Photometric redshift of the GRB 981226 host galaxy

No optical afterglow was found for the dark burst GRB 981226 and hence no absorption redshift has been obtained. We here use ground-based and space imaging observations to analyse the spectral energy distribution (SED) of the host galaxy. By comparison with synthetic template spectra we determine the photometric redshift of the GRB 981226 host to be z_phot = 1.11+/-0.06 (68% confidence level). While the age-metallicity degeneracy for the host SED complicates the determination of accurate ages, metallicity, and extinction, the photometric redshift is robust. The inferred z_phot value is also robust compared to a Bayesian redshift estimator which gives z_phot=0.94+/-0.13. The characteristics for this host are similar to other GRB hosts previously examined. Available low resolution spectra show no emission lines at the expected wavelengths. The photometric redshift estimate indicates an isotropic energy release consistent with the Amati relation for this GRB which had a spectrum characteristic of an X-ray flash.Comment: Accepted for publication in ApJ Letter

Delayed soft X-ray emission lines in the afterglow of GRB 030227

Strong, delayed X-ray line emission is detected in the afterglow of GRB 030227, appearing near the end of the XMM-Newton observation, nearly twenty hours after the burst. The observed flux in the lines, not simply the equivalent width, sharply increases from an undetectable level (<1.7e-14 erg/cm^2/s, 3 sigma) to 4.1e-14 erg/cm^2/s in the final 9.7 ks. The line emission alone has nearly twice as many detected photons as any previous detection of X-ray lines. The lines correspond well to hydrogen and/or helium-like emission from Mg, Si, S, Ar and Ca at a redshift z=1.39. There is no evidence for Fe, Co or Ni--the ultimate iron abundance must be less than a tenth that of the lighter metals. If the supernova and GRB events are nearly simultaneous there must be continuing, sporadic power output after the GRB of a luminosity >~5e46 erg/s, exceeding all but the most powerful quasars.Comment: Submitted to ApJL. 14 pages, 3 figures with AASLaTe

3P_2-3F_2 pairing in neutron matter with modern nucleon-nucleon potentials

We present results for the $^3P_2 - ^3F_2$ pairing gap in neutron matter with several realistic nucleon-nucleon potentials, in particular with recent, phase-shift equivalent potentials. We find that their predictions for the gap cannot be trusted at densities above $\rho\approx 1.7\rho_0$, where $\rho_0$ is the saturation density for symmetric nuclear matter. In order to make predictions above that density, potential models which fit the nucleon-nucleon phase shifts up to about 1 GeV are required.Comment: Revtex style, 19 pages, 6 figures inlude

A "kilonova" associated with short-duration gamma-ray burst 130603B

Short-duration gamma-ray bursts (SGRBs) are intense flashes of cosmic gamma-rays, lasting less than ~2 s, whose origin is one of the great unsolved questions of astrophysics today. While the favoured hypothesis for their production, a relativistic jet created by the merger of two compact stellar objects (specifically, two neutron stars, NS-NS, or a neutron star and a black hole, NS-BH), is supported by indirect evidence such as their host galaxy properties, unambiguous confirmation of the model is still lacking. Mergers of this kind are also expected to create significant quantities of neutron-rich radioactive species, whose decay should result in a faint transient in the days following the burst, a so-called "kilonova". Indeed, it is speculated that this mechanism may be the predominant source of stable r-process elements in the Universe. Recent calculations suggest much of the kilonova energy should appear in the near-infrared (nIR) due to the high optical opacity created by these heavy r-process elements. Here we report strong evidence for such an event accompanying SGRB 130603B. If this simplest interpretation of the data is correct, it provides (i) support for the compact object merger hypothesis of SGRBs, (ii) confirmation that such mergers are likely sites of significant r-process production and (iii) quite possibly an alternative, un-beamed electromagnetic signature of the most promising sources for direct detection of gravitational waves.Comment: preprint of paper appearing in Nature (3 Aug 2013

