arXiv:0906.5355v1 [astro-ph.CO] 29 Jun 2009 ae)o rdce u o e icvrdphenomena discovered yet of not afterglows but orphan (e.g., con- predicted poorly or disruptio tidal either novae, flares) red of luminous su- types (e.g., events novae, many reason- strained exist classical Besides op- there (e.g., the pernovae), 1). populations of is (Figure knowledge well-studied project space present-day ably this phase our of in transient goal gaps tical main the The fill to sky. tran- variable optical and the sient systematically explore to designed ment oryepoe tbs n r iefrinvestigation for ripe are and remain space best phase at the explored su- of areas or poorly large novae, pop- Thus, classical source max- pernovae). microlensing, selected to (typically for cadence) probability ulations have of discovery however, terms the projects, in imize these (especially of designed majority been time-domain The of understanding impor- science. our provided to have contributions and tant task challenging this tempted leading of progress. prospect significant best to the have instruments wide-field lcrncades [email protected] address: Electronic rnO Ofek O. Eran Djorgovski rpittpstuigL using 2009 typeset 30, Preprint June version Draft nrwJ Drake J. Andrew h aoa rnin atr PF sa experi- an is (PTF) Factory Transient Palomar The ubro uvy smaie nTbe1 aeat- have 1) Table in (summarized surveys of number A 15 11 reRau Arne eateto hsc Atohsc) nvriyo Oxfor of University (Astrophysics), Physics of Department XLRN H PIA RNIN K IHTEPLMRTRANSI PALOMAR THE WITH SKY TRANSIENT OPTICAL THE EXPLORING al nttt o hoeia hsc n eateto P of Department and Physics Theoretical for Institute Kavli h cetfi oiainfrPFaddsrb ndti h g the detail Su in Synoptic headings: describe and Large Subject PTF the for PT like motivation from surveys scientific learned the sky be synoptic can large that sta future lessons Lyrae The n RR galactic objects). (through active near-Earth dynamics and galactic sour supernovae known understanding to of into avatars members an various new many their supernovae discover in .Ia also will pr macronovae, PTF theoretically supernovae, for bursts. fallback search to as and such space strateg phase operation transient PTF The the Telescope. Oschin Samuel 48-inch ihafil fve f79deg 7.9 yea of to view minutes of from field scales a time with on sky variable and transient 9 h aoa rnin atr PF sawd-edexperime wide-field a is (PTF) Factory Transient Palomar The nrrdPoesn n nlssCne,Clfri Insti California Center, Analysis and Processing Infrared 5 1 eateto srnm n srpyis enyvnaSt Pennsylvania Astrophysics, and Astronomy of Department 1 ee .Fox B. Derek , 1 atc pia bevtre,M 0-4 aionaInst California 105-24, MS Observatories, Optical Caltech oetM Quimby M. Robert , 4 1,2 10 ihlo cec etr S102,Clfri Institute California 100-22, MS Center, Science Michelson 7 hiia .Kulkarni R. Shrinivas , 1. 13 pte cec etr S206 aionaIsiueo T of Institute California 220-6, MS Center, Science Spitzer eateto srpyis mrcnMsu fNtrlHis Natural of Museum American Astrophysics, of Department 1 A 6 lxiV Filippenko V. Alexei , a ube lblTlsoeNtok 70CroaD.Sant Dr. Cortona 6740 Network, Telescope Global Cumbres Las INTRODUCTION 12 T eoioCne o srpyis ezanIsiueo Sc of Institute Weizmann Astrophysics, for Center Benoziyo E 3 tl mltajv 6/22/04 v. emulateapj style X oubaAtohsc aoaoy oubaUiest,N University, Columbia Laboratory, Astrophysics Columbia eateto srnm,Uiest fClfri,Berkel California, of University Astronomy, of Department 2 uenve usr n cieGlci uli tr,Ext Stars, Nuclei, Galactic Active and Quasars Supernovae, γ a-lnkIsiuefretaersra hsc,Garch Physics, extraterrestrial for Institute Max-Planck rybrt) ee dedicated Here, bursts). -ray 5 8 vsa Gal-Yam Avishay , arneBree ainlLbrtr,Bree,C 94720 CA Berkeley, Laboratory, National Berkeley Lawrence 14 nvriyo aiona at abr,C 30,UAand USA 93106, CA Barbara, Santa California, of University 2 1 ila .Reach T. William , n lt cl f1 of scale plate a and 1 Poznanski ihlsM Law M. Nicholas , 3 ai .Helfand J. 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TABLE 1 Comparison of PTF with other untargeted transient and variable surveys

a b Survey D Scale FoV Cadence mR,lim Coverage Lifetime Reference [m] [′′ pxl−1] [deg2] [mag] deg2 night−1 Palomar Transient Factory 1.26 1.0 7.78 1 min – 5 d 21.0 1000 ongoing Law et al. 2009 ROTSE-IIIc 0.45 3.25 3.42 1 d 18.5d 450 ongoing Quimby 2006 Palomar-Quest 1.26 0.88 9.4 30 min – days 21.0e 500 2003-2008 Djorgovski et al. 2008 SDSS-II Supernova Search 2.5 0.4 1.5 2 d 22.6 150 2005-2008 Frieman et al. 2008a Catalina Real-time Transient Survey 0.7 2.5 8 10 min – yr 19.5f 1200 ongoing Drake et al. 2008 Supernovae Legacy Survey 3.6 0.08 1 3 d-5 yr 24.3 2 2003-2008 Astier et al. 2006 SkyMapper 1.33 0.5 5.7 0.2 d – 1 yr 19.0 1000 start 2009 B. Schmidt, pers. com. Pan-STARRS1 3πg 1.8 0.3 7 7 d 21.5 6000 start 2009 Young et al. 2008 Large Synoptic Survey Telescope 8.4 0.19 9.62 3 d 24.5 3300 start 2014 Ivezic et al. 2008

aTelescope diameter bTypical limiting magnitude for single pointing cTexas Supernovae Search (till 2007) and ROTSE Supernovae Verification Project (since 2007) dUnfiltered eRG610 filter fV -band filter gPan-STARRS1 3π imaging survey.

a 60s exposure. -26 Long GRB Orphan 2.2. Observing Strategy -24 Afterglows -22 The first few months after first light in December 13th Luminous Supernovae 2008 have been used for commissioning of the instru- -20 CCSNe ment and software. Initial observations were taken to -18 Fallback SNe Ia construct a fiducial reference image of the sky for later Supernovae Short GRB Tidal Disruption Flares -16 .Ia Orphan use in transient detection. Afterglows Following commissioning, PTF will be operating on (mag) R -14 Macro Novae 80% (∼ 290 night yr−1) of the P48 nights until at least M Luminous -12 Red Novae LBVs the end of 2012. During this time several predefined long- -10 term surveys and a number of evolving experiments will Classical Novae be performed. The primary experiments are the 5 day -8 cadence survey (5DC), the dynamic cadence experiment -6 (DyC), a monitoring of the Orion star-forming region -4 (see § 3.10), and a narrow-band all-sky survey. The re- 1 10 100 spective time allocations, cadences, and photometric fil- Decay Time (days) ters are summarized in Table 2.

