arXiv subjects

John Banovetz

Publications and source records attributed to John Banovetz.

18 recordsLinked to original sources

arXiv2026

The "dark dips" phenomenon in the LSST Camera on-sky images

When the commissioning camera (ComCam), and then the LSST Camera, started taking on-sky images at the Vera Rubin Observatory, some of the ITL STA3800 CCDs exhibited a previously undocumented effect. When a sufficiently bright star is superimposed over the sky background, the sensor columns that contain the star appear slightly darker than the background, both above and below the position of the star. The visual appearance of these "dark dips" in the background is enhanced by a slight excess of flux within the neighboring columns, suggesting that they are caused by a lateral field distortion that shifts charges away from the central columns. This effect is not uniform across sensors, reaching an amplitude of up to seven percent of the background in the worst cases, but being undetectable in other sensors under the same conditions. For the affected sensors, the threshold required for the dips to become detectable also varies, from a few hundred to a few thousands saturated pixels within the star footprint. We developed means to quantify the dips, and studied the effect statistically over hundreds of frames, in order to categorize each sensor. In particular, we found no significant dependence on the filter color. We then developed a strategy to dynamically mask the affected columns during the Instrument Signature Removal process, to avoid any potential effect on photometric and astrometric performance.

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arXiv2026

The On-Sky Performance of the LSST Camera CCD Array

The focal plane of the LSST Camera contains 189 individual science CCDs, arranged into 21 raft tower modules, along with 4 wavefront and 8 guider CCDs located in 4 additional corner RTMs. Altogether, the LSST Camera CCDs compose the largest focal plane ever constructed. The LSST Camera is the primary instrument of Rubin Observatory, which will begin the Legacy Survey of Space and Time in 2026. In this paper, we describe the on-sky performance of the LSST Camera CCDs, from receipt at NSF/DOE Vera C. Rubin Observatory in May 2024 to on-sky observations during the first year of operations. We discuss the process to establish functionality of several CCDs which were affected by an electrical short and faulty analog-digital converter, optimizations of readout timing in response to changes in the survey strategy, and implementation of enhanced focal plane safety measures through an active clearing mechanism on the CCDs. Finally, we discuss sensor features observed on-sky, and global performance during the first year of operations. The operations to date of the LSST Camera CCDs have demonstrated the capability of performing a wide, fast, and deep optical imaging survey of the entire southern sky at the Rubin Observatory.

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arXiv2026

The Rubin Observatory Target-of-Opportunity System in the First Year of Operations

The NSF/DOE Vera C. Rubin Observatory is a discovery machine, with unprecedented survey speed, which can be used to identify exotic astrophysical transients. In its prime mission, the ten year Legacy Survey of Space and Time will use 3% of its total time for Target of Opportunity observations, which includes response to gravitational wave events, high energy neutrinos, potentially-hazardous asteroids, and other astrophysical phenomena. Target of Opportunity observations exist outside of the usual LSST operational mode, requiring special attention to maximize performance. We review the Rubin Target of Opportunity system during its first year of Rubin Observatory operations, the Targets of Opportunity pursued since LSST first light, and the overall efficiency of the system.

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arXiv2026

GRB 260310A/SN 2026fgk: Photometric and Spectroscopic Evolution of a Nearby GRB-Supernova and an Exceptionally Bright Afterglow at z=0.153

