Showing papers by "Anthony L. Piro published in 2017"
TL;DR: A measurement of the Hubble constant is reported that combines the distance to the source inferred purely from the gravitational-wave signal with the recession velocity inferred from measurements of the redshift using the electromagnetic data.
Abstract: On 17 August 2017, the Advanced LIGO1 and Virgo2 detectors observed the gravitational-wave event GW170817—a strong signal from the merger of a binary neutron-star system3. Less than two seconds after the merger, a γ-ray burst (GRB 170817A) was detected within a region of the sky consistent with the LIGO–Virgo-derived location of the gravitational-wave source4, 5, 6. This sky region was subsequently observed by optical astronomy facilities7, resulting in the identification8, 9, 10, 11, 12, 13 of an optical transient signal within about ten arcseconds of the galaxy NGC 4993. This detection of GW170817 in both gravitational waves and electromagnetic waves represents the first ‘multi-messenger’ astronomical observation. Such observations enable GW170817 to be used as a ‘standard siren’14, 15, 16, 17, 18 (meaning that the absolute distance to the source can be determined directly from the gravitational-wave measurements) to measure the Hubble constant. This quantity represents the local expansion rate of the Universe, sets the overall scale of the Universe and is of fundamental importance to cosmology. Here we report a measurement of the Hubble constant that combines the distance to the source inferred purely from the gravitational-wave signal with the recession velocity inferred from measurements of the redshift using the electromagnetic data. In contrast to previous measurements, ours does not require the use of a cosmic ‘distance ladder’19: the gravitational-wave analysis can be used to estimate the luminosity distance out to cosmological scales directly, without the use of intermediate astronomical distance measurements. We determine the Hubble constant to be about 70 kilometres per second per megaparsec. This value is consistent with existing measurements20, 21, while being completely independent of them. Additional standard siren measurements from future gravitational-wave sources will enable the Hubble constant to be constrained to high precision.
892 citations
TL;DR: A rapid astronomical search located the optical counterpart of the neutron star merger GW170817 and shows how these observations can be explained by an explosion known as a kilonova, which produces large quantities of heavy elements in nuclear reactions.
Abstract: On 17 August 2017, the Laser Interferometer Gravitational-Wave Observatory (LIGO) and the Virgo interferometer detected gravitational waves (GWs) emanating from a binary neutron star merger, GW170817. Nearly simultaneously, the Fermi and INTEGRAL (INTErnational Gamma-Ray Astrophysics Laboratory) telescopes detected a gamma-ray transient, GRB 170817A. At 10.9 hours after the GW trigger, we discovered a transient and fading optical source, Swope Supernova Survey 2017a (SSS17a), coincident with GW170817. SSS17a is located in NGC 4993, an S0 galaxy at a distance of 40 megaparsecs. The precise location of GW170817 provides an opportunity to probe the nature of these cataclysmic events by combining electromagnetic and GW observations.
880 citations
Carnegie Institution for Science1, University of California, Santa Cruz2, Carnegie Learning3, Lawrence Berkeley National Laboratory4, University of California, Berkeley5, Pennsylvania State University6, University of Copenhagen7, Johns Hopkins University8, Space Telescope Science Institute9, California Institute of Technology10, Diego Portales University11, Massachusetts Institute of Technology12, University of Notre Dame13, Joint Institute for Nuclear Astrophysics14, National Autonomous University of Mexico15, University of La Serena16, Herzberg Institute of Astrophysics17, University of Victoria18, Valparaiso University19, Texas A&M University20, Catholic University of the North21, Millennium Institute22, University of Sydney23
TL;DR: In this paper, the authors present ultraviolet, optical, and infrared light curves of SSS17a extending from 10.9 hours to 18 days post-merger, showing that the late-time light curve indicates that SSS 17a produced at least 0.05 solar masses of heavy elements, demonstrating that neutron star mergers play a role in rapid neutron capture (r-process) nucleosynthesis in the universe.
Abstract: On 17 August 2017, gravitational waves (GWs) were detected from a binary neutron star merger, GW170817, along with a coincident short gamma-ray burst, GRB 170817A. An optical transient source, Swope Supernova Survey 17a (SSS17a), was subsequently identified as the counterpart of this event. We present ultraviolet, optical, and infrared light curves of SSS17a extending from 10.9 hours to 18 days postmerger. We constrain the radioactively powered transient resulting from the ejection of neutron-rich material. The fast rise of the light curves, subsequent decay, and rapid color evolution are consistent with multiple ejecta components of differing lanthanide abundance. The late-time light curve indicates that SSS17a produced at least ~0.05 solar masses of heavy elements, demonstrating that neutron star mergers play a role in rapid neutron capture (r-process) nucleosynthesis in the universe.
582 citations
Carnegie Institution for Science1, University of California, Santa Cruz2, Carnegie Learning3, University of California, Berkeley4, Lawrence Berkeley National Laboratory5, Pennsylvania State University6, University of Copenhagen7, Space Telescope Science Institute8, Johns Hopkins University9, California Institute of Technology10, Massachusetts Institute of Technology11, Diego Portales University12, Joint Institute for Nuclear Astrophysics13, University of Notre Dame14, National Autonomous University of Mexico15, University of La Serena16, Herzberg Institute of Astrophysics17, University of Victoria18, Valparaiso University19, Texas A&M University20, Catholic University of the North21, Millennium Institute22, University of Sydney23
TL;DR: The late-time light curve indicates that SSS17a produced at least ~0.05 solar masses of heavy elements, demonstrating that neutron star mergers play a role in rapid neutron capture (r-process) nucleosynthesis in the universe.