TABLE 2 Fig. 1.— R-band peak magnitude as a function of characteristic Summary of Main PTF Experiments decay timescale (typically the time to fade from peak by 2 magni- tudes) for luminous optical transients and variables. Filled boxes mark well-studied classes with a large number of known members Experiment Exposure Cadences Filter (classical novae, Type Ia supernovae [SNe Ia], core-collapse su- % of total pernovae [CCSNe], luminous blue variables [LBVs]). Vertically 5DC 41 5 d R hatched boxes show classes for which only few (∼< 4) candidate DyC 40 1min–3d g, R members have been suggested so far (luminous red novae, tidal dis- Orion 11 1min R ruption flares, luminous supernovae). Horizontally hatched boxes FullMoon 8 – Hα are classes which are believed to exist, but have not yet been de- tected (orphan afterglows of short- and long GRBs). The positions of theoretically predicted events (fall-back supernovae, macrono- vae, .Ia supernovae [.Ia]) are indicated by empty boxes. See text The 5DC experiment will at any given time monitor for references related to each science case. The brightest transients an active area of ∼ 2700deg2 with a mean cadence of (on-axis afterglows of GRBs) and events detectable predominantly 2 in the Milky Way (e.g., dwarf novae) are omitted for clarity (see 5 d. Over the year, a total footprint of ∼ 10, 000deg Table 4 for a more complete list). Regions indicate the general (largely overlapping with the SDSS) with Galactic lati- ◦ ◦ ◦ location of each class and are not exclusive. The color of each box tude |b| > 30 , and −15 <δJ2000 < 86 will be observed. corresponds to the mean g − r color at peak (blue, g − r < 0 mag; green, 0 1 mag). This experiment will be performed using the R-band fil- ∼ ∼ ter, and typically two 60s exposures separated by 1hr will be taken in each epoch. As part of the 5DC, we will also observe ∼ 60 fields containing nearby galaxies. Note tensity (FWHM) ∼ 2.0′′and 5σ limiting magnitudes of that these galaxies (with the exception of M31) will cover R ≈ 21.0, g′ ≈ 21.6 and Hα ≈ 18mag can be reached in only a small fraction of the camera FoV. PTF Science 3

Binning angular size [deg] archiving can be found in (Law et al. 2009). −3 −2 −1 0 0 10 10 10 10 10 3. PTF SCIENCE GOALS The PTF design is optimized for repeated coverage of −1 10 IPHAS (Galactic plane only)PTF SHASSA VTSS a large sky area in a short amount of time. This is crucial for pursuing the primary science goal, namely to investi- WHAM −2 10 gate the various populations of transients and variables. In addition, it allows the usage of deeper, coadded im- −3 ages to study persistent sources, ranging from Galactic Sensitivity [R] Sensitivity 10 foreground stars to distant galaxies. While it is not pos-

−4 sible to predict all of the science that PTF will enable, 10 0 1 2 3 4 10 10 10 10 10 a few key areas of interest have been defined and will be Binning angular size ["] summarized below. Here, we first address transient and variable sources from our neighborhood to high redshift, Fig. 2.— The surface brightness sensitivity (Rayleigh, R) of the followed by regularly variable classes and science with PTF Hα survey as a function of the angular size. The smallest the coadded data products. An overview of the sections angular size is determined by the pixel size (filled circle). Bin- is given in Table 3, while Table 4 summarizes the proper- ning is expected to improve sensitivity in proportion to the square ties, universal rates, and PTF predictions for transients root of the number of pixels. The proposed survey will have bet- ter sensitivity by more than two orders of magnitude over previ- and variables. ous surveys (e.g., SHASSA; Gaustad et al. 2001, VTSS; Dennison et al. 1998). The only survey with superior sensitivity (IPHAS; Walton et al. 2004) is limited to the Galactic plane (|b| < 5◦) TABLE 3 Summary of Science Drivers discussed in § 3

The DyC experiment is designed to explore transient Science Driver Main Survey Section phenomena on time scales shorter than 5 d and longer Cataclysmic variables DyC, 5DC 3.1 than about 1 min. Here, several different g- and/or Classical novae 5DC 3.2 R-band surveys will be conducted during the first six Luminous red novae, .Ia supernovae DyC, 5DC 3.3 months of operation. Strategies for subsequent DyC ob- Type Ia supernovae 5DC 3.4 Core-collapse supernovae 5DC 3.5 servations will be decided after the initial results have Luminous & pair-instability supernovae 5DC 3.6 been analyzed. Blazars 5DC 3.7 During bright time 3π sr narrow-band (Hα, Hαoff , Tidal disruption flares 5DC 3.8 [O III]) surveys will be conducted. Here, ∼ 4000 tiles cov- (Orphan) GRB afterglows DyC, 5DC 3.9 ◦ ering the sky at δJ2000 > −28 will be observed at least Exoplanet transits in Orion Orion 3.10 twice in each filter. The estimated 5σ point source flux Eclipsing Objects Around Cool Stars DyC 3.11 limit for the Hα survey will be ∼ 2 × 10−17 ergcm−2 s−1 RR Lyrae stars 5DC 3.12 (∼ 0.6 Rayleigh). Better sensitivity by a factor of ∼60 Galactic Variable Stars DyC,5DC 3.13 can be achieved by binning the Hα images to a resolu- Microlensing 5DC 3.14 tion of 1′. This sensitivity will constitute an improve- Near-Earth objects 5DC 3.15 PTF as follow-up instrument ToO 3.16 ment over that of previous surveys by a factor of ∼ 250 Coadded & narrow- band data Dyc, 5DC, NB 3.17 (Figure 2).

