Showing papers by "Nathan Smith published in 2016"
TL;DR: In this article, the sky localization of the first observed compact binary merger is presented, where the authors describe the low-latency analysis of the LIGO data and present a sky localization map.
Abstract: A gravitational-wave (GW) transient was identified in data recorded by the Advanced Laser Interferometer Gravitational-wave Observatory (LIGO) detectors on 2015 September 14. The event, initially designated G184098 and later given the name GW150914, is described in detail elsewhere. By prior arrangement, preliminary estimates of the time, significance, and sky location of the event were shared with 63 teams of observers covering radio, optical, near-infrared, X-ray, and gamma-ray wavelengths with ground- and space-based facilities. In this Letter we describe the low-latency analysis of the GW data and present the sky localization of the first observed compact binary merger. We summarize the follow-up observations reported by 25 teams via private Gamma-ray Coordinates Network circulars, giving an overview of the participating facilities, the GW sky localization coverage, the timeline, and depth of the observations. As this event turned out to be a binary black hole merger, there is little expectation of a detectable electromagnetic (EM) signature. Nevertheless, this first broadband campaign to search for a counterpart of an Advanced LIGO source represents a milestone and highlights the broad capabilities of the transient astronomy community and the observing strategies that have been developed to pursue neutron star binary merger events. Detailed investigations of the EM data and results of the EM follow-up campaign are being disseminated in papers by the individual teams.
288 citations
TL;DR: In this article, the authors used the higher level data products provided by the LEGUS team for spectral data reduction at the MMT observatory in the US-US Virgin Islands.
Abstract: Some of the data reported here were obtained at the MMT Observatory, a joint facility of the University of Arizona and the Smithsonian Institution. We thank the staffs at Lick and MMT Observatories for their assistance with the observations. We also appreciate the help of Jeff Silverman for some of the Lick observations. Data from Steward Observatory facilities were obtained as part of the observing programme AZTEC: Arizona Transient Exploration and Characterization. Lindsey Kabot assisted with early stages of the MMT spectral data reduction. The work presented here is based in part on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. These are based in part on observations associated with programme #13364 (Legacy ExtraGalactic UV Survey, LEGUS). This paper has made use of the higher level data products provided by the LEGUS team.; NS and JEA received partial support from National Science Foundation (NSF) grants AST-1210599 and AST-1312221. MMK acknowledges support from the Carnegie-Princeton fellowship. Funding for this effort was provided in part by the Spitzer SPIRITS Cycles 10-12 exploration science programme. The supernova research of AVF's group at U.C. Berkeley presented here is supported by Gary & Cynthia Bengier, the Christopher R. Redlich Fund, the TABASGO Foundation, and NSF grant AST-1211916. KAIT and its ongoing operation were made possible by donations from Sun Microsystems, Inc., the Hewlett-Packard Company, AutoScope Corporation, Lick Observatory, the NSF, the University of California, the Sylvia & Jim Katzman Foundation, and the TABASGO Foundation. Research at Lick Observatory is partially supported by a generous gift from Google. JJ is supported by an NSF Graduate Research Fellowship under Grant No. DGE-1144469.
105 citations
TL;DR: In some cases, these complications make it difficult to definitively tell the difference between a core-collapse or thermonuclear explosion, or to distinguish between a nonterminal eruption, failed SN, or weak SN as mentioned in this paper.
Abstract: Supernovae (SNe) that show evidence of strong shock interaction between their ejecta and pre-existing, slower circumstellar material (CSM) constitute an interesting, diverse, and still poorly understood category of explosive transients. The chief reason that they are extremely interesting is because they tell us that in a subset of stellar deaths, the progenitor star may become wildly unstable in the years, decades, or centuries before explosion. This is something that has not been included in standard stellar evolution models, but may significantly change the end product and yield of that evolution, and complicates our attempts to map SNe to their progenitors. Another reason they are interesting is because CSM interaction is an efficient engine for making bright transients, allowing super-luminous transients to arise from normal SN explosion energies, and allowing transients of normal SN luminosities to arise from sub-energetic explosions or low radioactivity yield. CSM interaction shrouds the fast ejecta in bright shock emission, obscuring our normal view of the underlying explosion, and the radiation hydrodynamics of the interaction is challenging to model. The CSM interaction may also be highly non-spherical, perhaps linked to binary interaction in the progenitor system. In some cases, these complications make it difficult to definitively tell the difference between a core-collapse or thermonuclear explosion, or to discern between a non-terminal eruption, failed SN, or weak SN. Efforts to uncover the physical parameters of individual events and connections to possible progenitor stars make this a rapidly evolving topic that continues to challenge paradigms of stellar evolution.
91 citations
University of Arizona1, Northwestern University2, New York University3, Ohio University4, Harvard University5, Carnegie Institution for Science6, University of Warwick7, University of Leicester8, National Radio Astronomy Observatory9, University of California, Berkeley10, Pennsylvania State University11, California Institute of Technology12, University of Copenhagen13, George Washington University14
TL;DR: In this paper, the authors used the NASA Swift grant and the NASA ADA grant to conduct experiments on the HST-HF-51348.001 and the Hubble Space Telescope.