Abstract: On 2017 August 17, gravitational waves were detected from a binary neutron star merger, GW170817, along with a coincident short gamma-ray burst, GRB170817A. An optical transient source, Swope Supernova Survey 17a (SSS17a), was subsequently identified as the counterpart of this event. We present ultraviolet, optical and infrared light curves of SSS17a extending from 10.9 hours to 18 days post-merger. We constrain the radioactively-powered transient resulting from the ejection of neutron-rich material. The fast rise of the light curves, subsequent decay, and rapid color evolution are consistent with multiple ejecta components of differing lanthanide abundance. The late-time light curve indicates that SSS17a produced at least ~0.05 solar masses of heavy elements, demonstrating that neutron star mergers play a role in r-process nucleosynthesis in the Universe.
328 citations
Carnegie Institution for Science1, Carnegie Learning2, Diego Portales University3, Millennium Institute4, Lawrence Berkeley National Laboratory5, University of California, Berkeley6, University of California, Santa Cruz7, University of Copenhagen8, Space Telescope Science Institute9, Johns Hopkins University10, California Institute of Technology11, Massachusetts Institute of Technology12, National Autonomous University of Mexico13, Herzberg Institute of Astrophysics14, University of Victoria15, Valparaiso University16, Texas A&M University17, Joint Institute for Nuclear Astrophysics18, University of Sydney19
TL;DR: In this article, the authors reported time-series spectroscopy of SSS17a from 11.75 hours until 8.5 days after the merger, and measured the photosphere cooling from 11, 000 − 900 + 3400 to 9300 − 300 + 300 kelvin and determined a photospheric velocity of roughly 30% of the speed of light.
Abstract: On 17 August 2017, Swope Supernova Survey 2017a (SSS17a) was discovered as the optical counterpart of the binary neutron star gravitational wave event GW170817. We report time-series spectroscopy of SSS17a from 11.75 hours until 8.5 days after the merger. Over the first hour of observations, the ejecta rapidly expanded and cooled. Applying blackbody fits to the spectra, we measured the photosphere cooling from 11 , 000 − 900 + 3400 to 9300 − 300 + 300 kelvin, and determined a photospheric velocity of roughly 30% of the speed of light. The spectra of SSS17a began displaying broad features after 1.46 days and evolved qualitatively over each subsequent day, with distinct blue (early-time) and red (late-time) components. The late-time component is consistent with theoretical models of r-process–enriched neutron star ejecta, whereas the blue component requires high-velocity, lanthanide-free material.
267 citations
University of California, Santa Cruz1, University of California, Berkeley2, Lawrence Berkeley National Laboratory3, University of Copenhagen4, Carnegie Institution for Science5, University of Hawaii6, Carnegie Learning7, Space Telescope Science Institute8, Johns Hopkins University9, University of La Serena10
TL;DR: In this paper, the authors synthesize the optical to near-infrared photometry and spectroscopy of SSS17a collected by the One-Meter Two-Hemisphere collaboration, finding that SSS 17a is unlike other known transients.
Abstract: Eleven hours after the detection of gravitational wave source GW170817 by the Laser Interferometer Gravitational-Wave Observatory and Virgo Interferometers, an associated optical transient, SSS17a, was identified in the galaxy NGC 4993. Although the gravitational wave data indicate that GW170817 is consistent with the merger of two compact objects, the electromagnetic observations provide independent constraints on the nature of that system. We synthesize the optical to near-infrared photometry and spectroscopy of SSS17a collected by the One-Meter Two-Hemisphere collaboration, finding that SSS17a is unlike other known transients. The source is best described by theoretical models of a kilonova consisting of radioactive elements produced by rapid neutron capture (the r-process). We conclude that SSS17a was the result of a binary neutron star merger, reinforcing the gravitational wave result.
261 citations
TL;DR: The location of the binary neutron star merger event GW170817 provides an opportunity to probe the nature of these cataclysmic events by combining electromagnetic and gravitational-wave observations.
Abstract: On 2017 August 17, the Laser Interferometer Gravitational-wave Observatory (LIGO) and the Virgo interferometer detected gravitational waves emanating from a binary neutron star merger, GW170817. Nearly simultaneously, the Fermi and INTEGRAL telescopes detected a gamma-ray transient, GRB 170817A. 10.9 hours after the gravitational wave trigger, we discovered a transient and fading optical source, Swope Supernova Survey 2017a (SSS17a), coincident with GW170817. SSS17a is located in NGC 4993, an S0 galaxy at a distance of 40 megaparsecs. The precise location of GW170817 provides an opportunity to probe the nature of these cataclysmic events by combining electromagnetic and gravitational-wave observations.
217 citations
TL;DR: In this article, the optical and near-infrared photometry and spectroscopy of SSS17a collected by the One-Meter Two-Hemisphere collaboration were analyzed.
Abstract: 11 hours after the detection of gravitational wave source GW170817 by the Laser Interferometer Gravitational-Wave Observatory and Virgo Interferometers, an associated optical transient SSS17a was discovered in the galaxy NGC 4993. While the gravitational wave data indicate GW170817 is consistent with the merger of two compact objects, the electromagnetic observations provide independent constraints of the nature of that system. Here we synthesize all optical and near-infrared photometry and spectroscopy of SSS17a collected by the One-Meter Two-Hemisphere collaboration. We find that SSS17a is unlike other known transients. The source is best described by theoretical models of a kilonova consisting of radioactive elements produced by rapid neutron capture (the r-process). We find that SSS17a was the result of a binary neutron star merger, reinforcing the gravitational wave result.
