arXiv subjects

K. Maguire

Publications and source records attributed to K. Maguire.

At least 109 records · Page 6Linked to original sources

arXiv2016

Radio observations of a sample of broad-lined type Ic supernovae discovered by PTF/iPTF: A search for relativistic explosions

Long duration gamma-ray bursts are a rare subclass of stripped-envelope core-collapse supernovae that launch collimated relativistic outflows (jets). All gamma-ray-burst-associated supernovae are spectroscopically of Type Ic with broad lines, but the fraction of broad-lined Type Ic supernovae harboring low-luminosity gamma-ray-burst remains largely unconstrained. Some supernovae should be accompanied by off-axis $γ$-ray burst jets that remain invisible initially, but then emerge as strong radio sources (as the jets decelerate). However, this critical prediction of the jet model for gamma-ray bursts has yet to be verified observationally. Here, we present K. G. Jansky Very Large Array observations of 15 broad-lined supernovae of Type Ic discovered by the Palomar Transient Factory in an untargeted manner. Most of the supernovae in our sample exclude radio emission observationally similar to that of the radio-loud, relativistic SN\,1998bw. We constrain the fraction of 1998bw-like broad-lined Type Ic supernovae to be <~ 41% (99.865% confidence). Most of the events in our sample also exclude off-axis jets similar to GRB 031203 and GRB 030329, but we cannot rule out off-axis gamma-ray-bursts expanding in a low-density wind environment. Three supernovae in our sample are detected in the radio. PTF11qcj and PTF14dby show late-time radio emission with average ejecta speeds of ~(0.3-0.4)c, on the dividing line between relativistic and "ordinary" supernovae. The speed of PTF11cmh radio ejecta is poorly constrained. We estimate that <~ 85% (99.865% confidence) of the broad-lined Type Ic supernovae in our sample may harbor off-axis $γ$-ray-bursts expanding in media with densities in the range probed by this study.

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arXiv2016

Early observations of the nearby type Ia supernova SN 2015F

We present photometry and time-series spectroscopy of the nearby type Ia supernova (SN Ia) SN 2015F over $-16$ days to $+80$ days relative to maximum light, obtained as part of the Public ESO Spectroscopic Survey of Transient Objects (PESSTO). SN 2015F is a slightly sub-luminous SN Ia with a decline rate of $Δm15(B)=1.35 \pm 0.03$ mag, placing it in the region between normal and SN 1991bg-like events. Our densely-sampled photometric data place tight constraints on the epoch of first light and form of the early-time light curve. The spectra exhibit photospheric C II $λ6580$ absorption until $-4$ days, and high-velocity Ca II is particularly strong at $<-10$ days at expansion velocities of $\simeq$23000\kms. At early times, our spectral modelling with syn++ shows strong evidence for iron-peak elements (Fe II, Cr II, Ti II, and V II) expanding at velocities $>14000$ km s$^{-1}$, suggesting mixing in the outermost layers of the SN ejecta. Although unusual in SN Ia spectra, including V II in the modelling significantly improves the spectral fits. Intriguingly, we detect an absorption feature at $\sim$6800 Å that persists until maximum light. Our favoured explanation for this line is photospheric Al II, which has never been claimed before in SNe Ia, although detached high-velocity C II material could also be responsible. In both cases the absorbing material seems to be confined to a relatively narrow region in velocity space. The nucleosynthesis of detectable amounts of Al II would argue against a low-metallicity white dwarf progenitor. We also show that this 6800 Å feature is weakly present in other normal SN Ia events, and common in the SN 1991bg-like sub-class.

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arXiv2016

OGLE16aaa - a Signature of a Hungry Super Massive Black Hole

We present the discovery and first three months of follow-up observations of a currently on-going unusual transient detected by the OGLE-IV survey, located in the centre of a galaxy at redshift z=0.1655. The long rise to absolute magnitude of -20.5 mag, slow decline, very broad He and H spectral features make OGLE16aaa similar to other optical/UV Tidal Disruption Events (TDEs). Weak narrow emission lines in the spectrum and archival photometric observations suggest the host galaxy is a weak-line Active Galactic Nucleus (AGN), which has been accreting at higher rate in the past. OGLE16aaa, along with SDSS J0748, seems to form a sub-class of TDEs by weakly or recently active super-massive black holes (SMBHs). This class might bridge the TDEs by quiescent SMBHs and flares observed as "changing-look QSOs", if we interpret the latter as TDEs. If this picture is true, the previously applied requirement for identifying a flare as a TDE that it had to come from an inactive nucleus, could be leading to observational bias in TDE selection, thus affecting TDE-rate estimations.