The association of broad-lined Type Ic supernovae with long-duration gamma-ray bursts (GRBs) has been known for 28 years. However, only about seventy gamma-ray burst supernovae (GRB-SNe) have been identified, of which only half have spectroscopic classifications. At $z=0.153$, GRB 260310A is the 12th spectroscopically confirmed GRB-SN discovered within 1 Gpc, offering a critical opportunity to follow one of these rare supernovae in detail. We present optical to near-infrared imaging and spectroscopy of GRB 260310A and SN 2026fgk out to 65 d after discovery. The optical afterglow is among the brightest ever observed from a GRB. Spectra obtained more than two weeks after the explosion reveal broad absorption features that securely identify SN 2026fgk as a Type Ic-BL supernova. Modeling of the multi-wavelength ($grizJK_s$) lightcurve shows that the supernova is approximately half the luminosity ($k_\textrm{98bw}=0.4-0.6$) of the canonical GRB-SN 1998bw. We derive a nickel mass of $M_\textrm{Ni}=0.4-0.5$ $M_\odot$ with a total ejected mass of $M_\textrm{ej}\approx4-6 $ $M_\odot$ and kinetic energy $E_\textrm{K}=(3-8)\times10^{51}$ erg. The GRB exploded at an extremely large offset of 15 kpc from its host galaxy. Long-slit spectra reveal a ``bridge'' of nebular emission extending along the galaxy's disk to the GRB location, which has a sub-solar metallicity ($\sim$\,$0.4Z_\odot$), compared to a near solar metallicity for the host galaxy. This indicates that the large offset arises from the galaxy's extended light profile rather than an isolated environment.

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arXiv2026

EP260321a/SN 2026gzf: The Faintest Shock Breakout Associated with a Broad-Lined Supernova

The explosion of a star is first marked by the shock wave breaking out of the stellar surface, producing a burst of ultraviolet and X-ray radiation. These events are observationally rare, despite likely accompanying the majority of supernovae. Here, we report on our multi-wavelength observing campaign of the closest Einstein Probe fast X-ray transient EP260321a at $z=0.0344$. The thermal ($kT=130$ eV) X-ray emission with peak luminosity $1.0\times10^{45}$ erg s$^{-1}$ points to a shock breakout origin. We demonstrate that EP260321a is accompanied by a broad-lined Type Ic supernova, SN 2026gzf. The supernova properties, including its spectral evolution, lightcurve evolution, and expansion velocities, are all typical of the energetic stripped-envelope supernovae associated with gamma-ray bursts. However, deep X-ray upper limits obtained with the \textit{Chandra X-ray Observatory} do not detect an X-ray afterglow, and instead exclude the afterglow of known gamma-ray bursts or fast X-ray transients. If the stellar explosion launched a successful relativistic jet, we require that it had both a low Lorentz factor $Γ_0$\,$<$\,$30$ and a kinetic energy $E_\textrm{kin}$\,$<$\,$10^{49}$ erg for a stellar wind density of $A_*$\,$\gtrsim$\,$1$. We propose that EP260321a originated from a mildly relativistic, weak outflow that was choked by the progenitor star. This scenario is capable of naturally explaining its low X-ray luminosity and lack of prompt gamma-ray emission. EP260321a bridges the gap between SN 2008D and low-luminosity GRBs, suggesting a greater diversity in the physical parameters of stripped stars as they undergo terminal collapse.

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arXiv2026

Uncovering the Next Galactic Supernova with the Vera C. Rubin Observatory

Supernovae are observed to occur approximately 1-2 times per century in a galaxy like the Milky Way. Based on historical records, however, the last core-collapse galactic supernova observed by humans occurred almost 1,000 years ago. Luckily, we are well positioned to catch the next one with the advent of new neutrino detectors and astronomical observatories. Neutrino observatories can provide unprecedented triggers for a galactic supernova event as they are likely to see a supernova neutrino signal anywhere from minutes to days before the shock breakout causes the supernova to brighten in optical wavelengths. Given its large etendue, the Vera C. Rubin Observatory is ideally positioned to rapidly localize the optical counterpart based on the neutrino trigger. In this paper we simulate events to study the efficiency with which supernovae are optimally localized by the Vera C. Rubin Observatory. We find that the observatory is ideal for initial localization of nearly all observable supernova triggers and has a 57-97% chance of catching any supernova based on theoretical stellar mass density predictions and observations. We provide an analysis of optimal filter selection and exposure times and discuss observational caveats.

