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A hot and fast ultra-stripped supernova that likely formed a compact neutron star binary

TL;DR: The discovery of iPTF 14gqr is interpreted as evidence for ultra-stripped supernovae that form neutron stars in compact binary systems.
Abstract: Compact neutron star binary systems are produced from binary massive stars through stellar evolution involving up to two supernova explosions. The final stages in the formation of these systems have not been directly observed. We report the discovery of iPTF 14gqr (SN 2014ft), a type Ic supernova with a fast-evolving light curve indicating an extremely low ejecta mass (≈0.2 solar masses) and low kinetic energy (≈2 × 1050 ergs). Early photometry and spectroscopy reveal evidence of shock cooling of an extended helium-rich envelope, likely ejected in an intense pre-explosion mass-loss episode of the progenitor. Taken together, we interpret iPTF 14gqr as evidence for ultra-stripped supernovae that form neutron stars in compact binary systems.

Summary (8 min read)


  • Taken together, the authors interpret iPTF 14gqr as evidence for ultra-stripped supernovae that form neutron stars in compact binary systems.
  • If massive enough, the highly stripped core eventually collapses to produce a faint and fast evolving SN explosion which ejects a small amount of material (7, 8).

Discovery and follow-up of iPTF 14gqr

  • The authors obtained rapid ultraviolet (UV), optical and near-infrared (NIR) follow-up observations of the source, including a sequence of four spectra within 24 hours from the first detection (12).
  • The authors early spectra also exhibit blackbody continua with temperatures consistent with those inferred from the photometry, superimposed with intermediate width emission lines of He II, C III and C IV.
  • Additional constraints based on light travel time arguments also suggest that the envelope was located at r ≤ 6 × 1015 cm from the progenitor (12).

An ultra-stripped progenitor

  • The low ejecta mass and explosion energy, as well as the presence of an extended He-rich envelope, indicate an unusual progenitor channel for iPTF 14gqr.
  • The temporal coincidence of the ejection with the final SN suggests that the envelope was likely associated with an intense pre-SN mass loss episode of the progenitor (12).
  • The timescale of the ejection is similar to that expected for silicon flashes (∼ 2 weeks before explosion) in the terminal evolution of low mass metal cores (29), that have been suggested to lead to elevated mass loss episodes prior to the explosion.
  • The presence of the extended He-rich envelope in iPTF 14gqr along with the lack of He in the low mass of ejecta suggest that the progenitor was highly stripped by a compact companion, such that only a thin He layer was retained on its surface.
  • While wide binaries containing a NS and another compact object may be formed in noninteracting systems of binary massive stars, ultra-stripped SNe have been suggested to precede the formation of almost all compact NS binary systems (8).

Author contributions

  • KD and MMK initiated the study, conducted analysis and wrote the manuscript.
  • DAP, GED and YC conducted Keck and Palomar observations and contributed to data reduction and manuscript preparation.
  • AH conducted the VLA observations and data reduction.
  • TJM and PAM prepared the ultrastripped SN models presented in the paper.
  • EOO, CF, AGY, RL, PEN and ALP contributed to manuscript preparation.

Data and materials availability

  • All photometric data used in this paper are provided in the supplementary material (Table S1 and Table S2), while all spectra are available via the WISeREP repository at https: //
  • The codes used for the ultra-stripped SN modeling are presented in (50), while the synthetic spectra presented in this paper are available at https: //


  • The authors nominally adopt the average MJD 56943.75 ± 0.43 as the explosion date, and calculate all phases with reference to this epoch.
  • The actual explosion could have taken place before the last non-detection depending on the behavior of the early emission.
  • Hence, the authors allow the explosion time to vary as a free parameter in their modeling, and discuss the last non-detection individually in the context of the physical models.

Optical light curves

  • The authors obtained g band photometry of iPTF 14gqr with the P48 CFH12K camera, along with additional follow-up photometry in the Bgri bands with the automated 60-inch telescope at Palomar Observatory (P60; (56)).
  • Point spread function (PSF) photometry was performed on the P48 images using the Palomar Transient Factory Image Differencing and Extraction pipeline (11), while the P60 images were reduced using an automated pipeline (57).
  • Since P60 obtained contemporaneous observations with LCO with much higher signal to noise ratio, the authors chose not to include the LCO data in their analysis.
  • The authors triggered Swift follow-up of the source in the V , B, UVW1 and UVW2 bands with the Swift Ultra-Violet/Optical Telescope (UVOT; (61)) and X-ray follow-up with the Swift X-ray telescope (XRT; (62)).
  • The corresponding flux limits are summarized in Table S2.

