arXiv subjects

N. Blagorodnova

Publications and source records attributed to N. Blagorodnova.

At least 19 recordsLinked to original sources

arXiv2026

Archival transients detected with the MeerLICHT telescope I: Supernovae

Wide-field optical transient surveys collectively discover $\sim$50 new transients per night, making rapid, multi-filter and/or spectroscopic follow-up of all but the most exceptional events unfeasible. Consequently, the (early) light-curve properties of most supernovae (SNe), particularly sub-luminous events, are often poorly characterised. Here, we showcase recovery of key parameters by combining publicly available data from multiple, contemporaneous surveys. We built a catalogue of $125$ SNe by cross-matching the MeerLICHT (ML) transient survey with the Transient Name Server list of spectroscopically classified SNe detected between August 2017 and October 2022. For a subset of $14$ SNe with good multi-survey photometric coverage, we combined ML-$q$, ZTF-$g,r$, and ATLAS-$c,o$ data to construct composite early-time light curves. We then applied an expanding fireball ($t^2$) model to constrain their explosion dates and rest-frame rise times. We find that this simple model provides a reliable description for the early emission of most SNe in our sample and successfully constrains their rise time, a key parameter for characterising SN categories and probing progenitor origins. This multi-survey approach, only using standard survey products, provides a powerful method to characterise large numbers of SNe that would otherwise be lost, a technique that will be essential for maximising the scientific return from current and future surveys such as GOTO, BlackGEM, the Vera C. Rubin Observatory's LSST, and Global Open Transient Telescope Array (GOTTA).

astro-ph.SR↗

arXiv2026

Comparative Study of Two Luminous Red Novae I. Progenitor Modeling and Dust Formation

Luminous red novae are astrophysical transients associated with unstable mass transfer in interacting binaries and are commonly interpreted as outcomes of common-envelope evolution, possibly ending in merger. These interactions can liberate large amounts of gas, part of which may later condense into dust. We study the luminous red novae AT2021biy and AT2021blu to constrain their binary progenitors, estimate the mass ejected during the outbursts, and infer the dust mass from the infrared evolution of their remnants. We computed two grids of binary stellar-evolution tracks with the MESA binary module, constrained by pre-outburst photometry. We applied mass-transfer instability criteria to select progenitors able to merge on timescales compatible with archival observations. From these models, we estimated the gas mass lost during the mass-transfer phase and lower and upper bounds on the envelope mass that could be ejected during common-envelope evolution using the available orbital energy. We compared these ejecta-mass estimates with values inferred from light-curve models. Finally, we modeled mid-infrared NEOWISE data to derive dust masses up to ~3 years post-outburst, providing an additional lower limit on the total ejecta mass. We constrained the donor masses to Md = 18-23 Msun for AT2021biy and Md = 14 +/- 0.5 Msun for AT2021blu. Lower limits on the ejected envelope mass are 0.03-2.98 Msun for AT2021biy and 0.02-0.1 Msun for AT2021blu. Comparison with light-curve models favors intermediate mass ratios, q = 3-10 for AT2021biy and q = 5-15 for AT2021blu. The inferred dust masses are 1-5 orders of magnitude below the estimated ejected envelope masses, implying that only a small fraction of the gas condenses into dust. Their evolution is consistent with shock interaction and suggests pre-existing circumstellar material, in line with the pre-outburst mass loss predicted by our MESA models.

astro-ph.SR↗

arXiv2026

XP-TEAL: Gaia XP Tool for Emission and Absorption Lines II. Gaia-HELIX catalogue of H$\alpha$ emitters in Gaia BP/RP spectra

