arXiv subjects

Joel Johansson

Publications and source records attributed to Joel Johansson.

At least 73 records · Page 4Linked to original sources

arXiv2020

The SPIRITS sample of Luminous Infrared Transients: Uncovering Hidden Supernovae and Dusty Stellar Outbursts in Nearby Galaxies

We present a systematic study of the most luminous ($M_{\mathrm{IR}}$ [Vega magnitudes] brighter than $-14$) infrared (IR) transients discovered by the SPitzer InfraRed Intensive Transients Survey (SPIRITS) between 2014 and 2018 in nearby galaxies ($D < 35$ Mpc). The sample consists of nine events that span peak IR luminosities of $M_{[4.5],\mathrm{peak}}$ between $-14$ and $-18.2$, show IR colors between $0.2 < ([3.6]{-}[4.5]) < 3.0$, and fade on timescales between $55$ days $< t_{\mathrm{fade}} < 480$ days. The two reddest events ($A_V > 12$) show multiple, luminous IR outbursts over several years and have directly detected, massive progenitors in archival imaging. With analyses of extensive, multiwavelength follow-up, we suggest the following possible classifications: five obscured core-collapse supernovae (CCSNe), two erupting massive stars, one luminous red nova, and one intermediate-luminosity red transient. We define a control sample of all optically discovered transients recovered in SPIRITS galaxies and satisfying the same selection criteria. The control sample consists of eight CCSNe and one Type Iax SN. We find that 7 of the 13 CCSNe in the SPIRITS sample have lower bounds on their extinction of $2 < A_V < 8$. We estimate a nominal fraction of CCSNe in nearby galaxies that are missed by optical surveys as high as $38.5^{+26.0}_{-21.9}$% (90% confidence). This study suggests that a significant fraction of CCSNe may be heavily obscured by dust and therefore undercounted in the census of nearby CCSNe from optical searches.

astro-ph.HE↗

arXiv2019

Quantum error correction for the toric code using deep reinforcement learning

We implement a quantum error correction algorithm for bit-flip errors on the topological toric code using deep reinforcement learning. An action-value Q-function encodes the discounted value of moving a defect to a neighboring site on the square grid (the action) depending on the full set of defects on the torus (the syndrome or state). The Q-function is represented by a deep convolutional neural network. Using the translational invariance on the torus allows for viewing each defect from a central perspective which significantly simplifies the state space representation independently of the number of defect pairs. The training is done using experience replay, where data from the algorithm being played out is stored and used for mini-batch upgrade of the Q-network. We find performance which is close to, and for small error rates asymptotically equivalent to, that achieved by the Minimum Weight Perfect Matching algorithm for code distances up to $d=7$. Our results show that it is possible for a self-trained agent without supervision or support algorithms to find a decoding scheme that performs on par with hand-made algorithms, opening up for future machine engineered decoders for more general error models and error correcting codes.

quant-ph↗

arXiv2018

iPTF 16hgs: A double-peaked Ca-rich gap transient in a metal poor, star forming dwarf galaxy