Optical spectroscopy

  • All spectra were reduced using standard tasks in IRAF and IDL, including wavelength calibration using arc lamps and flux calibration using standard stars.
  • The spectroscopic observations are summarized in Table S3.
  • The authors were unable to obtain a high signal-to-noise ratio (SNR) spectrum of the transient at epochs beyond≈ 30 days from light curve peak.
  • The authors also obtained a spectrum of the apparent host galaxy nucleus with APO DIS on 2014 October 14 which was found to exhibit narrow emission lines of Hα, Hβ, [SII], [NII], [OII] and [OIII].
  • Additionally, the authors obtained one spectrum of the transient location ∼ 800 days after the explosion as a part of a spectroscopic mask observation and did not detect any nebular emission features at the source location.

NIR imaging

  • The data were processed using a custom reduction pipeline including flat-fielding and sky subtraction as well as special filtering steps to remove artifacts associated with the replacement detector in use at the time.
  • The source is well-detected in all three filters in the final stacks.

Radio observations

  • Each observation was performed using C-band (centered at 6.1 GHz) and K-band (centered at 22 GHz) in the C configuration.
  • The authors analyzed the data with standard AIPS routines, using 3C 48 as the flux calibrator and NVSS J234029+264157 as the phase calibrator.
  • The authors observations resulted in null detections in both bands at each epoch.
  • The observational limits are 11.6 microJanskys (µJy) and 11.7µJy at C-band and K-band [measured as the 1σ root-mean-squared (RMS) noise of the reduced image], respectively, on 2014 October 15.

Late-time imaging

  • The data were reduced and processed with standard image reduction procedures in lpipe (73).
  • This constrains the presence of any stellar association at the location of the transient toMR >−11.4 mag andMg >−11.1 mag.
  • Late-time images of the host galaxy region are shown in Figure S14.

Host environment spectroscopy

  • IPTF 14gqr was discovered in the outskirts of an extended spiral galaxy showing clear signs of tidal interactions with nearby companions.
  • The authors selected a total of 32 extended sources classified as galaxies (including the apparent spiral host) in the Sloan Digital Sky Survey (SDSS) within 5.4′ of the transient location (out of a total of 254 objects) to place the slits on the spectroscopic mask, along with one slit at the location of the transient.
  • The spectra were reduced with standard routines in IRAF.
  • Amongst the galaxies whose redshifts could be determined, the faintest source had SDSS magnitude of r ≈ 22.11 mag, while the same for galaxies within 100 kpc of the transient was r ≈ 21.60 mag.

Basic properties

  • The authors find the peak magnitudes, time of maximum and corresponding rise time (between assumed explosion time and peak of light curve) in each filter by fitting a low order polynomial to the photometry near peak.
  • The absence of photometric data points beyond ∼ 10 days after peak does not allow us to estimate the more commonly used quantity ∆m15, the drop in magnitude in 15 days after light curve peak.
  • The uncertainties on these parameters were estimated by Monte Carlo sampling of 1000 realizations of the photometric data points using their associated uncertainties.
  • The rise times of the light curves are shorter in the bluer bands as typically observed in Type Ib/c SNe (74).
  • The rapid first peak of the light curve is perhaps the most distinguishing feature of iPTF 14gqr when compared to this sample of transients, and hence the authors compare this first peak to that of other known SNe exhibiting double peaked light curves in Figure S5.

Optical / UV SEDs

  • In particular, the authors have two epochs with photometric data from all optical / UV bands, and the resulting blackbody SEDs are shown in Figure 3.
  • The first epoch was within the first peak of the light curve (at ≈ 14 hours after explosion), where the UV / optical photometry is consistent with a blackbody of temperature > 30,000 K.
  • This spectrum is also well described by a blackbody consistent with the photometric fit within the uncertainties.
  • The UV photometric points are found to be significantly fainter than the optical blackbody fit at this epoch (with T ∼ 10000 K), which is indicative of significant line blanketing at UV wavelengths (as expected from Fe group elements in the ejecta).
  • The NIR photometric magnitudes obtained near this epoch (≈ 1 day earlier) are also consistent with the optical blackbody fit.