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arXiv2016

Superluminous supernova 2015bn in the nebular phase: evidence for the engine-powered explosion of a stripped massive star

We present nebular-phase imaging and spectroscopy for the hydrogen-poor superluminous supernova SN 2015bn, at redshift z=0.1136, spanning +250-400 d after maximum light. The light curve exhibits a steepening in the decline rate from 1.4 mag/(100 d) to 1.7 mag/(100 d), suggestive of a significant decrease in the opacity. This change is accompanied by a transition from a blue continuum superposed with photospheric absorption lines to a nebular spectrum dominated by emission lines of oxygen, calcium and magnesium. There are no obvious signatures of circumstellar interaction or large nickel mass. We show that the spectrum at +400 d is virtually identical to a number of energetic Type Ic supernovae such as SN 1997dq, SN 2012au, and SN 1998bw, indicating similar core conditions and strengthening the link between `hypernovae'/long gamma-ray bursts and superluminous supernovae. A single explosion mechanism may unify these events that span absolute magnitudes of -22 < M_B < -17. Both the light curve and spectrum of SN 2015bn are consistent with an engine-driven explosion ejecting 7-30 M$_\odot$ of oxygen-dominated ejecta (for reasonable choices in temperature and opacity). A strong and relatively narrow O II $λ$7774 line, seen in a number of these energetic events but not in normal supernovae, may point to an inner shell that is the signature of a central engine.

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arXiv2016

A search for an optical counterpart to the gravitational wave event GW151226

We present a search for an electromagnetic counterpart of the gravitational wave source GW151226. Using the Pan-STARRS1 telescope we mapped out 290 square degrees in the optical i_ps filter starting 11.5hr after the LIGO information release and lasting for a further 28 days. The first observations started 49.5hr after the time of the GW151226 detection. We typically reached sensitivity limits of i_ps = 20.3-20.8 and covered 26.5% of the LIGO probability skymap. We supplemented this with ATLAS survey data, reaching 31% of the probability region to shallower depths of m~19. We found 49 extragalactic transients (that are not obviously AGN), including a faint transient in a galaxy at 7Mpc (a luminous blue variable outburst) plus a rapidly decaying M-dwarf flare. Spectral classification of 20 other transient events showed them all to be supernovae. We found an unusual transient, PS15dpn, with an explosion date temporally coincident with GW151226 which evolved into a type Ibn supernova. The redshift of the transient is secure at z=0.1747 +/- 0.0001 and we find it unlikely to be linked, since the luminosity distance has a negligible probability of being consistent with that of GW151226. In the 290 square degrees surveyed we therefore do not find a likely counterpart. However we show that our survey strategy would be sensitive to NS-NS mergers producing kilonovae at D < 100 Mpc which is promising for future LIGO/Virgo searches.

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arXiv2016

Pan-STARRS and PESSTO search for an optical counterpart to the LIGO gravitational wave source GW150914

We searched for an optical counterpart to the first gravitational wave source discovered by LIGO (GW150914), using a combination of the Pan-STARRS1 wide-field telescope and the PESSTO spectroscopic follow-up programme. As the final LIGO sky maps changed during analysis, the total probability of the source being spatially coincident with our fields was finally only 4.2 per cent. Therefore we discuss our results primarily as a demonstration of the survey capability of Pan-STARRS and spectroscopic capability of PESSTO. We mapped out 442 square degrees of the northern sky region of the initial map. We discovered 56 astrophysical transients over a period of 41 days from the discovery of the source. Of these, 19 were spectroscopically classified and a further 13 have host galaxy redshifts. All transients appear to be fairly normal supernovae and AGN variability and none is obviously linked with GW150914. We illustrate the sensitivity of our survey by defining parameterised lightcurves with timescales of 4, 20 and 40 days and use the sensitivity of the Pan-STARRS1 images to set limits on the luminosities of possible sources. The Pan-STARRS1 images reach limiting magnitudes of i = 19.2, 20.0 and 20.8 respectively for the three timescales. For long timescale parameterised lightcurves (with FWHM=~40d) we set upper limits of M_i <= -17.2 -0.9/+1.4 if the distance to GW150914 is D = 400 +/- 200Mpc. The number of type Ia SN we find in the survey is similar to that expected from the cosmic SN rate, indicating a reasonably complete efficiency in recovering supernova like transients out to D = 400 +/- 200 Mpc.

