Ori Dosovitz Fox

A relativistic type Ibc supernova without a detected γ-ray burst

Long duration γ-ray bursts (GRBs) mark the explosive death of some massive stars and are a rare sub-class of type Ibc supernovae. They are distinguished by the production of an energetic and collimated relativistic outflow powered by a central engine (an accreting black hole or neutron star). Observationally, this outflow is manifested in the pulse of γ-rays and a long-lived radio afterglow. Until now, central-engine-driven supernovae have been discovered exclusively through their γ-ray emission, yet it is expected that a larger population goes undetected because of limited satellite sensitivity or beaming of the collimated emission away from our line of sight. In this framework, the recovery of undetected GRBs may be possible through radio searches for type Ibc supernovae with relativistic outflows. Here we report the discovery of luminous radio emission from the seemingly ordinary type Ibc SN 2009bb, which requires a substantial relativistic outflow powered by a central engine. A comparison with our radio survey of type Ibc supernovae reveals that the fraction harbouring central engines is low, about one per cent, measured independently from, but consistent with, the inferred rate of nearby GRBs. Independently, a second mildly relativistic supernova has been reported.

The Diversity of Massive Star Outbursts. I. Observations of SN2009ip, UGC 2773 OT2009-1, and Their Progenitors

Despite both being outbursts of luminous blue variables (LBVs), SN 2009ip and UGC 2773 OT2009-1 have very different progenitors, spectra, circumstellar environments, and possibly physical mechanisms that generated the outbursts. From pre-eruption Hubble Space Telescope images, we determine that SN 2009ip and UGC 2773 OT2009-1 have initial masses of {approx}> 60 and {approx}> 25 M{sub sun}, respectively. Optical spectroscopy shows that at peak, SN 2009ip had a 10,000 K photosphere and its spectrum was dominated by narrow H Balmer emission, similar to classical LBV giant outbursts, also known as supernova impostors. The spectra of UGC 2773 OT2009-1, which also have narrow H{alpha} emission, are dominated by a forest of absorption lines, similar to an F-type supergiant. Blueshifted absorption lines corresponding to ejecta at a velocity of 2000-7000 km s{sup -1} are present in later spectra of SN 2009ip-an unprecedented observation for LBV outbursts, indicating that the event was the result of a supersonic explosion rather than a subsonic outburst. The velocity of the absorption lines increases between two epochs, suggesting that there were two explosions in rapid succession. A rapid fading and rebrightening event concurrent with the onset of the high-velocity absorption lines is consistent with the double-explosion model. Amorexa0» near-infrared excess is present in the spectra and photometry of UGC 2773 OT2009-1 that is consistent with {approx}2100 K dust emission. We compare the properties of these two events and place them in the context of other known massive star outbursts such as {eta} Car, NGC 300 OT2008-1, and SN 2008S. This qualitative analysis suggests that massive star outbursts have many physical differences that can manifest as the different observables seen in these two interesting objects.«xa0less

NEAR-INFRARED PHOTOMETRY OF THE TYPE IIn SN 2005ip: THE CASE FOR DUST CONDENSATION

Near-infrared photometric observations of the Type IIn supernova (SN) 2005ip in NGC 2906 reveal large fluxes (>1.3 mJy) in the Ks -band over more than 900 days. While warm dust can explain the late-time Ks -band emission of SN 2005ip, the nature of the dust heating source is ambiguous. Shock heating of pre-existing dust by post-shocked gas is unlikely because the forward shock is moving too slowly to have traversed the expected dust-free cavity by the time observations first reveal the Ks emission. While an infrared light echo model correctly predicts a near-infrared luminosity plateau, heating dust to the observed temperatures of ~ 1400-1600 K at a relatively large distance from the supernova (1018 cm) requires an extraordinarily high early supernova luminosity (~1 × 1011 L ☉). The evidence instead favors condensing dust in the cool, dense shell between the forward and reverse shocks. Both the initial dust temperature and the evolutionary trend toward lower temperatures are consistent with this scenario. We infer that radiation from the circumstellar interaction heats the dust. While this paper includes no spectroscopic confirmation, the photometry is comparable to other supernovae that do show spectroscopic evidence for dust formation. Observations of dust formation in supernovae are sparse, so these results provide a rare opportunity to consider supernovae Type IIn as dust sources.

DISENTANGLING THE ORIGIN AND HEATING MECHANISM OF SUPERNOVA DUST: LATE-TIME SPITZER SPECTROSCOPY OF THE TYPE IIn SN 2005ip

This paper presents late-time near-infrared and Spitzer mid-infrared photometric and spectroscopic observations of warm dust in the Type IIn SN 2005ip in NGC 2906. The spectra show evidence for two dust components with different temperatures. Spanning the peak of the thermal emission, these observations provide strong constraints on the dust mass, temperature, and luminosity, which serve as critical diagnostics for disentangling the origin and heating mechanism of each component. The results suggest that the warmer dust has a mass of {approx}5 x 10{sup -4} M{sub sun}, originates from newly formed dust in the ejecta, or possibly the cool, dense shell, and is continuously heated by the circumstellar interaction. By contrast, the cooler component likely originates from a circumstellar shock echo that forms from the heating of a large, pre-existing dust shell {approx}0.01-0.05 M{sub sun} by the late-time circumstellar interaction. The progenitor wind velocity derived from the blue edge of the He I 1.083 {mu}m P Cygni profile indicates a progenitor eruption likely formed this dust shell {approx}100 years prior to the supernova explosion, which is consistent with a Luminous Blue Variable progenitor star.