Abstract: NASA through Einstein Postdoctoral Fellowship [PF4-150121]; James Arthur Fellowship at NYU; NASA Swift grant [NNX16AB04G]; NSF [AST-1411763]; NASA ADA [NNX15AE50G]; NASA through Hubble Fellowship - Space Telescope Science Institute [HST-HF-51348.001]; NASA [NAS 5-26555]; [14A-344]; [13830]
84 citations
06 Dec 2016
TL;DR: In some cases, these complications make it difficult to definitively tell the difference between a core-collapse or thermonuclear explosion, or to distinguish between a nonterminal eruption, failed SN, or weak SN.
Abstract: Supernovae (SNe) that show evidence of strong shock interaction between their ejecta and pre-existing, slower circumstellar material (CSM) constitute an interesting, diverse, and still poorly understood category of explosive transients. The chief reason that they are extremely interesting is because they tell us that in a subset of stellar deaths, the progenitor star may become wildly unstable in the years, decades, or centuries before explosion. This is something that has not been included in standard stellar evolution models, but may significantly change the end product and yield of that evolution, and complicates our attempts to map SNe to their progenitors. Another reason they are interesting is because CSM interaction is an efficient engine for making bright transients, allowing super-luminous transients to arise from normal SN explosion energies, and allowing transients of normal SN luminosities to arise from sub-energetic explosions or low radioactivity yield. CSM interaction shrouds the fast ejecta in bright shock emission, obscuring our normal view of the underlying explosion, and the radiation hydrodynamics of the interaction is challenging to model. The CSM interaction may also be highly non-spherical, perhaps linked to binary interaction in the progenitor system. In some cases, these complications make it difficult to definitively tell the difference between a core-collapse or thermonuclear explosion, or to discern between a non-terminal eruption, failed SN, or weak SN. Efforts to uncover the physical parameters of individual events and connections to possible progenitor stars make this a rapidly evolving topic that continues to challenge paradigms of stellar evolution.
83 citations
Harvard University1, Fermilab2, University of Pennsylvania3, Syracuse University4, Goddard Space Flight Center5, University of Maryland, College Park6, University of Chicago7, Ohio University8, University of California, Santa Cruz9, University of Illinois at Urbana–Champaign10, University of Arizona11, Pennsylvania State University12, Autonomous University of Madrid13, Stanford University14, Lawrence Berkeley National Laboratory15, University of California, Berkeley16, New York University17, Columbia University18, Space Telescope Science Institute19, Sao Paulo State University20, University College London21, Rhodes University22, Princeton University23, University of Wisconsin-Madison24, Institut d'Astrophysique de Paris25, University of Southampton26, University of Portsmouth27, Ludwig Maximilian University of Munich28, University of Michigan29, University of Cambridge30, Ohio State University31, Australian Astronomical Observatory32, University of São Paulo33, Texas A&M University34, Max Planck Society35, California Institute of Technology36, University of Sussex37
TL;DR: In this article, the authors report the results of a Dark Energy Camera optical follow-up of the GW151226, discovered by the Advanced Laser Interferometer Gravitational-wave Observatory detectors, starting 10 hr after the event was announced and spanning four epochs at 2--24 days after the GW detection.
Abstract: We report the results of a Dark Energy Camera optical follow-up of the gravitational-wave (GW) event GW151226, discovered by the Advanced Laser Interferometer Gravitational-wave Observatory detectors. Our observations cover 28.8 deg2 of the localization region in the i and z bands (containing 3% of the BAYESTAR localization probability), starting 10 hr after the event was announced and spanning four epochs at 2--24 days after the GW detection. We achieve 5sigma point-source limiting magnitudes of i≈ 21.7 and z≈ 21.5, with a scatter of 0.4 mag, in our difference images. Given the two-day delay, we search this area for a rapidly declining optical counterpart with ≳ 3sigma significance steady decline between the first and final observations. We recover four sources that pass our selection criteria, of which three are cataloged active galactic nuclei. The fourth source is offset by 5.8 arcsec from the center of a galaxy at a distance of 187 Mpc, exhibits a rapid decline by 0.5 mag over 4 days, and has a red color of i-z≈ 0.3 mag. These properties could satisfy a set of cuts designed to identify kilonovae. However, this source was detected several times, starting 94 days prior to GW151226, in the Pan-STARRS Survey for Transients (dubbed as PS15cdi) and is therefore unrelated to the GW event. Given its long-term behavior, PS15cdi is likely a Type IIP supernova that transitioned out of its plateau phase during our observations, mimicking a kilonova-like behavior. We comment on the implications of this detection for contamination in future optical follow-up observations.
79 citations
Fermilab1, Harvard University2, University of Pennsylvania3, University of Illinois at Urbana–Champaign4, Space Telescope Science Institute5, Sao Paulo State University6, University College London7, Rhodes University8, Princeton University9, University of Cambridge10, University of Paris11, Carnegie Institution for Science12, Syracuse University13, Stanford University14, University of Portsmouth15, University of Maryland, College Park16, Goddard Space Flight Center17, Ohio University18, University of Southampton19, Ludwig Maximilian University of Munich20, California Institute of Technology21, University of Michigan22, Cardiff University23, University of Arizona24, Pennsylvania State University25, Los Alamos National Laboratory26, Lawrence Berkeley National Laboratory27, University of California, Berkeley28, Ohio State University29, Australian Astronomical Observatory30, Texas A&M University31, University of São Paulo32, New York University33, Columbia University34, Max Planck Society35, University of Sussex36, Brookhaven National Laboratory37, Argonne National Laboratory38
TL;DR: In this paper, the results of a deep search for an optical counterpart to the GW150914, the first trigger from the Advanced LIGO GW detectors, were reported.