201 citations
TL;DR: In this paper, the authors show that the multi-band light curves of SNe IIL are well fit by ordinary red supergiants surrounded by dense circumstellar material (CSM) and that the inferred extent of this material, coupled with a typical wind velocity of ~10-100 km s−1, suggests enhanced activity by these stars during the last ~months to ~years of their lives, which may be connected with advanced stages of nuclear burning.
Abstract: A longstanding problem in the study of supernovae (SNe) has been the relationship between the Type IIP and Type IIL subclasses Whether they come from distinct progenitors or they are from similar stars with some property that smoothly transitions from one class to another has been the subject of much debate Here, using one-dimensional radiation-hydrodynamic SN models, we show that the multi-band light curves of SNe IIL are well fit by ordinary red supergiants surrounded by dense circumstellar material (CSM) The inferred extent of this material, coupled with a typical wind velocity of ~10-100 km s^(-1), suggests enhanced activity by these stars during the last ~months to ~years of their lives, which may be connected with advanced stages of nuclear burning Furthermore, we find that, even for more plateau-like SNe, dense CSM provides a better fit to the first ~20 days of their light curves, indicating that the presence of such material may be more widespread than previously appreciated Here we choose to model the CSM with a wind-like density profile, but it is unclear whether this just generally represents some other mass distribution, such as a recent mass ejection, thick disk, or even inflated envelope material Better understanding the exact geometry and density distribution of this material will be an important question for future studies
160 citations
TL;DR: In this article, the relativistic ejecta and the non-thermal processes occurring within the merging neutron star gravitational wave event GW170817 have been observed throughout the entire electromagnetic spectrum from radio waves to $gamma$-rays.
Abstract: The merging neutron star gravitational wave event GW170817 has been observed throughout the entire electromagnetic spectrum from radio waves to $\\gamma$-rays. The resulting energetics, variability, and light curves are shown to be consistent with GW170817 originating from the merger of two neutron stars, in all likelihood followed by the prompt gravitational collapse of the massive remnant. The available $\\gamma$-ray, X-ray and radio data provide a clear probe for the nature of the relativistic ejecta and the non-thermal processes occurring within, while the ultraviolet, optical and infrared emission are shown to probe material torn during the merger and subsequently heated by the decay of freshly synthesized $r$-process material. The simplest hypothesis that the non-thermal emission is due to a low-luminosity short $\\gamma$-ray burst (sGRB) seems to agree with the present data. While low luminosity sGRBs might be common, we show here that the collective prompt and multi-wavelength observations are also consistent with a typical, powerful sGRB seen off-axis. Detailed follow-up observations are thus essential before we can place stringent constraints on the nature of the relativistic ejecta in GW170817.
144 citations
TL;DR: In this article, the relativistic ejecta and the non-thermal processes occurring within the merging neutron star gravitational wave event GW170817 have been observed throughout the entire electromagnetic spectrum from radio waves to $\gamma$-rays.
Abstract: The merging neutron star gravitational wave event GW170817 has been observed throughout the entire electromagnetic spectrum from radio waves to $\gamma$-rays. The resulting energetics, variability, and light curves are shown to be consistent with GW170817 originating from the merger of two neutron stars, in all likelihood followed by the prompt gravitational collapse of the massive remnant. The available $\gamma$-ray, X-ray and radio data provide a clear probe for the nature of the relativistic ejecta and the non-thermal processes occurring within, while the ultraviolet, optical and infrared emission are shown to probe material torn during the merger and subsequently heated by the decay of freshly synthesized $r$-process material. The simplest hypothesis that the non-thermal emission is due to a low-luminosity short $\gamma$-ray burst (sGRB) seems to agree with the present data. While low luminosity sGRBs might be common, we show here that the collective prompt and multi-wavelength observations are also consistent with a typical, powerful sGRB seen off-axis. Detailed follow-up observations are thus essential before we can place stringent constraints on the nature of the relativistic ejecta in GW170817.
Carnegie Institution for Science1, Carnegie Learning2, Diego Portales University3, Millennium Institute4, Lawrence Berkeley National Laboratory5, University of California, Berkeley6, University of California, Santa Cruz7, University of Copenhagen8, Johns Hopkins University9, Space Telescope Science Institute10, California Institute of Technology11, Massachusetts Institute of Technology12, National Autonomous University of Mexico13, University of Victoria14, Herzberg Institute of Astrophysics15, Valparaiso University16, Texas A&M University17, Joint Institute for Nuclear Astrophysics18, University of Sydney19
TL;DR: Spectra of a neutron star merger are unlike other astronomical transients and demonstrate rapid evolution of the source and Kilpatrick et al. show how these observations can be explained by an explosion known as a kilonova, which produces large quantities of heavy elements in nuclear reactions.
Abstract: On 2017 August 17, Swope Supernova Survey 2017a (SSS17a) was discovered as the optical counterpart of the binary neutron star gravitational wave event GW170817. We report time-series spectroscopy of SSS17a from 11.75 hours until 8.5 days after merger. Over the first hour of observations the ejecta rapidly expanded and cooled. Applying blackbody fits to the spectra, we measure the photosphere cooling from $11,000^{+3400}_{-900}$ K to $9300^{+300}_{-300}$ K, and determine a photospheric velocity of roughly 30% of the speed of light. The spectra of SSS17a begin displaying broad features after 1.46 days, and evolve qualitatively over each subsequent day, with distinct blue (early-time) and red (late-time) components. The late-time component is consistent with theoretical models of r-process-enriched neutron star ejecta, whereas the blue component requires high velocity, lanthanide-free material.