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arXiv2026

The Vera C. Rubin Observatory Data Preview 1

We present Rubin Data Preview 1 DP1, the first data from the NSF DOE Vera C Rubin Observatory, comprising raw and calibrated single epoch images, coadds, difference images, detection catalogs, and ancillary data products. DP1 is based on 1792 optical near infrared exposures acquired over 48 distinct nights by the Rubin Commissioning Camera LSSTComCam on the Simonyi Survey Telescope at the Summit Facility on Cerro Pachón Chile in late 2024. DP1 covers $\sim$15 deg$^2$ distributed across seven roughly equal-sized non-contiguous fields, each independently observed in six broad photometric bands $ugrizy$. The median FWHM of the point spread function across all bands is approximately 1.14 arcseconds, with the sharpest images reaching about 0.58 arcseconds. The 5$σ$ point source depths for coadded images in the deepest field the Extended Chandra Deep Field South are $u$ = 24.55, $g$ = 26.18, $r$ = 25.96, $i$ = 25.71, $z$ = 25.07, $y$ = 23.1. Other fields are no more than 2.2 magnitudes shallower in any band where they have nonzero coverage. DP1 contains approximately 2.3 million distinct astrophysical objects, of which 1.6 million are extended in at least one band in coadds and 431 solar system objects of which 93 are new discoveries. DP1 is approximately 3.5 TB in size and is available to Rubin data rights holders via the Rubin Science Platform a cloud based environment for the analysis of petascale astronomical data. While small compared to future LSST releases its high quality and diversity of data support a broad range of early science investigations ahead of full operations in 2026.

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arXiv2026

The DESI Transients Survey: Legacy Classifications and Methodology

We present the first systematic spectroscopic observations of extragalactic transients from the Dark Energy Spectroscopic Instrument (DESI), as part of the DESI Transients Survey program. With 5,000 fibers and an ${\sim} 8$ deg$^2$ field of view, we exploit DESI as a machine for the discovery and classification of transients. We present transient classifications from archival DESI data in Data Releases 1 and 2, relying on a combination of a secondary target program and serendipitous observations. We also present observations from the first 6 months of the DESI spare fiber program dedicated to transients. The program is run in coordination with a dedicated DECam time-domain survey, serving as a pathfinder for what we will be able to achieve in conjunction with the Rubin Observatory Legacy Survey of Space and Time (LSST). We classify over 250 transients, of which the majority were previously unclassified. The sample comprises thermonuclear and core-collapse supernovae and tidal disruption events (TDEs), including a TDE observed before its discovery in imaging. We demonstrate DESI's ability to classify a population of faint transients down to $r\sim 22.5$ mag during main survey operations, with negligible impacts on DESI's main observations.

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arXiv2025

AT2025ulz and S250818k: Leveraging DESI spectroscopy in the hunt for a kilonova associated with a sub-solar mass gravitational wave candidate

On August 18th, 2025, the LIGO--Virgo--KAGRA collaboration reported a sub-threshold gravitational wave candidate detection consistent with a sub-solar-mass neutron star merger, denoted S250818k. An optical transient, AT2025ulz, was discovered within the localization region. AT2025ulz initially appeared to meet the expected behavior of kilonova (KN) emission, the telltale signature of a binary neutron star merger. The transient subsequently rebrightened after $\sim$\,$5$ days and developed spectral features characteristic of a Type IIb supernova. In this work, we analyze the observations of the host galaxy of AT2025ulz obtained by the Dark Energy Spectroscopic Instrument (DESI). From the DESI spectrum, we obtain a secure redshift of $z = 0.084840 \pm 0.000006$, which places the transient within $2σ$ of the gravitational wave distance and results in an integral overlap between the gravitational wave alert and the transient location of $\log_{10}\mathcal{I} \approx 3.9-4.2$. Our analysis of the host galaxy's spectral energy distribution reveals a star-forming, dusty galaxy with stellar mass ${\sim} 10^{10}~M_\odot$, broadly consistent with the population of both short gamma-ray bursts and core-collapse supernova host galaxies. We also present our follow-up of DESI-selected candidate host galaxies using the Fraunhofer Telescope at the Wendelstein Observatory, and show the promise of DESI for associating or rejecting candidate electromagnetic counterparts to gravitational wave alerts. These results emphasize the value of DESI's extensive spectroscopic dataset in rapidly characterizing host galaxies, enabling spectroscopic host subtraction, and guiding targeted follow-up.