Calcium rich gap transients represent an intriguing new class of faint and fast evolving supernovae that exhibit strong [Ca II] emission in their nebular phase spectra. In this paper, we present the discovery and follow-up observations of iPTF 16hgs -- an intermediate luminosity and fast evolving transient that exhibited a double peaked light curve. Exhibiting a typical Type Ib spectrum in the photospheric phase and an early transition to a [Ca II] dominated nebular phase, we show that iPTF 16hgs shows properties consistent with the class of Ca-rich gap transients, with two interesting exceptions. First, while the second peak of the light curve is similar to other Ca-rich gap transients (suggesting $M_{ej}$ of 0.4 M$_\odot$ and peak luminosity of $3 \times 10^{41}$ ergs s$^{-1}$), we show that the first blue and fast declining (over $2$ days) peak is unique to this source. Second, with Integral Field Unit observations of the host galaxy, we find that iPTF 16hgs occurred in the outskirts (projected offset of $6$ kpc $ = 1.9 R_{eff}$) of a low metallicity (0.4 Z$_\odot$), star forming, dwarf spiral galaxy. Using deep late-time VLA and uGMRT observations, we place stringent limits on the local environment of the source, ruling out a large parameter space of circumstellar densities and mass loss environments of the progenitor. If iPTF 16hgs shares explosion physics with the class of Ca-rich gap transients, the presence of the first peak can be explained by enhanced mixing of 0.01 M$_\odot$ of $^{56}$Ni into the outer layers the ejecta, reminiscent of some models of He-shell detonations on WDs. On the other hand, if iPTF 16hgs is physically unrelated to the class, the first peak is consistent with shock cooling emission (of an envelope with a mass of 0.08 M$_\odot$ and radius of 13 R$_\odot$) associated with a core-collapse explosion of a highly stripped massive star in a close binary system.

astro-ph.HE↗

arXiv2018

SPIRITS 16tn in NGC 3556: A heavily obscured and low-luminosity supernova at 8.8 Mpc

We present the discovery by the SPitzer InfraRed Intensive Transients Survey (SPIRITS) of a likely supernova (SN) in NGC 3556 at only 8.8 Mpc, which, despite its proximity, was not detected by optical searches. A luminous infrared (IR) transient at $M_{[4.5]} = -16.7$ mag (Vega), SPIRITS 16tn is coincident with a dust lane in the inclined, star-forming disk of the host. Using IR, optical, and radio observations, we attempt to determine the nature of this event. We estimate $A_V \approx$ 8 - 9 mag of extinction, placing it among the three most highly obscured IR-discovered SNe to date. The [4.5] light curve declined at a rate of 0.013 mag day$^{-1}$, and the $[3.6] - [4.5]$ color grew redder from 0.7 to $\gtrsim$ 1.0 mag by 184.7 days post discovery. Optical/IR spectroscopy shows a red continuum, but no clearly discernible features, preventing a definitive spectroscopic classification. Deep radio observations constrain the radio luminosity of SPIRITS 16tn to $L_ν \lesssim 10^{24}$ erg s$^{-1}$ Hz$^{-1}$ between 3 - 15 GHz, excluding many varieties of radio core-collapse SNe. A type Ia SN is ruled out by the observed red IR color, and lack of features normally attributed to Fe-peak elements in the optical and IR spectra. SPIRITS 16tn was fainter at [4.5] than typical stripped-envelope SNe by $\approx$ 1 mag. Comparison of the spectral energy distribution to SNe II suggests SPIRITS 16tn was both highly obscured, and intrinsically dim, possibly akin to the low-luminosity SN 2005cs. We infer the presence of an IR dust echo powered by a peak luminosity of the transient of $5 \times 10^{40}$ erg s$^{-1} < L_{\mathrm{peak}} < 4\times10^{43}$ erg s$^{-1}$, consistent with the observed range for SNe II. This discovery illustrates the power of IR surveys to overcome the compounding effects of visible extinction and optically sub-luminous events in completing the inventory of nearby SNe.

