Person: Margutti, Raffaella
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Margutti
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Raffaella
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Margutti, Raffaella
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Publication Slowly Fading Super-Luminous Supernovae That Are Not Pair-Instability Explosions(Nature Publishing Group, 2013) Nicholl, M.; Smartt, S. J.; Jerkstrand, A.; Inserra, C.; McCrum, M.; Kotak, R.; Fraser, M.; Wright, D.; Chen, T.-W.; Smith, K.; Young, D. R.; Sim, S. A.; Valenti, S.; Howell, D. A.; Bresolin, F.; Kudritzki, R. P.; Tonry, J. L.; Huber, M. E.; Rest, A.; Pastorello, A.; Tomasella, L.; Cappellaro, E.; Benetti, S.; Mattila, S.; Kankare, E.; Kangas, T.; Leloudas, G.; Sollerman, J.; Taddia, F.; Berger, E.; Chornock, R; Narayan, Gautham; Stubbs, Christopher; Foley, R. J.; Lunnan, R; Soderberg, Alicia; Sanders, Nathan Edward; Milisavljevic, Danny; Margutti, Raffaella; Kirshner, Robert; Elias-Rosa, N.; Morales-Garoffolo, A.; Taubenberger, S.; Botticella, M. T.; Gezari, S.; Urata, Y.; Rodney, S.; Riess, A. G.; Scolnic, D.; Wood-Vasey, W. M.; Burgett, W. S.; Chambers, K.; Flewelling, H. A.; Magnier, E. A.; Kaiser, N.; Metcalfe, N.; Morgan, J.; Price, P. A.; Sweeney, W.; Waters, C.Super-luminous supernovae that radiate more than 10\(^{44}\) ergs per second at their peak luminosity have recently been discovered in faint galaxies at redshifts of 0.1–4. Some evolve slowly, resembling models of ‘pair-instability’ supernovae. Such models involve stars with original masses 140–260 times that of the Sun that now have carbon–oxygen cores of 65–130 solar masses. In these stars, the photons that prevent gravitational collapse are converted to electron–positron pairs, causing rapid contraction and thermonuclear explosions. Many solar masses of \(^{56}\)Ni are synthesized; this isotope decays to \(^{56}\)Fe via \(^{56}\)Co, powering bright light curves. Such massive progenitors are expected to have formed from metal-poor gas in the early Universe. Recently, supernova 2007bi in a galaxy at redshift 0.127 (about 12 billion years after the Big Bang) with a metallicity one-third that of the Sun was observed to look like a fading pair-instability supernova. Here we report observations of two slow-to-fade super-luminous supernovae that show relatively fast rise times and blue colours, which are incompatible with pair-instability models. Their late-time light-curve and spectral similarities to supernova 2007bi call the nature of that event into question. Our early spectra closely resemble typical fast-declining super-luminous supernovae, which are not powered by radioactivity. Modelling our observations with 10–16 solar masses of magnetar-energized ejecta demonstrates the possibility of a common explosion mechanism. The lack of unambiguous nearby pair-instability events suggests that their local rate of occurrence is less than 6 × 10\(^{−6}\) times that of the core-collapse rate.Publication Rapidly evolving and luminous transients from Pan-STARRS1(IOP Publishing, 2014) Drout, Maria Rebecca; Chornock, R; Soderberg, Alicia; Sanders, Nathan Edward; McKinnon, R.; Rest, Armin; Foley, R. J.; Milisavljevic, Danny; Margutti, Raffaella; Berger, Edo; Calkins, Michael; Fong, W; Gezari, S.; Huber, M. E.; Kankare, E.; Kirshner, Robert; Leibler, C.; Lunnan, R; Mattila, S.; Marion, G. H.; Narayan, Gautham; Riess, A. G.; Roth, K. C.; Scolnic, D.; Smartt, S. J.; Tonry, J. L.; Burgett, W. S.; Chambers, K. C.; Hodapp, K. W.; Jedicke, R.; Kaiser, N.; Magnier, E. A.; Metcalfe, N.; Morgan, J. S.; Price, P. A.; Waters, C.In the past decade, several rapidly evolving transients have been discovered whose timescales