Context: With Gaia's third Data Release (DR3), low-resolution BP/RP (XP) spectra became available for more than 219 million sources. In previous work, we developed a fast method for detecting absorption and emission lines while measuring their equivalent widths directly from the XP spectral coefficients. Aims: We conduct a systematic search for H$\alpha$ emitters in the Gaia DR3 XP spectra. Methods: We measured the equivalent width of the Balmer H$\alpha$ line for all sources with Gaia XP spectra and selected an initial sample of 556100 sources depicting an H$\alpha$ emission-like feature at $2\sigma$ level or above. Using a semi-supervised classifier complemented by manual spectral labelling, we removed sources that merely masqueraded as emission-line stars. Results: We find that 95% of the initial candidates are most likely cool M-type stars, where a molecular absorption band gives rise to a local maximum that can mimic H$\alpha$ emission. Subsequently, 28394 sources were flagged as bona fide H$\alpha$ emitters using the Gaia DR3 XP spectra. The majority are Be-like candidates (26287), M-type emission-line stars (717), Herbig Ae/Be candidates (525), quasi-stellar objects (204), Wolf-Rayet stars (177), cataclysmic variables (51), and carbon stars (18), among other sources. Our equivalent widths and stellar classifications agree well with results from higher-resolution studies and recent Gaia XP spectra-based catalogues. Ground-based spectroscopic follow-up for some of the newly found H$\alpha$ emitters reinforces our confidence in the catalogue.

astro-ph.SR↗

arXiv2025

Analysis of mass-transferring binary candidates in the Milky Way

Mass transfer between stars in binary systems profoundly impacts their evolution, yet many aspects of this process (especially the stability, mass loss, and eventual fate of such systems) remain poorly understood. One promising avenue to constrain these processes is through the identification and characterisation of systems undergoing active mass transfer. Inspired by the slow brightening preceding stellar merger transients, we worked on a method to identify Galactic mass-transferring binaries in which the donor is a Hertzsprung gap (HG) star. We constructed an initial sample of HG stars using the Gaia EDR3 contribution Starhorse catalogue, and we identified candidate mass-transferring systems by selecting sources that exhibit Balmer emission features (using the low-resolution Gaia XP spectra), mid-infrared excess (from WISE photometry), and photometric variability (inferred from the error in the Gaia G-band magnitude). This multi-criteria selection yielded a sample of 67 candidates, which we further analysed using complementary photometric and spectroscopic data. Among our candidates, we identified at least nine eclipsing binaries and some sources that are potential binaries as well. Three sources in our sample are strong candidates for mass-transferring binaries with a yellow component, and three more are binaries with a Be star. Notably, four sources in our sample are strong candidates for hosting a compact companion, based on their ultraviolet or X-ray signatures. The main sources of contamination in our search are hot but highly reddened stars (primarily Oe and Be stars). As an additional outcome of this work, we present a refined catalogue of 308 bona fide HG stars, selected using improved extinction corrections and stricter emission-line criteria. This enhanced sample is expected to contain a significantly higher fraction of scientifically valuable mass-transferring binaries.

astro-ph.SR↗

arXiv2025

OGLE-2002-BLG-360: a dusty anomaly among red nova remnants

OGLE-2002-BLG-360 is an example of a Galactic red nova, the aftermath of a non-compact stellar merger. The dusty nature of the circumstellar environment makes observations of this particular source difficult, meaning the properties of the central star and its surrounding environment are poorly understood. We aim to establish the parameters of the merger remnant, as well as of the dusty environment and its structure. We attempt to establish similarities with other Galactic red novae and try to understand how such an environment has been formed. We use optical, infrared, and sub-millimetre observations to construct the spectral energy distribution (SED) between 2 um and 1.27 mm for an epoch 15-21 years after the red nova eruption. We use the RADMC-3D radiative transfer code to model the SED and retrieve the physical properties of both the central star and the surrounding dust. We show that the SED is best replicated by a spherically symmetric model consisting of an M-type supergiant surrounded by 0.012 Msun of dust concentrated within two spherical shells. The dust extends out to a maximum distance of 9500 AU from the central source, whilst the inner shell extends out to 1000 AU. The dust composition is dominated by iron grains (58%), but also contains olivine silicates (25%) and alumina dust (17%), which are both required to reproduce the profile of the observed 10 um absorption feature. The inner shell likely originates from merger and post-merger ejecta, whilst the outer shell consists of material lost much earlier, before the merger event occurred. Evolution of the SED indicates continued dust formation within the expanding inner shell, which may be analogous to winds of red supergiants. The object is extremely dusty compared to other red nova remnants.

astro-ph.SR↗

arXiv2025

Cluster-lensed supernova yields from the Vera C. Rubin Observatory and Nancy Grace Roman Space Telescope

