arXiv subjects

Glen Petitpas

Publications and source records attributed to Glen Petitpas.

At least 19 recordsLinked to original sources

arXiv2026

An Ultra-Short Period Super-Earth and a Sub-Neptune Orbiting the K dwarf TOI-4311

We report the discovery and characterisation of the multi-planetary system around TOI-4311, a K dwarf kinematically between the Galactic thick disk and Hercules stream. TOI-4311 hosts an ultra-short-period super-Earth (P$\sim$0.99 d, $1.376\substack{+0.077\\-0.080}$ R$_\oplus$) and a longer period sub-Neptune (P$\sim$15 d, $2.47\substack{+0.12\\-0.11}$ R$_\oplus$) that was first detected in the TESS photometry. Using follow-up observations with CHEOPS and HARPS, we refine the planetary radius of both planets, derive the mass of planet b ($4.5\substack{+1.5\\-1.4}$ M$_\oplus$) and confirm the planetary nature of planet c. Intriguingly, a third periodic signal is clearly detected in our HARPS RVs that we cannot link to stellar activity. This signal could be attributed to a third planet (P$\sim$38 d, Msin(i)=$26.4\substack{+6.3\\-6.8}$ M$_\oplus$) in the system, however with the current photometric dataset we do not find a transit. Our dynamical analysis highlights that this potential outer planet would remain stable. Using the precise radius and mass for TOI-4311 b we model its interior structure and find that it is very dense given the host star's galactic kinematics and chemistry. Hence this system could challenge current formation theories and provide insights into planet formation across the galaxy.

astro-ph.EP↗

arXiv2026

QLP Data Release Notes 004: TESS-Gaia Light Curve Photometry Implementation

The Quick-Look Pipeline (QLP; Huang et al. 2020, Kunimoto et al. 2021 and references therein) generates light curves for up to 2 million stars every 27.4 days observed by TESS as part of its planet search. As machine learning methods enable deeper searches and scientific priorities shift toward fainter stars, there is a motivation for QLP to perform better at fainter magnitudes. We have adopted the photometry methods employed by the TESS-Gaia Light Curve package (Han & Brandt 2023), which has been shown to have better noise characteristics than the original QLP photometry from 10.5 $<$ $T$ $<$ 13.5. We still perform aperture photometry and deliver 3 apertures, and 3 levels of detrending for all stars brighter than $T$ = 13.5, so the changes should be seamless for external users. This method is implemented as of Sector 94 in QLP light curves and is providing users with higher precision light curves and allows detection of fainter signals in our planet searches.

astro-ph.EP↗

arXiv2026

Resolved Dust Emission and CO Isotopologues in Giant Molecular Clouds of the Andromeda Galaxy

Dust emission at submillimeter wavelengths can be used to reliably trace the basic properties of molecular clouds. Early results from a recent Submillimeter Array (SMA) survey of the Andromeda Galaxy (M31) include the first detections of resolved dust continuum emission from individual giant molecular clouds (GMCs) in an external spiral galaxy. This paper updates on the now-complete SMA survey of 80 Herschel-identified giant molecular associations (GMAs) in M31. The SMA survey simultaneously probes dust continuum emission at 230 GHz and the $J = 2 \rightarrow 1$ transitions of the CO isotopologues, $^{12}\rm CO$, $^{13}\rm CO$, and $\rm C^{18}O$ at a spatial resolution of $\lesssim 15~\mathrm{pc}$. Dust continuum emission was detected in 71 cloud cores, of which 26 were resolved. This more than doubles the size of the previous sample. By comparing dust and CO observations with identical astrometry, we directly measure the dust mass to-light ratios, $\rm α^{\prime}_{^{12}CO}$, and $\rm α^{\prime}_{^{13}CO}$. We derive $<α^{\prime}_{\rm ^{12}\rm CO}>~=~0.070~\pm~0.031~M_{\odot}\,(\rm K~km~s^{-1}~pc^{2})^{-1}$ and $<α^{\prime}_{\rm ^{13}\rm CO}>~=~0.37~\pm~0.20~M_{\odot}\,(\rm K~km~s^{-1}~pc^{2})^{-1}$ for the increased sample, which are in agreement with previously reported values. From virial analysis, we find that 80% of the GMC regions traced by resolved dust emission are bound and close to virial equilibrium. Finally, we update our analysis on the metallicity dependence of $\rm α^{\prime}_{\rm CO}$ by combining SMA observations with existing MMT/Hectospec optical spectroscopy toward H II regions. We find no trend in $\rm α^{\prime}_{\rm CO}$ with metallicity, supporting the previous findings.

