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We present the discovery of an optical transient (OT) in Messier 51, designated M51 OT2019-1 (also ZTF 19aadyppr, AT 2019abn, ATLAS19bzl), by the Zwicky Transient Facility (ZTF). The OT rose over 15 days to an observed luminosity of Mr = -13 (νLν = 9 × 106 Lo), in the luminosity gap between novae and typical supernovae (SNe). Spectra during the outburst show a red continuum, Balmer emission with a velocity width of ≈400 km s-1, Ca ii and [Ca ii] emission, and absorption features characteristic of an F-type supergiant. The spectra and multiband light curves are similar to the so-called "SN impostors" and intermediate-luminosity red transients (ILRTs). We directly identify the likely progenitor in archival Spitzer Space Telescope imaging with a 4.5 μm luminosity of M[4.5] ≈ -12.2 mag and a [3.6]-[4.5] color redder than 0.74 mag, similar to those of the prototype ILRTs SN 2008S and NGC 300 OT2008-1. Intensive monitoring of M51 with Spitzer further reveals evidence for variability of the progenitor candidate at [4.5] in the years before the OT. The progenitor is not detected in pre-outburst Hubble Space Telescope optical and near-IR images. The optical colors during outburst combined with spectroscopic temperature constraints imply a higher reddening of E(B - V) ≈ 0.7 mag and higher intrinsic luminosity of Mr ≈ -14.9 mag (νLν = 5.3 × 107 Lo) near peak than seen in previous ILRT candidates. Moreover, the extinction estimate is higher on the rise than on the plateau, suggestive of an extended phase of circumstellar dust destruction. These results, enabled by the early discovery of M51 OT2019-1 and extensive pre-outburst archival coverage, offer new clues about the debated origins of ILRTs and may challenge the hypothesis that they arise from the electron-capture induced collapse of extreme asymptotic giant branch stars.

We present the discovery of an optical transient (OT) in Messier 51, designated M51 OT2019-1 (also ZTF 19aadyppr, AT 2019abn, ATLAS19bzl), by the Zwicky Transient Facility (ZTF). The OT rose over 15 days to an observed luminosity of Mr = -13 (νLν = 9 × 106 Lo), in the luminosity gap between novae and typical supernovae (SNe). Spectra during the outburst show a red continuum, Balmer emission with a velocity width of ≈400 km s-1, Ca ii and [Ca ii] emission, and absorption features characteristic of an F-type supergiant. The spectra and multiband light curves are similar to the so-called "SN impostors" and intermediate-luminosity red transients (ILRTs). We directly identify the likely progenitor in archival Spitzer Space Telescope imaging with a 4.5 μm luminosity of M[4.5] ≈ -12.2 mag and a [3.6]-[4.5] color redder than 0.74 mag, similar to those of the prototype ILRTs SN 2008S and NGC 300 OT2008-1. Intensive monitoring of M51 with Spitzer further reveals evidence for variability of the progenitor candidate at [4.5] in the years before the OT. The progenitor is not detected in pre-outburst Hubble Space Telescope optical and near-IR images. The optical colors during outburst combined with spectroscopic temperature constraints imply a higher reddening of E(B - V) ≈ 0.7 mag and higher intrinsic luminosity of Mr ≈ -14.9 mag (νLν = 5.3 × 107 Lo) near peak than seen in previous ILRT candidates. Moreover, the extinction estimate is higher on the rise than on the plateau, suggestive of an extended phase of circumstellar dust destruction. These results, enabled by the early discovery of M51 OT2019-1 and extensive pre-outburst archival coverage, offer new clues about the debated origins of ILRTs and may challenge the hypothesis that they arise from the electron-capture induced collapse of extreme asymptotic giant branch stars.

We present results from the MOSFIRE Deep Evolution Field survey on broad flux from the nebular emission lines Hα, [N ii], [O iii], Hβ, and [S ii]. The sample consists of 127 star-forming galaxies at 1.37

We present results from the MOSFIRE Deep Evolution Field survey on broad flux from the nebular emission lines Hα, [N ii], [O iii], Hβ, and [S ii]. The sample consists of 127 star-forming galaxies at 1.37