2.3. Follow-up Strategies The key to a successful transient survey lies in the 3.1. Cataclysmic Variables availability of follow-up resources, specifically multi- color imaging and spectroscopy. Most other wide-field Cataclysmic variables (CVs) form a broad family of searches aim to do both discovery and follow-up ob- highly variable and dynamical stellar binaries in which servations, with the same instrument, or have spectro- matter from a low-mass donor (M∼< 1 M⊙) is accreted scopic follow-up biased heavily toward a specific sci- onto a white dwarf (M≈ 1 M⊙; e.g., Warner 1995). Vari- ence goal (e.g., ESSENCE, SNLS, and SDSS-II with ability, from milliseconds to hundreds of years, arises SNe Ia). In contrast, PTF will perform multi-color from different physical processes, and conclusions derived photometry for all candidate transients using a vari- from CVs have been extrapolated, upward or downward ety of facilities. Here, a large fraction of Palomar in scale, to other phenomena such as active galactic nu- 60-inch (optical; Cenko et al. 2006), LCOGT1 (optical) clei (AGNs) and X-ray binaries. Despite being studied Super-LOTIS (optical; Park et al. 1999), KAIT (opti- for several decades, many details concerning the viscous cal; Filippenko et al. 2001), and PAIRITEL (near-IR; turbulence in the accretion disk, interaction of the ac- Bloom et al. 2006) time has been set aside. Additional creted matter with the atmosphere of the white dwarf, spectroscopy is planned at the Palomar Hale 5-m, MDM irregularities within regular photometric behavior, and Observatory, William Herrschel 4.2 m, and Lick 3 m tele- the final fate of these objects, are still missing. scopes. An important subclass of CVs is the so-called dwarf no- A detailed discussion of all aspects mentioned in this vae (DNe), which show quasi-periodic outbursts (on time section as well as the data reduction, analysis, and scales of weeks to years) with amplitudes of 3–8 mag and durations of typically 3–20 d. These transient events are 1 http://lcogt.net/ the result of a sudden viscosity change in the accretion 4 A. Rau et al. disk. The origin of this change is still controversial; in- for classical novae as their proxies. Previous detections stabilities in the disk (Meyer & Meyer-Hofmeister 1981) of “tramp” planetary nebulae and novae in the Virgo or in the secondary star (Bath et al. 1986) may both be cluster (Feldmeier et al. 2004) and the Fornax cluster responsible. Increasing the sample of well-studied events (Neill et al. 2005) suggest that 16% to 40% of all stars in will help to distinguish between these models. rich clusters reside in intracluster space outside of galax- The current estimate of the space density of ies. PTF will probe whether the same is true of less dense DNe ranges from ∼ 3 × 10−5 pc−3 (observations; environments like the Local Group, or of intergalactic Schwope et al. 2002) to as much as ∼ 10−4 pc−3 (the- space in general. In the 5DC, novae originating in a space ory; Kolb 1993). For typical values of peak magnitude volume at least four times larger than the Local Group (9 > MR > 4mag) and recurrence time scale (1yr; can be detected (out to a distance of D =2.5 Mpc). We Rau et al. 2007b), this suggests the detection of about expect ∼16 tramp novae to be found every year if 10% 100 DNe yr−1 in the 5DC. of the stars in and around the Local Group are tramps2. In special cases, the secondary can be another white Conversely, if zero intergalactic tramps are found, an up- dwarf or a hydrogen-depleted star in a tight orbit, whose per limit on the baryon contribution in the Universe from evolution is dictated by gravitational wave radiation. De- intergalactic tramp stars of ∼1–2% can be set after one pending on the orbital period, mass transfer can either year. be through a stable or unstable disk or via direct impact. These so-called AM CVn stars are of particular interest 3.3. Other Transients in Nearby Galaxies as they form the dominant population of gravitational Observations suggest a paucity of transients between wave sources detectable with the future Laser Interfer- the peak absolute brightness of classical novae (MR ∼> ometer Space Antenna (LISA) mission. Merging white −10 mag) and supernovae (MR ∼< −14 mag). However, dwarfs are also strong progenitor candidates for SNe Ia recent discovery of a number of enigmatic events in this (e.g., Iben & Tutukov 1984; Webbink 1984) and thus are gap have demonstrated the potential for exciting discov- important tracers of binary stellar evolution. eries with dedicated experiments. AM CVn systems with an unstable accretion disk ex- One of these newly emerging classes are the lumi- hibit photometric outbursts similar to those of hydrogen- nous red novae (LRNe), whose origin and explosion rich dwarf novae and can be detected as transient events physics still pose unsolved puzzles. This elusive group with PTF. However, with an inferred space density of −6 −3 of sources includes only four known members: M31 RV ∼ (1 − 3) × 10 pc (Roelofs et al. 2007), AM CVn (Rich et al. 1989), V4332 Sgr (Martini et al. 1999), stars are rare compared with normal CVs. Furthermore, V838 Mon (Brown et al. 2002), and M85 OT2006-1 only 5-6% of the population resides within the instability (Kulkarni et al. 2007). Their observational properties range in which outbursts occur, and He ionization results differ from those of classical novae and typical supernovae in much shorter time scales of these events. Thus, only by showing a slowly evolving outburst with an optical a few of these elusive sources are expected to be found plateau lasting weeks to months, followed by a strong in the DyC experiments. redward evolution resembling a transition from stellar type ∼F to ∼M and colder (e.g., Rau et al. 2007a). 3.2. Classical Novae Several formation models have been proposed, In some CVs the matter accreted onto the primary including stellar mergers (Soker & Tylenda 2003), white dwarf can experience a thermonuclear runaway, rare novae (Iben & Tutukov 1992), and supernovae driving substantial mass loss from the system. These (Pastorello et al. 2007); these scenarios need to be classical nova eruptions reach absolute peak magnitudes assessed with an increased sample of accurately studied events. Also, the underlying stellar popu- of −5 ∼> MR ∼> −10 mag (< MR >∼ −7.5 mag in M31; Shafter et al. 2009) and fade on time scales of days to lation of the known sample has a large diversity, weeks (e.g., Warner 2008). ranging from a B-star cluster in the Milky Way A typical M31-like galaxy produces ∼ 2 × 10−10 novae (V838 Mon; Af¸sar & Bond 2007) to the bulge of −1 −1 M31 (M31 RV; Rich et al. 1989). This leads to the yr L⊙,K (Ferrarese et al. 2003), translating into ∼30 −1 question of whether the known LRNe form one homo- yr . PTF will repeatedly image 60 large, nearby (m- geneous class of objects (with the explosion physics M < 29 mag) galaxies as part of the 5DC. We anticipate −1 −1 being independent of the stellar population), or if ∼10 novae yr galaxy to lie above the detection limit. different scenarios apply to each of the individual Thus, a typical coverage of three months per year for sample members. Note that two additional sources each galaxy will provide ∼150 extragalactic classical nova at the bright end of the distribution, SN 2008S discoveries every year. (e.g., Arbour & Boles 2008; Prieto et al. 2008) and The spatial and luminosity distributions of these no- NGC300 OT (e.g., Monard 2008), have been found vae inside their host galaxies will provide invaluable tests recently. Associations with extreme asymptotic giant of cataclysmic-binary evolution theory. Predictions that branch (AGB) stars have been proposed for these events fast novae should predominantly arise in spiral arms (Thompson et al. 2008). (della Valle et al. 1994) are still lacking conclusive ob- Based on rates estimated from the number of known servational evidence (e.g., Neill & Shara 2004). The ex- −13 −1 −1 LRNe (1.5×10 yr L⊙,K ; Ofek et al. 2008), we ex- pected dramatic enlargement of the number of accurately −1 sampled nova light curves will help to test this prediction. pect to discover > 1.5yr during the 5DC coverage of In addition to targeting nearby galaxies, PTF will 2 This assumes 8 months per year observation of the ∼2700 deg2 place the first meaningful limits on the space density of the 5DC and ∼60 novae yr−1 detected in the Local Group of intergalactic “tramp stars” (Shara 2006) by searching (mostly M31 and the Galaxy). PTF Science 5 galaxies within 16 Mpc. Over a four-year lifetime of PTF, this will more than double the known sample and pro- vide valuable insight into the origin and properties of these rare transients. The regular PTF monitoring of nearby galaxies will also allow a search for a number of theoretically pre- dicted, but not yet observationally confirmed, popula- tions of transients. Among these are the faint ther- monuclear supernovae from AM CVn binaries (“.Ia SNe”, one-tenth as bright for one-tenth the time as a SN Ia; Bildsten et al. 2007). Helium that accretes onto the white dwarf primary can undergo unstable thermonu- clear flashes. At wide binary separations (Porb > 25 min) a large mass will be accumulated before ignition, lead- ing to violent flashes in which high pressure allows the burning to produce radioactive elements to power a faint (−15 ∼> MR ∼> −17 mag) and rapidly rising (2–5 d) thermonuclear supernova. The local Galactic AM CVn space density implies one such explosion every 5,000– 11 15,000yr in 10 M⊙ of old stars (∼2–6% of the SNe Ia rate in E/SO galaxies), giving an expected DyC yield of a few per year. The first possible manifestations of this class in nature have recently been found with SN 2008ha Fig. 3.— Impact of 1000 well-studied, well-calibrated, low- (Foley et al. 2009) and SN 2005E (Perets et al. 2009). redshift Hubble-flow SNe Ia when mated to near-term simulated high-redshift surveys (z = 0.9). 3.4. Type Ia Supernovae Observations of SNe Ia provided the first direct and, to date, the best evidence for the acceleration data, will allow the construction of the most accurate of the expansion of the Universe, propelled by some SN Ia Hubble diagram yet. kind of mysterious “dark energy” (Riess et al. 1998; The purely statistical impact of a large number of low- Perlmutter et al. 1999); see Frieman et al. (2008b) for redshift SNe Ia on the determination of the cosmic pa- a review. To determine whether the equation-of-state rameters is illustrated in Figure 3. A simulated data set parameter of the dark energy3 is consistent with Ein- of 1000 SNe Ia centered at z = 0.08 is paired with 500 stein’s cosmological constant, enormous efforts are un- SNe Ia distributed in the redshift range 0.2 redshifts (up to z ≈ 1.7). an important improvement. SN Ia cosmology relies on comparison of the appar- The large area covered by the 5DC experiment will ent brightnesses of high-redshift events to those at low include a sizable number of relatively nearby, Abell- redshift, to measure accurate relative distances. PTF is like galaxy clusters. SNe Ia occurring in these clusters expected to discover ≈ 500 SNe Ia yr−1 during the 5DC will be of particular interest. The SN rate in galaxy in the nearby smooth Hubble flow (0.03 ∼