astro-ph.GA↗

arXiv2025

A Disintegrating Rocky Planet with Prominent Comet-like Tails Around a Bright Star

We report the discovery of BD+05$\,$4868$\,$Ab, a transiting exoplanet orbiting a bright ($V=10.16$) K-dwarf (TIC 466376085) with a period of 1.27 days. Observations from NASA's Transiting Exoplanet Survey Satellite (TESS) reveal variable transit depths and asymmetric transit profiles that are characteristic of comet-like tails formed by dusty effluents emanating from a disintegrating planet. Unique to BD+05$\,$4868$\,$Ab is the presence of prominent dust tails in both the trailing and leading directions that contribute to the extinction of starlight from the host star. By fitting the observed transit profile and analytically modeling the drift of dust grains within both dust tails, we infer large grain sizes ($\sim1-10\,μ$m) and a mass loss rate of $10\,M_{\rm \oplus}\,$Gyr$^{-1}$, suggestive of a lunar-mass object with a disintegration timescale of only several Myr. The host star is probably older than the Sun and is accompanied by an M-dwarf companion at a projected physical separation of 130 AU. The brightness of the host star, combined with the planet's relatively deep transits ($0.8-2.0\%$), presents BD+05$\,$4868$\,$Ab as a prime target for compositional studies of rocky exoplanets and investigations into the nature of catastrophically evaporating planets.

astro-ph.EP↗

arXiv2024

CO isotopologue-derived molecular gas conditions and CO-to-H$_2$ conversion factors in M51

Over the past decade, several millimeter interferometer programs have mapped the nearby star-forming galaxy M51 at a spatial resolution of ${\le}170$ pc. This study combines observations from three major programs: the PdBI Arcsecond Whirlpool Survey (PAWS), the SMA M51 large program (SMA-PAWS), and the Surveying the Whirlpool at Arcseconds with NOEMA (SWAN). The dataset includes the (1-0) and (2-1) rotational transitions of $^{12}$CO, $^{13}$CO, and C$^{18}$O isotopologues. The observations cover the $r{<}\rm 3\,kpc$ region including center and part of the disk, thereby ensuring strong detections of the weaker $^{13}$CO and C$^{18}$O lines. All observations are convolved in this analysis to an angular resolution of 4$''$, corresponding to a physical scale of ${\sim}$170 pc. We investigate empirical line ratio relations and quantitatively evaluate molecular gas conditions such as temperature, density, and the CO-to-H$_2$ conversion factor ($α_{\rm CO}$). We employ two approaches to study the molecular gas conditions: (i) assuming local thermal equilibrium (LTE) to analytically determine the CO column density and $α_{\rm CO}$, and (ii) using non-LTE modeling with RADEX to fit physical conditions to observed CO isotopologue intensities. We find that the $α_{\rm CO}$ values {in the center and along the inner spiral arm} are $\sim$0.5 dex (LTE) and ${\sim}$0.1 dex (non-LTE) below the Milky Way inner disk value. The average non-LTE $α_{\rm CO}$ is $2.4{\pm}0.5$ M$_\odot$ pc$^{-2}$ (K km s$^{-1}$)$^{-1}$. While both methods show dispersion due to underlying assumptions, the scatter is larger for LTE-derived values. This study underscores the necessity for robust CO line modeling to accurately constrain the molecular ISM's physical and chemical conditions in nearby galaxies.