We present the results of optical, near-infrared, and mid-infrared observations of M101 OT2015-1 (PSN J14021678+5426205), a luminous red transient in the Pinwheel galaxy (M101), spanning a total of 16 years. The light curve showed two distinct peaks with absolute magnitudes Mr ≤ -12.4 and Mr ∼ -12, on 2014 November 11 and 2015 February 17, respectively. The spectral energy distributions during the second maximum show a cool outburst temperature of ≈3700 K and low expansion velocities (≈-300 km s-1) for the H I, Ca II, Ba II, and K I lines. From archival data spanning 15-8 years before the outburst, we find a single source consistent with the optically discovered transient, which we attribute to being the progenitor; it has properties consistent with being an F-type yellow supergiant with L ∼ 8.7×104 L-, Teff ≈ 7000 K, and an estimated mass of M1 = 18 ± 1 M-. This star has likely just finished the H-burning phase in the core, started expanding, and is now crossing the Hertzsprung gap. Based on the combination of observed properties, we argue that the progenitor is a binary system, with the more evolved system overfilling the Roche lobe. Comparison with binary evolution models suggests that the outburst was an extremely rare phenomenon, likely associated with the ejection of the common envelope of a massive star. The initial mass of the primary fills the gap between the merger candidates V838 Mon (5-10 M-) and NGC 4490-OT (30M-).

We present the results of optical, near-infrared, and mid-infrared observations of M101 OT2015-1 (PSN J14021678+5426205), a luminous red transient in the Pinwheel galaxy (M101), spanning a total of 16 years. The light curve showed two distinct peaks with absolute magnitudes Mr ≤ -12.4 and Mr ∼ -12, on 2014 November 11 and 2015 February 17, respectively. The spectral energy distributions during the second maximum show a cool outburst temperature of ≈3700 K and low expansion velocities (≈-300 km s-1) for the H I, Ca II, Ba II, and K I lines. From archival data spanning 15-8 years before the outburst, we find a single source consistent with the optically discovered transient, which we attribute to being the progenitor; it has properties consistent with being an F-type yellow supergiant with L ∼ 8.7×104 L-, Teff ≈ 7000 K, and an estimated mass of M1 = 18 ± 1 M-. This star has likely just finished the H-burning phase in the core, started expanding, and is now crossing the Hertzsprung gap. Based on the combination of observed properties, we argue that the progenitor is a binary system, with the more evolved system overfilling the Roche lobe. Comparison with binary evolution models suggests that the outburst was an extremely rare phenomenon, likely associated with the ejection of the common envelope of a massive star. The initial mass of the primary fills the gap between the merger candidates V838 Mon (5-10 M-) and NGC 4490-OT (30M-).

The supernova (SN) PTF11iqb was initially classified as a Type IIn event caught very early after explosion. It showed narrowWolf-Rayet (WR) spectral features on day 2 (as in SN 1998S and SN 2013cu), but the narrow emission weakened quickly and the spectrum morphed to resemble Types II-L and II-P. At late times, Ha exhibited a complex, multipeaked profile reminiscent of SN 1998S. In terms of spectroscopic evolution, we find that PTF11iqb was a near twin of SN 1998S, although with somewhat weaker interaction with circumstellar material (CSM) at early times, and stronger interaction at late times. We interpret the spectral changes as caused by early interaction with asymmetric CSM that is quickly (by day 20) enveloped by the expanding SN ejecta photosphere, but then revealed again after the end of the plateau when the photosphere recedes. The light curve can be matched with a simple model for CSM interaction (with a mass-loss rate of roughly 10-4 M⊙ yr-1) added to the light curve of a normal SN II-P. The underlying plateau requires a progenitor with an extended hydrogen envelope like a red supergiant at the moment of explosion, consistent with the slow wind speed ( < 80 km s-1) inferred from narrow Ha emission. The cool supergiant progenitor is significant because PTF11iqb showed WR features in its early spectrum - meaning that the presence of such WR features does not necessarily indicate a WR-like progenitor. Overall, PTF11iqb bridges SNe IIn with weaker pre-SN mass-loss seen in SNe II-L and II-P, implying a continuum between these types.