astro-ph.HE↗

arXiv2017

No evidence of circumstellar gas surrounding Type Ia Supernova SN 2017cbv

Nearby type Ia supernovae (SNe Ia), such as SN 2017cbv, are useful events to address the question of what the elusive progenitor systems of the explosions are. Hosseinzadeh et al. (2017) suggested that the early blue excess of the lightcurve of SN 2017cbv could be due to the supernova ejecta interacting with a non-degenerate companion star. Some SN Ia progenitor models suggest the existence of circumstellar (CS) environments in which strong outflows create low density cavities of different radii. Matter deposited at the edges of the cavities, should be at distances at which photoionisation due to early ultraviolet (UV) radiation of SNe Ia causes detectable changes to the observable Na I D and Ca II H&K absorption lines. To study possible narrow absorption lines from such material, we obtained a time-series of high-resolution spectra of SN 2017cbv at phases between $-14.8$ and $+83$ days with respect to $B$-band maximum, covering the time at which photoionisation is predicted to occur. Both narrow Na I D and Ca II H&K are detected in all spectra, with no measurable changes between the epochs. We use photoionisation models to rule out the presence of Na I and Ca II gas clouds along the line-of-sight of SN 2017cbv between $\sim8\times10^{16}$--$2\times10^{19}$~cm and $\sim10^{15}$--$10^{17}$~cm, respectively. Assuming typical abundances, the mass of a homogenous spherical CS gas shell with radius $R$ must be limited to $M^{\rm CSM}_{\rm HI}<3\times10^{-4}\times(R/10^{17}[{\rm cm}])^2$ M$_{\odot}$. The bounds point to progenitor models that deposit little gas in their CS environment.

astro-ph.SR↗

arXiv2017

The dusty aftermath of SN Hunt248: merger-burst remnant?

SN Hun248 was classified as a nonterminal eruption (a SN "impostor") from a directly identified and highly variable cool hypergiant star. The 2014 outburst achieved peak luminosity equivalent to that of the historic eruption of luminous blue variable (LBV) Eta Car, and exhibited a multipeaked optical light curve that rapidly faded after ~100 days. We report ultraviolet (UV) through optical observations of SN Hunt248 with the Hubble Space Telescope (HST) about 1 yr after the outburst, and mid-infrared observations with the Spitzer Space Telescope before the burst and in decline. The HST data reveal a source that is a factor of ~10 dimmer in apparent brightness than the faintest available measurement of the precursor star. The UV-optical spectral energy distribution (SED) requires a strong Balmer continuum, consistent with a hot B4-B5 photosphere attenuated by grey circumstellar extinction. Substantial mid-infrared excess of the source is consistent with thermal emission from hot dust with a mass of 10^{-6} - 10^{-5} MSun and a geometric extent that is comparable to the expansion radius of the ejecta from the 2014 event. SED modeling indicates that the dust consists of relatively large grains (>0.3 um), which could be related to the grey circumstellar extinction that we infer for the UV-optical counterpart. Revised analysis of the precursor photometry is also consistent with grey extinction by circumstellar dust, and suggests that the initial mass of the star could be twice as large as previously estimated (nearly ~60 MSun). Reanalysis of the earlier outburst data shows that the peak luminosity and outflow velocity of the eruption are consistent with a trend exhibited by stellar merger candidates, prompting speculation that SN Hunt248 may also have stemmed from a massive stellar merger or common-envelope ejection.

astro-ph.SR↗

arXiv2017

Type Ibn Supernovae Show Photometric Homogeneity and Spectral Diversity at Maximum Light

Type Ibn supernovae (SNe) are a small yet intriguing class of explosions whose spectra are characterized by low-velocity helium emission lines with little to no evidence for hydrogen. The prevailing theory has been that these are the core-collapse explosions of very massive stars embedded in helium-rich circumstellar material (CSM). We report optical observations of six new SNe Ibn: PTF11rfh, PTF12ldy, iPTF14aki, iPTF15ul, SN 2015G, and iPTF15akq. This brings the sample size of such objects in the literature to 22. We also report new data, including a near-infrared spectrum, on the Type Ibn SN 2015U. In order to characterize the class as a whole, we analyze the photometric and spectroscopic properties of the full Type Ibn sample. We find that, despite the expectation that CSM interaction would generate a heterogeneous set of light curves, as seen in SNe IIn, most Type Ibn light curves are quite similar in shape, declining at rates around 0.1 mag/day during the first month after maximum light, with a few significant exceptions. Early spectra of SNe Ibn come in at least two varieties, one that shows narrow P Cygni lines and another dominated by broader emission lines, both around maximum light, which may be an indication of differences in the state of the progenitor system at the time of explosion. Alternatively, the spectral diversity could arise from viewing-angle effects or merely from a lack of early spectroscopic coverage. Together, the relative light curve homogeneity and narrow spectral features suggest that the CSM consists of a spatially confined shell of helium surrounded by a less dense extended wind.