astro-ph.GA↗

arXiv2024

Probing the high frequency variability of NGC 5044: the key to AGN feedback

The active galactic nucleus (AGN) feeding and feedback process in the centers of galaxy clusters and groups is still not well understood. NGC 5044 is the ideal system in which to study AGN feedback. It hosts the largest known reservoir of cold gas in any cool-core galaxy group, and features several past epochs of AGN feedback imprinted as cavities in the X-ray bright intragroup medium (IGrM), as well as parsec scale jets. We present Submillimeter Array (SMA), Karl G. Jansky Very Large Array (VLA), James Clerk Maxwell Telescope (JCMT), and Atacama Large Millimeter/submillimeter Array (ALMA) high frequency observations of NGC 5044 to assess the time variability of the mmwaveband emission from the accretion disk, and quantify the Spectral Energy Distribution (SED) from the radio to sub-millimeter band. The SED is well described by advection dominated accretion flow (ADAF) model and self-absorbed jet emission from an aging plasma with tau = 1kyr. We find a characteristic variability timescale of 150 days, which constrains the ADAF emission region to about 0.1pc, and the magnetic field to 4.7mG in the jets and and 870G in the accretion disk. A longer monitoring/sampling will allow to understand if the underlying process is truly periodic in nature.

astro-ph.GA↗

arXiv2024

The Molecular Clouds of M31

Deep interferometric observations of CO and dust continuum emission are obtained with the Sub-Millimeter Array (SMA) at 230 GHz to investigate the physical nature of the giant molecular cloud (GMC) population in the Andromeda galaxy (M31). We use J = 2-1 $^{12}$CO and $^{13}$CO emission to derive the masses, sizes and velocity dispersions of 162 spatially resolved GMCs. We perform a detailed study of a subset of 117 GMCs that exhibit simple, single component line profile shapes. Examining the Larson scaling relations for these GMCs we find: 1- a highly correlated mass-size relation in both $^{12}$CO and $^{13}$CO emission; 2- a weakly correlated $^{12}$CO linewidth-size (LWS) relation along with a weaker, almost non-existent, $^{13}$CO LWS relation, suggesting a possible dependence of the LWS relation on spatial scale; and 3-that only 43\% of these GMCs are gravitationally bound. We identify two classes of GMCs based on the strength and extent of their $^{13}$CO emission. Examination of the Larson relations finds that both classes are individually characterized by strong $^{12}$CO mass-size relations and much weaker $^{12}$CO and $^{13}$CO LWS relations. The majority (73\%) of strong $^{13}$CO emitting GMCs are found to be gravitationally bound. However, only 25\% of the weak $^{13}$CO emitting GMCs are bound. The resulting breakdown in the Larson relations in the weak $^{13}$CO emitting population decouples the mass-size and LWS relations demonstrating that independent physical causes are required to understand the origin of each. Finally, in nearly every aspect, the physical properties of the M31 GMCs are found to be very similar to those of local Milky Way clouds.

astro-ph.GA↗

arXiv2023

Minutes-duration Optical Flares with Supernova Luminosities

In recent years, certain luminous extragalactic optical transients have been observed to last only a few days. Their short observed duration implies a different powering mechanism from the most common luminous extragalactic transients (supernovae) whose timescale is weeks. Some short-duration transients, most notably AT2018cow, display blue optical colours and bright radio and X-ray emission. Several AT2018cow-like transients have shown hints of a long-lived embedded energy source, such as X-ray variability, prolonged ultraviolet emission, a tentative X-ray quasiperiodic oscillation, and large energies coupled to fast (but subrelativistic) radio-emitting ejecta. Here we report observations of minutes-duration optical flares in the aftermath of an AT2018cow-like transient, AT2022tsd (the "Tasmanian Devil"). The flares occur over a period of months, are highly energetic, and are likely nonthermal, implying that they arise from a near-relativistic outflow or jet. Our observations confirm that in some AT2018cow-like transients the embedded energy source is a compact object, either a magnetar or an accreting black hole.

