Two$Years$of$Discoveries$from$the$ $All4Sky$Automated...
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Two Years of Discoveries from the AllSky Automated Survey for Supernovae Thomas W.S. Holoien (Ohio State) and the ASASSN Team TWSH is supported by the DOE ComputaFonal Science Graduate Fellowship, grant number DEFG0297ER25308. Contact: [email protected] Presented at the 2015 DOE CSGF Annual Program Review in Arlington, VA, July 2015 IntroducFon About ASASSN Even in the modern era, only human eyes scan the enFre opFcal sky for the violent, variable, and transient events that shape our universe. The AllSky Automated Survey for SuperNovae (ASASSN or "Assassin") is changing this by monitoring the visible sky to 17 th magnitude every 23 days using mulFple telescopes in the northern and southern hemispheres. Our automated pipeline schedules observaFons, processes data and scans images for new potenFal candidates without human interacFon, requiring sophisFcated algorithms to avoid false posiFve detecFons. Having been in operaFon for two years, ASASSN is now generaFng new transient discoveries daily, and has discovered over 450 new cataclysmic variable stars, over 190 new supernovae, and two Fdal disrupFon events, including the closest ever discovered at opFcal wavelengths. ASASSN is finding nearby transients that would not be found by any other professional or amateur survey and the nearby nature of ASASSN discoveries allows for detailed followup across a wide wavelength coverage. Here we present details on the ASASSN survey and its data processing pipeline as well as informaFon on discoveries made by ASASSN in its first two years of operaFon. Discovery StaFsFcs The primary science goal of ASASSN is a complete and unbiased census of bright, nearby supernovae, a task that has never been a^empted by any previous project. Our early results with supernovae have been extremely encouraging, but ASASSN has also discovered many other types of bright transients. In just over two years of operaFon, ASASSN has found: • 474 new cataclysmic variable (CV) stars, • 41 Mdwarf flares with ΔV≥4, • 15 blazar flares, • 2 Fdal disrupFon events (TDEs), and • 194 Supernovae (147 Type Ia, 37 Type II, 6 Type Ib/Ic, 1 SLSNI, 3 Untyped) Figures 2 and 3 below compare ASASSN supernova discoveries to those of other professional and amateur surveys since the ASASSN “Cassius” unit came online in May 2014. ASASSN is now discovering roughly half of all bright supernovae, and the ASASSN sample appears to be less biased in terms of host galaxy magnitude and distance from the host galaxy nucleus than other searches. ASASSN also finds most of the remaining bright supernovae, but is not the first to report them. Figure 3: Comparison of the number of bright (V<17 mag) SNe discovered by different searches during the first full year ASASSN was operaFonal in both hemispheres. The “All Amateurs” bar comprises all discoveries made by amateur astronomers. ASASSN discovered over half of all bright SNe during this Fme. Figure 4: The distribuFon of bright SNe as a funcFon of absolute host galaxy magnitude and the offset of the SN from the center of the host. The red do^ed horizontal line indicates the median offset for ASASSN SNe, while the blue dashed verFcal line indicates median host absolute magnitude for ASASSN SNe. Among searches for bright SNe, ASASSN appears to be the least biased, discovering SNe across the enFre parameter space (giant and dwarf galaxies, galaxy cores and outskirts). Notable Discoveries Below we highlight some of the most notable discoveries made by ASASSN in the last two years. ASASSN14ae and ASASSN14li (Holoien et al. 2014, Holoien et al. 2015) At redshios z=0.0436 and z=0.0206, these are the nearest TDE candidates ever discovered at opFcal wavelengths. Figure 5: Spectral Fme sequences of ASASSN14ae (leo) and ASASSN14li (right). The longlived blue conFnuum and broad emission lines are characterisFc of Fdal disrupFon events. ASASSN14lp (Shappee et al. 2015) This Type Ia supernova in NGC 4666 (d=15 Mpc) was the second brightest supernova of 2014. Figure 6: EarlyFme mulFwavelength light curves of ASASSN14lp with powerlaw fits. The supernova was discovered roughly two days aoer first light, indicated by the verFcal orange bar. References & Websites Works cited: • Dong et al. 2015, arXiv: 1507.03010 • Holoien et al. 2014, MNRAS, 445, 3263 • Holoien et al. 2015, arXiv: 1507.01598 • Shappee et al. 2015, arXiv: 1507.04257 For more informaFon, please see our websites: ASASSN Homepage ASASSN Supernovae TWSH Homepage ASASSN Data Pipeline With roughly 60 GB of raw data taken per night and thousands of possible transient sources in every image, the ASASSN pipeline requires automaFon and sophisFcated source detecFon algorithms to run with as li^le human interacFon as possible. The basics of the ASASSN data processing pipeline are summarized in the Figure below: • ObservaFons are