astro-ph.HE↗

arXiv2017

SPIRITS: Uncovering Unusual Infrared Transients With Spitzer

We present an ongoing, systematic search for extragalactic infrared transients, dubbed SPIRITS --- SPitzer InfraRed Intensive Transients Survey. In the first year, using Spitzer/IRAC, we searched 190 nearby galaxies with cadence baselines of one month and six months. We discovered over 1958 variables and 43 transients. Here, we describe the survey design and highlight 14 unusual infrared transients with no optical counterparts to deep limits, which we refer to as SPRITEs (eSPecially Red Intermediate Luminosity Transient Events). SPRITEs are in the infrared luminosity gap between novae and supernovae, with [4.5] absolute magnitudes between -11 and -14 (Vega-mag) and [3.6]-[4.5] colors between 0.3 mag and 1.6 mag. The photometric evolution of SPRITEs is diverse, ranging from < 0.1 mag/yr to > 7 mag/yr. SPRITEs occur in star-forming galaxies. We present an in-depth study of one of them, SPIRITS 14ajc in Messier 83, which shows shock-excited molecular hydrogen emission. This shock may have been triggered by the dynamic decay of a non-hierarchical system of massive stars that led to either the formation of a binary or a proto-stellar merger.

astro-ph.HE↗

arXiv2016

Asphericity, Interaction, and Dust in the Type II-P/II-L Supernova 2013ej in Messier 74

SN 2013ej is a well-studied core-collapse supernova (SN) that stemmed from a directly identified red supergiant (RSG) progenitor in galaxy M74. The source exhibits signs of substantial geometric asphericity, X-rays from persistent interaction with circumstellar material (CSM), thermal emission from warm dust, and a light curve that appears intermediate between supernovae of Types II-P and II-L. The proximity of this source motivates a close inspection of these physical characteristics and their potential interconnection. We present multi-epoch spectropolarimetry of SN 2013ej during the first 107 days, and deep optical spectroscopy and ultraviolet through infrared photometry past ~800 days. SN 2013ej exhibits the strongest and most persistent continuum and line polarization ever observed for a SN of its class during the recombination phase. Modeling indicates that the data are consistent with an oblate ellipsoidal photosphere, viewed nearly edge-on, and probably augmented by optical scattering from circumstellar dust. We suggest that interaction with an equatorial distribution of CSM, perhaps the result of binary evolution, is responsible for generating the photospheric asphericity. Relatedly, our late-time optical imaging and spectroscopy shows that asymmetric CSM interaction is ongoing, and the morphology of broad H-alpha emission from shock-excited ejecta provides additional evidence that the geometry of the interaction region is ellipsoidal. Alternatively, a prolate ellipsoidal geometry from an intrinsically bipolar explosion is also a plausible interpretation of the data, but would probably require a ballistic jet of radioactive material capable of penetrating the hydrogen envelope early in the recombination phase (abridged).