Bolometric light curve

  • The authors construct a bolometric light curve of iPTF 14gqr using three methods.
  • The authors first fit a Planck blackbody function to the observed photometry at all epochs where they have detections in 3 or more filters to obtain a best-fitting blackbody and corresponding temperature, radius and luminosity.
  • The corresponding radius and temperature evolution is also shown in Figure 4.
  • Since the authors do not have simultaneous spectroscopy with all epochs of multi-band photometry, they choose to scale the fluxes obtained from a trapezoidal integration by an average factor of 1.48, while conservatively adding an uncertainty of 10% to account for the possible errors on this fraction.
  • Hence, the authors use the pseudo-bolometric luminosities for modeling the properties of the second light curve peak.

First peak

  • The spectroscopic sequence for iPTF 14gqr is shown in Figure 3.
  • The He II λ4686 line is a common prominent feature of the flash ionized spectra of these events, and the C III λ4650 and C IV λ5801 lines were also observed in iPTF 13ast.
  • The spectral evolution of the C high ionization lines in the early spectra is very similar to that seen in the WC sub-type evolution of galactic Wolf-Rayet stars (82, 83).
  • In particular, the C III λ5696 / C IV λ5801 ratio increases in the later and cooler sub-types (WC7 - WC9) of this class, consistent with the increasing ratio observed in this source with decreasing photospheric temperature.

Photospheric phase

  • The authors compare the photospheric phase spectra of iPTF 14gqr to those of other fast and normal Type Ic SNe in Figure S7.
  • The comparison clearly shows that the photospheric spectra of iPTF 14gqr remain relatively blue and featureless compared to those of the normal Type Ic SNe (SN 1994I and SN 2004aw) at similar phases.
  • SNe generally also exhibit the nearby Fe II lines of λ5018 and λ4924, which are blended into a single blue-shifted feature with respect to the λ5169 line .
  • The three features are blended into a single broad absorption component in the case of the high velocity Type Ic-BL SNe, and can potentially cause errors in a velocity measurement if this effect is not taken into account (86).

Early nebular phase

  • The authors final spectrum (with good SNR) was obtained ≈ 34 days after explosion, and show that the source was transitioning very early into the nebular phase.
  • The authors compare the only nebular spectrum of iPTF 14gqr to the nebular spectra of other Type I SNe which exhibited an early nebular transition at similar phases in Figure S8.
  • The best spectral match to iPTF 14gqr in this sample are to that of the Ca-rich gap transients PTF 10iuv and SN 2012hn.


  • Arnett Model for the main peak Type I SNe which do not show signs of interaction (such as iPTF 14gqr) are predominantly powered by energy released in the radioactive decay chain of 56Ni to 56Co to 56Fe.
  • The best-fitting explosion time is earlier than their last non-detection (0.43 days before assumed explosion), although the predicted flux from the Arnett model would be below their detection threshold.
  • The authors show the degeneracies between the various model parameters in Figure S9, where the degeneracy between t0 and τM is particularly prominent, since τM controls the width of the light curve.
  • As in the case of the Arnett model, the authors expect the simple assumptions of this model to produce values which are only approximately correct.

Interaction with a companion

  • Such interaction signatures have been previously observed in some Type Ia SNe ( (97–99); see (16) for a review of SN classification) where comparison of the data to theoretical models (100) allows the inference of the orbital separation of the binary system.
  • The authors see no evidence for the presence of broad lines, as expected from the reverse shock produced in the ejecta-companion interaction.
  • The authors consider the photometric properties of the first peak in a companion interaction scenario.
  • As shown in (100), the early luminosity evolution depends on the viewing angle of the observer, where the excess flux is most prominent along the direction of the companion and relatively weak along directions perpendicular to or oriented away from the companion.
  • This is readily apparent when comparing the luminosity and temperature evolution of the model with the observations – the analytical model predicts a luminosity evolution scaling with time as t−1/2, which is almost the same as the color temperature evolution, which scales as t−37/72.

Analysis of early spectra

  • The early spectra of iPTF 14gqr exhibit prominent emission features of highly ionized He and C that are broader (FWHM ∼ 3000 km s−1) than that typically observed in the flash ionized spectra of other core-collapse events.
  • The inferred radius of the optically thin material is larger than the envelope producing the early shock cooling emission as seen in the light curve, and suggests that the highly ionized lines likely arise from a lower density extension of the same envelope.
  • The authors thus constrain the first spectrum to have been taken between ≈ +14 h (for the assumed explosion time) and ≈ +36 h after explosion (for an explosion at 0.92 days before the assumed time).
  • Comparing to their observations, the authors note that the blue-shifted peak of the λ4686 feature and C III λ5696 lines in the +13.9 h and +25.2 h spectra can potentially be explained by LTT effects.