astro-ph.HE↗

arXiv2023

Tracing Dense Gas in Six Resolved GMCs of the Andromeda Galaxy

We present dense-gas--tracing molecular observations of six resolved Giant Molecular Clouds (GMCs) in the Andromeda Galaxy (M31). Using the NOEMA interferometer, we observed the transitions of HCN(1-0), HCO$^+$(1-0), and HNC(1-0), as well as $^{13}$CO(1-0) and 100 GHz continuum emission. This complements our earlier work with the Submillimeter Array (SMA), including resolved dust continuum detections of these clouds at 230 GHz. In this work, we first compare different continuum measurements to conclude that the average free-free contamination of the observed flux is 71% at 3 mm but only 13% at 1 mm, confirming that emission at 3 mm is less reliable than that at 1 mm for calculating dust masses of star-forming clouds. While the $^{13}$CO emission is more extended than both HCN and HCO$^+$ emission, which in turn is more extended than HNC emission, we find that both HCN and HCO$^+$ are spatially coincident with, and similarly extended as, the 230 GHz dust emission. This suggests that both the 230 GHz dust continuum and most importantly the HCN emission traces the dense gas component of these GMCs. From comparison of the molecular emission with dust masses derived from the 230 GHz continuum emission, we obtain the first direct measurements of the dust-mass-to-light ratios ($α^\prime_{HCN}$ and $α^\prime_{HCO^+}$) in GMCs of an external galaxy. For HCN, the result is broadly similar to a measurement in the local Perseus cloud suggesting that these are indeed dense gas conversion factors. A larger cloud sample will be required to assess whether HCN is tracing comparable cloud-scale density regimes across the environments of M31.

astro-ph.GA↗

arXiv2023

A Search for Extragalactic Fast Blue Optical Transients in ZTF and the Rate of AT2018cow-like Transients

We present a search for extragalactic fast blue optical transients (FBOTs) during Phase I of the Zwicky Transient Facility (ZTF). We identify 38 candidates with durations above half-maximum light 1 d < t1/2 < 12 d, of which 28 have blue (g-r<-0.2 mag) colors at peak light. Of the 38 transients (28 FBOTs), 19 (13) can be spectroscopically classified as core-collapse supernovae (SNe): 11 (8) H- or He-rich (Type II/IIb/Ib) SNe, 6 (4) interacting (Type IIn/Ibn) SNe, and 2 (1) H&He-poor (Type Ic/Ic-BL) SNe. Two FBOTs (published previously) had high-S/N predominantly featureless spectra and luminous radio emission: AT2018lug and AT2020xnd. Seven (five) did not have a definitive classification: AT 2020bdh showed tentative broad H$α$ in emission, and AT 2020bot showed unidentified broad features and was 10 kpc offset from the center of an early-type galaxy. Ten (six) have no spectroscopic observations or redshift measurements. We present multiwavelength (radio, millimeter, and/or X-ray) observations for five FBOTs (three Type Ibn, one Type IIn/Ibn, one Type IIb). Additionally, we search radio-survey (VLA and ASKAP) data to set limits on the presence of radio emission for 22 of the transients. All X-ray and radio observations resulted in non-detections; we rule out AT2018cow-like X-ray and radio behavior for five FBOTs and more luminous emission (such as that seen in the Camel) for four additional FBOTs. We conclude that exotic transients similar to AT2018cow, the Koala, and the Camel represent a rare subset of FBOTs, and use ZTF's SN classification experiments to measure the rate to be at most 0.1% of the local core-collapse SN rate.