THE HIGH-METALLICITY EXPLOSION ENVIRONMENT OF THE RELATIVISTIC SUPERNOVA 2009bb*

We investigate the environment of the nearby (d approximate to 40 Mpc) broad-lined Type Ic supernova (SN) 2009bb. This event was observed to produce a relativistic outflow likely powered by a central accreting compact object. While such a phenomenon was previously observed only in long-duration gamma-ray bursts (LGRBs), no LGRB was detected in association with SN 2009bb. Using an optical spectrum of the SN 2009bb explosion site, we determine a variety of interstellar medium properties for the host environment, including metallicity, young stellar population age, and star formation rate. We compare the SN explosion site properties to observations of LGRB and broad-lined SN Ic host environments on optical emission line ratio diagnostic diagrams. Based on these analyses, we find that the SN 2009bb explosion site has a metallicity between 1.7 Z(circle dot) and 3.5 Z(circle dot), in agreement with other broad-lined SN Ic host environments and at odds with the low-redshift LGRB host environments and recently proposed maximum metallicity limits for relativistic explosions. We consider the implications of these findings and the impact that SN 2009bbs unusual explosive properties and environment have on our understanding of the key physical ingredient that enables some SNe to produce a relativistic outflow.

Detector arrays for the James Webb Space Telescope near-infrared spectrograph

The James Webb Space Telescopes (JWST) Near Infrared Spectrograph (NIRSpec) incorporates two 5 μm cutoff (λco =5 μm) 2048×2048 pixel Teledyne HgCdTe HAWAII-2RG sensor chip assemblies. These detector arrays, and the two Teledyne SIDECAR application specific integrated circuits that control them, are operated in space at T ~ 37 K. In this article, we provide a brief introduction to NIRSpec, its detector subsystem (DS), detector readout in the space radiation environment, and present a snapshot of the developmental status of the NIRSpec DS as integration and testing of the engineering test unit begins.

The 55Fe x-ray energy response of mercury cadmium telluride near-infrared detector arrays

The accurate determination of a detectors fundamental parameters, including read noise, dark current, and QE, relies on a proper measurement of a detectors conversion gain (e- ADU-1). Charge coupling effects, such as interpixel capacitance, attenuate photon shot noise and result in an overestimation of conversion gain when implementing the photon transfer technique. An approach involving 55Fe X-rays provides a potentially straightforward measurement of conversion gain by comparing the observed instrumental counts (ADU) to the known charge (e-) liberated by the X-ray. This technique is already preferred within the CCD community, as the pair production energy for silicon is well established. In contrast, to date the pair production energy is unknown for HgCdTe, a material commonly used for near-infrared detectors. In this paper, we derive a preliminary calibration of the 55Fe X-ray energy response of HgCdTe using 8 HST WFC3 1.7 μm flight grade detectors. Our conversion of the X-ray intensities from counts into electrons implements a technique that restores the true gain via classical propagation of errors. For these detectors, our analysis yields preliminary results of good statistical precision: each Kα event generates 1849 ± 46 electrons, which corresponds to a pair production energy of 3.21 ± 0.08 eV. We are continuing to assess potential systematic effects to further refine the accuracy of this result.

Development of extended wavelength response InGaAs detectors for astronomical applications

We report the results of a program to mitigate defect induced (tunneling) dark current which arises from lattice mismatch between In0.82Ga0.18As extended wavelength detector material and the InP substrate upon which it is grown. Our goal is to produce material suitable for ground-based broadband astronomical observation by achieving a dark current level in individual 25x25μm array pixels which is less than the atmospheric airglow and telescope thermal emission in the astronomical H (1.50-1.80 μm) and Ks (2.00-2.32 μm) bands. We have cryogenically tested multiple growths of candidate materials, packaged as both individual diodes and focal plane arrays, supplied by Sensors Unlimited, Inc. (SU). Results indicate dark current levels, in the current generation of array materials, surpassing the requirements for broadband imaging, and with the potential to be used for narrow band imaging and low-resolution spectroscopy.

Characterization of the Detector Subsystem for the Near Infrared Spectrograph (NIRSpec) on the James Webb Space Telescope

We present interim results from the characterization test development for the Detector Subsystem of the Near-Infrared Spectrograph (NIRSpec). NIRSpec will be the primary near-infrared spectrograph on the James Webb Space Telescope (JWST). The Detector Subsystem consists of a Focal Plane Assembly containing two Teledyne HAWAII-2RG arrays, two Teledyne SIDECAR cryogenic application specific integrated circuits, and a warm Focal Plane Electronics box. The Detector Characterization Laboratory at NASAs Goddard Space Flight Center will perform the Detector Subsystem characterization tests. In this paper, we update the initial test results obtained with engineering grade components.

James Webb Space Telescope Near-Infrared Spectrograph : Dark Performance of the First Flight Candidate Detector Arrays

The James Webb Space Telescope (JWST) Near Infrared Spectrograph (NIRSpec) incorporates two 5 μm cutoff (λco =5 μm) 2048×2048 pixel Teledyne HgCdTe HAWAII-2RG sensor chip assemblies. These detector arrays, and the two Teledyne SIDECAR application specific integrated circuits that control them, are operated in space at Τ ~ 37 K. This article focuses on the measured performance of the first flight-candidate, and near-flight candidate, detector arrays. These are the first flight-packaged detector arrays that meet NIRSpecs challenging 6 e- rms total noise requirement. The current version of this paper has had a correction made to it at the request of the author. Please see the linked Errata for further details.