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arXiv2024

'Weather' in the LSST Camera: Investigating Patterns in Differenced Flat Images

During electro-optical testing of the camera for the upcoming Vera C. Rubin Observatory Legacy Survey of Space and Time, a unique low-signal pattern was found in differenced pairs of flat images used to create photon transfer curves, with peak-to-peak variations of a factor of 10^-3. A turbulent pattern of this amplitude was apparent in many differenced flat-fielded images. The pattern changes from image to image and shares similarities with atmospheric 'weather' turbulence patterns. We applied several strategies to determine the source of the turbulent pattern and found that it is representative of the mixing of the air and index of refraction variations caused by the internal camera purge system displacing air, which we are sensitive to due to our flat field project setup. Characterizing this changing environment with 2-D correlation functions of the 'weather' patterns provides evidence that the images reflect the changes in the camera environment due to the internal camera purge system. Simulations of the full optical system using the galsim and batoid codes show that the weather pattern affects the dispersion of the camera point-spread function at only the one part in 10^-4 level

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arXiv2024

Rubin ToO 2024: Envisioning the Vera C. Rubin Observatory LSST Target of Opportunity program

The Legacy Survey of Space and Time (LSST) at Vera C. Rubin Observatory is planned to begin in the Fall of 2025. The LSST survey cadence has been designed via a community-driven process regulated by the Survey Cadence Optimization Committee (SCOC), which recommended up to 3% of the observing time to carry out Target of Opportunity (ToO) observations. Experts from the scientific community, Rubin Observatory personnel, and members of the SCOC were brought together to deliver a recommendation for the implementation of the ToO program during a workshop held in March 2024. Four main science cases were identified: gravitational wave multi-messenger astronomy, high energy neutrinos, Galactic supernovae, and small potentially hazardous asteroids possible impactors. Additional science cases were identified and briefly addressed in the documents, including lensed or poorly localized gamma-ray bursts and twilight discoveries. Trigger prioritization, automated response, and detailed strategies were discussed for each science case. This document represents the outcome of the Rubin ToO 2024 workshop, with additional contributions from members of the Rubin Science Collaborations. The implementation of the selection criteria and strategies presented in this document has been endorsed in the SCOC Phase 3 Recommendations document (PSTN-056). Although the ToO program is still to be finalized, this document serves as a baseline plan for ToO observations with the Rubin Observatory.

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arXiv2023

HST Proper Motion Measurements of Supernova Remnant N132D: Center of Expansion and Age

We present proper motion measurements of oxygen-rich ejecta of the LMC supernova remnant N132D using two epochs of Hubble Space Telescope Advanced Camera for Surveys data spanning 16 years. The proper motions of 120 individual knots of oxygen-rich gas were measured and used to calculate a center of expansion (CoE) of $α$=05:25:01.71 and $δ$=-69:38:41.64 (J2000) with a 1-$σ$ uncertainty of 2.90 arcseconds. This new CoE measurement is 9.2 and 10.8 arcseconds from two previous CoE estimates based on the geometry of the optically emitting ejecta. We also derive an explosion age of 2770 $\pm$ 500 yr, which is consistent with recent age estimates of $\approx 2500$ yr made from 3D ejecta reconstructions. We verify our estimates of the CoE and age using a new automated procedure that detected and tracked the proper motions of 137 knots, with 73 knots that overlap with the visually identified knots. We find the proper motions of ejecta are still ballistic, despite the remnant's age, and are consistent with the notion that the ejecta are expanding into an ISM cavity. Evidence for explosion asymmetry from the parent supernova is also observed. Using the visually measured proper motion measurements and corresponding center of expansion and age, we compare N132D to other supernova remnants with proper motion ejecta studies.