Abstract: We report the results of a deep search for an optical counterpart to the gravitational wave (GW) event GW150914, the first trigger from the Advanced LIGO GW detectors. We used the Dark Energy Camera (DECam) to image a 102 deg2 area, corresponding to 38% of the initial trigger high-probability sky region and to 11% of the revised high-probability region. We observed in the i and z bands at 4–5, 7, and 24 days after the trigger. The median 5σ point-source limiting magnitudes of our search images are i = 22.5 and z = 21.8 mag. We processed the images through a difference-imaging pipeline using templates from pre-existing Dark Energy Survey data and publicly available DECam data. Due to missing template observations and other losses, our effective search area subtends 40 deg2, corresponding to a 12% total probability in the initial map and 3% in the final map. In this area, we search for objects that decline significantly between days 4–5 and day 7, and are undetectable by day 24, finding none to typical magnitude limits of i = 21.5, 21.1, 20.1 for object colors (i − z) = 1, 0, −1, respectively. Our search demonstrates the feasibility of a dedicated search program with DECam and bodes well for future research in this emerging field.
75 citations
University of Tokyo1, National Scientific and Technical Research Council2, California Institute of Technology3, Millennium Institute4, University of Chile5, Kyoto University6, San Diego State University7, University of California, Berkeley8, University of Arizona9, University of Illinois at Urbana–Champaign10
TL;DR: In this paper, the authors proposed a bilateral joint research project between Japan and Chile, which is based on the Japan Society for the Promotion of Science (JSPS) KAKENHI (26800100, 23224004, 26400222).
Abstract: STScI [GO-13684, GO-13822, AR-14295]; NASA [NAS5-26555, HST-HF-51325.01, NAS 5-26555]; NSF [AST-1211916, AST-1518052]; TABASGO Foundation (KAIT and research support); Sylvia & Jim Katzman Foundation; Clark and Sharon Winslow; Christopher R. Redlich Fund; WPI Initiative MEXT (Japan); Japan Society for the Promotion of Science (JSPS) KAKENHI [26800100, 23224004, 26400222]; JSPS Open Partnership Bilateral Joint Research Project between Japan and Chile; Millennium Institute of Astrophysics [IC120009]; FONDECYT [3140563]; PRIN-INAF; Alfred P. Sloan Foundation
73 citations
TL;DR: Abbott et al. as mentioned in this paper compared the four probability sky maps produced for the gravitational-wave transient GW150914, and provided additional details of the EM follow-up observations that were performed in the different bands.
Abstract: This Supplement provides supporting material for Abbott et al. (2016a). We briefly summarize past electromagnetic (EM) follow-up efforts as well as the organization and policy of the current EM follow-up program. We compare the four probability sky maps produced for the gravitational-wave transient GW150914, and provide additional details of the EM follow-up observations that were performed in the different bands.
73 citations
TL;DR: In this paper, the X-ray and optical afterglows of the short-duration GRB 15010101B were detected and the event was pinpointed to an early-type host galaxy at z = 0.1343 +/- 0.0030.
Abstract: We present the discovery of the X-ray and optical afterglows of the short-duration GRB 150101B, pinpointing the event to an early-type host galaxy at z=0.1343 +/- 0.0030. This makes GRB 150101B the most nearby short GRB with an early-type host galaxy discovered to date. Fitting the spectral energy distribution of the host galaxy results in an inferred stellar mass of ~7x10^10 M_sol, stellar population age of ~2-2.5 Gyr, and star formation rate of 9 deg. Using observations extending to ~30 days, we place upper limits of <(2-4)x10^41 erg s^-1 on associated kilonova emission. We compare searches following previous short GRBs to existing kilonova models, and demonstrate the difficulty of performing effective kilonova searches from cosmological short GRBs using current ground-based facilities. We show that at the Advanced LIGO/VIRGO horizon distance of 200 Mpc, searches reaching depths of ~23-24 AB mag are necessary to probe a meaningful range of kilonova models.
72 citations
TL;DR: For example, NASA's Spitzer mission grants [10136, 11063] and the Royal Thai Scholarship (RTS) as mentioned in this paper [10] were used for the Thai Spitzer project.
Abstract: NASA Spitzer mission grants [10136, 11063]; Royal Thai Scholarship; NASA; United States Air Force
Stockholm University1, Harvard University2, University of Virginia3, Queen's University Belfast4, Cardiff University5, University of California, Berkeley6, University of Arizona7, University of Notre Dame8, University of Bern9, Hofstra University10, University of Turku11, University of Cambridge12, Goddard Space Flight Center13, University of Texas at Austin14
TL;DR: In this paper, the Swedish National Space Board and NASA through grants from the Space Telescope Science Institute (STSISI) and the European Organization for Astronomical Research in the Southern Hemisphere, Chile (ESO Program) were used to support the work.