and luminosities are not easily explained by traditional supernovae (SNe) models. The sample size of these objects has remained small due, at least in part, to the challenges of detecting short timescale transients with traditional survey cadences. Here we present the results from a search within the Pan-STARRS1 Medium Deep Survey (PS1-MDS) for rapidly evolving and luminous transients. We identify 10 new transients with a time above half-maximum (t 1/2) of less than 12 days and –16.5 > M > –20 mag. This increases the number of known events in this region of SN phase space by roughly a factor of three. The median redshift of the PS1-MDS sample is z = 0.275 and they all exploded in star-forming galaxies. In general, the transients possess faster rise than decline timescale and blue colors at maximum light (g P1 – r P1 lesssim –0.2). Best-fit blackbodies reveal photospheric temperatures/radii that expand/cool with time and explosion spectra taken near maximum light are dominated by a blue continuum, consistent with a hot, optically thick, ejecta. We find it difficult to reconcile the short timescale, high peak luminosity (L > 1043 erg s–1), and lack of UV line blanketing observed in many of these transients with an explosion powered mainly by the radioactive decay of 56Ni. Rather, we find that many are consistent with either (1) cooling envelope emission from the explosion of a star with a low-mass extended envelope that ejected very little (<0.03 M ☉) radioactive material, or (2) a shock breakout within a dense, optically thick, wind surrounding the progenitor star. After calculating the detection efficiency for objects with rapid timescales in the PS1-MDS we find a volumetric rate of 4800-8000 events yr–1 Gpc–3 (4%-7% of the core-collapse SN rate at z = 0.2).Publication A Decade of Short-Duration Gamma-Ray Burst Broad-Band Afterglows: Energetics, Circumburst Densities, and Jet Opening Angles(IOP Publishing, 2015) Fong, W.; Berger, Edo; Margutti, Raffaella; Zauderer, BWe present a comprehensive catalog and analysis of broad-band afterglow observations for 103 short duration gamma-ray bursts (GRBs), comprised of all short GRBs from November 2004 to March 2015 with prompt follow-up observations in the X-ray, optical, near-infrared and/or radio bands. These afterglow observations have uncovered 71 X-ray detections, 30 optical/NIR detections, and 4 radio detections. Employing the standard afterglow synchrotron model, we perform joint probability analyses for a subset of 38 short GRBs with wellsampled light curves to infer the burst isotropic-equivalent energies and circumburst densities. For this subset, we find median isotropic-equivalent γ-ray and kinetic energies of Eγ,iso ≈ 2 × 1051 erg, and EK,iso ≈ (1 − 3) × 1051 erg, respectively, depending on the values of the model input parameters. We further find that short GRBs occur in low-density environments, with a median density of n ≈ (3 − 15) × 10−3 cm−3 , and that ≈ 80 − 95% of bursts have densities of n . 1 cm−3. We investigate trends between the circumburst densities and host galaxy properties, and find that events located at large projected offsets of & 10 effective radii from their hosts exhibit particularly low densities of n . 