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arXiv2016

SN 2015bn: a detailed multi-wavelength view of a nearby superluminous supernova

We present observations of SN 2015bn (= PS15ae = CSS141223-113342+004332 = MLS150211-113342+004333), a Type I superluminous supernova (SLSN) at redshift $z=0.1136$. As well as being one of the closest SLSNe I yet discovered, it is intrinsically brighter ($M_U\approx-23.1$) and in a fainter galaxy ($M_B\approx-16.0$) than other SLSNe at $z\sim0.1$. We used this opportunity to collect the most extensive dataset for any SLSN I to date, including densely-sampled spectroscopy and photometry, from the UV to the NIR, spanning $-$50 to +250 days from optical maximum. SN 2015bn fades slowly, but exhibits surprising undulations in the light curve on a timescale of 30-50 days, especially in the UV. The spectrum shows extraordinarily slow evolution except for a rapid transformation between +7 and +20-30 days. No narrow emission lines from slow-moving material are observed at any phase. We derive physical properties including the bolometric luminosity, and find slow velocity evolution and non-monotonic temperature and radial evolution. A deep radio limit rules out a healthy off-axis gamma-ray burst, and places constraints on the pre-explosion mass loss. The data can be consistently explained by a $\gtrsim10\,{\rm M}_\odot$ stripped progenitor exploding with $\sim 10^{51}\,$erg kinetic energy, forming a magnetar with a spin-down timescale of $\sim20$ days (thus avoiding a gamma-ray burst) that reheats the ejecta and drives ionization fronts. The most likely alternative scenario -- interaction with $\sim20\,{\rm M}_\odot$ of dense, inhomogeneous circumstellar material -- can be tested with continuing radio follow-up.

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arXiv2016

450 Days of Type II SN 2013ej in Optical and Near-Infrared

We present optical and near-infrared photometric and spectroscopic observations of SN 2013ej, in galaxy M74, from 1 to 450 days after the explosion. SN 2013ej is a hydrogen-rich supernova, classified as a Type IIL due to its relatively fast decline following the initial peak. It has a relatively high peak luminosity (absolute magnitude M$_\rm{V}$ = -17.6) but a small $^{56}$Ni production of ~0.023 M$_\odot$. Its photospheric evolution is similar to other Type II SNe, with shallow absorption in the Hα profile typical for a Type IIL. During transition to the radioactive decay tail at ~100 days, we find the SN to grow bluer in B - V colour, in contrast to some other Type II supernovae. At late times, the bolometric light curve declined faster than expected from $^{56}$Co decay and we observed unusually broad and asymmetric nebular emission lines. Based on comparison of nebular emission lines most sensitive to the progenitor core mass, we find our observations are best matched to synthesized spectral models with a M$_\rm{ZAMS}$ = 12 - 15 M$_\odot$ progenitor. The derived mass range is similar to but not higher than the mass estimated for Type IIP progenitors. This is against the idea that Type IIL are from more massive stars. Observations are consistent with the SN having a progenitor with a relatively low-mass envelope.

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arXiv2016

The type Iax supernova, SN 2015H: a white dwarf deflagration candidate

We present results based on observations of SN 2015H which belongs to the small group of objects similar to SN 2002cx, otherwise known as type Iax supernovae. The availability of deep pre-explosion imaging allowed us to place tight constraints on the explosion epoch. Our observational campaign began approximately one day post-explosion, and extended over a period of about 150 days post maximum light, making it one of the best observed objects of this class to date. We find a peak magnitude of M$_r$ = -17.27 $\pm$ 0.07, and a ($Δm_{15})_r$ = 0.69 $\pm$ 0.04. Comparing our observations to synthetic spectra generated from simulations of deflagrations of Chandrasekhar mass carbon-oxygen white dwarfs, we find reasonable agreement with models of weak deflagrations that result in the ejection of ~0.2 M$_{\odot}$ of material containing ~0.07 M$_{\odot}$ of 56Ni. The model light curve however, evolves more rapidly than observations, suggesting that a higher ejecta mass is to be favoured. Nevertheless, empirical modelling of the pseudo-bolometric light curve suggests that $\lesssim$0.6 M_sun of material was ejected, implying that the white dwarf is not completely disrupted, and that a bound remnant is a likely outcome.