astro-ph.SR↗

arXiv2016

High-redshift supernova rates measured with the gravitational telescope A1689

We present a ground-based near-infrared search for lensed supernovae behind the massive cluster Abell 1689 at z=0.18, one of the most powerful gravitational telescopes that nature provides. Our survey was based on multi-epoch $J$-band observations with the HAWK-I instrument on VLT, with supporting optical data from the Nordic Optical Telescope. Our search resulted in the discovery of five high-redshift, $0.671<z<1.703$, photometrically classified core-collapse supernovae with magnifications in the range $Δm$ = $-0.31$ to $-1.58$ mag, as calculated from lensing models in the literature. Thanks to the power of the lensing cluster, the survey had the sensitivity to detect supernovae up to very high-redshifts, $z$$\sim$$3$, albeit for a limited region of space. We present a study of the core-collapse supernova rates for $0.4\leq z< 2.9$, and find good agreement with both previous estimates, and the predictions from the star formation history. During our survey, we also discovered 2 type Ia supernovae in A1689 cluster members, which allowed us to determine the cluster Ia rate to be $0.14^{+0.19}_{-0.09}\pm0.01$ $\rm{SNuB}$$\,h^2$ (SNuB$\equiv 10^{-12} \,\rm{SNe} \, L^{-1}_{\odot,B} yr^{-1}$). The cluster rate normalized by the stellar mass is $0.10^{+0.13}_{-0.06}\pm0.02$ in $\rm SNuM$$\,h^2$ (SNuM$\equiv 10^{-12} \,\rm{SNe} \, M^{-1}_{\odot} yr^{-1}$). Furthermore, we explore the optimal future survey for improving the core-collapse supernova rate measurements at $z\gtrsim2$ using gravitational telescopes, as well as for the detections with multiply lensed images, and find that the planned WFIRST space mission has excellent prospects. Massive clusters can be used as gravitational telescopes to significantly expand the survey range of supernova searches, with important implications for the study of the high-$z$ transient universe.

astro-ph.GA↗

arXiv2016

SPIRITS 15c and SPIRITS 14buu: Two Obscured Supernovae in the Nearby Star-Forming Galaxy IC 2163

SPIRITS---SPitzer InfraRed Intensive Transients Survey---is an ongoing survey of nearby galaxies searching for infrared (IR) transients with Spitzer/IRAC. We present the discovery and follow-up observations of one of our most luminous ($M_{[4.5]} = -17.1\pm0.4$ mag, Vega) and red ($[3.6] - [4.5] = 3.0 \pm 0.2$ mag) transients, SPIRITS 15c. The transient was detected in a dusty spiral arm of IC 2163 ($D\approx35.5$ Mpc). Pre-discovery ground-based imaging revealed an associated, shorter-duration transient in the optical and near-IR (NIR). NIR spectroscopy showed a broad ($\approx 8400$ km s$^{-1}$), double-peaked emission line of He I at $1.083 μ$m, indicating an explosive origin. The NIR spectrum of SPIRITS 15c is similar to that of the Type IIb SN 2011dh at a phase of $\approx 200$ days. Assuming $A_V = 2.2$ mag of extinction in SPIRITS 15c provides a good match between their optical light curves. The IR light curves and the extreme $[3.6]-[4.5]$ color cannot be explained using only a standard extinction law. Another luminous ($M_{4.5} = -16.1\pm0.4$ mag) event, SPIRITS 14buu, was serendipitously discovered in the same galaxy. The source displays an optical plateau lasting $\gtrsim 80$ days, and we suggest a scenario similar to the low-luminosity Type IIP SN 2005cs obscured by $A_V \approx 1.5$ mag. Other classes of IR-luminous transients can likely be ruled out in both cases. If both events are indeed SNe, this may suggest $\gtrsim 18\%$ of nearby core-collapse SNe are missed by currently operating optical surveys.

astro-ph.HE↗

arXiv2016

A Systematic Study of Mid-Infrared Emission from Core-Collapse Supernovae with SPIRITS