TL;DR: In this paper, a large sample of twenty well-observed Type II supernova (SN II) light curves was used to constrain the progenitor zero-age main-sequence (ZAMS) mass, explosion energy, and the mass and radial extent of dense CSM.
Abstract: Recent modeling of hydrogen-rich Type II supernova (SN II) light curves suggests the presence of dense circumstellar material (CSM) surrounding the exploding progenitor stars. This has important implications for the activity and structure of massive stars near the end of their lives. Since previous work focused on just a few events, here we expand to a larger sample of twenty well-observed SNe II. For each event we are able to constrain the progenitor zero-age main-sequence (ZAMS) mass, explosion energy, and the mass and radial extent of dense CSM. We then study the distribution of each of these properties across the full sample of SNe. The inferred ZAMS masses are found to be largely consistent with a Salpeter distribution with minimum and maximum masses of 10.4 and 22.9 Msun, respectively. We also compare the individual ZAMS masses we measure with specific SNe II that have pre-explosion imaging to check their consistency. Our masses are generally comparable to or larger than the pre-explosion imaging masses, potentially helping ease the red supergiant problem. The explosion energies vary from (0.1-1.3)x10^51 erg, and for ~70% of the SNe we obtain CSM masses in the range between 0.18-0.83 Msun. We see a potential correlation between the CSM mass and explosion energy, which suggests that pre-explosion activity has a strong impact on the structure of the star. This may be important to take into account in future studies of the ability of the neutrino mechanism to explode stars. We also see a possible correlation between the CSM's radial extent and ZAMS mass, which could be related to the time with respect to explosion when the CSM is first generated.
TL;DR: In this paper, the authors combine relativistic calculations of NS masses using realistic EOSs with Monte Carlo population synthesis based on the mass distribution of NS binaries in our Galaxy to predict the distribution of fates expected.
Abstract: Following merger, a neutron star (NS) binary can produce roughly one of three different outcomes: (1) a stable NS, (2) a black hole (BH), or (3) a supra-massive, rotationally-supported NS, which then collapses to a BH following angular momentum losses. Which of these fates occur and in what proportion has important implications for the electromagnetic transient associated with the mergers and the expected gravitational wave signatures, which in turn depend on the high density equation of state (EOS). Here we combine relativistic calculations of NS masses using realistic EOSs with Monte Carlo population synthesis based on the mass distribution of NS binaries in our Galaxy to predict the distribution of fates expected. For many EOSs, a significant fraction of the remnants are NSs or supra-massive NSs. This lends support to scenarios where a quickly spinning, highly magnetized NS may be powering an electromagnetic transient. This also indicates that it will be important for future gravitational wave (GW) observatories to focus on high frequencies to study the post merger GW emission. Even in cases where individual GW events are too low in signal to noise to study the post merger signature in detail, the statistics of how many mergers produce NSs versus BHs can be compared with our work to constrain the EOS. To match short gamma-ray burst (SGRB) X-ray afterglow statistics, we find that the stiffest EOSs are ruled out. Furthermore, many popular EOSs require ~60-70% of SGRBs to be from NS-BH mergers rather than just binary NSs.
University of California, Davis1, University of Arizona2, European Southern Observatory3, Las Cumbres Observatory Global Telescope Network4, University of California, Santa Barbara5, Liverpool John Moores University6, University of Southampton7, Max Planck Society8, University of California, Santa Cruz9, Weizmann Institute of Science10, University of Pittsburgh11, University of Copenhagen12, University of North Carolina at Chapel Hill13, University of Turku14, Florida State University15, Rutgers University16, Queen's University Belfast17, Texas Tech University18, Brera Astronomical Observatory19, Carnegie Institution for Science20, Royal Institute of Technology21, Aarhus University22
TL;DR: In this paper, the authors presented an analysis of the Type II supernova DLT16am (SN~2016ija) during the DLT40 one day cadence supernova search at NGC~1532.
Abstract: We present our analysis of the Type II supernova DLT16am (SN~2016ija). The object was discovered during the ongoing $\rm{D}<40\,\rm{Mpc}$ (DLT40) one day cadence supernova search at $r\sim20.1\,\rm{mag}$ in the `edge-on' nearby ($D=20.0\pm1.9\,\rm{Mpc}$) galaxy NGC~1532. The subsequent prompt and high-cadenced spectroscopic and photometric follow-up revealed a highly extincted transient, with $E(B-V)=1.95\pm0.15\,\rm{mag}$, consistent with a standard extinction law with $R_V=3.1$ and a bright ($M_V=-18.49\pm0.65\,\rm{mag}$) absolute peak-magnitude. The comparison of the photometric features with those of large samples of Type II supernovae reveals a fast rise for the derived luminosity and a relatively short plateau phase, with a slope of $S_{50V}=0.84\pm0.04\,\rm{mag}/50\,\rm{d}$ consistent with the photometric properties typical of those of fast declining Type II supernovae. Despite the large uncertainties on the distance and the extinction in the direction of DLT16am, the measured photospheric expansion velocity and the derived absolute $V$-band magnitude at $\sim50\,\rm{d}$ after the explosion match the existing luminosity-velocity relation for Type II supernovae.
TL;DR: Pan et al. as discussed by the authors presented an analysis of the host-galaxy environment of Swope Supernova Survey 2017a (SSS17a), the discovery of an electromagnetic counterpart to a gravitational-wave source, GW170817.
