphs beyond 30 kpc?
Be Aware of the Contamination
• Sesar et al. (2007):
• Smaller number of epochs in SDSS Stripe 82
• Could not properly remove non-RR Lyrae stars
• ~30% contamination in our RR Lyrae sample
• Detection of false halo substructures
Psc