bias. This will provide an accurate picture of the cosmic CCSN population and present observational constraints Palomar-Quest SN SN2004dh on theoretical models for low- and high-metallicity ex- plosions. Assuming galactic luminosity functions mea- sured by the SDSS at z =0.1 and the linear metallicity- luminosity relation (Tremonti et al. 2004), we can esti- mate that at least ∼ 15% of the SNe detected by PTF will reside in galaxies which are as metal poor as the Large Magellanic Cloud (LMC), and about 20% of those will reside in galaxies more metal-poor than the Small 30" 30" Magellanic Cloud (SMC). SNe II-P, a subset of CCSNe, have been shown Fig. 4.— Comparison of two CCSNe at similar red- to be standardizable by an empirical correlation shift and magnitude from the Caltech Core-Collapse Program (Hamuy & Pinto 2002; Nugent et al. 2006). Their in- (Gal-Yam et al. 2007). The left and right images show an un- trinsic inhomogeneity can be calibrated well and the re- named SN discovered in an untargeted (SN Factory; 1) and SN 2004dh found in a targeted search (Lick Observatory Supernova sulting distance precision for cosmology is about 10% Search; Li et al. 2000)), respectively. Note the LMC-like faintness (Poznanski et al. 2009), only slightly worse than that of of the host in the left panel compared to the luminous SN 2004dh SNe Ia (7 %; Astier et al. 2006). PTF will populate the host. Such low-luminosity (and probably low-metallicity) hosts are SNe II-P Hubble diagram with about 20 Hubble-flow likely to produce new types of SNe. Thus, a sample drawn from an untargeted survey such as the PTF 5DC will provide a more events per month to build an entirely independent and accurate picture of the cosmic SN population. novel test of the cosmology inferred from SNe Ia. Finally, with dense sampling of virtually every nearby galaxy observable from the northern hemisphere, PTF mation about the first PTF transient discoveries can be will be a powerful discovery machine for the most under- found in (Law et al. 2009). luminous (or rapidly decaying) events, providing ad- ditional clues to the nature of cosmic explosions with 3.5. Core-Collapse Supernovae very faint optical displays (e.g., Gal-Yam et al. 2006a; Bildsten et al. 2007; Pastorello et al. 2004). The study of core-collapse supernovae (CCSNe) is crit- ical to understanding the final stages of massive-star evo- 3.6. Luminous Supernovae and Pair-Instability lution and the formation of neutron stars and black holes, Supernovae natural laboratories for general relativity. Furthermore, CCSNe produce heavy elements, dust, and cosmic rays; The first stars to form in the Universe typically their explosion shocks trigger (and inhibit) star forma- ended their brief lives through pair-instability super- tion; and their energy input to the interstellar medium novae (e.g., Barkat et al. 1967; Heger & Woosley 2002), is a crucial ingredient in modeling galaxy formation. but it was long believed that this exit was not avail- CCSNe will likely form one of the most luminous and able to the metal-enriched stars of the modern era. Re- distant populations of transients for PTF. Their typi- cently, however, the discovery of SN 2006gy has pro- cal peak absolute magnitudes4 range from M = −14 vided what may be the first evidence for such an explo- R sion (Ofek et al. 2007; Smith et al. 2007), and surpris- to −21 mag (< MR >≈ −17.8 mag), thus allowing de- tections out to z ≈ 0.4 for the most luminous events. ingly, this extremely luminous (brighter than −20mag Based on discovery statistics from the Supernova Factory for 150 d), long-lived supernova was found in the local project (1), the 5DC is expected to reveal ∼ 200 events Universe. The pair-instability mechanism requires a star yr−1 shortly after explosion down to R ≈ 19.5 mag. to meet its end with a substantial mass still bound to it. Most nearby SNe are discovered by repeated imag- The rate of such events in the local Universe will thus sig- ing of catalogued galaxies (e.g., Filippenko et al. 2001). nificantly augment our understanding of the top end of This introduces a possible bias, skewing the result- the stellar initial mass function as well as the role metal- ing sample strongly toward events in large, luminous, licity plays in shedding mass prior to the explosion. As metal-rich galaxies (Figure 4). Previous untargeted sur- SN 2006gy-like events are luminous, expected to occur veys have uncovered peculiar SNe, occurring in small, frequently in the early Universe, and relatively simple low-luminosity, and probably metal-poor galaxies (e.g. to model, they may serve as cosmological probes in the Young et al. 2008). Metallicity has a strong impact James Webb Space Telescope era. Events discovered by on the pre-SN evolution of massive stars, influencing PTF in the local Universe may serve as a proving ground wind mass loss (and thus the final core mass and com- for their utility. The estimated event rate of ∼100Gpc−3 yr−1 sug- position), loss of angular momentum, and the opacity −1 (e.g., Fryer et al. 2007). Also, long-duration gamma-ray gest that about 20 (200) SN 2006gy-like events yr bursts (GRBs), which are associated with very energetic above R = 18mag (21.0mag) can be discovered dur- CCSNe, have been found in faint, low-metallicity host ing the course of the 5DC. It is important to note galaxies (e.g., Stanek et al. 2006; Modjaz et al. 2008). that the handfull of known events have all been dis- The 5DC provides an untargeted search with thou- covered in blind surveys (e.g., Texas Supernova Search, sands of anonymous galaxies in each frame, allowing (Quimby 2006); Catalina Real-time Transient Survey, one to construct a supernova sample without host-galaxy (Drake et al. 2009)), such as PTF. The most luminous supernova yet identified is 4 Determined from 72 CCSNe from (Richardson et al. 2002) as- SN 2005ap, found by the TSS (Quimby et al. 2007). suming MB −MR ≈ 0 mag. Smith et al. (2008) suggest that SN 2005ap may be PTF Science 7 physically similar to SN 2006gy, and Quimby et al. follow-up observations; a joint analysis of such multi- (2007) note a possible connection to the engines power- wavelength, synoptic observations of blazar flares could ing GRBs. With only weakly diluted black-body spectra lead to better constraints for theoretical models. Such and rapid photometric evolution, SN 2005ap-like events statistical monitoring of large areas of the sky is com- offer another possible probe of the early U1niverse, and plementary to the more traditional follow-up monitoring PTF can help reveal their physical identity. While a rate of selected samples of known blazars (e.g., Carini 2004). cannot accurately be measured from a single event, we We estimate that PTF will see at least a few tens of po- speculate that SN 2005ap-like events are roughly half as tential Fermi blazars per clear night, of which roughly common as sources similar to SN 2006gy. one will have a strong optical blazar flare. While there is not yet any conclusive evidence that Blazars are known to vary significantly on all time SN 2005ap, SN 2006gy, or any of the extremely luminous scales where data exist, with the power spectra well rep- SNe are indeed related to Pair-Instability explosions, resented by a power law, so in principle an arbitrarily there is no conclusive evidence that they are not. PTF large fluctuation can occur given a sufficiently long time will significantly expand the sample of well-studied lumi- interval. In practice, fluctuations at a level of several nous SNe and perhaps provide an answer as to whether tenths of a magnitude are common on time scales of hours or not PISNe occur in the local Universe. or days, and fluctuations at a level of 1 or 2mag are com- monly seen on time scales of months, but with rise or 3.7. Blazars fall times as short as a day or even less. This should be The light curves of blazars (AGN with the jet pointed contrasted with the variability of normal quasars, where towards the observer; e.g., Urry & Padovani 1995) are typical variations on a scale of several tenths of a magni- dominated by Doppler-boosted instabilities and other tude occur on a time scale of years, and dramatic (e.g., phenomena associated with relativistic outflows, rather magnitude or greater) changes are extremely rare on the than by the accretion-driven variability of ordinary AGN. time scales probed by the existing observations. Thus, variability is one of their most notable character- istics, offering both a method for discovery and insight 3.8. Tidal Disruption Flares into their physics. −2/3 Blazars are likely the dominant contributors to Stars passing within a distance of 5M7 Schwarzschild radii of a supermassive black hole (SMBH) the cosmic γ-ray background (Narumoto & Totani 2006; 7 Giommi et al. 2006). They also form the main fore- of MSMBH = 10 M7 M⊙ will be torn apart by the strong ground population at high radio frequencies, and an un- tidal gravitational field (e.g., Hills 1975; Rees 1988). derstanding of them will be essential for proper mod- While for M7 ∼> 20 the disruption of a main-sequence eling of the cosmic microwave background radiation at star happens inside the event horizon, for less massive high angular frequencies, such as for the Planck mis- SMBHs this should give rise to a detectable flare of sion (see, e.g., Giommi et al. 2006; Giommi et al. 2007; emission. To date, only a few candidate tidal disrup- Wright et al. 2009). Moreover, a growing number tion flares (TDFs) have been found, primarily in the of blazars has been detected at TeV energies (e.g., ROSAT All Sky Survey archive (e.g., Li et al. 2002; Horan & Weekes 2004; Horns 2008). Even more intrigu- Gezari et al. 2003; Halpern et al. 2004; Komossa 2005) ingly, beamed AGN are perhaps among the most plau- and in restframe-UV monitoring of otherwise dormant sible sources of ultra-high energy cosmic rays, reaching galaxies (e.g., Renzini et al. 1995; Gezari et al. 2006; energies of 1021 eV (e.g., Dermer 2007). These cosmic Gezari et al. 2008). accelerators are bound to play an increasingly important The flare emission is predicted to be dominated by role in the future of astro-particle physics. an optically thick accretion disk with a temperature 5 −1/4 The Fermi mission will play a dominant role in the Teff ≈ 3 × 10 M7 K (Ulmer 1999), peaking in the studies of blazars over the next several years. Ground- far-UV. Line emission from unbound (ejected) material based studies from synoptic sky surveys like PTF will (Strubbe & Quataert 2009) is expected to significantly provide valuable complementary data for maximum enhance the black-body continuum flux in the optical. scientific returns. First, archival analysis of multi- This can lead to a peak absolute magnitude in the rest epoch data from PTF, combined with other, previ- frame of MR ≈ −15 to −19 mag (see also Strubbe & ous and ongoing synoptic surveys such as Palomar Quataert 2008) and observationally confirmed by Gezari Quest (Djorgovski et al. 2008) or the Catalina Sky Sur- et al. 2008), roughly comparable to the absolute mag- vey (Drake et al. 2009), can be used to define purely nitude of a supernova. The single-epoch PTF sensitivi- variability-based (or variability- and color-based) sam- ties suggest that the TDF population will be probed to ples of blazars. This will provide an important check on ∼ 200M7 Mpc (z =0.05), corresponding to a volumetric the selection effects in the more traditional, radio-based 3/2 −1 −1 rate of 40M7 yr over the entire sky or about 3 yr samples. Archival light curves and measures of variabil- in the 5DC. ity can be used in a joint analysis with data from radio to One of the principal difficulties in pursuing these events γ-rays. This will result in larger, more complete samples is in distinguishing TDFs from nuclear SNe and ordinary of blazars, crucial for the studies described above. AGN variability. Here both the particular light curve (a Second, real-time detection of optical flares of blazars, rapid rise over days to weeks followed by a power-law de- correlated with the γ-ray data stream from Fermi, can cline5) and spectral evolution provide valuable guidance. be used to detect γ-ray loud blazars at fainter flux lev- Historical variability limits from the DeepSky project6 els than what would be statistically justifiable from the γ-rays alone, or to lead to new blazar discoveries on 5 The decline of interloping SNe should be exponential. their own. These detections can be used to trigger other 6 http://supernova.lbl.gov/∼nugent/deepsky.html . 8 A. Rau et al. can further constrain patterns of low-level AGN activity. searches can be used to constrain interesting properties We expect roughly 10% of rapidly risig events in galac- of the GRB population. tic nuclei to be TDFs (as opposed to SNe). Having The discovery of an orphan afterglow would serve as ∼2kpc resolution at z =0.05, we must contend not only a dramatic confirmation of the “jet model” for GRBs. with nuclear transient events but the light of the host- Multiple events would begin to map out the beaming galaxy bulge itself. Thus, events from lower-mass (105– distribution and, in addition, provide inputs to physi- 6 10 M⊙) SMBHs may be more reliably identified since cal models of relativistic outflows. Perhaps the most in- their bulges are expected to be comparatively faint. triguing possibility relates to the merging compact object Even if the yield from PTF is only a few iron-clad model of the short bursts (Fox et al. 2005). Detectable cases, the ensuing multi-frequency investigations will short-burst orphan afterglows will arise from a relatively have great value in providing feedback for TDF mod- nearby (D ∼< 20 Mpc) merger event, potentially within els and for influencing strategies for future TDF ob- range of current gravitational wave detectors. By pro- serving campaigns. These discoveries will provide a viding a temporal window to searches, and thus increas- window into the demographics of SMBHs and detailed ing their sensitivity, the discovery of an orphan afterglow follow-up observations could allow for an entirely new could even in the best case provoke a first direct detection way of measuring black hole mass, thus offering an in- of gravitational waves (Nakar et al. 2006). dependent test of the MSMBH–σ∗ relation of galaxies Rapidly evolving “no-host” transients identified in (e.g., Ferrarese & Merritt 2000; Gebhardt et al. 2000; previous orphan afterglow searches (Becker et al. 2004; Tremaine et al. 2002). Rau et al. 2006; Malacrino et al. 2007) are now at- tributed to flare-star activity (Kulkarni & Rau 2006). 3.9. Untriggered and Orphan GRB Afterglows The upper limits on event rates derived from these sur- veys are consistent with an expectation for detection of a By far the most luminous (up to MR = −37mag) tran- sients that PTF may detect are the afterglows of GRBs few orphan afterglows per year in PTF survey work, as- for which the ultrarelativistic collimated outflows are suming the foreground “fog” of flare star and CV activity pointed toward the Earth. GRB statistics from BATSE (Rau et al. 2007b) can be successfully penetrated. onboard CGRO suggest that a few such events happen every day in the Universe (Paciesas et al. 1999), corre- 3.10. Transiting Exoplanets Around Young Stars −2 −1 sponding to ∼ 0.02deg yr . Out of these, ∼ 50% The majority of the ∼300 currently known exoplan- remain brighter than R = 20mag for at least 1000s and 7 ets have been found around relatively old stars (1–7 Gyr; can in principle be discovered blindly with PTF. These Saffe et al. 2005). In contrast, little is known about the untriggered afterglows may appear as fast transients in distribution and frequency of planets orbiting stars of a single or pair of images of the 5DC; however, the ex- −1 1–100Myr age. These objects have broadened spectral pected rate is very small (∼ 0.5yr ). lines (> 200 − 500m s−1), which complicate, and make A more numerous population of transients is pre- more difficult, the discovery of planets via radial-velocity dicted by the collimated nature of GRBs, observation- variations. Here, the detection of planetary transits is a ally suggested by the “jet breaks” in afterglow light more promising method. curves (e.g., Harrison et al. 1999; Stanek et al. 1999; Observations of transiting planets allow one to deter- Frail et al. 2000; Frail et al. 2001). These orphan after- mine important physical characteristics and place sig- glows arise when the initial GRB, and its associated af- nificant constraints on the internal structure of planets terglow light, are directed away from the observer. Here, (Burrows et al. 2000). Specifically, the radius (obtain- the deceleration of the relativistic outflow, the associated able only for transiting planets) provides a direct es- decrease in special-relativistic beaming, and the hydro- timate of the age, composition, and surface tempera- dynamic spreading of the collimated jet combine at the ture (Saumon et al. 1996). Studies show the existence jet-break time, tjet, to irradiate a rapidly increasing frac- of “inflated” planets with unexpectedly large radii or low tion of the sky (e.g., Rhoads 1999). Observers illumi- densities (e.g., WASP-1b, HAT-P-1b; Bakos et al. 2006; nated during this transition will detect a steeply rising Cameron et al. 2007) that current models fail to explain (∆t ≈ tjet/10) transient that proceeds to behave as a (Pont et al. 2007). Next, assessing the distribution and post-jet break, on-axis afterglow. It will fade as a power- −α frequency of planets around young stars can also set de- law (Fν ∝ t ) with α ≈ 2.3, referenced to the (uncon- tailed constraints on the time scales of formation and strained) burst time, resulting in a decay by ∼ 1mag evolution of planetary systems (e.g., Baraffe et al. 2003). over a time scale of ∆t ≈ 1.5tjet. Note that the typical During 40 consecutive nights in each of the first observed jet-break times for GRBs are ∼1 to 10 d. three years after commissioning, PTF will provide high Predicted event rates for PTF are a func- photometric precision measurements (0.1–2%) for ∼ tion of the estimated GRB rate at low red- 50, 000 stars toward the Orion region. Approximately shift (Guetta et al. 2005a; Nakar et al. 2006), 5–10% of these stars will be young stars (1–10My; the observed optical afterglow luminosity dis- Carpenter et al. 2001). The large number of dedicated tribution (Kann et al. 2008), and the esti- consecutive nights results in a > 90% sensitivity to or- mated beaming (or jet break) distributions ∼ (Guetta et al. 2005a; Nakar et al. 2006). There are bital periods of Porb . 10 d (see Figure 5). If the substantial uncertainties in each of these functions; thus, fraction of the systems with favorable inclination is ∼ even upper limits from well-defined orphan afterglow 10% and the planetary distribution and frequency are similar to those of main-sequence stars (1 out of 150; 7 By this we mean, not by follow-up observations in response to Marcy et al. 2004), we anticipate 10–15 transiting plan- a trigger with high-energy observations. ets to be found with this experiment. However, even a PTF Science 9 null detection would set valuable limits on the presence of The higher-mass M-dwarfs that have been probed giant planets with short period orbits. The transit search have a low Jupiter-mass planet companion frequency is based upon a box-shaped matched filter algorithm and (<∼2%; eg. Johnson et al. 2007), but theory predicts a uses frequency filtering and variability-fitting to reduce large population of lower-mass planets (Ida & Lin 2005; the effects of the intrinsic variability of the stars (e.g., Kennedy & Kenyon 2008). The characteristics of the Airgrain et al. 2007). These techniques have been very lower-mass M-dwarf planet population are essentially un- successful in finding small transit signals in intrinsically known, mostly because the stars are too faint for cur- variable stars (e.g., CoRoT-7b; Leger et al. 2009). rent radial-velocity planet searches. As M-dwarfs are the The transit survey is most sensitive to Jupiter sized most common stars in our galaxy, there is a clear gap to (and mass) planets in few day orbits around stars of be addressed in our knowledge of the galactic planetary . 1 M⊙. Follow-up observations will include high spatial population. resolution imaging to search for background eclipsing bi- The PTF R-band DyC experiment offers an opportu- naries, and medium resolution spectroscopy and radial nity to search M-dwarfs for stellar eclipses and planetary velocity monitoring (∼ 500m s−1 precision) to rule out transits. The survey is expected to greatly increase the stellar or brown companions. Jupiter-sized planets in number of known eclipsing cool star systems (vital for short orbital periods produce radial velocity variations calibration of the mass-to-luminosity relation at the low on the order of a few hundred meters per second. Higher end), to obtain detailed statistics on the population of precision monitoring (50 − 200m s−1), coupled with the close substellar companions, to watch for variability and known orbital period determined from the photometric activity, and ultimately to be capable of detecting low- observations, should provide sufficient precision to con- mass transiting planets. firm the presence or absence of the candidate planets. By specifically targeting faint M-dwarfs, we greatly re- The Orion observations will also provide a unique duce the normally extreme precision requirements for dataset for a variety of aspects of stellar astrophysics. planet transit surveys. Going down to mR=20.0, the The high-precision time-series data will enable the search faintest stars in the survey will have approximately for, and characterization of, eclipsing binary systems SNR=10 per image, sufficient to detect planets as small suitable for testing star formation and evolution models, as Saturn (0.087 R⊙) around M5 dwarfs (∼0.2 R⊙) with characterizing the activity and rotation periods of young SNR=2 in each of many observations during transits. stars, and identifying and characterizing previously un- With few-percent photometric precision on bright M- known young stars in the Orion region. dwarfs, PTF could detect Neptune-radius planets. In each R-band high-cadence PTF field we will be able to search a few thousand M-dwarfs for transitory flux decreases, depending on galactic latitude. By covering a very large sample of stars, but at relatively low photo- metric precision and with observation gaps, this survey will be complementary to targeted cool star transit sur- veys such as the MEarth project (Irwin et al. 2009). Assuming a representative DyC observing setup, we expect to search approx. 105 M-dwarfs per year for com- panions in a variety of orbits. Scaling against other M- dwarf eclipsing binary surveys, the survey could find tens of new M-dwarf eclipsing binary systems per year. As- suming that 2% of M-dwarfs have giant planetary com- panions with periods <30 d, in a uniform period distri- bution, and modeling detection probability factors from the survey cadences, transit lengths, weather losses and the inclination ranges of the possible systems, PTF also has the possibility of detecting several bona-fide transit- ing planet systems per year. Follow up efforts will in- Fig. 5.— Prediction of the window function for the Orion pro- clude extensive photometric and spectroscopic observing gram. The dashed and solid lines correspond to the detection prob- abilities of one and two transits, respectively. The white (photon) programs to eliminate false detections, and ultimately in- noise is assumed to be 0.01 mag, and the red (systematic) noise is frared radial-velocity measurements (using, for example, assumed to be 10% of the total photometric noise. Other input pa- T-EDI on the Palomar Hale 5m Telescope; Muirhead et rameters are stellar/planetary radius = 1.0/0.1 R⊙, 40 consecutive al. (2008)) to confirm the presence of planets. nights, and a 1 min observing cadence. 3.12. RR Lyrae Stars RR Lyrae are short-period, yellow or white giant pul- 3.11. Eclipsing Objects Around Cool Stars sating variables. They are the most well-calibrated, Current radial-velocity surveys for extrasolar planets near-field distance indicators known. With a mean preferentially target bright FGKM stars with masses magnitude of MR ≈ 0.3 ± 0.2 mag for stars with within a factor of two of M⊙. Thus far only ∼10 −2.6 <[Fe/H]< −1.6 dex and a weak metallicity de- planetary systems have been detected around stars pendence, RR Lyrae have been used to measure dis- with masses < 0.5M⊙ and radial-velocity surveys of tances throughout the Local Group. They have also M-dwarfs have been limited to the brightest M0 to been used to probe the kinematics and the global den- M3 stars (e.g., Endl et al. 2006; Johnson et al. 2007). sity distribution of the Galactic halo (Vivas & Zinn 2003; 10 A. Rau et al.