Radio analysis

  • Radio emission in SNe arises from synchrotron radiation produced by shock accelerated electrons in the circumstellar medium.
  • The authors show a comparison of the observed radio light curves of other Type Ib/c SNe to the radio limits on iPTF 14gqr in Figure S11.
  • Since their observations were obtained at relatively early times after the explosion (within ∼ 10 days of explosion), the authors assume that the shock velocity is constant, instead of assuming a density structure for the outer envelope and a corresponding velocity evolution.
  • The 22 GHz radio upper limits barely intersect the optically thick locus of the models, while the 6 GHz upper limits are well above the optically thick locus.
  • Hence, these upper limits do not constrain the cicrumstellar environment.

Ultra-stripped SN modeling

  • The authors compare the bolometric light curve and peak photospheric spectra of iPTF 14gqr to models of ultra-stripped SNe (as described in (7,28)) in Figure 5.
  • Hence, the authors compare these models to the bolometric luminosity for the first peak, and to the pseudo-bolometric luminosity for the second peak.
  • This assumption is valid because most of the lines are formed just above the photosphere.
  • As shown earlier, the low γ-ray opacity of the ejecta also suggest that the lack of He excitation lines is likely due to a genuine low abundance of He in the ejecta, even in the limit of very low 56Ni mixing.
  • The authors modeling of the peak photospheric spectra and light curve of iPTF 14gqr in the context of ultra-stripped SNe suggest that the 56Ni needs to be centrally located in order to explain the lack of line blanketing at < 4000 Å near peak optical light.

Host identification

  • IPTF 14gqr was discovered at a large projected offset of ≈ 24′′ from the nearest apparent host galaxy, a two-tailed spiral galaxy showing signs of tidal interaction with at least three companion galaxies.
  • The authors nominally adopt this galaxy as the host of iPTF 14gqr, but also discuss several other possible scenarios below.
  • It was not possible to rule out the presence of a faint dwarf galaxy or globular cluster underneath the transient.
  • The authors thus undertook deep late-time imaging of the host region and did not find any stellar association down to absolute magnitude limits ofMr > −11.4 mag and Mg > −11.1 mag.
  • They are not stringent enough to rule out the entire population of dwarf galaxies and stellar clusters given the observed luminosity function of these systems in the local group (118–120).

Host properties

  • The authors estimate the metallicity of the host galaxy using the pyMCZ code (123) to calculate the host oxygen metallicity (12 + log(O/H)).
  • The authors fit the broadband photometry measurements of the galaxy to estimate parameters for the host stellar population.
  • Thus, taken at face value, the host galaxy of iPTF 14gqr is indeed similar to the typical host galaxies of Type Ic SNe.

Explosion site properties

  • The 29 kpc central offset of the location of iPTF 14gqr corresponds to a host normalized offset of≈.
  • 8 Reff (where Reff is the half-light radius of the galaxy), placing this source at the extreme high end of the distribution of host offsets found for all SNe ( (135); (77)).
  • IPTF 14gqr has the second largest host offset in terms of physical distance when compared to the PTF sample of core-collapse SNe, with SN 2010jp (PTF 10aaxi; (136)) as the only other corecollapse event with a larger offset (≈ 33 kpc).
  • This would be in contrast to the general trend where Type Ib/c SNe are found to be more likely to be associated with H II regions than Type II events, in accordance with the shorter lifetimes of their more massive progenitors (139,141).

Tidally interacting environment

  • As shown in Figure S2, the galaxies marked Obj2 and Obj3 were found to be at a redshift consistent with that of the nominal host Obj1.
  • The small systemic velocities arise in particular due to the requirement of wide binary systems that can survive the common envelope (CE) ejection after the High Mass X-ray Binary (HMXB) phase (see (40) for a review).
  • There are several possible explanations of this discrepancy.
  • The authors late-time images of the host galaxy clearly show that the tidal tails of the host galaxy extend to larger projected distances compared to the offset of iPTF 14gqr, and hence a faint tidal tail at the location of iPTF 14gqr is not unexpected.
  • There are also known examples of tidal dwarf galaxies forming in tidal tails that can host star formation several 100 Myrs after the formation of the parent tail (144, 148).

The nature of the companion star

  • Stripping of the outer H and He envelopes in stripped envelope SNe can arise either due to mass loss via strong winds or due to stripping by a binary companion (2).
  • The authors thus first consider the possibility of explaining the highly stripped progenitor of iPTF 14gqr from single star evolution.
  • Several theoretical calculations for a wide range of stellar mass loss rates and metallicity show that the minimum progenitor mass from single star evolution of massive stars is > 5 M (152– 154), and hence the authors expect ejecta masses of>.
  • This is again an order of magnitude lower than these predictions.
  • This allows only the most compact companions to explain the stripping.