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arXiv2016

On the diversity of super-luminous supernovae: ejected mass as the dominant factor

We assemble a sample of 24 hydrogen-poor super-luminous supernovae (SLSNe). Parameterizing the light curve shape through rise and decline timescales shows that the two are highly correlated. Magnetar-powered models can reproduce the correlation, with the diversity in rise and decline rates driven by the diffusion timescale. Circumstellar interaction models can exhibit a similar rise-decline relation, but only for a narrow range of densities, which may be problematic for these models. We find that SLSNe are approximately 3.5 magnitudes brighter and have light curves 3 times broader than SNe Ibc, but that the intrinsic shapes are similar. There are a number of SLSNe with particularly broad light curves, possibly indicating two progenitor channels, but statistical tests do not cleanly separate two populations. The general spectral evolution is also presented. Velocities measured from Fe II are similar for SLSNe and SNe Ibc, suggesting that diffusion time differences are dominated by mass or opacity. Flat velocity evolution in most SLSNe suggests a dense shell of ejecta. If opacities in SLSNe are similar to other SNe Ibc, the average ejected mass is higher by a factor 2-3. Assuming $κ=0.1\,$cm$^2\,$g$^{-1}$, we estimate a mean (median) SLSN ejecta mass of 10$\,$M$_\odot$ (6$\,$M$_\odot$), with a range of 3-30$\,$M$_\odot$. Doubling the assumed opacity brings the masses closer to normal SNe Ibc, but with a high-mass tail. The most probable mechanism for generating SLSNe seems to be the core-collapse of a very massive hydrogen-poor star, forming a millisecond magnetar.

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arXiv2015

Type II supernova energetics and comparison of light curves to shock-cooling models

During the first few days after explosion, Type II supernovae (SNe) are dominated by relatively simple physics. Theoretical predictions regarding early-time SN light curves in the ultraviolet (UV) and optical bands are thus quite robust. We present, for the first time, a sample of $57$ $R$-band Type II SN light curves that are well monitored during their rise, having $>5$ detections during the first 10 days after discovery, and a well-constrained time of explosion to within $1-3$ days. We show that the energy per unit mass ($E/M$) can be deduced to roughly a factor of five by comparing early-time optical data to the model of Rabinak & Waxman (2011), while the progenitor radius cannot be determined based on $R$-band data alone. We find that Type II SN explosion energies span a range of $E/M=(0.2-20)\times 10^{51} \; \rm{erg/(10 M}_\odot$), and have a mean energy per unit mass of $\left\langle E/M \right\rangle = 0.85\times 10^{51} \; \rm{erg/(10 M}_\odot$), corrected for Malmquist bias. Assuming a small spread in progenitor masses, this indicates a large intrinsic diversity in explosion energy. Moreover, $E/M$ is positively correlated with the amount of $^{56}\rm{Ni}$ produced in the explosion, as predicted by some recent models of core-collapse SNe. We further present several empirical correlations. The peak magnitude is correlated with the decline rate ($Δm_{15}$), the decline rate is weakly correlated with the rise time, and the rise time is not significantly correlated with the peak magnitude. Faster declining SNe are more luminous and have longer rise times. This limits the possible power sources for such events.

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arXiv2015

A comparative study of Type II-P and II-L supernova rise times as exemplified by the case of LSQ13cuw

We report on our findings based on the analysis of observations of the Type II-L supernova LSQ13cuw within the framework of currently accepted physical predictions of core-collapse supernova explosions. LSQ13cuw was discovered within a day of explosion, hitherto unprecedented for Type II-L supernovae. This motivated a comparative study of Type II-P and II-L supernovae with relatively well-constrained explosion epochs and rise times to maximum (optical) light. From our sample of twenty such events, we find evidence of a positive correlation between the duration of the rise and the peak brightness. On average, SNe II-L tend to have brighter peak magnitudes and longer rise times than SNe II-P. However, this difference is clearest only at the extreme ends of the rise time versus peak brightness relation. Using two different analytical models, we performed a parameter study to investigate the physical parameters that control the rise time behaviour. In general, the models qualitatively reproduce aspects of the observed trends. We find that the brightness of the optical peak increases for larger progenitor radii and explosion energies, and decreases for larger masses. The dependence of the rise time on mass and explosion energy is smaller than the dependence on the progenitor radius. We find no evidence that the progenitors of SNe II-L have significantly smaller radii than those of SNe II-P.