Abstract: Author(s): Pan, YC; Kilpatrick, CD; Simon, JD; Xhakaj, E; Boutsia, K; Coulter, DA; Drout, MR; Foley, RJ; Kasen, D; Morrell, N; Murguia-Berthier, A; Osip, D; Piro, AL; Prochaska, JX; Ramirez-Ruiz, E; Rest, A; Rojas-Bravo, C; Shappee, BJ; Siebert, MR | Abstract: We present an analysis of the host-galaxy environment of Swope Supernova Survey 2017a (SSS17a), the discovery of an electromagnetic counterpart to a gravitational-wave source, GW170817. SSS17a occurred 1.9 kpc (in projection; 10.″2) from the nucleus of NGC 4993, an S0 galaxy at a distance of 40 Mpc. We present a Hubble Space Telescope (HST) pre-trigger image of NGC 4993, Magellan optical spectroscopy of the nucleus of NGC 4993 and the location of SSS17a, and broadband UV-through-IR photometry of NGC 4993. The spectrum and broadband spectral-energy distribution indicate that NGC 4993 has a stellar mass of and star formation rate of 0.003 yr-1, and the progenitor system of SSS17a likely had an age of g2.8 Gyr. There is no counterpart at the position of SSS17a in the HST pre-trigger image, indicating that the progenitor system had an absolute magnitude mag. We detect dust lanes extending out to almost the position of SSS17a and g100 likely globular clusters associated with NGC 4993. The offset of SSS17a is similar to many short gamma-ray-burst offsets, and its progenitor system was likely bound to NGC 4993. The environment of SSS17a is consistent with an old progenitor system such as a binary neutron star system.
Las Cumbres Observatory Global Telescope Network1, University of California, Santa Barbara2, Texas A&M University3, Queen's University Belfast4, University of California, Davis5, Texas Tech University6, Carnegie Learning7, University of Hawaii8, Space Telescope Science Institute9, University of Rochester10
TL;DR: In this paper, the first light-curve peak of SN 2016gkg was obtained from the Las Cumbres Observatory Global Telescope network, the Asteroid Terrestrial-impact Last Alert System, the Swift satellite and various amateur-operated telescopes.
Abstract: SN 2016gkg is a nearby Type IIb supernova discovered shortly after explosion. Like several other Type IIb events with early-time data, SN 2016gkg displays a double-peaked light curve, with the first peak associated with the cooling of a low-mass extended progenitor envelope. We present unprecedented intranight-cadence multi-band photometric coverage of the first light-curve peak of SN 2016gkg obtained from the Las Cumbres Observatory Global Telescope network, the Asteroid Terrestrial-impact Last Alert System, the Swift satellite and various amateur-operated telescopes. Fitting these data to analytical shock-cooling models gives a progenitor radius of ~25-140 solar radii with ~2-30 x 10^-2 solar masses of material in the extended envelope (depending on the model and the assumed host-galaxy extinction). Our radius estimates are broadly consistent with values derived independently (in other works) from HST imaging of the progenitor star. However, the shock-cooling model radii are on the lower end of the values indicated by pre-explosion imaging. Hydrodynamical simulations could refine the progenitor parameters deduced from the shock-cooling emission and test the analytical models.
University of Pittsburgh1, Goddard Space Flight Center2, University of Maryland, College Park3, Polytechnic University of Catalonia4, Joint Institute for Nuclear Astrophysics5, Arizona State University6, University of Alabama7, Carnegie Institution for Science8, University of Maryland, Baltimore9, University of Texas at Arlington10
TL;DR: In this paper, a new method was proposed to determine ejecta neutronization using Ca and S lines in the X-ray spectra of Type Ia supernova remnants (SNRs).
Abstract: The physical process whereby a carbon--oxygen white dwarf explodes as a Type Ia supernova (SN Ia) remains highly uncertain. The degree of neutronization in SN Ia ejecta holds clues to this process because it depends on the mass and the metallicity of the stellar progenitor, and on the thermodynamic history prior to the explosion. We report on a new method to determine ejecta neutronization using Ca and S lines in the X-ray spectra of Type Ia supernova remnants (SNRs). Applying this method to \textit{Suzaku} data of Tycho, Kepler, 3C 397 and G337.2$-$0.7 in the Milky Way, and N103B in the Large Magellanic Cloud, we find that the neutronization of the ejecta in N103B is comparable to that of Tycho and Kepler, which suggests that progenitor metallicity is not the only source of neutronization in SNe Ia. We then use a grid of SN Ia explosion models to infer the metallicities of the stellar progenitors of our SNRs. The implied metallicities of 3C 397, G337.2$-$0.7, and N103B are major outliers compared to the local stellar metallicity distribution functions, indicating that progenitor metallicity can be ruled out as the origin of neutronization for these SNRs. Although the relationship between ejecta neutronization and equivalent progenitor metallicity is subject to uncertainties stemming from the $^{12}$C$\,$+$^{16}$O reaction rate, which affects the Ca/S mass ratio, our main results are not sensitive to these details.
TL;DR: In this article, the authors discovered Swope Supernova Survey 2017a (SSS17a) in the LIGO/Virgo Collaboration (LVC) localization volume of GW170817, the first detected binary neutron star (BNS) merger, only 10.9 hours after the trigger.