Through gravitational lensing, galaxy clusters can magnify supernovae (SNe) and create multiple images of the same SN. This enables measurements of cosmological parameters, which will be increasingly important in light of upcoming telescopic surveys. We study the prospects of detecting strongly lensed SNe in cluster fields with the Nancy Grace Roman Space Telescope (Roman)'s High Latitude Time Domain Survey (HLTDS) and the Vera C. Rubin Observatory's Legacy Survey of Space and Time (LSST). We employed two approaches: one focusing on known multiply imaged galaxies behind clusters, along with the SN rates specific to those galaxies, and another based on the expected number of lensed SNe exploding in a given volume behind a galaxy cluster. We collected all the clusters in the literature that feature a well-constrained lens model and multiply imaged galaxies behind clusters with high-quality data for the lensed galaxies. This allowed us to determine the SN rate for each galaxy. We provide predictions for 46 clusters visible to the Vera C. Rubin Observatory, as well as for 9 observable by Roman's HLTDS, depending on whether the clusters fall within the survey's observing field. We predict that the number of multiply imaged SNe discovered by LSST in its first three years is $3.95 \pm 0.89$ from the first approach or $4.94 \pm 1.02$ from the second. For the HLTDS, the expected number of multiply imaged SNe ranges from $0.38 \pm 0.15$ to $5.2 \pm 2.2$, depending on the specific cluster observed, however, the fields to be targeted remain a matter of discussion. We conclude that LSST offers great prospects for detecting multiply imaged SNe. Our predictions are effectively lower limits, as we only considered the most massive and well-studied clusters. We provide a recommendation for HLTDS observing field selection, namely: either MACS J0553.4-3342 or Abell 1758a should be observed by the survey.

astro-ph.GA↗

arXiv2024

The BlackGEM telescope array I: Overview

The main science aim of the BlackGEM array is to detect optical counterparts to gravitational wave mergers. Additionally, the array will perform a set of synoptic surveys to detect Local Universe transients and short time-scale variability in stars and binaries, as well as a six-filter all-sky survey down to ~22nd mag. The BlackGEM Phase-I array consists of three optical wide-field unit telescopes. Each unit uses an f/5.5 modified Dall-Kirkham (Harmer-Wynne) design with a triplet corrector lens, and a 65cm primary mirror, coupled with a 110Mpix CCD detector, that provides an instantaneous field-of-view of 2.7~square degrees, sampled at 0.564\arcsec/pixel. The total field-of-view for the array is 8.2 square degrees. Each telescope is equipped with a six-slot filter wheel containing an optimised Sloan set (BG-u, BG-g, BG-r, BG-i, BG-z) and a wider-band 440-720 nm (BG-q) filter. Each unit telescope is independent from the others. Cloud-based data processing is done in real time, and includes a transient-detection routine as well as a full-source optimal-photometry module. BlackGEM has been installed at the ESO La Silla observatory as of October 2019. After a prolonged COVID-19 hiatus, science operations started on April 1, 2023 and will run for five years. Aside from its core scientific program, BlackGEM will give rise to a multitude of additional science cases in multi-colour time-domain astronomy, to the benefit of a variety of topics in astrophysics, such as infant supernovae, luminous red novae, asteroseismology of post-main-sequence objects, (ultracompact) binary stars, and the relation between gravitational wave counterparts and other classes of transients