astro-ph.HE↗

arXiv2023

QLP Data Release Notes 003: GPU-based Transit Search

The Quick-Look Pipeline (QLP; Huang et al. 2020, Kunimoto et al. 2021 and references therein) searches for transit signals in the multi-sector light curves of several hundreds of thousand stars observed by TESS every 27.4-day sector. The computational expense of the planet search has grown considerably over time, especially as the TESS observing baseline continues to increase in the second Extended Mission. Starting in Sector 59, QLP has switched to a significantly faster GPU-based transit search capable of searching an entire sector in only ~1 day. We describe its implementation and performance.

astro-ph.EP↗

arXiv2022

Simultaneous Radio and Optical Polarimetry of GRB 191221B Afterglow

Gamma-ray bursts (GRBs) are the most luminous transients in the universe and are utilized as probes of early stars, gravitational wave counterparts, and collisionless shock physics. In spite of studies on polarimetry of GRBs in individual wavelengths that characterized intriguing properties of prompt emission and afterglow, no coordinated multi-wavelength measurements have yet been performed. Here, we report the first coordinated simultaneous polarimetry in the optical and radio bands for the afterglow associated with the typical long GRB 191221B. Our observations successfully caught the radio emission, which is not affected by synchrotron self-absorption, and show that the emission is depolarized in the radio band compared to the optical one. Our simultaneous polarization angle measurement and temporal polarization monitoring indicate the existence of cool electrons that increase the estimate of jet kinetic energy by a factor of $>$ 4 for this GRB afterglow. Further coordinated multi-wavelength polarimetric campaigns would improve our understanding of the total jet energies and magnetic field configurations in the emission regions of various types of GRBs, which are required to comprehend the mass scales of their progenitor systems and the physics of collisionless shocks.

astro-ph.HE↗

arXiv2022

A very luminous jet from the disruption of a star by a massive black hole

Tidal disruption events (TDEs) are bursts of electromagnetic energy released when supermassive black holes (SMBHs) at the centers of galaxies violently disrupt a star that passes too close. TDEs provide a new window to study accretion onto SMBHs; in some rare cases, this accretion leads to launching of a relativistic jet, but the necessary conditions are not fully understood. The best studied jetted TDE to date is Swift J1644+57, which was discovered in gamma-rays, but was too obscured by dust to be seen at optical wavelengths. Here we report the optical discovery of AT2022cmc, a rapidly fading source at cosmological distance (redshift z=1.19325) whose unique lightcurve transitioned into a luminous plateau within days. Observations of a bright counterpart at other wavelengths, including X-rays, sub-millimeter, and radio, supports the interpretation of AT2022cmc as a jetted TDE containing a synchrotron "afterglow", likely launched by a SMBH with spin $a \gtrsim 0.3$. Using 4 years of Zwicky Transient Facility (ZTF) survey data, we calculate a rate of $0.02 ^{+ 0.04 }_{- 0.01 }$ Gpc$^{-3}$ yr$^{-1}$ for on-axis jetted TDEs based on the luminous, fast-fading red component, thus providing a measurement complementary to the rates derived from X-ray and radio observations. Correcting for the beaming angle effects, this rate confirms that about 1% of TDEs have relativistic jets. Optical surveys can use AT2022cmc as a prototype to unveil a population of jetted TDEs.

astro-ph.HE↗

arXiv2022

Luminous Millimeter, Radio, and X-ray Emission from ZTF20acigmel (AT2020xnd)