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arXiv2022

Inferencing Progenitor and Explosion Properties of Evolving Core-collapse Supernovae from Zwicky Transient Facility Light Curves

We analyze a sample of 45 Type II supernovae from the Zwicky Transient Facility (ZTF) public survey using a grid of hydrodynamical models in order to assess whether theoretically-driven forecasts can intelligently guide follow up observations supporting all-sky survey alert streams. We estimate several progenitor properties and explosion physics parameters including zero-age-main-sequence (ZAMS) mass, mass-loss rate, kinetic energy, 56Ni mass synthesized, host extinction, and the time of explosion. Using complete light curves we obtain confident characterizations for 34 events in our sample, with the inferences of the remaining 11 events limited either by poorly constraining data or the boundaries of our model grid. We also simulate real-time characterization of alert stream data by comparing our model grid to various stages of incomplete light curves (t less than 25 days, t less than 50 days, all data), and find that some parameters are more reliable indicators of true values at early epochs than others. Specifically, ZAMS mass, time of explosion, steepness parameter beta, and host extinction are reasonably constrained with incomplete light curve data, whereas mass-loss rate, kinetic energy and 56Ni mass estimates generally require complete light curves spanning greater than 100 days. We conclude that real-time modeling of transients, supported by multi-band synthetic light curves tailored to survey passbands, can be used as a powerful tool to identify critical epochs of follow up observations. Our findings are relevant to identify, prioritize, and coordinate efficient follow up of transients discovered by Vera C. Rubin Observatory.

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arXiv2022

Supernova host galaxy association and photometric classification of over 10,000 light curves from the Zwicky Transient Facility

Here we present a catalog of 12,993 photometrically-classified supernova-like light curves from the Zwicky Transient Facility, along with candidate host galaxy associations. By training a random forest classifier on spectroscopically classified supernovae from the Bright Transient Survey, we achieve an accuracy of 80% across four supernova classes resulting in a final data set of 8208 Type Ia, 2080 Type II, 1985 Type Ib/c, and 720 SLSN. Our work represents a pathfinder effort to supply massive data sets of supernova light curves with value-added information that can be used to enable population-scale modeling of explosion parameters and investigate host galaxy environments.

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arXiv2021

The Center of Expansion and Age of the Oxygen-rich Supernova Remnant 1E 0102.2-7219

We present new proper motion measurements of optically emitting oxygen-rich knots of supernova remnant 1E 0102.2-7219 (E0102), which are used to estimate the remnant's center of expansion and age. Four epochs of high resolution Hubble Space Telescope images spanning 19 yr were retrieved and analyzed. We found a robust center of expansion of alpha=1:04:02.48 and delta=-72:01:53.92 (J2000) with 1-sigma uncertainty of 1.77 arcseconds using 45 knots from images obtained with the Advanced Camera for Surveys using the F475W filter in 2003 and 2013 having the highest signal-to-noise ratio. We also estimate an upper limit explosion age of 1738 +/- 175 yr by selecting knots with the highest proper motions, that are assumed to be the least decelerated. We find evidence of an asymmetry in the proper motions of the knots as a function of position angle. We conclude that these asymmetries were most likely caused by interaction between E0102's original supernova blast wave and an inhomogeneous surrounding environment, as opposed to intrinsic explosion asymmetry. The observed non-homologous expansion suggests that the use of a free expansion model inaccurately offsets the center of expansion and leads to an overestimated explosion age. We discuss our findings as they compare to previous age and center of expansion estimates of E0102 and their relevance to a recently identified candidate central compact object.