The remnant of the explosion

  • When considering the required presence of a close compact companion to explain the low ejecta mass, a possible explanation of the expanding envelope could be due to a common envelope ejection preceding the terminal core-collapse.
  • Multiple theoretical studies on the evolution of compact.
  • He stars indeed suggest that they undergo rapid expansion at the onset of the He shell burning phase and as they approach core-collapse, reaching radii of the order of 102 − 103 R (162).
  • The peak luminosity of iPTF 14gqr is much larger than those of the Ca-rich gap transients, which occupy the luminosity ‘gap’ between novae and SNe (peak absolute magnitude −15.5 ≥ Mpeak ≥ −16.5).

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TL;DR: In this paper, a suite of seven 3D supernova simulations of non-rotating low-mass progenitors using multi-group neutrino transport is presented, where the mass outflow rate already exceeds the accretion rate onto the proto-neutron star and the mass and angular momentum of the compact remnant have closely approached their final value, barring the possibility of later fallback.
Abstract: We present a suite of seven 3D supernova simulations of non-rotating low-mass progenitors using multi-group neutrino transport. Our simulations cover single star progenitors with zero-age main sequence masses between $9.6 M_\odot$ and $12.5 M_\odot$ and (ultra)stripped-envelope progenitors with initial helium core masses between $2.8 M_\odot$ and $3.5 M_\odot$. We find explosion energies between $0.1\,\mathrm{Bethe}$ and $0.4\,\mathrm{Bethe}$, which are still rising by the end of the simulations. Although less energetic than typical events, our models are compatible with observations of less energetic explosions of low-mass progenitors. In six of our models, the mass outflow rate already exceeds the accretion rate onto the proto-neutron star, and the mass and angular momentum of the compact remnant have closely approached their final value, barring the possibility of later fallback. While the proto-neutron star is still accelerated by the gravitational tug of the asymmetric ejecta, the acceleration can be extrapolated to obtain estimates for the final kick velocity. We obtain gravitational neutron star masses between $1.22 M_\odot$ and $1.44 M_\odot$, kick velocities between $11\, \mathrm{km}\, \mathrm{s}^{-1}$ and $695\, \mathrm{km}\, \mathrm{s}^{-1}$, and spin periods from $20\, \mathrm{ms}$ to $2.7\,\mathrm{s}$, which suggests that typical neutron star birth properties can be naturally obtained in the neutrino-driven paradigm. We find a loose correlation between the explosion energy and the kick velocity. There is no indication of spin-kick alignment, but a correlation between the kick velocity and the neutron star angular momentum, which needs to be investigated further as a potential point of tension between models and observations.

149 citations

Cites background from "A hot and fast ultra-stripped super..."

  • ...A number of promising ultra-stripped supernova candidates have been identified based on observed properties of rapidly decaying supernova light curves (Drout et al. 2013; Moriya et al. 2017; De et al. 2018)....


  • ...…explosion energies and nickel masses observed for hydrogen-rich low-mass progenitors (Pejcha & Prieto 2015) as well as for the ultra-stripped supernova candidates SN 2005ek (Drout et al. 2013; Tauris et al. 2013), SN 2010X (Kasliwal et al. 2010; Moriya et al. 2017) and iPTF 14gqr (De et al. 2018)....


Journal ArticleDOI

134 citations

Cites background from "A hot and fast ultra-stripped super..."

  • ...See Woosley (2019) for further details and a comparison to SN 2014ft (De et al. 2018)....


  • ...Some subset might be fast blue optical transients (Kleiser et al. 2018; Woosley 2019), SN 2014ft-like objects (De et al. 2018), Type Ibn supernovae, or even Type Ic-BL supernovae....