astro-ph.IM↗

arXiv2021

Gaia Photometric Science Alerts

Since July 2014, the Gaia mission has been engaged in a high-spatial-resolution, time-resolved, precise, accurate astrometric, and photometric survey of the entire sky. Aims: We present the Gaia Science Alerts project, which has been in operation since 1 June 2016. We describe the system which has been developed to enable the discovery and publication of transient photometric events as seen by Gaia. Methods: We outline the data handling, timings, and performances, and we describe the transient detection algorithms and filtering procedures needed to manage the high false alarm rate. We identify two classes of events: (1) sources which are new to Gaia and (2) Gaia sources which have undergone a significant brightening or fading. Validation of the Gaia transit astrometry and photometry was performed, followed by testing of the source environment to minimise contamination from Solar System objects, bright stars, and fainter near-neighbours. Results: We show that the Gaia Science Alerts project suffers from very low contamination, that is there are very few false-positives. We find that the external completeness for supernovae, $C_E=0.46$, is dominated by the Gaia scanning law and the requirement of detections from both fields-of-view. Where we have two or more scans the internal completeness is $C_I=0.79$ at 3 arcsec or larger from the centres of galaxies, but it drops closer in, especially within 1 arcsec. Conclusions: The per-transit photometry for Gaia transients is precise to 1 per cent at $G=13$, and 3 per cent at $G=19$. The per-transit astrometry is accurate to 55 milliarcseconds when compared to Gaia DR2. The Gaia Science Alerts project is one of the most homogeneous and productive transient surveys in operation, and it is the only survey which covers the whole sky at high spatial resolution (subarcsecond), including the Galactic plane and bulge.

astro-ph.IM↗

arXiv2020

The Broad Absorption Line Tidal Disruption Event iPTF15af: Optical and Ultraviolet Evolution

We present multi-wavelength observations of the tidal disruption event (TDE) iPTF15af, discovered by the intermediate Palomar Transient Factory (iPTF) survey at redshift $z=0.07897$. The optical and ultraviolet (UV) light curves of the transient show a slow decay over five months, in agreement with previous optically discovered TDEs. It also has a comparable black-body peak luminosity of $L_{\rm{peak}} \approx 1.5 \times 10^{44}$ erg/s. The inferred temperature from the optical and UV data shows a value of (3$-$5) $\times 10^4$ K. The transient is not detected in X-rays up to $L_X < 3 \times 10^{42}$erg/s within the first five months after discovery. The optical spectra exhibit two distinct broad emission lines in the He II region, and at later times also H$α$ emission. Additionally, emission from [N III] and [O III] is detected, likely produced by the Bowen fluorescence effect. UV spectra reveal broad emission and absorption lines associated with high-ionization states of N V, C IV, Si IV, and possibly P V. These features, analogous to those of broad absorption line quasars (BAL QSOs), require an absorber with column densities $N_{\rm{H}} > 10^{23}$ cm$^{-2}$. This optically thick gas would also explain the non-detection in soft X-rays. The profile of the absorption lines with the highest column density material at the largest velocity is opposite that of BAL QSOs. We suggest that radiation pressure generated by the TDE flare at early times could have provided the initial acceleration mechanism for this gas. Spectral UV line monitoring of future TDEs could test this proposal.

astro-ph.HE↗

arXiv2020

Type IIn supernova light-curve properties measured from an untargeted survey sample

We present a sample of supernovae Type IIn (SNe IIn) from the untargeted, magnitude-limited surveys of the Palomar Transient Factory (PTF) and its successor, the intermediate PTF (iPTF). The SNe IIn found and followed by the PTF/iPTF were used to select a sample of 42 events with useful constraints on the rise times as well as with available post-peak photometry. The sample SNe were discovered in 2009-2016 and have at least one low-resolution classification spectrum, as well as photometry from the P48 and P60 telescopes at Palomar Observatory. We study the light-curve properties of these SNe IIn using spline fits (for the peak and the declining portion) and template matching (for the rising portion). We find that the typical rise times are divided into fast and slow risers at $20\pm6$ d and $50\pm11$ d, respectively. The decline rates are possibly divided into two clusters, but this division has weak statistical significance. We find no significant correlation between the peak luminosity of SNe IIn and their rise times, but the more luminous SNe IIn are generally found to be more long-lasting. Slowly rising SNe IIn are generally found to decline slowly. The SNe in our sample were hosted by galaxies of absolute magnitude $-22 \lesssim M_g \lesssim -13$ mag. The K-corrections at light-curve peak of the SNe IIn in our sample are found to be within 0.2 mag for the observer's frame $r$-band, for SNe at redshifts $z < 0.25$. By applying K-corrections and also including ostensibly "superluminous" SNe IIn, we find that the peak magnitudes are $M_{\rm peak}^{r} = -19.18\pm1.32$ mag. We conclude that the occurrence of conspicuous light-curve bumps in SNe IIn, such as in iPTF13z, are limited to $1.4^{+14.6}_{-1.0} \%$ of the SNe IIn. We also investigate a possible sub-type of SNe IIn with a fast rise to a $\gtrsim 50$ d plateau followed by a slow, linear decline.