Abstract: Swedish National Space Board; NASA through grants from the Space Telescope Science Institute [13401, 13405]; NASA [NAS5-26555]; European Organization for Astronomical Research in the Southern Hemisphere, Chile (ESO Program) [094.D-0505(C)]; Swedish Research Council
Fermilab1, Harvard University2, University of Pennsylvania3, University of Illinois at Urbana–Champaign4, Space Telescope Science Institute5, Sao Paulo State University6, University College London7, Rhodes University8, Princeton University9, University of Cambridge10, University of Paris11, Carnegie Institution for Science12, Syracuse University13, Stanford University14, University of Portsmouth15, University of Maryland, College Park16, Goddard Space Flight Center17, Ohio University18, University of Southampton19, Ludwig Maximilian University of Munich20, California Institute of Technology21, University of Michigan22, Cardiff University23, University of Arizona24, Pennsylvania State University25, Los Alamos National Laboratory26, University of California, Berkeley27, Lawrence Berkeley National Laboratory28, Ohio State University29, Australian Astronomical Observatory30, Texas A&M University31, University of São Paulo32, New York University33, Columbia University34, Max Planck Society35, University of Sussex36, Brookhaven National Laboratory37, Argonne National Laboratory38
TL;DR: In this article, a deep search for an optical counterpart to the GW150914, the first trigger from the Advanced LIGO gravitational wave detectors, was conducted using the DECam.
Abstract: We report initial results of a deep search for an optical counterpart to the gravitational wave event GW150914, the first trigger from the Advanced LIGO gravitational wave detectors. We used the Dark Energy Camera (DECam) to image a 102 deg$^2$ area, corresponding to 38% of the initial trigger high-probability sky region and to 11% of the revised high-probability region. We observed in i and z bands at 4-5, 7, and 24 days after the trigger. The median $5\sigma$ point-source limiting magnitudes of our search images are i=22.5 and z=21.8 mag. We processed the images through a difference-imaging pipeline using templates from pre-existing Dark Energy Survey data and publicly available DECam data. Due to missing template observations and other losses, our effective search area subtends 40 deg$^{2}$, corresponding to 12% total probability in the initial map and 3% of the final map. In this area, we search for objects that decline significantly between days 4-5 and day 7, and are undetectable by day 24, finding none to typical magnitude limits of i= 21.5,21.1,20.1 for object colors (i-z)=1,0,-1, respectively. Our search demonstrates the feasibility of a dedicated search program with DECam and bodes well for future research in this emerging field.
TL;DR: The authors analyzed eight epochs of the Hubble Space Telescope H$\alpha$+[N II] imaging of Eta Carinae's outer ejecta and found that the detected ejecta are divided into three apparent age groups, dating to around 1250 A.D., to around 1550 A., and to during or shortly before the Great Eruption of the 1840s.
Abstract: We analyze eight epochs of Hubble Space Telescope H$\alpha$+[N II] imaging of Eta Carinae's outer ejecta. Proper motions of nearly 800 knots reveal that the detected ejecta are divided into three apparent age groups, dating to around 1250 A.D., to around 1550 A.D., and to during or shortly before the Great Eruption of the 1840s. Ejecta from these groups reside in different locations and provide a firm constraint that Eta Car experienced multiple major eruptions prior to the 19th century. The 1250 and 1550 events did not share the same axisymmetry as the Homunculus; the 1250 event was particularly asymmetric, even one-sided. In addition, the ejecta in the S ridge, which have been associated with the Great Eruption, appear to predate the ejection of the Homunculus by several decades. We detect essentially ballistic expansion across multiple epochs. We find no evidence for large-scale deceleration of the observed knots that could power the soft X-ray shell by plowing into surrounding material, suggesting that the observed X-rays arise instead from fast, rarefied ejecta from the 1840s overtaking the older dense knots. Early deceleration and subsequent coasting cannot explain the origin of the older outer ejecta---significant episodic mass loss prior to the 19th century is required. The timescale and geometry of the past eruptions provide important constraints for any theoretical physical mechanisms driving Eta Car's behavior. Non-repeating mechanisms such as the merger of a close binary in a triple system would require additional complexities to explain the observations.
TL;DR: In this article, the authors used the ERC under the European Union's 7th Framework Programme (7th Framework Program (FP7th) to support the work of the authors of this paper.
Abstract: MMT; WHT [SW2014a39]; STFC via an Ernest Rutherford Fellowship; NASA grant; NSF pre-doctoral fellowship; ERC under the European Union's 7th Framework Programme [320964]
TL;DR: In this article, the authors used the HST from the Space Telescope Science Institute (STS-13787) as a data collection platform for the first HST mission to the International Journal of Astronautics (IJOA).
Abstract: National Aeronautics and Space Administration (NASA) through HST from the Space Telescope Science Institute [GO-13787]; NASA [NAS5-26555]; National Science Foundation (NSF) [AST-1210599, AST-1312221]; National Science Foundation
TL;DR: In this paper, the authors proposed a method to detect the presence of a cancer in the human brain using a neural network in the early stages of the development of artificial neural networks.