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arXiv2020

Three-Dimensional Kinematic Reconstruction of the Optically-Emitting, High-Velocity, Oxygen-Rich Ejecta of Supernova Remnant N132D

We present a three-dimensional kinematic reconstruction of the optically-emitting, oxygen-rich ejecta of supernova remnant N132D in the Large Magellanic Cloud. Data were obtained with the 6.5 m Magellan telescope in combination with the IMACS+GISMO instrument and survey [O III] $λλ$4959,5007 line emission in a ${\sim}$3$^{\prime}~\times$ 3$^{\prime}$ region centered on N132D. The spatial and spectral resolution of our data enable detailed examination of the optical ejecta structure. The majority of N132D's optically bright oxygen ejecta are arranged in a torus-like geometry tilted approximately 28$^{\circ}$ with respect to the plane of the sky. The torus has a radius of 4.4 pc ($D_{\rm LMC}$/50 kpc), exhibits a blue-shifted radial velocity asymmetry of $-3000$ to $+2300$ km s$^{-1}$, and has a conspicuous break in its circumference. Assuming homologous expansion from the geometric center of O-rich filaments, the average expansion velocity of 1745 km s$^{-1}$ translates to an age since explosion of 2450 $\pm$ 195 yr. A faint, spatially-separated "runaway knot" (RK) with total space velocity of 3650 km s$^{-1}$ is nearly perpendicular to the torus plane and coincident with X-ray emission that is substantially enhanced in Si relative to the LMC and N132D's bulk ejecta. These kinematic and chemical signatures suggest that the RK may have had its origin deep within the progenitor star. Overall, the main shell morphology and high-velocity, Si-enriched components of N132D have remarkable similarity with that of Cassiopeia A, which was the result of a Type IIb supernova explosion. Our results underscore the need for further observations and simulations that can robustly reconcile whether the observed morphology is dominated by explosion dynamics or shaped by interaction with the environment.

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arXiv2018

Evidence for a pulsar wind nebula in the Type Ib-peculiar supernova SN 2012au

We present an optical spectrum of the energetic Type Ib supernova (SN) 2012au obtained at an unprecedented epoch of 6.2 years after explosion. Forbidden transition emission lines of oxygen and sulfur are detected with expansion velocities of 2300 km/s. The lack of narrow H Balmer lines suggests that interaction with circumstellar material is not a dominant source of the observed late-time emission. We also present a deep Chandra observation that reveals no X-ray emission down to a luminosity of L_X < 2 x 10^{38} erg/s (0.5-10 keV). Our findings are consistent with the notion that SN 2012au is associated with a diverse subset of SNe, including long-duration gamma-ray burst SNe and superluminous SNe, harboring pulsar/magnetar wind nebulae that influence core-collapse explosion dynamics on a wide range of energy scales. We hypothesize that these systems may all evolve into a similar late-time phase dominated by forbidden oxygen transitions, and predict that emission line widths should remain constant or broaden a few per cent per year due to the acceleration of ejecta by the pulsar/magnetar bubble.

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arXiv2016

Rotational Dynamics and Star Formation in the Nearby Dwarf Galaxy NGC 5238

We present new HI spectral line images of the nearby low-mass galaxy NGC 5238, acquired with the Karl G. Jansky Very Large Array (VLA). Located at a distance of 4.51+/-0.04 Mpc, NGC 5238 is an actively star-forming galaxy with widespread H-alpha and UV continuum emission. The source is included in many ongoing and recent nearby galaxy surveys, but until this work the spatially resolved qualities of its neutral interstellar medium have remained unstudied. Our HI images resolve the disk on physical scales of ~400 pc, allowing us to undertake a detailed comparative study of the gaseous and stellar components. The HI disk is asymmetric in the outer regions, and the areas of high HI mass surface density display a crescent-shaped morphology that is slightly offset from the center of the stellar populations. The HI column density exceeds 10^21 cm^-2 in much of the disk. We quantify the degree of co-spatiality of dense HI gas and sites of ongoing star formation as traced by far-UV and H-alpha emission. The neutral gas kinematics are complex; using a spatially-resolved position-velocity analysis, we infer a rotational velocity of 31+/-5 km/s. We place NGC 5238 on the baryonic Tully-Fisher relation and contextualize the system amongst other low-mass galaxies.

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