10−4 cm−3 , consistent with an IGM-like environment. Using late-time afterglow data for 11 events, we find a median jet opening angle of θj = 16±10◦ . We also calculate a median beaming factor of fb ≈ 0.04, leading to a beaming-corrected total energy release of Etrue ≈ 1.6 × 1050 erg. Furthermore, we calculate a beaming-corrected event rate of ℜtrue = 270+1580 −180 Gpc−3 yr−1 , or ≈ 8 +47 −5 yr−1 within a 200 Mpc volume, the Advanced LIGO/Virgo typical detection distance for NS-NS binaries.Publication Toward Characterization of the Type IIP Supernova Progenitor Population: A Statistical Sample of Light Curves from Pan-STARRS1(IOP Publishing, 2015) Sanders, Nathan Edward; Soderberg, Alicia; Gezari, S.; Betancourt, M.; Chornock, R; Berger, Edo; Foley, R. J.; Challis, Peter; Drout, Maria Rebecca; Kirshner, Robert; Lunnan, R; Marion, G. H.; Margutti, Raffaella; McKinnon, R.; Milisavljevic, Danny; Narayan, G.; Rest, A.; Kankare, E.; Mattila, S.; Smartt, S. J.; Huber, M. E.; Burgett, W. S.; Draper, P.W.; Hodapp, K. W.; Kaiser, N.; Kudritzki, R. P.; Magnier, E. A.; Metcalfe, N.; Morgan, J. S.; Price, P. A.; Tonry, J. L.; Wainscoat, R. J.; Waters, C.In recent years, wide-field sky surveys providing deep multiband imaging have presented a new path for indirectly characterizing the progenitor populations of core-collapse supernovae (SNe): systematic light-curve studies. We assemble a set of 76 grizy-band Type IIP SN light curves from Pan-STARRS1, obtained over a constant survey program of 4 yr and classified using both spectroscopy and machine-learning-based photometric techniques. We develop and apply a new Bayesian model for the full multiband evolution of each light curve in the sample. We find no evidence of a subpopulation of fast-declining explosions (historically referred to as "Type IIL" SNe). However, we identify a highly significant relation between the plateau phase decay rate and peak luminosity among our SNe IIP. These results argue in favor of a single parameter, likely determined by initial stellar mass, predominantly controlling the explosions of red supergiants. This relation could also be applied for SN cosmology, offering a standardizable candle good to an intrinsic scatter of lesssim 0.2 mag. We compare each light curve to physical models from hydrodynamic simulations to estimate progenitor initial masses and other properties of the Pan-STARRS1 Type IIP SN sample. We show that correction of systematic discrepancies between modeled and observed SN IIP light-curve properties and an expanded grid of progenitor properties are needed to enable robust progenitor inferences from multiband light-curve samples of this kind. This work will serve as a pathfinder for photometric studies of core-collapse SNe to be conducted through future wide-field transient searches.Publication A Jet Break in the X-Ray Light Curve of Short Grb 111020a: Implications for Energetics and Rates(IOP Publishing, 2012) Fong, W; Berger, Edo; Margutti, Raffaella; Zauderer, B; Troja, E.; Czekala, Ian; Chornock, R; Gehrels, N.; Sakamoto, T.; Fox, D. B.; Podsiadlowski, P.We present broad-band observations of the afterglow and environment of the short GRB 111020A. An extensive X-ray light curve from Swift/XRT, XMM-Newton and Chandra, spanning ∼ 100 seconds to 10 days after the burst, reveals a significant break at δt ≈2 days with pre- and post-break decline rates of αX,1 ≈ −0.78 and αX,2 . −1.7, respectively. Interpreted as a jet break, we infer a collimated outflow with an opening angle of θj ≈ 3 − 8◦. The resulting beaming-corrected γ-ray (10 − 1000 keV band) and blastwave kinetic energies are (2−3)×1048 erg and (0.3−2)×1049 erg, respectively, with the range depending on the unknown redshift of the burst. We report a radio afterglow limit of <39 µJy (3σ) from EVLA observations which, along with our finding that νc < νX , constrains the circumburst density to n0 ∼ 0.01 − 0.1 cm−3. Optical observations provide an afterglow limit of i & 24.4 mag at 18 hours after the burst, and reveal a potential host galaxy with i ≈ 24.3 mag. The sub-arcsecond localization from Chandra provides a precise offset of 0.80′′ ±0.11′′ (1σ) from this galaxy corresponding to an offset