We present a systematic study of mid-infrared (mid-IR) emission from 141 nearby supernovae (SNe) observed with the InfraRed Array Camera (IRAC) on Spitzer.These SNe reside in one of the 190 galaxies within 20 Mpc drawn from the ongoing SPIRITS program. We detect 8 Type Ia SNe and 36 core-collapse SNe. All Type I SNe become undetectable within 3 years of explosion. About 22$\pm$11% of Type II SNe continue to be detected at late-times. Dust luminosity, temperature, and a lower liit on mass are obtained by fitting the SED using photometry with IRAC bands 1 and 2. The mass estimate does not distinguish between pre-existing and newly produced dust. We observe warm dust masses between $10^{-2}$ and $10^{-6}$ $\rm M_{\odot}$ and dust temperatures from 200 K to 1280 K.We present detailed case studies of two extreme Type II-P SNe: SN 2011ja and 2014bi. SN 2011ja was over-luminous ([4.5] = -15.6 mag) at 900 days post-explosion accompanied by the growing dust mass. This suggests either an episode of dust formation or an intensifying CSM interactions heating up pre-existing dust. SN 2014bi showed a factor of 10 decrease in dust mass over one month suggesting either an episode of dust destruction or a fading source of dust heating. A rebrightening of the Type Ib SN 2014C is observed and attributed to CSM interactions. This observation adds to a small number of stripped-envelope SNe that have mid-IR excess. The observations suggest that the CSM shell around SN 2014C is originated from an LBV-like eruption roughly 100 years before the explosion. We also report detections of SN1974E, 1979C, 1980K, 1986J, and 1993J detected more than 20 years post-explosion. The number of outlying SNe identified in this work demonstrates the power of late time mid-IR observations of a large sample of SNe to identify events with unusual evolution.

astro-ph.SR↗

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.

astro-ph.HE↗

arXiv2015

An Excess of Mid-Infrared Emission from the Type Iax SN 2014dt

Supernovae Type Iax (SNe Iax) are less energetic and less luminous than typical thermonuclear explosions. A suggested explanation for the observed characteristics of this subclass is a binary progenitor system consisting of a CO white dwarf primary accreting from a helium star companion. A single-degenerate explosion channel might be expected to result in a dense circumstellar medium (CSM), although no evidence for such a CSM has yet been observed for this subclass. Here we present recent Spitzer observations of the SN Iax 2014dt obtained by the SPIRITS program nearly one year post-explosion that reveal a strong mid-IR excess over the expected fluxes of more normal SNe Ia. This excess is consistent with 1E-5 M_solar of newly formed dust, which would be the first time that newly formed dust has been observed to form in a normal Type Ia. The excess, however, is also consistent with a dusty CSM that was likely formed in pre-explosion mass-loss, thereby suggesting a single degenerate progenitor system. Compared to other SNe Ia that show significant shock interaction (SNe Ia-CSM) and interacting core-collapse events (SNe IIn), this dust shell in SN 2014dt is less massive. We consider the implications that such a pre-existing dust shell has for the progenitor system, including a binary system with a mass donor that is a red giant, a red supergiant, and an asymptotic giant branch star.

astro-ph.HE↗

arXiv2015

The Needle in the 100 deg2 Haystack: Uncovering Afterglows of Fermi GRBs with the Palomar Transient Factory

The Fermi Gamma-ray Space Telescope has greatly expanded the number and energy window of observations of gamma-ray bursts (GRBs). However, the coarse localizations of tens to a hundred square degrees provided by the Fermi GRB Monitor instrument have posed a formidable obstacle to locating the bursts' host galaxies, measuring their redshifts, and tracking their panchromatic afterglows. We have built a target-of-opportunity mode for the intermediate Palomar Transient Factory in order to perform targeted searches for Fermi afterglows. Here, we present the results of one year of this program: 8 afterglow discoveries out of 35 searches. Two of the bursts with detected afterglows (GRBs 130702A and 140606B) were at low redshift (z=0.145 and 0.384 respectively) and had spectroscopically confirmed broad-line Type Ic supernovae. We present our broadband follow-up including spectroscopy as well as X-ray, UV, optical, millimeter, and radio observations. We study possible selection effects in the context of the total Fermi and Swift GRB samples. We identify one new outlier on the Amati relation. We find that two bursts are consistent with a mildly relativistic shock breaking out from the progenitor star, rather than the ultra-relativistic internal shock mechanism that powers standard cosmological bursts. Finally, in the context of the Zwicky Transient Facility, we discuss how we will continue to expand this effort to find optical counterparts of binary neutron star mergers that may soon be detected by Advanced LIGO and Virgo.

