Shocks and dust formation in nova V809 Cep

The discovery that many classical novae produce detectable GeV $\gamma$-ray emission has raised the question of the role of shocks in nova eruptions. Here we use radio observations of nova V809 Cep (Nova Cep 2013) with the Jansky Very Large Array to show that it produced non-thermal emission indicative of particle acceleration in strong shocks for more than a month starting about six weeks into the eruption, quasi-simultaneous with the production of dust. Broadly speaking, the radio emission at late times -- more than a six months or so into the eruption -- is consistent with thermal emission from $10^{-4} M_\odot$ of freely expanding, $10^4$~K ejecta. At 4.6 and 7.4 GHz, however, the radio light-curves display an initial early-time peak 76 days after the discovery of the eruption in the optical ($t_0$). The brightness temperature at 4.6 GHz on day 76 was greater than $10^5 K$, an order of magnitude above what is expected for thermal emission. We argue that the brightness temperature is the result of synchrotron emission due to internal shocks within the ejecta. The evolution of the radio spectrum was consistent with synchrotron emission that peaked at high frequencies before low frequencies, suggesting that the synchrotron from the shock was initially subject to free-free absorption by optically thick ionized material in front of the shock. Dust formation began around day 37, and we suggest that internal shocks in the ejecta were established prior to dust formation and caused the nucleation of dust

Wide-field dynamic astronomy in the near-infrared with Palomar Gattini-IR and DREAMS

There have been a dramatic increase in the number of optical and radio transient surveys due to astronomical transients such as gravitational waves and gamma ray bursts, however, there have been a limited number of wide-field infrared surveys due to narrow field-of-view and high cost of infrared cameras, we present two new wide-field near-infrared fully automated surveyors; Palomar Gattini-IR and the Dynamic REd All-sky Monitoring Survey (DREAMS). Palomar Gattini-IR, a 25 square degree J-band imager that begun science operations at Palomar Observatory, USA in October 2018; we report on survey strategy as well as telescope and observatory operations and will also providing initial science results. DREAMS is a 3.75 square degree wide-field imager that is planned for Siding Spring Observatory, Australia; we report on the current optical and mechanical design and plans to achieve on-sky results in 2020. DREAMS is on-track to be one of the first astronomical telescopes to use an Indium Galium Arsenide (InGaAs) detector and we report initial on-sky testing results for the selected detector package. DREAMS is also well placed to take advantage and provide near-infrared follow-up of the LSST

Palomar Gattini-IR: Survey overview, data processing system, on-sky performance and first results

Palomar Gattini-IR is a new wide-field, near-infrared (NIR) robotic time domain survey operating at Palomar Observatory. Using a 30 cm telescope mounted with a H2RG detector, Gattini-IR achieves a field of view (FOV) of 25 sq. deg. with a pixel scale of 8.”7 in J-band. Here, we describe the system design, survey operations, data processing system and on-sky performance of Palomar Gattini-IR. As a part of the nominal survey, Gattini-IR scans ≈7500 square degrees of the sky every night to a median 5σ depth of 15.7 AB mag outside the Galactic plane. The survey covers ≈15,000 square degrees of the sky visible from Palomar with a median cadence of 2 days. A real-time data processing system produces stacked science images from dithered raw images taken on sky, together with point-spread function (PSF)-fit source catalogs and transient candidates identified from subtractions within a median delay of ≈4 hr from the time of observation. The calibrated data products achieve an astrometric accuracy (rms) of ≈0.”7 with respect to Gaia DR2 for sources with signal-to-noise ratio > 10, and better than ≈0.”35 for sources brighter than ≈12 Vega mag. The photometric accuracy (rms) achieved in the PSF-fit source catalogs is better than ≈3% for sources brighter than ≈12 Vega mag and fainter than the saturation magnitude of ≈8.5 Vega mag, as calibrated against the Two Micron All Sky Survey catalog. The detection efficiency of transient candidates injected into the images is better than 90% for sources brighter than the 5σ limiting magnitude. The photometric recovery precision of injected sources is 3% for sources brighter than 13 mag, and the astrometric recovery rms is ≈0.”9. Reference images generated by stacking several field visits achieve depths of ≳16.5 AB mag over 60% of the sky, while it is limited by confusion in the Galactic plane. With a FOV ≈40× larger than any other existing NIR imaging instrument, Gattini-IR is probing the reddest and dustiest transients in the local universe such as dust obscured supernovae in nearby galaxies, novae behind large columns of extinction within the galaxy, reddened microlensing events in the Galactic plane and variability from cool and dust obscured stars. We present results from transients and variables identified since the start of the commissioning period