astro-ph.SR↗

arXiv2019

Full orbital solution for the binary system in the northern Galactic disc microlensing event Gaia16aye

Gaia16aye was a binary microlensing event discovered in the direction towards the northern Galactic disc and was one of the first microlensing events detected and alerted to by the Gaia space mission. Its light curve exhibited five distinct brightening episodes, reaching up to I=12 mag, and it was covered in great detail with almost 25,000 data points gathered by a network of telescopes. We present the photometric and spectroscopic follow-up covering 500 days of the event evolution. We employed a full Keplerian binary orbit microlensing model combined with the motion of Earth and Gaia around the Sun to reproduce the complex light curve. The photometric data allowed us to solve the microlensing event entirely and to derive the complete and unique set of orbital parameters of the binary lensing system. We also report on the detection of the first-ever microlensing space-parallax between the Earth and Gaia located at L2. The properties of the binary system were derived from microlensing parameters, and we found that the system is composed of two main-sequence stars with masses 0.57$\pm$0.05 $M_\odot$ and 0.36$\pm$0.03 $M_\odot$ at 780 pc, with an orbital period of 2.88 years and an eccentricity of 0.30. We also predict the astrometric microlensing signal for this binary lens as it will be seen by Gaia as well as the radial velocity curve for the binary system. Events such as Gaia16aye indicate the potential for the microlensing method of probing the mass function of dark objects, including black holes, in directions other than that of the Galactic bulge. This case also emphasises the importance of long-term time-domain coordinated observations that can be made with a network of heterogeneous telescopes.

astro-ph.SR↗

arXiv2019

ZTF18aalrxas: A Type IIb Supernova from a very extended low-mass progenitor

We investigate ZTF18aalrxas, a double-peaked Type IIb core-collapse supernova (SN) discovered during science validation of the Zwicky Transient Facility (ZTF). ZTF18aalrxas was discovered while the optical emission was still rising towards the initial cooling peak (0.7 mag over 2 days). Our observations consist of multi-band (UV, optical) light-curves, and optical spectra spanning from $\approx0.7$ d to $\approx180$ d past the explosion. We use a Monte-Carlo based non-local thermodynamic equilibrium (NLTE) model, that simultanously reproduces both the $\rm ^{56}Ni$ powered bolometric light curve and our nebular spectrum. This model is used to constrain the synthesized radioactive nickel mass (0.17 $\mathrm{M}_{\odot}$) and the total ejecta mass (1.7 $\mathrm{M}_{\odot}$) of the SN. The cooling emission is modeled using semi-analytical extended envelope models to constrain the progenitor radius ($790-1050$ $\mathrm{R}_{\odot}$) at the time of explosion. Our nebular spectrum shows signs of interaction with a dense circumstellar medium (CSM), and this spetrum is modeled and analysed to constrain the amount of ejected oxygen ($0.3-0.5$ $\mathrm{M}_{\odot}$) and the total hydrogen mass ($\approx0.15$ $\mathrm{M}_{\odot}$) in the envelope of the progenitor. The oxygen mass of ZTF18aalrxas is consistent with a low ($12-13$ $\mathrm{M}_{\odot}$) Zero Age Main Sequence mass progenitor. The light curves and spectra of ZTF18aalrxas are not consistent with massive single star SN Type IIb progenitor models. The presence of an extended hydrogen envelope of low mass, the presence of a dense CSM, the derived ejecta mass, and the late-time oxygen emission can all be explained in a binary model scenario.

astro-ph.HE↗

arXiv2019

Discovery of Highly Blueshifted Broad Balmer and Metastable Helium Absorption Lines in a Tidal Disruption Event