Observations of the extragalactic ($z=0.0141$) transient AT2018cow established a new class of energetic explosions shocking a dense medium, which produce luminous emission at millimeter and sub-millimeter wavelengths. Here we present detailed millimeter- through centimeter-wave observations of a similar transient, ZTF20acigmel (AT2020xnd) at $z=0.2433$. Using observations from the NOrthern Extended Millimeter Array and the Very Large Array, we model the unusual millimeter and radio emission from AT2020xnd under several different assumptions, and ultimately favor synchrotron radiation from a thermal electron population (relativistic Maxwellian). The thermal-electron model implies a fast but sub-relativistic ($v\approx0.3c$) shock and a high ambient density ($n_e\approx4\times10^{3}$cm$^{-3}$ at $Δt\approx40$ days). The X-ray luminosity of $L_X\approx10^{43}$ erg sec$^{-1}$ exceeds simple predictions from the radio and UVOIR luminosity and likely has a separate physical origin, such as a central engine. Using the fact that month-long luminous ($L_ν\approx 2\times10^{30}$ erg sec$^{-1}$ Hz$^{-1}$ at 100 GHz) millimeter emission appears to be a generic feature of transients with fast ($t_{1/2}\approx3$ days) and luminous ($M_\mathrm{peak}\approx -21 $mag) optical light curves, we estimate the rate at which transients like AT2018cow and AT2020xnd will be detected by future wide-field millimeter transient surveys such as CMB-S4, and conclude that energetic explosions in dense environments may represent a significant population of extragalactic transients in the 100 GHz sky.

astro-ph.HE↗

arXiv2021

Simultaneous Deep Measurements of CO isotopologues and Dust Emission in Giant Molecular Clouds in the Andromeda Galaxy

We present simultaneous measurements of emission from dust continuum at 230 GHz and the J=2-1 $^{12}$CO, $^{13}$CO and C$^{18}$O isotopologues at $\sim$ 15 pc resolution from individual Giant Molecular Clouds (GMCs) in the Andromeda galaxy (M31). These observations were obtained in an ongoing survey of this galaxy being conducted with the Submillimeter Array (SMA). Initial results describing the continuum and $^{12}$CO emission were published earlier. Here we primarily analyze the observations of $^{13}$CO and C$^{18}$O emission and compare them to the measurements of dust continuum and $^{12}$CO emission. We also report additional dust continuum and CO measurements from newly added GMCs to the M31 sample. We detect spatially resolved $^{13}$CO emission with high signal-to-noise in 31 objects. We find the extent of the $^{13}$CO emission to be nearly comparable to that of $^{12}$CO, typically covering 75\% of the area of the $^{12}$CO emission. We derive $^{13}$CO and C$^{18}$O abundances of 2.9 $\times 10^{-6}$ and 4.4 $\times 10^{-7}$ relative to H$_2$, respectively, by comparison with hydrogen column densities of the same regions derived from the dust continuum observations assuming a Milky Way gas-to-dust ratio. We find the isotopic abundance ratio [$^{13}$CO]/[C$^{18}$O] = 6.7$\pm$2.9 to be consistent with the Milky Way value (8.1). Finally, we derive the mass-to-light conversion factors for all three CO species to be $α_{12} = 8.7 \pm 3.9$, $α_{13} = 48.9 \pm 20.4$ and $α_{18} = 345^{+25}_{-31}$ M$_\odot$ (K km s$^{-1}$pc$^2$)$^{-1}$ for the J=2-1 transitions of $^{12}$CO, $^{13}$CO and C$^{18}$O, respectively.

astro-ph.GA↗

arXiv2020

Two Component Jets of GRB160623A as Shocked Jet cocoon afterglow

Two components of jets associated with the afterglow of the gamma-ray burst GRB 160623A were observed with multi-frequency observations including long-term monitoring in a sub-millimetre range (230 GHz) using the SMA. The observed light curves with temporal breaks suggests on the basis of the standard forward-shock synchrotron radiation model that the X-ray radiation is narrowly collimated with an opening angle $θ_{n,j}<\sim6^{\circ}$ whereas the radio radiation originated from wider jets ($\sim27^{\circ}$). The temporal and spectral evolutions of the radio afterglow agree with those expected from a synchrotron radiation modelling with typical physical parameters except for the fact that the observed wide jet opening angle for the radio emission is significantly larger than the theoretical maximum opening angle. By contrast, the opening angle of the X-ray afterglow is consistent with the typical value of GRB jets. Since the theory of the relativistic cocoon afterglow emission is similar to that of a regular afterglow with an opening angle of $\sim30^{\circ}$, the observed radio emission can be interpreted as the shocked jet cocoon emission. This result therefore indicates that the two components of the jets observed in the GRB 160623A afterglow is caused by the jet and the shocked jet cocoon afterglows.