Arrays of Josephson junctions in an environment with vanishing impedance

The Hamiltonian operator for an unbiased array of Josephson junctions with gate voltages is constructed when only Cooper pair tunnelling and charging effects are taken into account. The supercurrent through the system and the pumped current induced by changing the gate voltages periodically are discussed with an emphasis on the inaccuracies in the Cooper pair pumping. Renormalisation of the Hamiltonian operator is used in order to reliably parametrise the effects due to inhomogeneity in the array and non-ideal gating sequences. The relatively simple model yields an explicit, testable prediction based on three experimentally motivated and determinable parameters.Comment: 13 pages, 9 figures, uses RevTeX and epsfig, Revised version, Better readability and some new result

UV star-formation rates of GRB host galaxies

We study a magnitude-limited sample of 10 gamma-ray burst (GRB) host galaxies with known spectroscopic redshifts (0.43 < z < 2.04). From an analysis of the spectral energy distributions (SEDs), based on published broad-band optical and near-infrared photometry, we derive photometric redshifts, galaxy types, ages of the dominant stellar populations, internal extinctions, and ultraviolet (UV) star-formation rates (SFRs) of the host galaxies. The photometric redshifts are quite accurate despite the heterogeneous nature of the sample: The r.m.s. errors are sigma(z) = 0.21 and sigma(Delta z/(1+z_spec)) = 0.16 with no significant systematic offsets. All the host galaxies have SEDs similar to young starburst galaxies with moderate to low extinction. A comparison of specific SFRs with those of high-redshift galaxies in the Hubble Deep Fields shows that GRB hosts are most likely similar to the field galaxies with the largest specific SFRs. On the other hand, GRB hosts are not significantly younger than starburst field galaxies at similar redshifts, but are found to be younger than a sample of all types of field galaxies.Comment: 15 pages, 7 figures, accepted for publication in A&

The Host Galaxy of GRB 990712

We present a comprehensive study of the z=0.43 host galaxy of GRB 990712, involving ground-based photometry, spectroscopy, and HST imaging. The broad-band UBVRIJHKs photometry is used to determine the global spectral energy distribution (SED) of the host galaxy. Comparison with that of known galaxy types shows that the host is similar to a moderately reddened starburst galaxy with a young stellar population. The estimated internal extinction in the host is Av=0.15+/-0.1 and the star-formation rate (SFR) from the UV continuum is 1.3+/-0.3 M_sun/yr, (not corrected for the effects of extinction). Other galaxy template spectra than starbursts failed to reproduce the observed SED. We also present VLT spectra leading to the detection of Halpha from the GRB host galaxy. A SFR of 2.8+/-0.7 M_sun/yr, is inferred from the Halpha line flux, and the presence of a young stellar population is supported by a large equivalent width. Images from HST/STIS show that the host has two separate knots, which could be two distinct star-forming regions.Comment: 11 pages, accepted for publication in Astronomy and Astrophysic

The nature of GRB-selected submillimeter galaxies: hot and young

We present detailed fits of the spectral energy distributions (SEDs) of four submillimeter (submm) galaxies selected by the presence of a gamma-ray burst (GRB) event (GRBs 980703, 000210, 000418 and 010222). These faint ~3 mJy submm emitters at redshift ~1 are characterized by an unusual combination of long- and short-wavelength properties, namely enhanced submm and/or radio emission combined with optical faintness and blue colors. We exclude an active galactic nucleus as the source of long-wavelength emission. From the SED fits we conclude that the four galaxies are young (ages <2 Gyr), highly starforming (star formation rates ~150 MSun/yr), low-mass (stellar masses ~10^10 MSun) and dusty (dust masses ~3x10^8 MSun). Their high dust temperatures (Td>45 K) indicate that GRB host galaxies are hotter, younger, and less massive counterparts to submm-selected galaxies detected so far. Future facilities like Herschel, JCMT/SCUBA-2 and ALMA will test this hypothesis enabling measurement of dust temperatures of fainter GRB-selected galaxies.Comment: 9 pages, 2 figures, submitted to ApJ, for SED templates, see http://archive.dark-cosmology.dk