Ivezi´cet al. 2004; Kinman et al. 2007). Having many ied with PTF. In particular, the combination of PTF thousands of RR Lyrae stars over a significant fraction variability information and SDSS photometric colors can of the sky will enable us to better constrain not only characterize stellar variability across the Hertzsprung- the stellar density as a function of radius, but also the Russel diagram. Characterizing the detailed stellar vari- three-dimensional shape of the Galactic halo. ability is also imperative in the search of genuine tran- Another strong motivation for extending the sample sients. of RR Lyrae variables is the mapping of substructures Understanding the processes that lead to luminosity within the halo. It is still not completely clear whether changes in stars is vital to decipher the stellar evolu- the Galaxy formed primarily in a single, homogeneous tion. This 5DC survey with its wide-area coverage will collapse (Eggen et al. 1962), or the majority of stars enable the discovery of rare sources such as R CrB stars were assimilated through the accretion of many smaller (Iben & et al. 1996), the non-radial magnetic pulsating galaxies and galactic fragments (Searle & Zinn 1978). Ap stars (Shibahashi 1987), and SX Phe stars. The na- The distribution of RR Lyrae candidates in the SDSS is ture of the later is uncertain as they can be the result of decidedly inhomogeneous, and a population of RR Lyrae stellar mergers or stars evolving towards the white dwarf stars associated with the Sagittarius tidal stream has stage (Cacciari & Clementini 1990). been found (Ivezi´cet al. 2004). Since then, several R CrB stars are also linked to stellar mergers, specifi- other large tidal streams believed to be the rem- cally the merger of hydrogen-deficient stars or of a Neu- nants of accreted galaxies have been detected out tron star with Helium rich star. The birthrate of R CrB to ∼ 50kpc (Yanny et al. 2003; Belokurov et al. 2006; stars is estimated to be 0.004–0.1yr−1 in the Milky Way Grillmair 2006a; Grillmair 2006b; Grillmair 2008, ; see (Iben & et al. 1996) and the predicted short life time Figure 6). A large-area survey for RR Lyrae stars will leads to estimates that approx. 1000 sources are cur- allow much more accurate distances and orbital trajec- rently existing in our galaxy. Using their space and ve- tories to be determined for these streams. Moreover, locity distribution, PTF may able to resolve the funda- with a clean sample of RR Lyrae stars selected through mental question to which population (e.g., thick disk) multi-epoch light curve analysis, this would enable us to they belong. extend our reach well beyond the ≈50 kpc achieved to We will construct light curves for all stars in the PTF date using turn-off stars in the SDSS, and detect addi- footprint in the range 141.34). Approximately half of those events will occur a boon to investigations of both the global structure of at |b| > 30◦. Extrapolating the (Han 2008) results to the Galactic halo and of the substructures within it. R = 21mag suggests 200–300 events yr−1 throughout the sky. 3.13. Other Galactic variables With a typical time scale of about 20 d, these events Beside the already mentioned RR Lyrae stars many can be detected in the 5DC with sufficient time to orga- more classes and subclasses of variables can be stud- nize follow-up observations with high temporal resolution PTF Science 11