We report the discovery of non-stellar hydrogen Balmer and metastable helium absorption lines accompanying a transient, high-velocity (0.05$c$) broad absorption line (BAL) system in the optical spectra of the tidal disruption event (TDE) AT2018zr ($z=0.071$). In the HST UV spectra, absorption of high- and low-ionization lines are also present at this velocity, making AT2018zr resemble a low-ionization broad absorption line (LoBAL) QSO. We conclude that these transient absorption features are more likely to arise in fast outflows produced by the TDE than absorbed by the unbound debris. In accordance with the outflow picture, we are able to reproduce the flat-topped H$α$ emission in a spherically expanding medium, without invoking the typical prescription of an elliptical disk. We also report the appearance of narrow ($\sim$1000~km~s$^{-1}$) NIII$λ$4640, HeII$\lambda4686$, H$α$, and H$β$, emission in the late-time optical spectra of AT2018zr, which may be a result of UV continuum hardening at late time as observed by Swift. Including AT2018zr, we find a high association rate (3 out of 4) of BALs in the UV spectra of TDEs. This suggests that outflows may be ubiquitous among TDEs and may be less sensitive to viewing angle effects compared to QSO outflows.

astro-ph.HE↗

arXiv2019

Gravity and Light: Combining Gravitational Wave and Electromagnetic Observations in the 2020s

As of today, we have directly detected exactly one source in both gravitational waves (GWs) and electromagnetic (EM) radiation, the binary neutron star merger GW170817, its associated gamma-ray burst GRB170817A, and the subsequent kilonova SSS17a/AT 2017gfo. Within ten years, we will detect hundreds of events, including new classes of events such as neutron-star-black-hole mergers, core-collapse supernovae, and almost certainly something completely unexpected. As we build this sample, we will explore exotic astrophysical topics ranging from nucleosynthesis, stellar evolution, general relativity, high-energy astrophysics, nuclear matter, to cosmology. The discovery potential is extraordinary, and investments in this area will yield major scientific breakthroughs. Here we outline some of the most exciting scientific questions that can be answered by combining GW and EM observations.

astro-ph.HE↗

arXiv2019

A Fully Automated Integral Field Spectrograph Pipeline for the SEDMachine: pysedm

Current time domain facilities are discovering hundreds of new galactic and extra-galactic transients every week. Classifying the ever-increasing number of transients is challenging, yet crucial to further our understanding of their nature, discover new classes, or ensuring sample purity, for instance, for Supernova Ia cosmology. The Zwicky Transient Facility is one example of such a survey. In addition, it has a dedicated very-low resolution spectrograph, the SEDMachine, operating on the Palomar 60-inch telescope. This spectrograph's primary aim is object classification. In practice most, if not all, transients of interest brighter than ~19 mag are typed. This corresponds to approximately 10 to 15 targets a night. In this paper, we present a fully automated pipeline for the SEDMachine. This pipeline has been designed to be fast, robust, stable and extremely flexible. pysedm enables the fully automated spectral extraction of a targeted point source object in less than 5 minutes after the end of the exposure. The spectral color calibration is accurate at the few percent level. In the 19 weeks since pysedm entered production in early August of 2018, we have classified, among other objects, about 400 Type Ia supernovae and 140 Type II supernovae. We conclude that low resolution, fully automated spectrographs such as the `SEDMachine with pysedm' installed on 2-m class telescopes within the southern hemisphere could allow us to automatically and simultaneously type and obtain a redshift for most (if not all) bright transients detected by LSST within z<0.2, notably potentially all Type Ia Supernovae. In comparison to the current SEDM design, this would require higher spectral resolution (R~1000) and slightly improved throughput. With this perspective in mind, pysedm has been designed to easily be adaptable to any IFU-like spectrograph (see https://github.com/MickaelRigault/pysedm).

astro-ph.IM↗

arXiv2018

A UV Resonance Line Echo from a Shell Around a Hydrogen-Poor Superluminous Supernova

