We report the results of our observing campaign on GRB 140903A, a nearby (z = 0.351) short duration (T 90 ∼0.3 s) gamma-ray burst discovered by Swift. We monitored the X-ray afterglow with Chandra up to 21 days after the burst, and detected a steeper decay of the X-ray flux after t j ≈1 day. Continued monitoring at optical and radio wavelengths showed a similar decay in flux at nearly the same time, and we interpret it as evidence of a narrowly collimated jet. By using the standard fireball model to describe the afterglow evolution, we derive a jet opening angle θ j ≈5 deg and a collimationcorrected total energy release E≈2×10 50 erg. We further discuss the nature of the GRB progenitor system. Three main lines disfavor a massive star progenitor: the properties of the prompt gamma-ray emission, the age and low star-formation rate of the host galaxy, and the lack of a bright supernova. We conclude that this event was likely originated by a compact binary merger.

We present imaging and spectroscopy of a hydrogen-poor superluminous supernova (SLSN) discovered by the intermediate Palomar Transient Factory: iPTF 13ajg. At a redshift of z=0.7403, derived from narrow absorption lines, iPTF 13ajg peaked at an absolute magnitude M u,AB = −22.5, one of the most luminous supernovae to date. The uBgRiz light curves, obtained with the P48, P60, NOT, DCT, and Keck telescopes, and the nine-epoch spectral sequence secured with the Keck and the VLT (covering 3 rest-frame months), are tied together photometrically to provide an estimate of the flux evolution as a function of time and wavelength, from which we also estimate the bolometric light curve. The observed bolometric peak luminosity of iPTF 13ajg is 3.2 × 10 44 erg s −1 , while the estimated total radiated energy is 1.3×10 51 erg. We detect narrow absorption lines of Mg I, Mg II, and Fe II, associated with the cold interstellar medium in the host galaxy, at two different epochs with X-shooter at the VLT, at a resolving power R ≈ 6000. From Voigt-profile fitting, we derive the column densities log N (Mg I) = 11.94±0.06, log N (Mg II) = 14.7±0.3, and log N (Fe II) = 14.25±0.10. These column densities, as well as the Mg I and Mg II equivalent widths of a sample of hydrogen-poor SLSNe taken from the literature, are at the low end of those derived for gamma-ray bursts (GRBs), whose progenitors are also thought to be massive stars. This suggests that the environments of SLSNe and GRBs are different. From the nondetection of Fe II fine-structure absorption lines, we derive a strict lower limit on the distance between the supernova and the narrow-line absorbing gas of 50 pc. The neutral gas responsible for the absorption in iPTF 13ajg exhibits a single narrow component with a low velocity width, ∆V = 76 km s −1 , indicating a low-mass host galaxy. No host-galaxy emission lines are detected, leading to an upper limit on the unobscured star-formation rate of SFR [O II] < 0.07 M yr −1 . Late-time imaging shows the host galaxy of iPTF 13ajg to be faint, with g AB ≈ 27.0 and R AB ≥ 26.0 mag, which roughly corresponds to M B,Vega −17.7 mag.Subject headings: ISM: atoms -supernovae: general -supernovae: individual: (iPTF 13ajg) c The May 8 X-shooter spectrum was taken with the K-band blocking slit, which improves the signal-to-noise ratio in the J and H bands, but limits the spectral coverage to below about 21000Å. d Owing to its low S/N, the ARC/DIS spectrum has not been used in the analysis.

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We report the discovery of a grand-design spiral galaxy associated with a double-lobed radio source. J1649+2635 (z = 0.0545) is a red spiral galaxy with a prominent bulge that it is associated with a L 1.4 GHz ∼10 24 W Hz −1 double-lobed radio source that spans almost 100 kpc. J1649+2635 has a black hole mass of M BH ∼ 3-7 × 10 8 M ⊙ and SFR ∼ 0.26 -2.6 M ⊙ year −1 . The galaxy hosts a ∼96 kpc diffuse optical halo, which is unprecedented for spiral galaxies. We find that J1649+2635 resides in an overdense environment with a mass of M dyn = 7.7 +7.9 −4.3 × 10 13 M ⊙ , likely a galaxy group below the detection threshold of the ROSAT All-Sky Survey. We suggest one possible scenario for the association of double-lobed radio emission from J1649+2635 is that the source may be similar to a Seyfert galaxy, located in a denser-than-normal environment. The study of spiral galaxies that host large-scale radio emission is important because although rare in the local Universe, these sources may be more common at high-redshifts.

We present optical and near-infrared (NIR) light curves and optical spectra of SN 2013dx, associated with the nearby (redshift 0.145) gamma-ray burst GRB 130702A. The prompt isotropic gamma-ray energy released from GRB 130702A is measured to be E 6.4 10 ,iso 1.0 50=ǵ -+ erg (1 keV to 10 MeV in the rest frame), placing it intermediate between low-luminosity GRBs like GRB 980425/SN 1998bw and the broader cosmological population. We compare the observed g r i z ¢ ¢ ¢ ¢ light curves of SN 2013dx to a SN 1998bw template, finding that SN 2013dx evolves ∼20% faster (steeper rise time), with a comparable peak luminosity. Spectroscopically, SN 2013dx resembles other broad-lined SNe Ic, both associated with (SN 2006aj and SN 1998bw) and lacking (SN 1997ef, SN 2007I, and SN 2010ah) gamma-ray emission, with photospheric velocities around peak of ∼ 21,000 km s −1 . We construct a quasi-bolometric (g r i z yJ ¢ ¢ ¢ ¢ ) light curve for SN 2013dx, only the fifth GRB-associated SN with extensive NIR coverage and the third with a bolometric light curve extending beyond t 40 days D > . Together with the measured photospheric velocity, we derive basic explosion parameters using simple analytic models. We infer a 56 Ni mass of M 0.37 0.01 Ni =  M  , an ejecta mass of M 3.1 0.1 ej =  M  , and a kinetic energy of E 8.2 0.43 10 K 51 ( ) = ´erg (statistical uncertainties only), consistent with previous GRB-associated supernovae. When considering the ensemble population of GRB-associated supernovae, we find no correlation between the mass of synthesized 56 Ni and high-energy properties, despite clear predictions from numerical simulations that M Ni should correlate with the degree of asymmetry. On the other hand, M Ni clearly correlates with the kinetic energy of the supernova ejecta across a wide range of core-collapse events.