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arXiv2015

LSQ14bdq: A Type Ic super-luminous supernova with a double-peaked light curve

We present data for LSQ14bdq, a hydrogen-poor super-luminous supernova (SLSN) discovered by the La Silla QUEST survey and classified by the Public ESO Spectroscopic Survey of Transient Objects. The spectrum and light curve are very similar to slow-declining SLSNe such as PTF12dam. However, detections within ~1 day after explosion show a bright and relatively fast initial peak, lasting for ~15 days, prior to the usual slow rise to maximum light. The broader, main peak can be fit with either central engine or circumstellar interaction models. We discuss the implications of the precursor peak in the context of these models. It is too bright and narrow to be explained as a normal 56Ni-powered SN, and we suggest that interaction models may struggle to fit the two peaks simultaneously. We propose that the initial peak may arise from the post-shock cooling of extended stellar material, and reheating by a central engine drives the second peak. In this picture, we show that an explosion energy of ~2x10^{52} erg and a progenitor radius of a few hundred solar radii would be required to power the early emission. The competing engine models involve rapidly spinning magnetars (neutron stars) or fall-back accretion onto a central black hole. The prompt energy required may favour the black hole scenario. The bright initial peak effectively rules out a compact Wolf-Rayet star as a progenitor, since the inferred energies and ejected masses become unphysical.

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arXiv2015

PESSTO : survey description and products from the first data release by the Public ESO Spectroscopic Survey of Transient Objects

The Public European Southern Observatory Spectroscopic Survey of Transient Objects (PESSTO) began as a public spectroscopic survey in April 2012. We describe the data reduction strategy and data products which are publicly available through the ESO archive as the Spectroscopic Survey Data Release 1 (SSDR1). PESSTO uses the New Technology Telescope with EFOSC2 and SOFI to provide optical and NIR spectroscopy and imaging. We target supernovae and optical transients brighter than 20.5mag for classification. Science targets are then selected for follow-up based on the PESSTO science goal of extending knowledge of the extremes of the supernova population. The EFOSC2 spectra cover 3345-9995A (at resolutions of 13-18 Angs) and SOFI spectra cover 0.935-2.53 micron (resolutions 23-33 Angs) along with JHK imaging. This data release contains spectra from the first year (April 2012 - 2013), consisting of all 814 EFOSC2 spectra and 95 SOFI spectra (covering 298 distinct objects), in standard ESO Phase 3 format. We estimate the accuracy of the absolute flux calibrations for EFOSC2 to be typically 15%, and the relative flux calibration accuracy to be about 5%. The PESSTO standard NIR reduction process does not yet produce high accuracy absolute spectrophotometry but the SOFI JHK imaging will improve this. Future data releases will focus on improving the automated flux calibration of the data products.

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arXiv2015

Nebular spectra and abundance tomography of the type Ia supernova SN 2011fe: a normal SN Ia with a stable Fe core

A series of optical and one near-infrared nebular spectra covering the first year of the Type Ia supernova SN 2011fe are presented and modelled. The density profile that proved best for the early optical/ultraviolet spectra, "rho-11fe", was extended to lower velocities to include the regions that emit at nebular epochs. Model rho-11fe is intermediate between the fast deflagration model W7 and a low-energy delayed-detonation. Good fits to the nebular spectra are obtained if the innermost ejecta are dominated by neutron-rich, stable Fe-group species, which contribute to cooling but not to heating. The correct thermal balance can thus be reached for the strongest [FeII] and [FeIII] lines to be reproduced with the observed ratio. The 56Ni mass thus obtained is 0.47 +/- 0.05 Mo. The bulk of 56Ni has an outermost velocity of ~8500 km/s. The mass of stable iron is 0.23 +/- 0.03 Mo. Stable Ni has low abundance, ~10^{-2} Mo. This is sufficient to reproduce an observed emission line near 7400 A. A sub-Chandrasekhar explosion model with mass 1.02 Mo and no central stable Fe does not reproduce the observed line ratios. A mock model where neutron-rich Fe-group species are located above 56Ni following recent suggestions is also shown to yield spectra that are less compatible with the observations. The densities and abundances in the inner layers obtained from the nebular analysis, combined with those of the outer layers previously obtained, are used to compute a synthetic bolometric light curve, which compares favourably with the light curve of SN 2011fe.