Abstract: We discovered Swope Supernova Survey 2017a (SSS17a) in the LIGO/Virgo Collaboration (LVC) localization volume of GW170817, the first detected binary neutron star (BNS) merger, only 10.9 hours after the trigger. No object was present at the location of SSS17a only a few days earlier, providing a qualitative spatial and temporal association with GW170817. Here we quantify this association, finding that SSS17a is almost certainly the counterpart of GW170817, with the chance of a coincidence being 5 mag in g within 7 days of our first data point while all other known transients of similar luminosity fade by <1 mag during the same time period. Its spectra are also unique, being mostly featureless, even as it cools. The rarity of "SSS17a-like" transients combined with the relatively small LVC localization volume and recent non-detection imply the extremely unlikely chance coincidence. We find that the volumetric rate of SSS17a-like transients is < 1.6 x 10^4 Gpc^-3 year^-1 and the Milky Way rate is <0.19 per century. A transient survey designed to discover similar events should be high cadence and observe in red filters. The LVC will likely detect substantially more BNS mergers than current optical surveys will independently discover SSS17a-like transients, however a 1-day cadence survey with LSST could discover an order of magnitude more events.
TL;DR: In this article, Swope Supernova Survey 2017a (SSS17a) was detected in the LIGO/Virgo Collaboration (LVC) localization volume of GW170817, the first detected binary neutron star (BNS) merger, only 10.9 hr after the trigger.
Abstract: We discovered Swope Supernova Survey 2017a (SSS17a) in the LIGO/Virgo Collaboration (LVC) localization volume of GW170817, the first detected binary neutron star (BNS) merger, only 10.9 hr after the trigger. No object was present at the location of SSS17a only a few days earlier, providing a qualitative spatial and temporal association with GW170817. Here, we quantify this association, finding that SSS17a is almost certainly the counterpart of GW170817, with the chance of a coincidence being ≤$9\times {10}^{-6}$ (90% confidence). We arrive at this conclusion by comparing the optical properties of SSS17a to other known astrophysical transients, finding that SSS17a fades and cools faster than any other observed transient. For instance, SSS17a fades >5 mag in g within 7 days of our first data point, while all other known transients of similar luminosity fade by <1 mag during the same time period. Its spectra are also unique, being mostly featureless, even as it cools. The rarity of “SSS17a-like” transients combined with the relatively small LVC localization volume and recent non-detection imply the extremely unlikely chance coincidence. We find that the volumetric rate of SSS17a-like transients is ≤$1.6\times {10}^{4}$ Gpc(−)(3) yr(−)(1) and the Milky Way rate is $\leqslant 0.19$ per century. A transient survey designed to discover similar events should be high cadence and observe in red filters. The LVC will likely detect substantially more BNS mergers than current optical surveys will independently discover SSS17a-like transients, however a 1 day cadence survey with the Large Synoptic Survey Telescope (LSST) could discover an order of magnitude more events.
TL;DR: In this article, the authors consider the hypothesis that two fast radio bursts are from the same neutron star embedded within a supernova remnant (SNR) that provides an evolving dispersion measure as the ejecta expands and becomes more diffuse.
Abstract: The fast radio bursts (FRBs) 110220 and 140514 were detected at telescope pointing locations within 9 arcmin of each other over three years apart, both within the same 14.4 arcmin beam of the Parkes radio telescope. Nevertheless, they generally have not been considered to be from the same source because of a vastly different dispersion measure (DM) for the two bursts by over $380\,{\rm pc\,cm^{-3}}$. Here we consider the hypothesis that these two FRBs are from the same neutron star embedded within a supernova remnant (SNR) that provides an evolving DM as the ejecta expands and becomes more diffuse. Using such a model and the observed DM change, it can be argued that the corresponding SN must have occurred within $\approx10.2$ years of FRB 110220. Furthermore, constraints can be placed on the SN ejecta mass and explosion energy, which appear to require a stripped envelope (Type Ib/c) SN and/or a very energetic explosion. A third FRB from this location would be even more constraining, allowing the component of the DM due to the SNR to be separated from the unchanging DM components due to the host galaxy and intergalactic medium. In the future, if more FRBs are found to repeat, the sort of arguments presented here can be used to test the young neutron star progenitor hypothesis for FRBs.
TL;DR: In this paper, a large grid of extended envelope models and compare these to SN 2016gkg to investigate what constraints can be derived from its light curve, including density profiles for both a convective envelope and an optically thick steady-state wind, which has not typically been considered for Type IIb SNe models.
Abstract: Many Type IIb supernovae (SNe) show a prominent additional early peak in their light curves, which is generally thought to be due to the shock cooling of extended hydrogen-rich material surrounding the helium core of the exploding star. The recent SN 2016gkg was a nearby Type IIb SN discovered shortly after explosion, which makes it an excellent candidate for studying this first peak. We numerically explode a large grid of extended envelope models and compare these to SN 2016gkg to investigate what constraints can be derived from its light curve. This includes exploring density profiles for both a convective envelope and an optically thick steady-state wind, the latter of which has not typically been considered for Type IIb SNe models. We find that roughly ~ 0.02 M⊙ of extended material with a radius of ≈ 180-260 R⊙ reproduces the photometric light curve data, consistent with pre-explosion imaging. These values are independent of the assumed density profile of this material, although a convective profile provides a somewhat better fit. We infer from our modeling that the explosion must have occurred within ≈2–3 hr of the first observed data point, demonstrating that this event was caught very close to the moment of explosion. Nevertheless, our best-fitting 1D models overpredict the earliest velocity measurements, which suggests that the hydrogen-rich material is not distributed in a spherically symmetric manner. We compare this to the asymmetries that have also been seen in the SN IIb remnant Cas A, and we discuss the implications of this for Type IIb SN progenitors and explosion models.
TL;DR: In this article, it was shown that the power-law evolution of the luminosity, temperature, and photospheric radius during these early times can be explained by cooling of shock heated material around the neutron star merger.