The supernova (SN) PTF11iqb was initially classified as a Type IIn event caught very early after explosion. It showed narrowWolf-Rayet (WR) spectral features on day 2 (as in SN 1998S and SN 2013cu), but the narrow emission weakened quickly and the spectrum morphed to resemble Types II-L and II-P. At late times, Ha exhibited a complex, multipeaked profile reminiscent of SN 1998S. In terms of spectroscopic evolution, we find that PTF11iqb was a near twin of SN 1998S, although with somewhat weaker interaction with circumstellar material (CSM) at early times, and stronger interaction at late times. We interpret the spectral changes as caused by early interaction with asymmetric CSM that is quickly (by day 20) enveloped by the expanding SN ejecta photosphere, but then revealed again after the end of the plateau when the photosphere recedes. The light curve can be matched with a simple model for CSM interaction (with a mass-loss rate of roughly 10-4 M⊙ yr-1) added to the light curve of a normal SN II-P. The underlying plateau requires a progenitor with an extended hydrogen envelope like a red supergiant at the moment of explosion, consistent with the slow wind speed ( < 80 km s-1) inferred from narrow Ha emission. The cool supergiant progenitor is significant because PTF11iqb showed WR features in its early spectrum - meaning that the presence of such WR features does not necessarily indicate a WR-like progenitor. Overall, PTF11iqb bridges SNe IIn with weaker pre-SN mass-loss seen in SNe II-L and II-P, implying a continuum between these types.

AX J1745.6-2901 is a high-inclination (eclipsing) neutron star Low Mass X-rayBinary (LMXB) located less than ~1.5 arcmin from Sgr A*. Ongoing monitoringcampaigns have targeted Sgr A* frequently and these observations also cover AXJ1745.6-2901. We present here an X-ray analysis of AX J1745.6-2901 using alarge dataset of 38 XMM-Newton observations, including eleven which caught AXJ1745.6-2901 in outburst. Fe K absorption is clearly seen when AX J1745.6-2901is in the soft state, but disappears during the hard state. The variability ofthese absorption features does not appear to be due to changes in the ionizingcontinuum. The small Kalpha/Kbeta ratio of the equivalent widths of the Fe xxvand Fe xxvi lines suggests that the column densities and turbulent velocitiesof the absorbing ionised plasma are in excess of N_H ~ 10^23 cm^-2 and v_turb>~ 500 km s^-1. These findings strongly support a connection between the wind(Fe K absorber) and the accretion state of the binary. These results revealstrong similarities between AX J1745.6-2901 and the eclipsing neutron starLMXB, EXO 0748-676, as well as with high-inclination black hole binaries, wherewinds (traced by the same Fe K absorption features) are observed only duringthe accretion-disc-dominated soft states, and disappear during the hard statescharacterised by jet emission.

AX J1745.6-2901 is a high-inclination (eclipsing) neutron star Low Mass X-rayBinary (LMXB) located less than ~1.5 arcmin from Sgr A*. Ongoing monitoringcampaigns have targeted Sgr A* frequently and these observations also cover AXJ1745.6-2901. We present here an X-ray analysis of AX J1745.6-2901 using alarge dataset of 38 XMM-Newton observations, including eleven which caught AXJ1745.6-2901 in outburst. Fe K absorption is clearly seen when AX J1745.6-2901is in the soft state, but disappears during the hard state. The variability ofthese absorption features does not appear to be due to changes in the ionizingcontinuum. The small Kalpha/Kbeta ratio of the equivalent widths of the Fe xxvand Fe xxvi lines suggests that the column densities and turbulent velocitiesof the absorbing ionised plasma are in excess of N_H ~ 10^23 cm^-2 and v_turb>~ 500 km s^-1. These findings strongly support a connection between the wind(Fe K absorber) and the accretion state of the binary. These results revealstrong similarities between AX J1745.6-2901 and the eclipsing neutron starLMXB, EXO 0748-676, as well as with high-inclination black hole binaries, wherewinds (traced by the same Fe K absorption features) are observed only duringthe accretion-disc-dominated soft states, and disappear during the hard statescharacterised by jet emission.

We present optical photometric and spectroscopic observations of the Type Ibn (SN 2006jclike) supernova (SN) iPTF13beo. Detected by the intermediate Palomar Transient Factory~3 h after the estimated first light, iPTF13beo is the youngest and the most distant (~430 Mpc) Type Ibn event ever observed. The iPTF13beo light curve is consistent with light curves of other Type Ibn SNe and with light curves of fast Type Ic events, but with a slightly faster rise-time of two days. In addition, the iPTF13beo R-band light curve exhibits a double-peak structure separated by ~9 d, not observed before in any Type Ibn SN. A low-resolution spectrum taken during the iPTF13beo rising stage is featureless, while a late-time spectrum obtained during the declining stage exhibits narrow and intermediate-width He I and Si II features with full width at half-maximum ≈2000-5000 km s-1 and is remarkably similar to the prototypical SN Ibn 2006jc spectrum. We suggest that our observations support a model of a massive star exploding in a dense He-rich circumstellar medium (CSM). A shock breakout in a CSM model requires an eruption releasing a total mass of ~0.1 M⊙ over a time-scale of couple of weeks prior to the SN explosion. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