scheduled to maximize the discovery rate of transients using the properFes of recent observaFons and expected sky noise from the Sun and the Moon in a new image • Data are downloaded from LCOGT as they are taken throughout the night. • Photometry of automated targets (such as known CVs) is released through ASASSN “patrol” websites • Transients confirmed by human scanners are announced on the ASASSN Transients site and through Astronomer’s Telegrams (ATels) • Flagged transient sources are scanned by human eyes and followup confirmaFon images are requested for likely candidate sources • Strong candidates are announced immediately • The automated pipeline reduces new images, performs image subtracFon, and eliminates poorquality data in realFme • Transient sources in images passing the quality cut are automaFcally detected and flagged for human scanning • Fields with bad images are scheduled for observaFon ASASSN15lh (Dong et al. 2015) With a peak absolute uband magnitude of M=23.5, this is the most luminous supernova ever discovered. Figure 7: Absolute restframe uband light curve of ASASSN15lh compared to other superluminous supernovae. ASASSN15lh is a full magnitude more luminous than any other SLSN. Figure 1: Sky map showing recent fields observed by ASASSN as of July 21, 2015. Colors indicate the Fme since the field was last observed. The enFre visible sky is covered every 23 days. ASASSN currently consists of two units, one in each hemisphere, hosted by the Las Cumbres Observatory Global Telescope Network (LCOGT). Our northern hemisphere unit, “Brutus,” is deployed at the LCOGT Haleakala staFon, and our Southern hemisphere unit, “Cassius,” is deployed at the LCOGT Cerro Tololo staFon. Both units are composed of four 14cm telescopes on a common mount, with each camera having a roughly 20 square degree field of view. Together, these telescopes allow us to survey approximately 20,000 square degrees each night down to roughly 17 th magnitude in Vband, giving us full sky coverage every 23 nights, weather permitng. UlFmately, we hope to add an addiFonal unit in each hemisphere, allowing nightly fullsky observaFon. A map of our recent sky coverage is shown below.
Transcript of Two$Years$of$Discoveries$from$the$ $All4Sky$Automated...
Two Years of Discoveries from the All-‐Sky Automated Survey for Supernovae
Thomas W.-‐S. Holoien (Ohio State) and the ASAS-‐SN Team
TW-‐SH is supported by the DOE ComputaFonal Science Graduate Fellowship, grant number DE-‐FG02-‐97ER25308. Contact: [email protected]‐state.edu
Presented at the 2015 DOE CSGF Annual Program Review in Arlington, VA, July 2015
IntroducFon
About ASAS-‐SN
Even in the modern era, only human eyes scan the enFre opFcal sky for the violent, variable, and transient events that shape our universe. The All-‐Sky Automated Survey for SuperNovae (ASAS-‐SN or "Assassin") is changing this by monitoring the visible sky to 17th magnitude every 2-‐3 days using mulFple telescopes in the northern and southern hemispheres. Our automated pipeline schedules observaFons, processes data and scans images for new potenFal candidates without human interacFon, requiring sophisFcated algorithms to avoid false posiFve detecFons. Having been in operaFon for two years, ASAS-‐SN is now generaFng new transient discoveries daily, and has discovered over 450 new cataclysmic variable stars, over 190 new supernovae, and two Fdal disrupFon events, including the closest ever discovered at opFcal wavelengths. ASAS-‐SN is finding nearby transients that would not be found by any other professional or amateur survey and the nearby nature of ASAS-‐SN discoveries allows for detailed follow-‐up across a wide wavelength coverage. Here we present details on the ASAS-‐SN survey and its data processing pipeline as well as informaFon on discoveries made by ASAS-‐SN in its first two years of operaFon.
Discovery StaFsFcs The primary science goal of ASAS-‐SN is a complete and unbiased census of bright, nearby supernovae, a task that has never
been a^empted by any previous project. Our early results with supernovae have been extremely encouraging, but ASAS-‐SN has also discovered many other types of bright transients. In just over two years of operaFon, ASAS-‐SN has found:
• 474 new cataclysmic variable (CV) stars, • 41 M-‐dwarf flares with ΔV≥4, • 15 blazar flares, • 2 Fdal disrupFon events (TDEs), and • 194 Supernovae (147 Type Ia, 37 Type II, 6 Type Ib/Ic, 1 SLSN-‐I, 3 Untyped)
Figures 2 and 3 below compare ASAS-‐SN supernova discoveries to those of other professional and amateur surveys since the ASAS-‐SN “Cassius” unit came online in May 2014. ASAS-‐SN is now discovering roughly half of all bright supernovae, and the ASAS-‐SN sample appears to be less biased in terms of host galaxy magnitude and distance from the host galaxy nucleus than other searches. ASAS-‐SN also finds most of the remaining bright supernovae, but is not the first to report them.