Abstract: Swope Supernova Survey 2017a (SSS17a) was discovered as the first optical counterpart to the gravitational wave event GW170817. Although its light curve on the timescale of weeks roughly matches the expected luminosity and red color of an r-process powered transient, the explanation for the blue emission from high velocity material over the first few days is not as clear. Here we show that the power-law evolution of the luminosity, temperature, and photospheric radius during these early times can be explained by cooling of shock heated material around the neutron star merger. This heating is likely from the interaction of the gamma-ray burst jet with merger debris, so-called cocoon emission. We summarize the properties of this emission and provide formulae that can be used to study future detections of shock cooling from merging neutron stars. This argues that optical transient surveys should search for such early, blue light if they wish to find off-axis gamma-ray bursts and double neutron star gravitational wave events as soon as possible after the merger.
TL;DR: In this article, the authors combine relativistic calculations of NS masses using realistic EOSs with Monte Carlo population synthesis based on the mass distribution of NS binaries in our Galaxy to predict the distribution of fates expected.
Abstract: Following merger, a neutron star (NS) binary can produce roughly one of three different outcomes: (1) a stable NS, (2) a black hole (BH), or (3) a supra-massive, rotationally-supported NS, which then collapses to a BH following angular momentum losses. Which of these fates occur and in what proportion has important implications for the electromagnetic transient associated with the mergers and the expected gravitational wave signatures, which in turn depend on the high density equation of state (EOS). Here we combine relativistic calculations of NS masses using realistic EOSs with Monte Carlo population synthesis based on the mass distribution of NS binaries in our Galaxy to predict the distribution of fates expected. For many EOSs, a significant fraction of the remnants are NSs or supra-massive NSs. This lends support to scenarios where a quickly spinning, highly magnetized NS may be powering an electromagnetic transient. This also indicates that it will be important for future gravitational wave (GW) observatories to focus on high frequencies to study the post merger GW emission. Even in cases where individual GW events are too low in signal to noise to study the post merger signature in detail, the statistics of how many mergers produce NSs versus BHs can be compared with our work to constrain the EOS. To match short gamma-ray burst (SGRB) X-ray afterglow statistics, we find that the stiffest EOSs are ruled out. Furthermore, many popular EOSs require ~60-70% of SGRBs to be from NS-BH mergers rather than just binary NSs.
TL;DR: In this paper, a large grid of extended envelope models and compare these to SN 2016gkg to investigate what constraints can be derived from its light curve, including density profiles for both a convective envelope and an optically thick steady-state wind, which has not typically been considered for Type IIb SNe models.
Abstract: Many Type IIb supernovae (SNe) show a prominent additional early peak in their light curves, which is generally thought to be due to the shock cooling of extended hydrogen-rich material surrounding the helium core of the exploding star. The recent SN 2016gkg was a nearby Type IIb SN discovered shortly after explosion, which makes it an excellent candidate for studying this first peak. We numerically explode a large grid of extended envelope models and compare these to SN 2016gkg to investigate what constraints can be derived from its light curve. This includes exploring density profiles for both a convective envelope and an optically thick steady-state wind, the latter of which has not typically been considered for Type IIb SNe models. We find that roughly $\sim0.02\,M_\odot$ of extended material with a radius of $\approx180-260\,R_\odot$ reproduces the photometric light curve data, consistent with pre-explosion imaging. These values are independent of the assumed density profile of this material, although a convective profile provides a somewhat better fit. We infer from our modeling that the explosion must have occurred within $\approx2-3\,{\rm hrs}$ of the first observed data point, demonstrating that this event was caught very close to the moment of explosion. Nevertheless, our best-fitting one-dimensional models overpredict the earliest velocity measurements, which suggests that the hydrogen-rich material is not distributed in a spherically symmetric manner. We compare this to the asymmetries seen in the SN IIb remnant Cas A, and we discuss the implications of this for Type IIb SN progenitors and explosion models.
TL;DR: In this article, it was shown that heating from exothermic weak reactions plays a significant role in raising the temperature of the WD, which is consistent with different net energies of the convective Urca process.
Abstract: The neutron excess at the time of explosion provides a powerful discriminant among models of Type Ia supernovae. Recent calculations of the carbon simmering phase in single degenerate progenitors have disagreed about the final neutron excess. We find that the treatment of mixing in convection zones likely contributes to the difference. We demonstrate that in MESA models, heating from exothermic weak reactions plays a significant role in raising the temperature of the WD. This emphasizes the important role that the convective Urca process plays during simmering. We briefly summarize the shortcomings of current models during this phase. Ultimately, we do not pinpoint the difference between the results reported in the literature, but show that the results are consistent with different net energetics of the convective Urca process. This problem serves as an important motivation for the development of models of the convective Urca process suitable for incorporation into stellar evolution codes.
TL;DR: Early observations of Type Ia supernovae (SNe Ia) provide a unique probe of their progenitor systems and explosion physics and are used to constrain the white dwarf explosion mechanism as mentioned in this paper.