HST-10 is one of the largest proplyds in the Orion Nebula and is located approximately 1′ SE of the Trapezium. Unlike other proplyds in Orion, however, the long-axis of HST-10 does not align with θ1 C, but is instead aligned with the rotational axis of the HST-10 disk. This cannot be easily explained using current photoevaporation models. In this Letter, we present high spatial resolution near-infrared images of the Orion proplyd HST-10 using Keck/NIRC2 with the Laser Guide Star Adaptive Optics system, along with multi-epoch analysis of HH objects near HST-10 using Hubble Space Telescope (HST) WFPC2 and Advanced Camera for Surveys cameras. Our narrowband near-IR images resolve the proplyd ionization front (IF) and circumstellar disk down to 23 AU at the distance to Orion in Br γ, He I, H2, and polycyclic aromatic hydrocarbon (PAH) emission. Br γ and He I emission primarily trace the IF (with the disk showing prominently in silhouette), while the H2 and PAH emission trace the surface of the disk itself. PAH emission also traces small dust grains within the proplyd envelope which is asymmetric and does not coincide with the IF. The curious morphology of the PAH emission may be due to UV heating by both θ1 COri and θ2 AOri. Multi-epoch HST images of the HST-10 field show proper motion of three knots associated with HH 517, clearly indicating that HST-10 has a jet. We postulate that the orientation of HST-10 is determined by the combined ram pressure of this jet and the FUV-powered photo-ablation flow from the disk surface. © 2014. The American Astronomical Society. All rights reserved.

HST-10 is one of the largest proplyds in the Orion Nebula and is located approximately 1′ SE of the Trapezium. Unlike other proplyds in Orion, however, the long-axis of HST-10 does not align with θ1 C, but is instead aligned with the rotational axis of the HST-10 disk. This cannot be easily explained using current photoevaporation models. In this Letter, we present high spatial resolution near-infrared images of the Orion proplyd HST-10 using Keck/NIRC2 with the Laser Guide Star Adaptive Optics system, along with multi-epoch analysis of HH objects near HST-10 using Hubble Space Telescope (HST) WFPC2 and Advanced Camera for Surveys cameras. Our narrowband near-IR images resolve the proplyd ionization front (IF) and circumstellar disk down to 23 AU at the distance to Orion in Br γ, He I, H2, and polycyclic aromatic hydrocarbon (PAH) emission. Br γ and He I emission primarily trace the IF (with the disk showing prominently in silhouette), while the H2 and PAH emission trace the surface of the disk itself. PAH emission also traces small dust grains within the proplyd envelope which is asymmetric and does not coincide with the IF. The curious morphology of the PAH emission may be due to UV heating by both θ1 COri and θ2 AOri. Multi-epoch HST images of the HST-10 field show proper motion of three knots associated with HH 517, clearly indicating that HST-10 has a jet. We postulate that the orientation of HST-10 is determined by the combined ram pressure of this jet and the FUV-powered photo-ablation flow from the disk surface. © 2014. The American Astronomical Society. All rights reserved.

We present optical photometric and spectroscopic observations of the Type Ibn (SN 2006jclike) supernova (SN) iPTF13beo. Detected by the intermediate Palomar Transient Factory~3 h after the estimated first light, iPTF13beo is the youngest and the most distant (~430 Mpc) Type Ibn event ever observed. The iPTF13beo light curve is consistent with light curves of other Type Ibn SNe and with light curves of fast Type Ic events, but with a slightly faster rise-time of two days. In addition, the iPTF13beo R-band light curve exhibits a double-peak structure separated by ~9 d, not observed before in any Type Ibn SN. A low-resolution spectrum taken during the iPTF13beo rising stage is featureless, while a late-time spectrum obtained during the declining stage exhibits narrow and intermediate-width He I and Si II features with full width at half-maximum ≈2000-5000 km s-1 and is remarkably similar to the prototypical SN Ibn 2006jc spectrum. We suggest that our observations support a model of a massive star exploding in a dense He-rich circumstellar medium (CSM). A shock breakout in a CSM model requires an eruption releasing a total mass of ~0.1 M⊙ over a time-scale of couple of weeks prior to the SN explosion. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.