Journal ArticleDOI
TL;DR: In this paper, light curves, explosion energies, and remnant masses for a grid of supernovae resulting from massive helium stars that have been evolved including mass loss are calculated for a set of stars in interacting systems.
Abstract: Light curves, explosion energies, and remnant masses are calculated for a grid of supernovae resulting from massive helium stars that have been evolved including mass loss. These presupernova stars should approximate the results of binary evolution for stars in interacting systems that lose their envelopes close to the time of helium core ignition. Initial helium star masses are in the range 2.5 to 40\,\Msun, which correspond to main sequence masses of about 13 to 90\,\Msun. Common Type Ib and Ic supernovae result from stars whose final masses are approximately 2.5 to 5.6\,\Msun. For heavier stars, a large fraction of collapses lead to black holes, though there is an island of explodability for presupernova masses near 10\,\Msun. The median neutron star mass in binaries is 1.35--1.38\,\Msun \ and the median black hole mass is between 9 and 11\,\Msun. Even though black holes less massive than 5 \Msun\ are rare, they are predicted down to the maximum neutron star mass. There is no empty ``gap'', only a less populated mass range. For standard assumptions regarding the explosions and nucleosynthesis, the models predict light curves that are fainter than the brighter common Type Ib and Ic supernovae. Even with a very liberal, but physically plausible increase in $^{56}$Ni production, the highest energy models are fainter, at peak, than 10$^{42.6}$\,erg\,s$^{-1}$, and very few approach that limit. The median peak luminosity ranges from 10$^{42.0}$ to 10$^{42.3}$\,erg\,s$^{-1}$. Possible alternatives to the standard neutrino-powered and radioactive-illuminated models are explored. Magnetars are a promising alternative. Several other unusual varieties of Type I supernovae at both high and low mass are explored.

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Journal ArticleDOI
Mansi M. Kasliwal1, Shreya Anand1, Tomas Ahumada2, Robert Stein3, Ana Sagués Carracedo4, Igor Andreoni1, Michael W. Coughlin5, Michael W. Coughlin1, Leo Singer2, Leo Singer6, E. C. Kool4, Kaushik De1, Harsh Kumar7, Mouza Almualla8, Yuhan Yao1, Mattia Bulla4, Dougal Dobie9, Dougal Dobie10, Dougal Dobie11, Simeon Reusch3, Daniel A. Perley12, S. Bradley Cenko6, S. Bradley Cenko2, Varun Bhalerao7, David L. Kaplan13, Jesper Sollerman4, Ariel Goobar4, Chris M. Copperwheat12, Eric C. Bellm14, G. C. Anupama15, Alessandra Corsi16, Samaya Nissanke17, Ivan Agudo18, Ashot Bagdasaryan1, Sudhanshu Barway15, Justin Belicki1, Joshua S. Bloom19, Joshua S. Bloom20, Bryce Bolin1, David A. H. Buckley, Kevin B. Burdge1, Rick Burruss1, M. D. Caballero-Garcia, Chris Cannella1, A. J. Castro-Tirado21, A. J. Castro-Tirado18, David O. Cook1, Jeff Cooke9, Virginia Cunningham2, Aishwarya S. Dahiwale1, Kunal Deshmukh7, S. Dichiara2, S. Dichiara6, Dmitry A. Duev1, Anirban Dutta15, Michael Feeney1, Anna Franckowiak, Sara Frederick2, Christoffer Fremling1, Avishay Gal-Yam22, Pradip Gatkine2, Shaon Ghosh23, Daniel A. Goldstein1, V. Zach Golkhou14, Matthew J. Graham1, Melissa L. Graham1, M. Hankins1, George Helou1, Y. D. Hu18, Y. D. Hu24, Wing-Huen Ip25, Amruta Jaodand1, Viraj Karambelkar1, Albert K. H. Kong26, Marek Kowalski3, Maitreya Khandagale7, Shrinivas R. Kulkarni1, Brajesh Kumar15, Russ R. Laher1, Kwan-Lok Li26, Ashish Mahabal1, Frank J. Masci1, Adam A. Miller27, Adam A. Miller28, Moses Mogotsi, S. R. Mohite13, Kunal Mooley1, Przemek Mróz1, Jeffrey A. Newman29, Chow-Choong Ngeow25, S. R. Oates30, Atharva Sunil Patil25, Shashi B. Pandey31, M. Pavana15, Elena Pian32, Reed Riddle1, R. Sanchez-Ramirez, Yashvi Sharma1, Avinash Singh15, Roger Smith1, Maayane T. Soumagnac19, Maayane T. Soumagnac22, Kirsty Taggart12, Hanjie Tan25, Anastasios Tzanidakis1, Eleonora Troja2, Eleonora Troja6, A. F. Valeev33, Richard Walters1, G. Waratkar7, Sara Webb9, Po-Chieh Yu25, Bin-Bin Zhang34, Rongpu Zhou19, Jeffry Zolkower1 
TL;DR: In this article, the authors present a systematic search for optical counterparts to 13 GW triggers involving at least one neutron star during LIGO/Virgo's third observing run (O3).
Abstract: We present a systematic search for optical counterparts to 13 gravitational wave (GW) triggers involving at least one neutron star during LIGO/Virgo's third observing run (O3). We searched binary neutron star (BNS) and neutron star black hole (NSBH) merger localizations with the Zwicky Transient Facility (ZTF) and undertook follow-up with the Global Relay of Observatories Watching Transients Happen (GROWTH) collaboration. The GW triggers had a median localization area of 4480 deg², median distance of 267Mpc and false alarm rates ranging from 1.5 yr⁻¹ to 10⁻²⁵ yr⁻¹. The ZTF coverage had a median enclosed probability of 39%, median depth of 20.8 mag, and median time lag between merger and the start of observations of 1.5 hr. The O3 follow-up by the GROWTH team comprised 340 UltraViolet/Optical/InfraRed (UVOIR) photometric points, 64 OIR spectra, and 3 radio images. We find no promising kilonova (radioactivity-powered counterpart) and we show how to convert the upper limits to constrain the underlying kilonova luminosity function. Initially, we assume that all GW triggers are bonafide astrophysical events regardless of false alarm rate and that kilonovae accompanying BNS and NSBH mergers are drawn from a common population, and later, we relax these assumptions. Assuming that all kilonovae are at least as luminous as the discovery magnitude of GW170817 (-16.1 mag), we calculate that our joint probability of detecting zero kilonovae is only 4.2%. If we assume that all kilonovae are brighter than -16.6 mag (extrapolated peak magnitude of GW170817) and fade at a rate of 1 mag day⁻¹ (similar to GW170817), the joint probability of zero detections is 7%. If we separate the NSBH and BNS populations, the joint probability of zero detections, assuming all kilonovae are brighter than -16.6 mag, is 9.7% for NSBH and 7.9% for BNS mergers. Moreover, no more than 10⁻⁴ or o > 30° to be consistent with our limits. We look forward to searches in the fourth GW observing run; even 17 neutron star mergers with only 50% coverage to a depth of -16 mag would constrain the maximum fraction of bright kilonovae to <25%.