of 5−7 kpc for z = 0.5−1.5. We find a high excess neutral Hydrogen column density of (7.5 ± 2.0) × 1021 cm−2 (z = 0). Our observations demonstrate that a growing fraction of short GRBs are collimated which may lead to a true event rate of & 100 − 1000 Gpc−3 yr−1, in good agreement with the NS-NS merger rate of ≈ 200 − 3000 Gpc−3 yr−1. This consistency is promising for coincident short GRB-gravitational wave searches in the forthcoming era of Advanced LIGO/VIRGO.Publication X-ray flare candidates in short gamma-ray bursts(Oxford University Press (OUP), 2011) Margutti, Raffaella; Chincarini, G.; Granot, J.; Guidorzi, C.; Berger, Edo; Bernardini, M. G.; Gehrels, N.; Soderberg, Alicia; Stamatikos, M.; Zaninoni, E.We present the first systematic study of X-ray flare candidates in short gamma-ray bursts (SGRBs) exploiting the large 6-year Swift database with the aim to constrain the physical nature of such fluctuations. We find that flare candidates appear in different types of SGRB host galaxy environments and show no clear correlation with the X-ray afterglow lifetime; flare candidates are detected both in SGRBs with a bright extended emission in the soft γ-rays and in SGRBs which do not show such component. We furthermore show that SGRB X-ray flare candidates only partially share the set of observational properties of long GRB (LGRB) flares. In particular, the main parameter driving the duration evolution of X-ray variability episodes in both classes is found to be the elapsed time from the explosion, with very limited dependence on the different progenitors, environments, central engine life-times, prompt variability time-scales and energy budgets. On the contrary, SGRB flare candidates significantly differ from LGRB flares in terms of peak luminosity, isotropic energy, flare-to-prompt luminosity ratio and relative variability flux. However, these differences disappear when the central engine time-scales and energy budget are accounted for, suggesting that (i) flare candidates and prompt pulses in SGRBs likely have a common origin; (ii) similar dissipation and/or emission mechanisms are responsible for the prompt and flare emission in long and short GRBs, with SGRBs being less energetic albeit faster evolving versions of the long class. Finally, we show that in strict analogy to the SGRB prompt emission, flares candidates fall off the lag-luminosity relation defined by LGRBs, thus strengthening the SGRB flare-prompt pulse connection.Publication The Afterglow and Environment of the Short Grb 111117a(IOP Publishing, 2012) Margutti, Raffaella; Berger, Edo; Fong, W; Zauderer, B; Cenko, S. B.; Greiner, J.; Soderberg, Alicia; Cucchiara, A.; Rossi, A.; Klose, S.; Schmidl, S.; Milisavljevic, Danny; Sanders, Nathan EdwardWe present multi-wavelength observations of the afterglow of the short GRB 111117A, and follow-up observations of its host galaxy. From rapid optical and radio observations we place limits of r & 25.5 mag at δt ≈ 0.55 d and Fν(5.8GHz) . 18 µJy at δt ≈ 0.50 d, respectively. However, using a Chandra observation at δt ≈ 3.0 d we locate the absolute position of the X-ray afterglow to an accuracy of 0.22′′ (1σ), a factor of about 6 times better than the Swift/XRT position. This allows us to robustly identify the host galaxy and to locate the burst at a projected offset of 1.25 ± 0.20′′ from the host centroid. Using optical and near-IR observations of the host galaxy we determine a photometric redshift of z = 1.3+0.3−0.2, one of the highest for any short GRB, and leading to a projected physical offset for the burst of 10.5 ± 1.7 kpc, typical of previous short GRBs. At this redshift, the isotropic γ-ray energy is Eγ,iso ≈ 3.0×1051 erg (rest-frame 23 − 2300 keV) with a peak energy of Epk ≈ 850 − 2300 keV (rest-frame). In conjunction with the isotropic X-ray energy, GRB 111117A appears to follow our recently-reported Ex,iso-Eγ,iso-Epk universal scaling. Using the X-ray data along with the optical and radio non-detections we find that for a blastwave kinetic energy of EK,iso ≈ Eγ,iso erg, the circumburst density is n0 ≈ 3×10−4 − 1 cm−3 (for a range of ǫB = 0.001 − 0.1). Similarly, from the non-detection of a break in the X-ray light curve at δt . 