astro-ph.HE↗

arXiv2020

First Resolved Dust Continuum Measurements of Individual Giant Molecular Clouds in the Andromeda Galaxy

In our local Galactic neighborhood, molecular clouds are best studied using a combination of dust measurements, to determine robust masses, sizes and internal structures of the clouds, and molecular-line observations to determine cloud kinematics and chemistry. We present here the first results of a program designed to extend such studies to nearby galaxies beyond the Magellanic Clouds. Utilizing the wideband upgrade of the Submillimeter Array (SMA) at 230 GHz we have obtained the first continuum detections of the thermal dust emission on sub-GMC scales ($\sim$ 15 pc) within the Andromeda galaxy (M31). These include the first resolved continuum detections of dust emission from individual GMCs beyond the Magellanic Clouds. Utilizing a powerful capability of the SMA, we simultaneously recorded CO(2-1) emission with identical $(u,\,v)$ coverage, astrometry and calibration, enabling the first measurements of the CO conversion factor, $α_{\rm\,CO(2-1)}$, toward individual GMCs across an external galaxy. Our direct measurement yields an average CO--to--dust mass conversion factor of $α^\prime_{\rm CO-dust} = 0.042\pm0.018$ $M_\odot$ (K km s$^{-1}$ pc$^2$)$^{-1}$ for the $J= 2-1$ transition. This value does not appear to vary with galactocentric radius. Assuming a constant gas-to-dust ratio of 136, the resulting $α_{\rm CO}$ $=$ 5.7 $\pm$ 2.4 $M_\odot$ (K km s$^{-1}$ pc$^2$)$^{-1}$ for the 2-1 transition is in excellent agreement with that of Milky Way GMCs, given the uncertainties. Finally, using the same analysis techniques, we compare our results with observations of the local Orion molecular clouds, placed at the distance of M31 and simulated to appear as they would if observed by the SMA.

astro-ph.GA↗

arXiv2019

Evidence for Late-stage Eruptive Mass-loss in the Progenitor to SN2018gep, a Broad-lined Ic Supernova: Pre-explosion Emission and a Rapidly Rising Luminous Transient

We present detailed observations of ZTF18abukavn (SN2018gep), discovered in high-cadence data from the Zwicky Transient Facility as a rapidly rising ($1.4\pm0.1$ mag/hr) and luminous ($M_{g,\mathrm{peak}}=-20$ mag) transient. It is spectroscopically classified as a broad-lined stripped-envelope supernova (Ic-BL SN). The high peak luminosity ($L_{\mathrm{bol}} \gtrsim 3 \times 10^{44}$ erg $\mathrm{sec}^{-1}$), the short rise time ($t_{\mathrm{rise}}= 3$ days in $g$-band), and the blue colors at peak ($g-r\sim-0.4$) 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 ($T_{\mathrm{eff}}\gtrsim40,000$ K) spectra of a stripped-envelope SN. A retrospective search revealed luminous ($M_g \sim M_r \approx -14\,$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 $E_\mathrm{γ,iso}<4.9 \times 10^{48}$ erg, a limit on X-ray emission $L_{\mathrm{X}} < 10^{40}\,$erg sec$^{-1}$, and a limit on radio emission $νL_ν\lesssim 10^{37}\,$erg sec$^{-1}$. Taken together, we find that the early ($<10\,$days) data are best explained by shock breakout in a massive shell of dense circumstellar material ($0.02\,M_\odot$) at large radii ($3 \times 10^{14}\,$cm) that was ejected in eruptive pre-explosion mass-loss episodes. The late-time ($>10$ days) light curve requires an additional energy source, which could be the radioactive decay of Ni-56.

astro-ph.HE↗