Abstract: NASA [PIDS 1083, 40204, 61002, 80015A, 80196, 80015, 10136, 10139, 11063, 11053]; National Science Foundation Graduate Research Fellowship [DGE-1144469]; United States Air Force; STScI Director's Discretionary Research Fund
Stockholm University1, Harvard University2, University of Virginia3, Queen's University Belfast4, Cardiff University5, University of California, Berkeley6, University of Arizona7, University of Notre Dame8, University of Bern9, Hofstra University10, University of Cambridge11, University of Turku12, Goddard Space Flight Center13, University of Texas at Austin14
TL;DR: In this paper, the authors presented spectral and imaging observations of SN 1987A obtained ~10,000 days after the explosion with HST/STIS and VLT/SINFONI at optical and near-infrared wavelengths.
Abstract: Due to its proximity, SN 1987A offers a unique opportunity to directly observe the geometry of a stellar explosion as it unfolds. Here we present spectral and imaging observations of SN 1987A obtained ~10,000 days after the explosion with HST/STIS and VLT/SINFONI at optical and near-infrared wavelengths. These observations allow us to produce the most detailed 3D map of H-alpha to date, the first 3D maps for [Ca II] \lambda \lambda 7292, 7324, [O I] \lambda \lambda 6300, 6364 and Mg II \lambda \lambda 9218, 9244, as well as new maps for [Si I]+[Fe II] 1.644 \mu m and He I 2.058 \mu m. A comparison with previous observations shows that the [Si I]+[Fe II] flux and morphology have not changed significantly during the past ten years, providing evidence that it is powered by 44Ti. The time-evolution of H-alpha shows that it is predominantly powered by X-rays from the ring, in agreement with previous findings. All lines that have sufficient signal show a similar large-scale 3D structure, with a north-south asymmetry that resembles a broken dipole. This structure correlates with early observations of asymmetries, showing that there is a global asymmetry that extends from the inner core to the outer envelope. On smaller scales, the two brightest lines, H-alpha and [Si I]+[Fe II] 1.644 \mu m, show substructures at the level of ~ 200 - 1000 km/s and clear differences in their 3D geometries. We discuss these results in the context of explosion models and the properties of dust in the ejecta.
TL;DR: In this article, the authors presented multi-epoch mid-infrared photometry and the optical discovery observations of the "impostor" supernova (SN) 2010da in NGC 300 using new and archival Spitzer Space Telescope images and ground-based observatories.
Abstract: We present multi-epoch mid-infrared (IR) photometry and the optical discovery observations of the "impostor" supernova (SN) 2010da in NGC 300 using new and archival Spitzer Space Telescope images and ground-based observatories. The mid-IR counterpart of SN 2010da was detected as SPIRITS 14bme in the SPitzer InfraRed Intensive Transient Survey (SPIRITS), an ongoing systematic search for IR transients. A sharp increase in the 3.6 $\mu$m flux followed by a rapid decrease measured ~150 d before and ~80 d after the initial outburst, respectively, reveal a mid-IR counterpart to the coincident optical and high luminosity X-ray outbursts. At late times after the outburst (~2000 d), the 3.6 and 4.5 $\mu$m emission increased to over a factor of 2 times the progenitor flux. We attribute the re-brightening mid-IR emission to continued dust production and increasing luminosity of the surviving system associated with SN 2010da. We analyze the evolution of the dust temperature, mass, luminosity, and equilibrium temperature radius in order to resolve the nature of SN 2010da. We address the leading interpretation of SN 2010da as an eruption from a luminous blue variable (LBV) high-mass X-ray binary (HMXB) system. We propose that SN 2010da is instead a supergiant (sg)B[e]-HMXB based on similar luminosities and dust masses exhibited by two other known sgB[e]-HMXB systems. Additionally, the SN 2010da progenitor occupies a similar region on a mid-IR color-magnitude diagram (CMD) with known sgB[e] stars in the Large Magellanic Cloud. The lower limit estimated for the orbital eccentricity of the sgB[e]-HMXB (e>0.82) from X-ray luminosity measurements is high compared to known sgHMXBs and supports the claim that SN 2010da may be associated with a newly formed HMXB system.
University of Tokyo1, National Scientific and Technical Research Council2, California Institute of Technology3, Millennium Institute4, University of Chile5, Kyoto University6, San Diego State University7, University of California, Berkeley8, University of Arizona9, University of Illinois at Urbana–Champaign10
TL;DR: In this article, the authors detect an object in the optical bands that is fainter than the pre-explosion object, which is likely not produced by dust absorption in the ejecta; thus, they confirm the connection of the progenitor candidate with the SN.
Abstract: Supernova (SN) iPTF13bvn in NGC 5806 was the first Type Ib SN to have been tentatively associated with a progenitor candidate in pre-explosion images. We performed deep ultraviolet (UV) and optical Hubble Space Telescope (HST) observations of the SN site 740 days after explosion. We detect an object in the optical bands that is fainter than the pre-explosion object. This dimming is likely not produced by dust absorption in the ejecta; thus, our finding confirms the connection of the progenitor candidate with the SN. The object in our data is likely dominated by the fading SN, which implies that the pre-SN flux is mostly due to the progenitor. We compare our revised pre-SN photometry with previously proposed progenitor models. Although binary progenitors are favored, models need to be refined. In particular, to comply with our deep UV detection limit, any companion star must be less luminous than a late-O star or substantially obscured by newly formed dust. A definitive progenitor characterization will require further observations to disentangle the contribution of a much fainter SN and its environment.