3 d, we infer a minimum opening angle for the outflow of θj & 3 − 10◦ (depending on the circumburst density). We conclude that Chandra observations of short GRBs are effective at determining precise positions and robust host galaxy associations in the absence of optical and radio detections.Publication Sn 2012au: A Golden Link Between Superluminous Supernovae and Their Lower-Luminosity Counterparts(IOP Publishing, 2013) Milisavljevic, Danny; Soderberg, Alicia; Margutti, Raffaella; Drout, Maria Rebecca; Marion, G. Howie; Sanders, Nathan Edward; Hsiao, Eric Y.; Lunnan, R; Chornock, R; Fesen, Robert A.; Parrent, Jerod T.; Levesque, Emily M.; Berger, Edo; Foley, Ryan J.; Challis, Pete; Kirshner, Robert P.; Dittmann, Jason Adam; Bieryla, Allyson; Kamble, Atish; Chakraborti, Sayan; De Rosa, Gisella; Fausnaugh, Michael; Hainline, Kevin N.; Chen, Chien-Ting; Hickox, Ryan C.; Morrell, Nidia; Phillips, Mark M.; Stritzinger, MaximilianWe present optical and near-infrared observations of SN 2012au, a slow-evolving supernova (SN) with properties that suggest a link between subsets of energetic and H-poor SNe and superluminous SNe. SN 2012au exhibited conspicuous SN Ib-like He I lines and other absorption features at velocities reaching ≈ 2×104 km s−1 in its early spectra, and a broad light curve that peaked at MB = −18.1 mag. Models of these data indicate a large explosion kinetic energy of ∼ 1052 erg and 56Ni mass ejection of MNi ≈ 0.3M⊙ on par with SN 1998bw. SN 2012au’s spectra almost one year after explosion show a blend of persistent Fe II P-Cyg absorptions and nebular emissions originating from two distinct velocity regions. These late-time emissions include strong [Fe II], [Ca II], [O I], Mg I], and Na I lines at velocities & 4500 km s−1, as well as O I and Mg I lines at noticeably smaller velocities . 2000 km s−1. Many of the late-time properties of SN 2012au are similar to the slow-evolving hypernovae SN 1997dq and SN 1997ef, and the superluminous SN 2007bi. Our observations suggest that a single explosion mechanism may unify all of these events that span −21 . MB . −17 mag. The aspherical and possibly jetted explosion was most likely initiated by the core collapse of a massive progenitor star and created substantial high-density, low-velocity Ni-rich material.Publication Ps1-12sk Is a Peculiar Supernova From a He-Rich Progenitor System in a Brightest Cluster Galaxy Environment(IOP Publishing, 2013) Sanders, Nathan Edward; Soderberg, Alicia; Foley, R. J.; Chornock, R; Milisavljevic, Danny; Margutti, Raffaella; Drout, Maria Rebecca; Moe, M; Berger, Edo; Brown, W. R.; Lunnan, R.; Smartt, S. J.; Fraser, M.; Kotak, R.; Magill, L.; Smith, K. W.; Wright, D.; Huang, K.; Urata, Y.; Mulchaey, J. S.; Rest, A.; Sand, D. J.; Chomiuk, L.; Friedman, A. S.; Kirshner, R. P.; Marion, G. H.; Tonry, J. L.; Burgett, W. S.; Chambers, K. C.; Hodapp, K. W.; Kudritzki, R. P.; Price, P. A.We report on our discovery and observations of the Pan-STARRS1 supernova (SN) PS1-12sk, a transient with properties that indicate atypical star formation in its host galaxy cluster or pose a challenge to popular progenitor system models for this class of explosion. The optical spectra of PS1- 12sk classify it as