Fig. 6.— A composite, filtered surface density map of stars in the SDSS Data Release 5. Stars in DR5 have been filtered to select stellar populations at different distances with color-magnitude sequences similar to that of the globular cluster M13 (e.g., Grillmair 2008). Lighter shades indicate areas of enhanced surface density, and different portions of the field have been filtered for stars at different distances. Varying noise levels are a consequence of the very different levels of foreground contamination using these different filters. The distances of the streams range from 4 kpc for Acheron, to 9 kpc for GD-1 and the Anticenter Stream, to ∼50 kpc for Sagittarius and Styx. for the later parts of the light curve, to search for plan- way, PTF will provide a valuable testing ground for NEO ets. Taking into account the PTF footprint, we expect searches with Pan-STARRS and LSST. The PTF NEO the 5DC to find about 5 stellar-stellar events per year. survey will be performed using the database of source ex- In addition, PTF will be sensitive to microlensing events tractions obtained by the main image-reduction pipeline. caused by other optically faint, massive objects. Non-stationary objects will be separated from the sta- tionary objects detected in the 5DC. 3.15. Solar System Objects Based on the estimated population of km-size near- Earth asteroids (Bottke et al. 2002), discovery statis- PTF will detect and measure orbits for many Solar tics (Moon et al. 2008), and the PTF observing strat- System bodies. In particular, asteroids will form the egy (which avoids the ecliptic plane), approximately 75 dominant variable foreground population. Depending on discoveries per year are within reach of the PTF; in prac- ecliptic latitude, the predicted number of known aster- tice, the highly experienced Catalina and LINEAR sur- oids brighter than R = 20.5mag ranges from ∼ 30deg−1 −1 veys are likely to report most of these discoveries first, (β = 0deg) to ∼ 0.01deg (β > 50 deg). so the main PTF contribution will be confirmation and Near-Earth Objects (NEOs) are a subgroup of aster- astrometry. oids and comets that have been nudged by the gravita- tional attraction of nearby planets into orbits that al- 3.16. low them to enter the Earth’s neighborhood. They are Transients Discovered Outside the Optical Band of astronomical interest as nearby samples of planetesi- Most of the time, PTF will operate in survey mode (see mals left over from the formation of the Solar System. § 2.2). However, the 7.9 deg2 field of view is also ideal to The Earth was built from such planetesimals, and the search for optical counterparts to transients discovered at outer layers of Earth, including the biosphere, have been other wavelengths (e.g., radio, γ-rays) or by other means strongly effected by asteroids and comets that impacted than electromagnetic radiation (e.g., gravitational waves, the early planet after it had solidified. neutrinos, ultra-high-energy cosmic-rays). The first di- NEO discovery and characterization is also critical to rect detection of gravitational waves is expected to come assessing the impact risk hazard, as objects of size 1km from the Laser Interferometer Gravitational-Wave Ob- could have catastrophic planet-wide consequences. Here, servatory (LIGO) in its enhanced (start ∼ 2009) and ad- PTF will contribute to NEO discovery and orbit deter- vanced (∼ 2013) stages. A variety of sources, including mination by delivering astrometric and photometric mea- nearby supernovae and merging compact objects, will be surements comparable (or even superior) to the those of found in this way. With typical positional uncertainties the best currently-operating surveys (Table 5). In this of a few degrees, only wide-field instruments like PTF 12 A. Rau et al.