astro-ph.HE↗

arXiv2013

SN 2000cx and SN 2013bh: Extremely Rare, Nearly Twin Type Ia Supernovae

The Type Ia supernova (SN Ia) SN 2000cx was one of the most peculiar transients ever discovered, with a rise to maximum brightness typical of a SN Ia, but a slower decline and a higher photospheric temperature. Thirteen years later SN 2013bh (aka iPTF13abc), a near identical twin, was discovered and we obtained optical and near-IR photometry and low-resolution optical spectroscopy from discovery until about 1 month past r-band maximum brightness. The spectra of both objects show iron-group elements (Co II, Ni II, Fe II, Fe III, and high-velocity features [HVFs] of Ti II), intermediate-mass elements (Si II, Si III, and S II), and separate normal velocity features (~12000 km/s) and HVFs (~24000 km/s) of Ca II. Persistent absorption from Fe III and Si III, along with the colour evolution, imply high blackbody temperatures for SNe 2013bh and 2000cx (~12000 K). Both objects lack narrow Na I D absorption and exploded in the outskirts of their hosts, indicating that the SN environments were relatively free of interstellar or circumstellar material and may imply that the progenitors came from a relatively old and low-metallicity stellar population. Models of SN 2000cx, seemingly applicable to SN 2013bh, imply the production of up to ~1 M_Sun of Ni-56 and (4.3-5.5)e-3 M_Sun of fast-moving Ca ejecta.

astro-ph.SR↗

arXiv2013

Herschel limits on far-infrared emission from circumstellar dust around nearby Type Ia supernovae

We report upper limits on dust emission at far-infrared (IR) wavelengths from three nearby Type Ia supernovae: SNe 2011by, 2011fe and 2012cg. Observations were carried out at 70 um and 160 um with the Photodetector Array Camera and Spectrometer (PACS) on board the Herschel Space Observatory. None of the supernovae were detected in the far-IR, allowing us to place upper limits on the amount of pre-existing dust in the circumstellar environment. Due to its proximity, SN 2011fe provides the tightest constraints, M_dust < 7 * 10^-3 M_sun at a 3 sigma-level for dust temperatures T_dust ~500 K assuming silicate or graphite dust grains of size a = 0.1 um. For SNe 2011by and 2012cg the corresponding upper limits are less stringent, with M_dust < 0.1 M_sun for the same assumptions.

astro-ph.CO↗

arXiv2013

Hunting for dark halo substructure using submilliarcsecond-scale observations of macrolensed radio jets

Dark halo substructure may reveal itself through secondary, small-scale gravitational lensing effects on light sources that are macrolensed by a foreground galaxy. Here, we explore the prospects of using Very Long Baseline Interferometry (VLBI) observations of multiply-imaged quasar jets to search for submilliarcsecond-scale image distortions produced by various forms of dark substructures in the 1e3-1e8 Msolar mass range. We present lensing simulations relevant for the angular resolutions attainable with the existing European VLBI Network (EVN), the global VLBI array, and an upcoming observing mode in which the Atacama Large Millimeter Array (ALMA) is connected to the global VLBI array. While observations of this type would not be sensitive to standard cold dark matter subhalos, they can be used to detect more compact forms of halo substructure predicted in alternative structure formation scenarios. By mapping ~5 strongly lensed systems, it should be possible to detect or robustly rule out primordial black holes in the 1e3-1e6 Msolar mass range if they constitute >1% percent of the dark matter in these lenses. Ultracompact minihalos are harder to detect using this technique, but 1e6-1e8 Msolar ultracompact minihalos could in principle be detected if they constitute >10% of the dark matter.

astro-ph.CO↗