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arXiv2015

Strong near-infrared carbon in the Type Ia supernova iPTF13ebh

We present near-infrared (NIR) time-series spectroscopy, as well as complementary ultraviolet (UV), optical, and NIR data, of the Type Ia supernova (SN Ia) iPTF13ebh, which was discovered within two days from the estimated time of explosion. The first NIR spectrum was taken merely 2.3 days after explosion and may be the earliest NIR spectrum yet obtained of a SN Ia. The most striking features in the spectrum are several NIR C I lines, and the C I λ1.0693 μm line is the strongest ever observed in a SN Ia. Interestingly, no strong optical C II counterparts were found, even though the optical spectroscopic time series began early and is densely-cadenced. Except at the very early epochs, within a few days from the time of explosion, we show that the strong NIR C I compared to the weaker optical C II appears to be general in SNe Ia. iPTF13ebh is a fast decliner with Δm15(B) = 1.79 $\pm$ 0.01, and its absolute magnitude obeys the linear part of the width-luminosity relation. It is therefore categorized as a "transitional" event, on the fast-declining end of normal SNe Ia as opposed to subluminous/91bg-like objects. iPTF13ebh shows NIR spectroscopic properties that are distinct from both the normal and subluminous/91bg-like classes, bridging the observed characteristics of the two classes. These NIR observations suggest composition and density of the inner core similar to that of 91bg-like events, and a deep reaching carbon burning layer not observed in slower declining SNe Ia. There is also a substantial difference between the explosion times inferred from the early-time light curve and the velocity evolution of the Si II λ0.6355 μm line, implying a long dark phase of ~ 4 days.

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arXiv2015

Near-infrared light curves of Type Ia supernovae: Studying the properties of the second maximum

Type Ia supernovae have been proposed to be much better distance indicators at near-infrared compared to optical wavelengths -- the effect of dust extinction is expected to be lower and it has been shown that SNe Ia behave more like `standard candles' at NIR wavelengths. To better understand the physical processes behind this increased uniformity, we have studied the $Y$, $J$ and $H$-filter light curves of 91 SNe Ia from the literature. We show that the phases and luminosities of the first maximum in the NIR light curves are extremely uniform for our sample. The phase of the second maximum, the late-phase NIR luminosity and the optical light curve shape are found to be strongly correlated, in particular more luminous SNe Ia reach the second maximum in the NIR filters at a later phase compared to fainter objects. We also find a strong correlation between the phase of the second maximum and the epoch at which the SN enters the Lira law phase in its optical colour curve (epochs $\sim$ 15 to 30 days after $B$ band maximum). The decline rate after the second maximum is very uniform in all NIR filters. We suggest that these observational parameters are linked to the nickel and iron mass in the explosion, providing evidence that the amount of nickel synthesised in the explosion is the dominating factor shaping the optical and NIR appearance of SNe Ia.

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arXiv2014

OGLE-2013-SN-079: a lonely supernova consistent with a helium shell detonation

We present observational data for a peculiar supernova discovered by the OGLE-IV survey and followed by the Public ESO Spectroscopic Survey for Transient Objects. The inferred redshift of $z=0.07$ implies an absolute magnitude in the rest-frame $I$-band of M$_{I}\sim-17.6$ mag. This places it in the luminosity range between normal Type Ia SNe and novae. Optical and near infrared spectroscopy reveal mostly Ti and Ca lines, and an unusually red color arising from strong depression of flux at rest wavelengths $<5000$ Å. To date, this is the only reported SN showing Ti-dominated spectra. The data are broadly consistent with existing models for the pure detonation of a helium shell around a low-mass CO white dwarf and "double-detonation" models that include a secondary detonation of a CO core following a primary detonation in an overlying helium shell.

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