Fermilab1, Harvard University2, University of Pennsylvania3, Ohio University4, University of Illinois at Urbana–Champaign5, Space Telescope Science Institute6, University of Southampton7, University of Arizona8, Sao Paulo State University9, University College London10, Rhodes University11, Institut d'Astrophysique de Paris12, Carnegie Institution for Science13, Stanford University14, University of Portsmouth15, University of Maryland, College Park16, Goddard Space Flight Center17, Ludwig Maximilian University of Munich18, California Institute of Technology19, University of Michigan20, Pennsylvania State University21, Los Alamos National Laboratory22, University of California, Berkeley23, Lawrence Berkeley National Laboratory24, Ohio State University25, Australian Astronomical Observatory26, Texas A&M University27, University of São Paulo28, Columbia University29, Max Planck Society30, University of Sussex31, Universidade Federal do Rio Grande do Sul32, Brookhaven National Laboratory33, Argonne National Laboratory34
TL;DR: In this paper, the authors constructed a complete catalog of LMC luminous red supergiants, the best candidates to undergo invisible core collapse, and collected catalogs of other candidates: less luminous RED supergiant, yellow supergiger, blue supergiant, luminous blue variable stars, and Wolf-Rayet stars.
Abstract: The collapse of a stellar core is expected to produce gravitational waves (GWs), neutrinos, and in most cases a luminous supernova. Sometimes, however, the optical event could be significantly less luminous than a supernova and a direct collapse to a black hole, where the star just disappears, is possible. The GW event GW150914 was detected by the LIGO Virgo Collaboration via a burst analysis that gave localization contours enclosing the Large Magellanic Cloud (LMC). Shortly thereafter, we used DECam to observe 102 deg2 of the localization area, including 38 deg2 on the LMC for a missing supergiant search. We construct a complete catalog of LMC luminous red supergiants, the best candidates to undergo invisible core collapse, and collected catalogs of other candidates: less luminous red supergiants, yellow supergiants, blue supergiants, luminous blue variable stars, and Wolf–Rayet stars. Of the objects in the imaging region, all are recovered in the images. The timescale for stellar disappearance is set by the free-fall time, which is a function of the stellar radius. Our observations at 4 and 13 days after the event result in a search sensitive to objects of up to about 200 solar radii. We conclude that it is unlikely that GW150914 was caused by the core collapse of a relatively compact supergiant in the LMC, consistent with the LIGO Collaboration analyses of the gravitational waveform as best interpreted as a high mass binary black hole merger. We discuss how to generalize this search for future very nearby core-collapse candidates.
TL;DR: In this article, the authors used the HST from the Space Telescope Science Institute (SSTI) to explore the Earth's magnetic field for the first time, and found that the magnetic field of the Earth is positively correlated with the distance from the Sun.
Abstract: NSF [AST-1312221, AST-1515559]; National Aeronautics and Space Administration (NASA) through HST from the Space Telescope Science Institute [AR-14316]; NASA [NAS5-26555]
TL;DR: In this paper, the authors re-examine the classifications of supernovae presented in the Lick Observatory Supernova Search (LOSS) volume-limited sample with a focus on the stripped-envelope SNe.
Abstract: We re-examine the classifications of supernovae (SNe) presented in the Lick Observatory Supernova Search (LOSS) volume-limited sample with a focus on the stripped-envelope SNe. The LOSS volume-limited sample, presented by Leaman et al. (2011) and Li et al. (2011b), was calibrated to provide meaningful measurements of SN rates in the local universe; the results presented therein continue to be used for comparisons to theoretical and modeling efforts. Many of the objects from the LOSS sample were originally classified based upon only a small subset of the data now available, however, and recent studies have both updated some subtype distinctions and improved our ability to perform robust classications, especially for stripped-envelope SNe. We re-examine the spectroscopic classifications of all events in the LOSS volume-limited sample (180 SNe and SN impostors) and update them if necessary. We discuss the populations of rare objects in our sample including broad-lined Type Ic SNe, Ca-rich SNe, SN 1987A-like events (we identify SN 2005io as SN 1987A-like here for the first time), and peculiar subtypes. The relative fractions of Type Ia SNe, Type II SNe, and stripped-envelope SNe in the local universe are not affected, but those of some subtypes are. Most significantly, after discussing the often unclear boundary between SNe Ib and Ic when only noisy spectra are available, we find a higher SN Ib fraction and a lower SN Ic fraction than calculated by Li et al. (2011b): spectroscopically normal SNe Ib occur in the local universe $1.7 \pm 0.9$ times more often than do normal SNe Ic.
TL;DR: In this article, extensive spectroscopy of the ongoing eruption of the transient object UGC2773-OT has been presented, and the authors suggest that its decade-long eruption is the best known analog of eta Car's 19th century eruption.
Abstract: While SN impostors resemble the Great Eruption of eta Car in the sense that their spectra show narrow H lines and they have typical peak absolute magnitudes of -13 to -14 mag, most extragalactic events observed so far are quite different from eta Car in duration. Their bright phases typically last for 100~d or less, rather than persisting for several years. The transient object UGC2773-OT had a similar peak absolute magnitude to other SN impostors, but with a gradual 5-yr prediscovery rise. In the 6 yr since discovery, it has faded very slowly (0.26 mag/yr). Overall, we suggest that its decade-long eruption is so far the best known analog of eta Car's 19th century eruption. We discuss extensive spectroscopy of the ongoing eruption. The spectra show interesting changes in velocity and line shape that we discuss in detail, including an asymmetric Halpha emission line that we show is consistent with the ejection of a bipolar nebula that could be very much like the Homunculus of eta Car. Moreover, changes in the line width, line profile, blue excess emission resembling that of Type IIn supernovae, and the intensity of Halpha suggest the presence of strong circumstellar interaction in the eruption at late times. This supports the hypothesis that the extended plateau of eta Car's eruption may have been powered by shock interaction as well. One interesting difference compared to eta Car, however, is that UGC2773-OT so far does not exhibit the repeated brief spikes in luminosity that have been associated with binary periastron events.