53 citations

Journal ArticleDOI
TL;DR: Ho et al. as discussed by the authors presented detailed observations of ZTF18abukavn (SN2018gep), which was discovered in high-cadence data from the Zwicky Transient Facility as a rapidly rising (1.4 ± 0.1 mag hr-1) and luminous (Mg, peak = -20 mag) transient.
Abstract: Author(s): Ho, AYQ; Goldstein, DA; Schulze, S; Khatami, DK; Perley, DA; Ergon, M; Gal-Yam, A; Corsi, A; Andreoni, I; Barbarino, C; Bellm, EC; Blagorodnova, N; Bright, JS; Burns, E; Cenko, SB; Cunningham, V; De, K; Dekany, R; Dugas, A; Fender, RP; Fransson, C; Fremling, C; Goldstein, A; Graham, MJ; Hale, D; Horesh, A; Hung, T; Kasliwal, MM; M. Kuin, NP; Kulkarni, SR; Kupfer, T; Lunnan, R; Masci, FJ; Ngeow, CC; Nugent, PE; Ofek, EO; Patterson, MT; Petitpas, G; Rusholme, B; Sai, H; Sfaradi, I; Shupe, DL; Sollerman, J; Soumagnac, MT; Tachibana, Y; Taddia, F; Walters, R; Wang, X; Yao, Y; Zhang, X | Abstract: We present detailed observations of ZTF18abukavn (SN2018gep), discovered in high-cadence data from the Zwicky Transient Facility as a rapidly rising (1.4 ± 0.1 mag hr-1) and luminous (Mg,peak = -20 mag) transient. It is spectroscopically classified as a broad-lined stripped-envelope supernova (Ic-BL SN). The high peak luminosity (Lbol ≳ 3 × 1044 erg s-1), the short rise time (trise = 3 days in g band), and the blue colors at peak (g-r ∼ -0.4) all resemble the high-redshift Ic-BL iPTF16asu, as well as several other unclassified fast transients. The early discovery of SN2018gep (within an hour of shock breakout) enabled an intensive spectroscopic campaign, including the highest-temperature (Teff ≳ 40,000 K) spectra of a stripped-envelope SN. A retrospective search revealed luminous (Mg ∼ Mr ≈ mag) emission in the days to weeks before explosion, the first definitive detection of precursor emission for a Ic-BL. We find a limit on the isotropic gamma-ray energy release E γ,iso l 4.9 × 10 48 erg, a limit on X-ray emission LX l 1040 erg s-1, and a limit on radio emission ν Lν ≲ 1037 erg s-1. Taken together, we find that the early (l 10 days) data are best explained by shock breakout in a massive shell of dense circumstellar material (0.02 M⊙) at large radii (3 × 1014 cm) that was ejected in eruptive pre-explosion mass-loss episodes. The late-time (g 10 days) light curve requires an additional energy source, which could be the radioactive decay of Ni-56.