Wide-field dynamic astronomy in the near-infrared with Palomar Gattini-IR and DREAMS

There have been a dramatic increase in the number of optical and radio transient surveys due to astronomical transients such as gravitational waves and gamma ray bursts, however, there have been a limited number of wide-field infrared surveys due to narrow field-of-view and high cost of infrared cameras, we present two new wide-field near-infrared fully automated surveyors; Palomar Gattini-IR and the Dynamic REd All-sky Monitoring Survey (DREAMS). Palomar Gattini-IR, a 25 square degree J-band imager that begun science operations at Palomar Observatory, USA in October 2018; we report on survey strategy as well as telescope and observatory operations and will also providing initial science results. DREAMS is a 3.75 square degree wide-field imager that is planned for Siding Spring Observatory, Australia; we report on the current optical and mechanical design and plans to achieve on-sky results in 2020. DREAMS is on-track to be one of the first astronomical telescopes to use an Indium Galium Arsenide (InGaAs) detector and we report initial on-sky testing results for the selected detector package. DREAMS is also well placed to take advantage and provide near-infrared follow-up of the LSST

Uncovering Shocking Mysteries Buried in the Ejecta of Classical Novae and Magnetars

This dissertation uses shocks to explain both the prevalence of radio synchroton emission and dust formation in classical novae, as well as the origin of fast radio bursts. First, we examine the radio lightcurves of nova V809 Cep and find that the peak brightness temperature exceeded 10⁵, an order of magnitude above what is expected for thermal emission. We argue that the brightness temperature is the result of synchrotron emission due to internal shocks within the ejecta. We then examine the radio lightcurves of seven novae with radio evidence for shocks (QU Vul, V1723 Aql, V5668 Sgr, V809 Cep, V357 Mus, V1324 Sco, PGIR20fbf) and IR/optical evidence for dust formation. We demonstrate that dust formation generally precedes the rise of radio non-thermal emission, and present evidence to suggest that shocks occur prior to the onset of dust formation but that the radio shock emission is initially being absorbed by a layer of photo-ionized gas ahead of the shock. We model the optical depth of the photo-ionized gas to demonstrate that the time required for the photo-ionized gas to become optically thin to radio frequencies can be longer than the time required for dust nucleation; thus, dust appears to form before the shock emission is visible. We further demonstrate that the radio spectral evolution in novae with no evidence for dust formation is markedly different from novae with evidence for shocks, suggesting that in novae without velocity or distance estimates, the radio spectral evolution could be used to constrain the presence of shocks. Finally, we demonstrate that novae with evidence for dust absorption are preferentially inclined edge, on suggesting that both shocks and dust form in the equatorial plane. Since internal shocks in nova ejecta are thought to lead to dust formation, localizing both phenomenon to the equatorial plane strengthens the connection between the two phenomena. We then use Particle-In-Cell (PIC) simulations to explore the synchroton maser instability as a potential mechanism for the formation of Fast Radio Bursts. Electromagnetic precursor waves generated by the synchrotron maser instability at relativistic magnetized shocks have been recently invoked to explain the coherent radio emission of Fast Radio Bursts. By means of two-dimensional particle-in-cell simulations, we explore the properties of the precursor waves in relativistic electron-positron perpendicular shocks as a function of the pre-shock magnetization σ ≳1 (i.e., the ratio of incoming Poynting flux to particle energy flux) and thermal spread Δᵧ ≡ /² = 10⁻⁵−10⁻¹. We measure the fraction of total incoming energy that is converted into precursor waves, as computed in the post-shock frame. At fixed magnetization, we find that is nearly independent of temperature as long as Δᵧ ≲ 10¹·⁵ (with only a modest decrease of a factor of three from Δᵧ = 10⁻⁵ to Δᵧ = 10¹·⁵, but it drops by nearly two orders of magnitude for Δᵧ ≳ 10⁻¹. For our reference σ = 1, the power spectrum of precursor waves is relatively broad (fractional width ∼ 1−3) for cold temperatures, whereas it shows pronounced line-like features with fractional width ∼ 0.2 for 10⁻³ ≲ Δᵧ ≲ 10¹·⁵. For σ ≳ 1, the precursor waves are beamed within an angle ≃ σ -⁻¹/² from the shock normal (as measured in the post-shock frame), as required so they can outrun the shock. Our results can provide physically-grounded inputs for FRB emission models based on maser emission from relativistic shocks