TL;DR: In this article, high spatial resolution (∼0.24 × 0.13) ALMA science verification (SV) data in band 7, in which four thermal emission lines of gaseous sodium chloride (NaCl) are present at high signal-to-noise ratio.
Abstract: Context. At the end of their lives, most stars lose a significant amount of mass through a stellar wind. The specific physical and chemical circumstances that lead to the onset of the stellar wind for cool luminous stars are not yet understood. Complex geometrical morphologies in the circumstellar envelopes prove that various dynamical and chemical processes are interlocked and that their relative contributions are not easy to disentangle. Aims. We aim to study the inner-wind structure (R< 250 R∗) of the well-known red supergiant VY CMa, the archetype for the class of luminous red supergiant stars experiencing high mass loss. Specifically, the objective is to unravel the density structure in the inner envelope and to examine the chemical interaction between gas and dust species. Methods. We analyse high spatial resolution (∼0″.24 × 0″.13) ALMA science verification (SV) data in band 7, in which four thermal emission lines of gaseous sodium chloride (NaCl) are present at high signal-to-noise ratio. Results. For the first time, the NaCl emission in the inner wind region of VY CMa is spatially resolved. The ALMA observations reveal the contribution of up to four different spatial regions. The NaCl emission pattern is different compared to the dust continuum and TiO2 emission already analysed from the ALMA SV data. The emission can be reconciled with an axisymmetric geometry, where the lower density polar/rotation axis has a position angle of ∼50° measured from north to east. However, this picture cannot capture the full morphological diversity, and discrete mass ejection events need to be invoked to explain localized higher-density regions. The velocity traced by the gaseous NaCl line profiles is significantly lower than the average wind terminal velocity, and much slower than some of the fastest mass ejections, signalling a wide range of characteristic speeds for the mass loss. Gaseous NaCl is detected far beyond the main dust condensation region. Realising the refractory nature of this metal halide, this hints at a chemical process that prevents all NaCl from condensing onto dust grains. We show that in the case of the ratio of the surface binding temperature to the grain temperature being ∼50, only some 10% of NaCl remains in gaseous form while, for lower values of this ratio, thermal desorption efficiently evaporates NaCl. Photodesorption by stellar photons does not seem to be a viable explanation for the detection of gaseous NaCl at 220 R∗ from the central star, so instead, we propose shock-induced sputtering driven by localized mass ejection events as an alternative. Conclusions. The analysis of the NaCl lines demonstrates the capabilities of ALMA to decode the geometric morphologies and chemical pathways prevailing in the winds of evolved stars. These early ALMA results prove that the envelopes surrounding evolved stars are far from homogeneous, and that a variety of dynamical and chemical processes dictate the wind structure.
TL;DR: In this article, the authors used a catalog of 152 LMC luminous red supergiants, candidates to undergo a core collapse without a visible supernova, and found that the positions of 144 of these are inside our images, and that all are detected.
Abstract: The collapse of the core of a star is expected to produce gravitational radiation. While this process will usually produce a luminous supernova, the optical signatue could be subluminous and a direct collapse to a black hole, with the star just disappearing, is possible. The gravitational wave event GW150914 reported by the LIGO Virgo Collaboration (LVC) on 2015 September 16, was detected by a burst analysis and whose high probability spatial localization included the Large Magellanic Cloud. Shortly after the announcement of the event, we used the Dark Energy Camera to observe 102 deg$^2$ of the localization area, including a 38 deg$^2$ area centered on the LMC. Using a catalog of 152 LMC luminous red supergiants, candidates to undergo a core collapse without a visible supernova, we find that the positions of 144 of these are inside our images, and that all are detected - none have disappeared. There are other classes of candidates: we searched existing catalogs of red supergiants, yellow supergiants, Wolf-Rayet stars, and luminous blue variable stars, recovering all that were inside the imaging area. Based on our observations, we conclude that it is unlikely that GW150914 was caused by the core collapse of a supergiant in the LMC, consistent with the LIGO Collaboration analyses of the gravitational wave form as best described by a binary black hole merger. We discuss how to generalize this search for future very nearby core collapse candidates.
TL;DR: In this article, the inner-wind structure (R < 250 Rstar) of the well-known red supergiant VY CMa is spatially resolved using high spatial resolution (0".24x0".13) ALMA Science Verification (SV) data in band 7.