Abstract: Early observations of Type Ia supernovae (SNe Ia) provide a unique probe of their progenitor systems and explosion physics. Here we report the intermediate Palomar Transient Factory (iPTF) discovery of an extraordinarily young SN Ia, iPTF 16abc. By fitting a power law to our early light curve, we infer that first light for the SN, that is when the SN could have first been detected by our survey, occurred only $0.15\pm_{0.07}^{0.15}$ days before our first detection. In the $\sim$24 hr after discovery, iPTF 16abc rose by $\sim$2 mag, featuring a near-linear rise in flux for $\gtrsim$3 days. Early spectra show strong C II absorption, which disappears after $\sim$7 days. Unlike the extensivelyobserved SN Ia SN 2011fe, the $(B-V)_0$ colors of iPTF 16abc are blue and nearly constant in the days after explosion. We show that our early observations of iPTF 16abc cannot be explained by either SN shock breakout and the associated, subsequent cooling or the SN ejecta colliding with a stellar companion. Instead, we argue that the early characteristics of iPTF 16abc, including (i) the rapid, near-linear rise, (ii) the nonevolving blue colors, and (iii) the strong C II absorption, are the result of either ejecta interaction with nearby, unbound material or vigorous mixing of radioactive $^{56}$Ni in the SN ejecta, or a combination of the two. In the next few years, dozens of very young \textit{normal} SNe Ia will be discovered, and observations similar to those presented here will constrain the white dwarf explosion mechanism.
TL;DR: In this paper, the chemical composition of the most metal-rich star in the Ursa Minor dwarf galaxy, COS 171, is dominated by nucleosynthesis from a low-metallicity, low-mass, sub-Chandrasekhar mass SN Ia.
Abstract: A longstanding problem is identifying the elusive progenitors of Type Ia supernovae (SNe Ia), which can roughly be split into Chandraksekhar and sub-Chandrasekhar mass events. An important difference between these two cases is the nucleosynthetic yield, which is altered by the increased neutron excess in Chandrasekhar progenitors due to their pre-explosion simmering and high central density.
From comparison with theoretical nucleosynthesis yields, we show that the chemical composition of the most metal-rich star in the Ursa Minor dwarf galaxy, COS 171, is dominated by nucleosynthesis from a low-metallicity, low-mass, sub-Chandrasekhar mass SN Ia. Key diagnostic abundance ratios include C/Fe, {\alpha}/Fe, Mn/Fe and Ni/Fe ratios, which could not have been produced by Chandrasekhar-mass SNe Ia, Core-Collapse Type II supernovae or Pair-Instsability supernovae. Strong deficiencies of Ni/Fe, Cu/Fe and Zn/Fe also suggest the absence of alpha-rich freeze-out nucleosynthesis, favoring low-mass WD progenitor SNe Ia. Based on comparisons of the measured Mn/Fe and Si/Fe ratios with detonation models, we estimate a WD mass near 0.95Msun. We also compare Mn/Fe and Ni/Fe ratios to the recent theoretical yields predicted by Shen et al., finding consistent results. To explain the COS 171 [Fe/H], at -1.35 dex, requires dilution of the ejecta from a single SNIa event with ~10^4 Msun of material; this is expected for a SN Ia remnant expanding into a warm interstellar medium with n~1 /cm^3. In the future, finding more stars with the unique chemical signatures we highlight here will be important for constraining the rate and environments of sub-Chandrasekhar SNe Ia.
TL;DR: In this paper, it was shown that heating from exothermic weak reactions plays a significant role in raising the temperature of the WD, which is consistent with different net energies of the convective Urca process.
Abstract: The neutron excess at the time of explosion provides a powerful discriminant among models of Type Ia supernovae. Recent calculations of the carbon simmering phase in single degenerate progenitors have disagreed about the final neutron excess. We find that the treatment of mixing in convection zones likely contributes to the difference. We demonstrate that in MESA models, heating from exothermic weak reactions plays a significant role in raising the temperature of the WD. This emphasizes the important role that the convective Urca process plays during simmering. We briefly summarize the shortcomings of current models during this phase. Ultimately, we do not pinpoint the difference between the results reported in the literature, but show that the results are consistent with different net energetics of the convective Urca process. This problem serves as an important motivation for the development of models of the convective Urca process suitable for incorporation into stellar evolution codes.
University of Pittsburgh1, University of Maryland, College Park2, Goddard Space Flight Center3, Polytechnic University of Catalonia4, Joint Institute for Nuclear Astrophysics5, Arizona State University6, University of Alabama7, Carnegie Institution for Science8, University of Maryland, Baltimore9, University of Texas at Arlington10
TL;DR: In this paper, a new method was proposed to determine ejecta neutronization using Ca and S lines in the X-ray spectra of Type Ia supernova remnants (SNRs).
Abstract: The physical process whereby a carbon--oxygen white dwarf explodes as a Type Ia supernova (SN Ia) remains highly uncertain. The degree of neutronization in SN Ia ejecta holds clues to this process because it depends on the mass and the metallicity of the stellar progenitor, and on the thermodynamic history prior to the explosion. We report on a new method to determine ejecta neutronization using Ca and S lines in the X-ray spectra of Type Ia supernova remnants (SNRs). Applying this method to \textit{Suzaku} data of Tycho, Kepler, 3C 397 and G337.2$-$0.7 in the Milky Way, and N103B in the Large Magellanic Cloud, we find that the neutronization of the ejecta in N103B is comparable to that of Tycho and Kepler, which suggests that progenitor metallicity is not the only source of neutronization in SNe Ia. We then use a grid of SN Ia explosion models to infer the metallicities of the stellar progenitors of our SNRs. The implied metallicities of 3C 397, G337.2$-$0.7, and N103B are major outliers compared to the local stellar metallicity distribution functions, indicating that progenitor metallicity can be ruled out as the origin of neutronization for these SNRs. Although the relationship between ejecta neutronization and equivalent progenitor metallicity is subject to uncertainties stemming from the $^{12}$C$\,$+$^{16}$O reaction rate, which affects the Ca/S mass ratio, our main results are not sensitive to these details.