a Type Ibn SN (c.f. SN 2006jc), dominated by intermediate-width (3×103 km s−1) and time variable He I emission. Our multi-wavelength monitoring establishes the rise time dt ∼ 9 − 23 days and shows an NUV-NIR SED with temperature & 17 × 103 K and a peak magnitude of Mz = −18.88 ± 0.02 mag. SN Ibn spectroscopic properties are commonly interpreted as the signature of a massive star (17 − 100 M⊙) explosion within a He-enriched circumstellar medium. However, unlike previous Type Ibn supernovae, PS1-12sk is associated with an elliptical brightest cluster galaxy, CGCG 208-042 (z = 0.054) in cluster RXC J0844.9+4258. The expected probability of an event like PS1-12sk in such environments is low given the measured infrequency of core-collapse SNe in red sequence galaxies compounded by the low volumetric rate of SN Ibn. Furthermore, we find no evidence of star formation at the explosion site to sensitive limits (ΣHα . 2×10−3 M⊙ yr−1 kpc−2). We therefore discuss white dwarf binary systems as a possible progenitor channel for SNe Ibn. We conclude that PS1-12sk represents either a fortuitous and statistically unlikely discovery, evidence for a top-heavy IMF in galaxy cluster cooling flow filaments, or the first clue suggesting an alternate progenitor channel for Type Ibn SNe.Publication Demographics of the Galaxies Hosting Short-Duration Gamma-Ray Bursts(IOP Publishing, 2013) Fong, W; Berger, Edo; Chornock, R; Margutti, Raffaella; Levan, A. J.; Tanvir, N. R.; Tunnicliffe, R. L.; Czekala, I.; Fox, D. B.; Perley, D. A.; Cenko, S. B.; Zauderer, B. A.; Laskar, T.; Persson, S. E.; Monson, A. J.; Kelson, D. D.; Birk, C.; Murphy, D.; Servillat, M.; Anglada, G.We present observations of the afterglows and host galaxies of three short-duration gamma-ray bursts (GRBs): 100625A, 101219A and 110112A. We find that GRB 100625A occurred in a z = 0.452 early-type galaxy with a stellar mass of ≈ 4.6×109 M⊙ and a stellar population age of ≈ 0.7 Gyr, and GRB 101219A originated in a starforming galaxy at z = 0.718 with a stellar mass of ≈ 1.4×109M⊙, a star formation rate of ≈ 16 M⊙ yr−1, and a stellar population age of ≈ 50 Myr. We also report the discovery of the optical afterglow of GRB 110112A, which lacks a coincident host galaxy to i & 26 mag and we cannot conclusively identify any field galaxy as a possible host. From afterglow modeling, the bursts have inferred circumburst densities of ≈ 10−4 − 1 cm−3, and isotropic-equivalent gamma-ray and kinetic energies of ≈ 1050 − 1051 erg. These three events highlight the diversity of galactic environments that host short GRBs. To quantify this diversity, we use the sample of 36 Swift short GRBs with robust associations to an environment (∼ 1/2 of 68 short bursts detected by Swift to May 2012) and classify bursts originating from four types of environments: late-type (≈ 50%), early-type (≈ 15%), inconclusive (≈ 20%), and “host-less” (lacking a coincident host galaxy to limits of & 26 mag; ≈ 15%). To find likely ranges for the true late- and early-type fractions, we assign each of the host-less bursts to either the late- or early-type category using probabilistic arguments, and consider the scenario that all hosts in the inconclusive category are early-type galaxies to set an upper bound on the early-type fraction. We calculate most likely ranges for the late- and early-type fractions of ≈ 60 − 80% and ≈ 20 − 40%, respectively. We find no clear trend between gamma-ray duration and host type. We also find no change to the fractions when excluding events recently claimed as possible contaminants from the long GRB/collapsar population. Our reported demographics are consistent with a short GRB rate driven by both stellar mass and star formation.