Hydrogen-poor superluminous supernovae (SLSN-I) are a class of rare and energetic explosions discovered in untargeted transient surveys in the past decade. The progenitor stars and the physical mechanism behind their large radiated energies ($\sim10^{51}$ erg) are both debated, with one class of models primarily requiring a large rotational energy, while the other requires very massive progenitors to either convert kinetic energy into radiation via interaction with circumstellar material (CSM), or engender a pair-instability explosion. Observing the structure of the CSM around SLSN-I offers a powerful test of some scenarios, though direct observations are scarce. Here, we present a series of spectroscopic observations of the SLSN-I iPTF16eh, which reveal both absorption and time- and frequency-variable emission in the Mg II resonance doublet. We show that these observations are naturally explained as a resonance scattering light echo from a circumstellar shell. Modeling the evolution of the emission, we find a shell radius of 0.1 pc and velocity of 3300 km s$^{-1}$, implying the shell was ejected three decades prior to the supernova explosion. These properties match theoretical predictions of pulsational pair-instability shell ejections, and imply the progenitor had a He core mass of $\sim 50-55~{\rm M}_{\odot}$, corresponding to an initial mass of $\sim 115~{\rm M}_{\odot}$.

astro-ph.HE↗

arXiv2018

Sifting for Sapphires: Systematic Selection of Tidal Disruption Events in iPTF

We present results from a systematic selection of tidal disruption events (TDEs) in a wide-area (4800~deg$^2$), $g+R$ band, Intermediate Palomar Transient Factory (iPTF) experiment. Our selection targets typical optically-selected TDEs: bright ($>$60\% flux increase) and blue transients residing in the center of red galaxies. Using photometric selection criteria to down-select from a total of 493 nuclear transients to a sample of 26 sources, we then use follow-up UV imaging with the Neil Gehrels Swift Telescope, ground-based optical spectroscopy, and light curve fitting to classify them as 14 Type Ia supernovae (SNe Ia), 9 highly variable active galactic nuclei (AGNs), 2 confirmed TDEs, and 1 potential core-collapse supernova. We find it possible to filter AGNs by employing a more stringent transient color cut ($g-r <$ $-$0.2 mag); further, UV imaging is the best discriminator for filtering SNe, since SNe Ia can appear as blue, optically, as TDEs in their early phases. However, when UV-optical color is unavailable, higher precision astrometry can also effectively reduce SNe contamination in the optical. Our most stringent optical photometric selection criteria yields a 4.5:1 contamination rate, allowing for a manageable number of TDE candidates for complete spectroscopic follow-up and real-time classification in the ZTF era. We measure a TDE per galaxy rate of 1.7$^{+2.9}_{-1.3}$ $\times$10$^{-4}$ gal$^{-1}$ yr$^{-1}$ (90\% CL in Poisson statistics). This does not account for TDEs outside our selection criteria, thus may not reflect the total TDE population, which is yet to be fully mapped.

astro-ph.HE↗

arXiv2018

Early Observations of the Type Ia Supernova iPTF 16abc: A Case of Interaction with Nearby, Unbound Material and/or Strong Ejecta Mixing

Early observations of Type Ia supernovae (SNe Ia) provide a unique probe of their progenitor systems and explosion physics. Here we report the intermediate Palomar Transient Factory (iPTF) discovery of an extraordinarily young SN Ia, iPTF 16abc. By fitting a power law to our early light curve, we infer that first light for the SN, that is when the SN could have first been detected by our survey, occurred only $0.15\pm_{0.07}^{0.15}$ days before our first detection. In the $\sim$24 hr after discovery, iPTF 16abc rose by $\sim$2 mag, featuring a near-linear rise in flux for $\gtrsim$3 days. Early spectra show strong C II absorption, which disappears after $\sim$7 days. Unlike the extensivelyobserved SN Ia SN 2011fe, the $(B-V)_0$ colors of iPTF 16abc are blue and nearly constant in the days after explosion. We show that our early observations of iPTF 16abc cannot be explained by either SN shock breakout and the associated, subsequent cooling or the SN ejecta colliding with a stellar companion. Instead, we argue that the early characteristics of iPTF 16abc, including (i) the rapid, near-linear rise, (ii) the nonevolving blue colors, and (iii) the strong C II absorption, are the result of either ejecta interaction with nearby, unbound material or vigorous mixing of radioactive $^{56}$Ni in the SN ejecta, or a combination of the two. In the next few years, dozens of very young \textit{normal} SNe Ia will be discovered, and observations similar to those presented here will constrain the white dwarf explosion mechanism.

astro-ph.HE↗