TABLE 4 Properties and Rates for Selected Transients and Variables

a b Class MR τ Universal Rate (UR) PTF Rate Reference −1 [mag] [days] [yr ] MR/τ/UR Dwarf Novae 9..4 3..20 3 × 10−5 pc−3 yr−1 100 1/2/3 −10 −1 −1 Classical novae −5.. − 10 2..100 2 × 10 yr L⊙,K 60..150 4/5/6 −13 −1 −1 Luminous red novae −10.. − 14 20..60 1.5 × 10 yr L⊙,K 1.5 7/7/8 −13 −1 −1 Fallback SNe −4.. − 21 0.5..2 10 yr L⊙,K 1 9/9/9 Macronovae −13.. − 15 0.3..3 10−4..−8 Mpc−3 yr−1 0.1 10/10/11 SNe .Ia −15.. − 17 2..5 (4..10) × 10−6 Mpc−3 yr−1 0.25..2 12/12/12 SNe Ia −17.. − 19.5 30..70 c3 × 10−5 Mpc−3 yr−1 500 13/13/14 Tidal disruption flares −15.. − 19 30..350 10−6 Mpc−3 yr−1 3 15/15/15 Core-collapse SNe −14.. − 21 20..300 5 × 10−5 Mpc−3 yr−1 200 16/*/17 Luminous SNe −19.. − 23 50..400 10−7 Mpc−3 yr−1 > 10 18/18/* Orphan afterglows (SGRB) −14.. − 18 5..15 3 × 10−7..−9 Mpc−3 yr−1 < 1 */*/* Orphan afterglows (LGRB) −22.. − 26 2..15 3 × 10−7..−9 Mpc−3 yr−1 < 1 */*/* On-axis LGRB afterglows .. − 37 1..15 4 × 10−10 Mpc−3 yr−1 0.5 */19/20

aTime to decay by 2 mag from peak b References for MR, τ and universal rate: 1: (Rau et al. 2007b), 2: (Sterken & Jaschek 2005); 3: (Schwope et al. 2002); 4: (Shafter et al. 2009); 5: (della Valle & Livio 1995); 6: (Ferrarese et al. 2003); 7: (Kulkarni et al. 2007); 8: (Ofek et al. 2008); 9: Fryer, C.L., priv. com.; 10: (Kulkarni 2005); 11: (Nakar et al. 2006); 12: (Bildsten et al. 2007); 13: (Jha et al. 2006); 14: (Dilday et al. 2008); 15: (Strubbe & Quataert 2009); 16: (Richardson et al. 2002); 17: (Cappellaro et al. 1999); 18: (Scannapieco et al. 2005); 19: (Fox et al. 2003); 20: (Guetta et al. 2005b); *: see text cUniversal rate at z< 0.12