Figure 3: Comparison of the number of bright (V<17 mag) SNe discovered by different searches during the first full year ASAS-‐SN was operaFonal in both hemispheres. The “All Amateurs” bar comprises all discoveries made by amateur astronomers. ASAS-‐SN discovered over half of all bright SNe during this Fme.
Figure 4: The distribuFon of bright SNe as a funcFon of absolute host galaxy magnitude and the offset of the SN from the center of the host. The red do^ed horizontal line indicates the median offset for ASAS-‐SN SNe, while the blue dashed verFcal line indicates median host absolute magnitude for ASAS-‐SN SNe. Among searches for bright SNe, ASAS-‐SN appears to be the least biased, discovering SNe across the enFre parameter space (giant and dwarf galaxies, galaxy cores and outskirts).
Notable Discoveries Below we highlight some of the most notable discoveries made by ASAS-‐SN in the last two years.
ASASSN-‐14ae and ASASSN-‐14li (Holoien et al. 2014, Holoien et al. 2015) At redshios z=0.0436 and z=0.0206, these are the nearest TDE candidates ever discovered at opFcal wavelengths.
Figure 5: Spectral Fme sequences of ASASSN-‐14ae (leo) and ASASSN-‐14li (right). The long-‐lived blue conFnuum and broad emission lines are characterisFc of Fdal disrupFon events.
ASASSN-‐14lp (Shappee et al. 2015) This Type Ia supernova in NGC 4666 (d=15 Mpc) was the second brightest supernova of 2014.
Figure 6: Early-‐Fme mulFwavelength light curves of ASASSN-‐14lp with power-‐law fits. The supernova was discovered roughly two days aoer first light, indicated by the verFcal orange bar.
References & Websites Works cited: • Dong et al. 2015, arXiv: 1507.03010 • Holoien et al. 2014, MNRAS, 445, 3263 • Holoien et al. 2015, arXiv: 1507.01598 • Shappee et al. 2015, arXiv: 1507.04257
For more informaFon, please see our websites:
ASAS-‐SN Homepage ASAS-‐SN Supernovae TW-‐SH Homepage
ASAS-‐SN Data Pipeline With roughly 60 GB of raw data taken per night and thousands of possible transient sources in every image, the ASAS-‐SN pipeline requires automaFon and sophisFcated source detecFon algorithms to run with as li^le human interacFon as possible. The basics of the ASAS-‐SN data processing pipeline are summarized in the Figure below:
• ObservaFons are scheduled to maximize the discovery rate of transients using the properFes of recent observaFons and expected sky noise from the Sun and the Moon in a new image
• Data are downloaded from LCOGT as they are taken throughout the night.
• Photometry of automated targets (such as known CVs) is released through ASAS-‐SN “patrol” websites
• Transients confirmed by human scanners are announced on the ASAS-‐SN Transients site and through Astronomer’s Telegrams (ATels)
• Flagged transient sources are scanned by human eyes and follow-‐up confirmaFon images are requested for likely candidate sources
• Strong candidates are announced immediately
• The automated pipeline reduces new images, performs image subtracFon, and eliminates poor-‐quality data in real-‐Fme
• Transient sources in images passing the quality cut are automaFcally detected and flagged for human scanning
• Fields with bad images are scheduled for observaFon
ASASSN-‐15lh (Dong et al. 2015) With a peak absolute u-‐band magnitude of M=-‐23.5, this is the most luminous supernova ever discovered.
Figure 7: Absolute rest-‐frame u-‐band light curve of ASASSN-‐15lh compared to other superluminous supernovae. ASASSN-‐15lh is a full magnitude more luminous than any other SLSN.
Figure 1: Sky map showing recent fields observed by ASAS-‐SN as of July 21, 2015. Colors indicate the Fme since the field was last observed. The enFre visible sky is covered every 2-‐3 days.
ASAS-‐SN currently consists of two units, one in each hemisphere, hosted by the Las Cumbres Observatory Global Telescope Network (LCOGT). Our northern hemisphere unit, “Brutus,” is deployed at the LCOGT Haleakala staFon, and our Southern hemisphere unit, “Cassius,” is deployed at the LCOGT Cerro Tololo staFon. Both units are composed of four 14-‐cm telescopes on a common mount, with each camera having a roughly 20 square degree field of view. Together, these telescopes allow us to survey approximately 20,000 square degrees each night down to roughly 17th magnitude in V-‐band, giving us full sky coverage every 2-‐3 nights, weather permitng. UlFmately, we hope to add an addiFonal unit in each hemisphere, allowing nightly full-‐sky observaFon. A map of our recent sky coverage is shown below.