44 citations

Cites background or methods from "A hot and fast ultra-stripped super..."

  • ...For example, the first peak observed in iPTF14gqr (De et al. 2018) was short-lived (2 days) and attributed to shock-cooling emission from material stripped by a compact companion. iPTF14gqr is different in a number of ways from SN2018gep: the spectra showed high-ionization emission lines, including…...


  • ...Under the assumption that the light curve represented postshock cooling emission, De et al. (2018) and Whitesides et al. (2017) both used one-zone analytic models from Piro (2015) to estimate the properties of the explosion and the CSM....


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Journal ArticleDOI
TL;DR: The Two Micron All Sky Survey (2MASS) as mentioned in this paper collected 25.4 Tbytes of raw imaging data from two dedicated 1.3 m diameter telescopes located at Mount Hopkins, Arizona and CerroTololo, Chile.
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Abstract: The parameterized extinction data of Fitzpatrick and Massa (1986, 1988) for the ultraviolet and various sources for the optical and near-infrared are used to derive a meaningful average extinction law over the 3.5 micron to 0.125 wavelength range which is applicable to both diffuse and dense regions of the interstellar medium. The law depends on only one parameter R(V) = A(V)/E(B-V). An analytic formula is given for the mean extinction law which can be used to calculate color excesses or to deredden observations. The validity of the law over a large wavelength interval suggests that the processes which modify the sizes and compositions of grains are stochastic in nature and very efficient.

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TL;DR: The emcee algorithm as mentioned in this paper is a Python implementation of the affine-invariant ensemble sampler for Markov chain Monte Carlo (MCMC) proposed by Goodman & Weare (2010).
Abstract: We introduce a stable, well tested Python implementation of the affine-invariant ensemble sampler for Markov chain Monte Carlo (MCMC) proposed by Goodman & Weare (2010). The code is open source and has already been used in several published projects in the astrophysics literature. The algorithm behind emcee has several advantages over traditional MCMC sampling methods and it has excellent performance as measured by the autocorrelation time (or function calls per independent sample). One major advantage of the algorithm is that it requires hand-tuning of only 1 or 2 parameters compared to ~N2 for a traditional algorithm in an N-dimensional parameter space. In this document, we describe the algorithm and the details of our implementation. Exploiting the parallelism of the ensemble method, emcee permits any user to take advantage of multiple CPU cores without extra effort. The code is available online at under the GNU General Public License v2.

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TL;DR: The solar chemical composition is an important ingredient in our understanding of the formation, structure, and evolution of both the Sun and our Solar System as discussed by the authors, and it is an essential refer...
Abstract: The solar chemical composition is an important ingredient in our understanding of the formation, structure, and evolution of both the Sun and our Solar System. Furthermore, it is an essential refer ...

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Journal ArticleDOI
TL;DR: In this paper, the authors measured the difference between the measured and predicted colors of a star, as derived from stellar parameters from the Sloan Extension for Galactic Understanding and Exploration Stellar Parameter Pipeline, and achieved uncertainties of 56, 34, 25, and 29 mmag in the colors u − g, g − r, r − i, and i − z, per star.
Abstract: We present measurements of dust reddening using the colors of stars with spectra in the Sloan Digital Sky Survey. We measure reddening as the difference between the measured and predicted colors of a star, as derived from stellar parameters from the Sloan Extension for Galactic Understanding and Exploration Stellar Parameter Pipeline. We achieve uncertainties of 56, 34, 25, and 29 mmag in the colors u – g, g – r, r – i, and i – z, per star, though the uncertainty varies depending on the stellar type and the magnitude of the star. The spectrum-based reddening measurements confirm our earlier "blue tip" reddening measurements, finding reddening coefficients different by –3%, 1%, 1%, and 2% in u – g, g – r, r – i, and i – z from those found by the blue tip method, after removing a 4% normalization difference. These results prefer an RV = 3.1 Fitzpatrick reddening law to O'Donnell or Cardelli et al. reddening laws. We provide a table of conversion coefficients from the Schlegel et al. (SFD) maps of E(B – V) to extinction in 88 bandpasses for four values of RV , using this reddening law and the 14% recalibration of SFD first reported by Schlafly et al. and confirmed in this work.

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