TABLE 5 ilarly, observations of the expected dim supernovae Comparison of PTF with other NEO surveys (Li & Paczy´nski 1998) or macronovae (Kulkarni 2005) associated with LIGO-detected merging compact objects Survey Da Scale FoV Exp. Mag. Limit Coverage will immediately lead to a trove of results. In particular, ′′ −1 2 2 [m] [ pxl ] [deg ] [s] [mag] [deg /hr] the ejected mass is sensitive to the equation of state of PTF 1.2 1.0 7.78 60 21.0 300 b dense matter and the type of binary (double neutron star LINEAR 1.0 2.3 2.0 5 19.2 1050 vs. neutron star/black hole). Spacewatchc 1.8 1.0 0.3 150 22.6 7.2 Spacewatch 0.9 1.0 2.9 120 21.7 70 The IceCube Neutrino Observatory (Klein et al. 2008) CSSd 1.5 1.0 1.2 60 21.5 600 will soon deliver automated alerts to follow-up observa- CSS 0.7 2.5 8.1 30 19.5 420 tions of detections of pairs of neutrinos. With typical ◦ CSS 0.5 1.8 4.2 60 19.0 92 positional uncertainties of these events of 1–2 , PTF can Pan-STARRS1e 1.8 0.3 3.0 30 24.0 360 help to find the optical counterparts. PTF will also advance our understanding of the new aTelescope diameter class of mysterious radio transients which has ma- bLincoln Laboratories Neart Earth Asteroid Research terialized in recent years (e.g., Levinson et al. 2002; chttp://spacewatch.lpl.arizona.edu/ d Gal-Yam et al. 2006b; Bower et al. 2007). These events Catalina Sky Survey; http://www.lpl.arizona.edu/css/ were discovered in archival data; thus, nothing is known about their transient appearance at other wavelengths. Furthermore, no quiescent X-ray, optical, near-infrared, will be able to search for optical counterparts, provide and radio counterparts have been found. The event arcsecond localizations, and allow estimates of distance. rate is overwhelming and estimated to be between 100 Theory suggests that a few percent of all stellar col- and 13,000deg−2 yr−1 with typical time scales of ∼0.1– lapses to neutron stars and black holes will result in 1 d. Within the framework of the dynamic cadence ex- strong gravitational waves (Dimmelmeier et al. 2007). periments, and in combination with new radio observa- Models include accretion-induced collapse leading to bar- tions, PTF will attempt to resolve the nature of these unstable neutron stars (Liu 2002), and stars that col- events and probe their possible association with the elu- lapse to black holes with very rapidly rotating cores sive Galactic population of isolated-old neutron stars (Janka et al. 2007). These events will likely be opti- (Ofek 2008). cally faint compared to standard supernovae, but still 3.17. detectable in the nearby Universe with PTF. Once iden- Science with Coadded Broad- and Narrow-Band tified, the light curves will provide insight into the Images explosion physics as well as into the fraction of ra- By the end of 2012, PTF will have observed each point- dioactive material advected into the black hole. Sim- ing in the 5DC footprint (i.e., ∼ 10, 000deg2) about 60 PTF Science 13 times. The combined R-band images will be deeper than optic surveys, such as LSST. the SDSS r-band images by about 1–2 mag. Although the typical image quality will be 2′′, these data will pro- vide an excellent deep fiducial sky for many astronomical This paper is based on observations obtained with the projects and can be mined for a variety of large-scale sci- Samuel Oschin Telescope and the 60-inch Telescope at ence applications. the Palomar Observatory as part of the Palomar Tran- As discussed in section 2.2, PTF will perform deep 3π sient Factory project, a scientific collaboration between sr surveys in several narrow-band filters, including Hα. the California Institute of Technology, Columbia Uni- The resulting sky map will provide an unprecedented versity, Las Cumbres Observatory, the Lawrence Berke- high-resolution view on the structure of the diffuse, ion- ley National Laboratory, the National Energy Research ized component of the interstellar medium in the Milky Scientific Computing Center, the University of Oxford, Way. This information will be vital for understanding the and the Weizmann Institute of Science. SRK and his dynamics and evolutionary history of the interstellar gas. group were partially supported by the NSF grant AST- Next, new structures, such as stellar wind bubbles, su- 0507734. J.S.B. and his group were partially supported pernova remnants, bow-shock nebulae, shells around old by a Hellman Family Grant, a Sloan Foundation Fel- novae (Shara et al. 2007), and planetary nebula shells lowship, NSF/DDDAS-TNRP grant CNS-0540352, and with large angular extent are anticipated to be found. a continuing grant from DOE/SciDAC. The Weizmann Furthermore, we will find low-surface-brightness star- Institute PTF partnership is supported by an ISF equip- forming galaxies in the local Universe, and based on the ment grant to AG. AG’s activity is further supported Hα emission strength we will be able to estimate the by a Marie Curie IRG grant from the EU, and by the star-formation rate (e.g., Kennicutt 1998) of the galaxies Minerva Foundation, Benoziyo Center for Astrophysics, within about 40 Mpc in our survey footprint (except for a research grant from Peter and Patricia Gruber Awards, galaxies in the zone of avoidance). and the William Z. and Eda Bess Novick New Scientists 4. Fund at the Weizmann Institute. EOO thanks partial CONCLUSION & OUTLOOK supports from NASA through grants HST-GO-11104.01- The Palomar Transient Factory is a wide-field A; NNX08AM04G; 07-GLAST1-0023; and HST-AR- (7.9 deg2) imaging facility at the Palomar 48-inch Oschin 11766.01-A. A.V.F. and his group are grateful for funding Schmidt telescope, dedicated to mining the optical sky from NSF grant AST–0607485, DOE/SciDAC grant DE- for transients and variables. Its main strengths are FC02-06ER41453, DOE grant DE-FG02-08ER41563, the the exceptionally large sky coverage to a depth of TABASGO Foundation, Gary and Cynthia Bengier, the R ≈ 21.0 mag and the almost full-time operation (80%). Sylvia and Jim Katzman Foundation, and the Richard Nearly real-time discovery of transient candidates will and Rhoda Goldman Fund. S.G.D. and A.A.M. were allow rapid follow-up observations with a wide range supported in part by NSF grants AST-0407448 and of committed telescopes, including optical and near- CNS-0540369, and also by the Ajax Foundation. The infrared photometry as well as spectroscopy. National Energy Research Scientific Computing Center, PTF is expected to uncover numerous new members which is supported by the Office of Science of the U.S. of a variety of source populations (see Table 4), rang- Department of Energy under Contract No. DE-AC02- ing from distant supernovae to nearby cataclysmic. Fur- 05CH11231, has provided resources for this project by thermore, the exploration of new regions in phase space supporting staff and providing computational resources (e.g., cadence, environment) often yields unexpected dis- and data storage. L.B.’s research is supported by the coveries. Thus, PTF is poised to provide an important NSF via grants PHY 05-51164 and AST 07-07633. MS contribution to filling the existing gaps in the transient acknowledges support from the Royal Society and the phase space (Figure 1), paving the path for future syn- University of Oxford Fell Fund.

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