Abstract: (abreviated) We aim to study the inner-wind structure (R<250 Rstar) of the well-known red supergiant VY CMa. We analyse high spatial resolution (~0".24x0".13) ALMA Science Verification (SV) data in band 7 in which four thermal emission lines of gaseous sodium chloride (NaCl) are present at high signal-to-noise ratio. For the first time, the NaCl emission in the inner wind region of VY CMa is spatially resolved. The ALMA observations reveal the contribution of up to four different spatial regions. The NaCl emission pattern is different compared to the dust continuum and TiO2 emission already analysed from the ALMA SV data. The emission can be reconciled with an axisymmetric geometry, where the lower density polar/rotation axis has a position angle of ~50 degrees measured from north to east. However, this picture can not capture the full morphological diversity, and discrete mass ejection events need to be invoked to explain localized higher-density regions. The velocity traced by the gaseous NaCl line profiles is significantly lower than the average wind terminal velocity, and much slower than some of the fastest mass ejections, signalling a wide range of characteristic speeds for the mass loss. Gaseous NaCl is detected far beyond the main dust condensation region. Realising the refractory nature of this metal halide, this hints at a chemical process preventing all NaCl from condensing onto dust grains. We show that in the case of the ratio of the surface binding temperature to the grain temperature being ~50, only some 10% of NaCl remains in gaseous form, while for lower values of this ratio thermal desorption efficiently evaporates NaCl. Photodesorption by stellar photons seems not to be a viable explanation for the detection of gaseous NaCl at 220 Rstar from the central star, and instead, we propose shock-induced sputtering driven by localized mass ejection events as alternative.
TL;DR: The VizieR catalog access tool, CDS, Strasbourg, France; NSF [AST-1009571, AST-1210311, AST 1210599, AST1210372] as mentioned in this paper.
Abstract: National Aeronautics and Space Administration; VizieR catalog access tool, CDS, Strasbourg, France; NSF [AST-1009571, AST-1210311, AST-1210599, AST-1210372]
TL;DR: In this article, the authors present spectropolarimetric observations of the nearby Type Ia SN 2014J in M82 over six epochs: +0, +7, +23, +51, +77, +109, and +111 days with respect to B-band maximum.
Abstract: We present spectropolarimetric observations of the nearby Type Ia SN 2014J in M82 over six epochs: +0, +7, +23, +51, +77, +109, and +111 days with respect to B-band maximum. The strong continuum polarization, which is constant with time, shows a wavelength dependence unlike that produced by linear dichroism in Milky Way dust. The observed polarization may be due entirely to interstellar dust or include a circumstellar scattering component. We find that the polarization angle aligns with the magnetic field of the host galaxy, arguing for an interstellar origin. Additionally, we confirm a peak in polarization at short wavelengths that would imply $R_V < 2 $ along the light of sight, in agreement with earlier polarization measurements. For illustrative purposes, we include a two component fit to the continuum polarization of our +51 day epoch that combines a circumstellar scattering component with interstellar dust where scattering can account for over half of the polarization at $4000$ A. Upon removal of the interstellar polarization signal, SN 2014J exhibits very low levels of continuum polarization. Asymmetries in the distribution of elements within the ejecta are visible through moderate levels of time-variable polarization in accordance with the Si II 6355 Aabsorption line. At maximum light, the line polarization reaches $\sim0.6$% and decreases to $\sim0.4\%$ one week later. This feature also forms a loop on the $q_{RSP}$-$u_{RSP}$ plane illustrating that the ion does not have an axisymmetric distribution. The observed polarization properties suggest the explosion geometry of SN 2014J is generally spheroidal with a clumpy distribution of silicon.
TL;DR: In this paper, a systematic study of mid-infrared (mid-IR) emission from 141 nearby supernovae (SNe) observed with the InfraRed Array Camera (IRAC) on Spitzer is presented.
Abstract: We present a systematic study of mid-infrared (mid-IR) emission from 141 nearby supernovae (SNe) observed with the InfraRed Array Camera (IRAC) on Spitzer.These SNe reside in one of the 190 galaxies within 20 Mpc drawn from the ongoing SPIRITS program. We detect 8 Type Ia SNe and 36 core-collapse SNe. All Type I SNe become undetectable within 3 years of explosion. About 22$\pm$11% of Type II SNe continue to be detected at late-times. Dust luminosity, temperature, and a lower liit on mass are obtained by fitting the SED using photometry with IRAC bands 1 and 2. The mass estimate does not distinguish between pre-existing and newly produced dust. We observe warm dust masses between $10^{-2}$ and $10^{-6}$ $\rm M_{\odot}$ and dust temperatures from 200 K to 1280 K.We present detailed case studies of two extreme Type II-P SNe: SN 2011ja and 2014bi. SN 2011ja was over-luminous ([4.5] = -15.6 mag) at 900 days post-explosion accompanied by the growing dust mass. This suggests either an episode of dust formation or an intensifying CSM interactions heating up pre-existing dust. SN 2014bi showed a factor of 10 decrease in dust mass over one month suggesting either an episode of dust destruction or a fading source of dust heating. A rebrightening of the Type Ib SN 2014C is observed and attributed to CSM interactions. This observation adds to a small number of stripped-envelope SNe that have mid-IR excess. The observations suggest that the CSM shell around SN 2014C is originated from an LBV-like eruption roughly 100 years before the explosion. We also report detections of SN1974E, 1979C, 1980K, 1986J, and 1993J detected more than 20 years post-explosion. The number of outlying SNe identified in this work demonstrates the power of late time mid-IR observations of a large sample of SNe to identify events with unusual evolution.