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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)
P60
Photo. followup
P48 wide-field imager →
Discovery engine
P200
Spec. followup
Fast spectroscopic typing
with SED Machine (R~100,
PI: Nick Konidaris, Caltech)
P48 wide-field imager →
Discovery engine
P60
P200
Photo. followup
Spec. followup
R~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)
Real-time Pipeline (transients)
PTF Image
Differencing
Engine (PTFIDE;
Frank Masci,
IPAC)
Real-time Pipeline (transients)
0.3% contamination, 0.7% of real transients missed
Time from exposure to alert: 20 – 40 min
IPAC Pipeline (variables & light curves)
coverage of the Galactic plane (|b| < 5 deg)
• 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)
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?
Estimated number of
observable faint MW satellites
• LSST should be able to
observe ~300 lowluminosity dSphs
• About 50 low-luminosity
dSphs in ~10,000 sq. deg
and between 60 - 100 kpc
Tollerud et al. (2008)
Low-luminosity
dSph
Segue I (MV = -1.5, D = 23 kpc, rh = 30 pc)
BHB
RR Lyrae
Only 6
RGB stars!
MSTO
Seg RGB → orange
Seg MS → blue
“Segue I”-like dSph at 60 kpc (MV = -1.5)
dSph RGB → orange
foreground → white
Segue I (MV = -1.5, D = 23 kpc, rh = 30 pc)
BHB
RR Lyrae
Only 6
RGB stars!
MSTO
Seg RGB → orange
Seg MS → blue
Table 4 of Boettcher, Willman et al. (2013)
Almost every dSph has at
least one RR Lyrae star →
use distant RR Lyrae stars
as tracers of low-luminosity
dSphs
Boo III
Boo II
1
1?
-2.0
?
(Sesar, submitted to ApJ)
(within 1.5' of Boo II @ 33 kpc)
~180 RRab stars between 60 and 100 kpc
Orange – Sgr?
“Segue I”-like dSph at 60 kpc
dSph is still
invisible in the
colormagnitude
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
123
98
74
49
37
Minimum
number of
dSphs needed
for a detection
27
19
Black pixels: parameter
space where detection is
possible at 3-sigma level
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)
Explosion!
Outburst!
No detection @ -60 & -50 days
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