Implications For The Origin Of GRB 051103 From LIGO Observations

We present the results of a LIGO search for gravitational waves (GWs) associated with GRB 051103, a short-duration hard-spectrum gamma-ray burst (GRB) whose electromagnetically determined sky position is coincident with the spiral galaxy M81, which is 3.6 Mpc from Earth. Possible progenitors for short-hard GRBs include compact object mergers and soft gamma repeater (SGR) giant flares. A merger progenitor would produce a characteristic GW signal that should be detectable at the distance of M81, while GW emission from an SGR is not expected to be detectable at that distance. We found no evidence of a GW signal associated with GRB 051103. Assuming weakly beamed gamma-ray emission with a jet semi-angle of 30 deg we exclude a binary neutron star merger in M81 as the progenitor with a confidence of 98%. Neutron star-black hole mergers are excluded with > 99% confidence. If the event occurred in M81 our findings support the the hypothesis that GRB 051103 was due to an SGR giant flare, making it the most distant extragalactic magnetar observed to date.Comment: 8 pages, 3 figures. For a repository of data used in the publication, go to: https://dcc.ligo.org/cgi-bin/DocDB/ShowDocument?docid=15166 . Also see the announcement for this paper on ligo.org at: http://www.ligo.org/science/Publication-GRB051103/index.ph

The HST/ACS Coma Cluster Survey. IV. Intergalactic Globular Clusters and the Massive Globular Cluster System at the Core of the Coma Galaxy Cluster

Intracluster stellar populations are a natural result of tidal interactions in galaxy clusters. Measuring these populations is difficult, but important for understanding the assembly of the most massive galaxies. The Coma cluster is one of the nearest truly massive galaxy clusters, and is host to a correspondingly large system of globular clusters (GCs). We use imaging from the HST/ACS Coma Cluster Survey to present the first definitive detection of a large population of intracluster GCs (IGCs) that fills the Coma cluster core and is not associated with individual galaxies. The GC surface density profile around the central massive elliptical galaxy, NGC 4874, is dominated at large radii by a population of IGCs that extend to the limit of our data (R<520 kpc). We estimate that there are 47000+/-1600 (random) +4000/-5000 (systematic) IGCs out to this radius, and that they make up ~70% of the central GC system, making this the largest GC system in the nearby Universe. Even including the GC systems of other cluster galaxies, IGCs still make up ~30-45% of the GCs in the cluster core. Observational limits from previous studies of the intracluster light (ICL) suggest that the IGC population has a high specific frequency. If the IGC population has a specific frequency similar to high-S_N dwarf galaxies, then the ICL has a total stellar mass of ~10^12 M_sun within the cluster core. The ICL makes up approximately half of the stellar luminosity and one-third of the stellar mass of the central (NGC4874+ICL) system. The color distribution of the IGC population is bimodal, with blue, metal-poor GCs outnumbering red, metal-rich GCs by a ratio of 4:1. The fraction of red IGCs (20%), and the red color of those GCs, implies that IGCs can originate from the halos of relatively massive, L* galaxies, and not solely from the disruption of dwarf galaxies. (Abridged)Comment: 18 pages, 9 figures, 3 tables. Accepted for publication in the Astrophysical Journal. Typos corrected, and fixed glitch in Figure

Very low latency search for low mass compact binary coalescences in the LIGO S6 and Virgo VSR2 data

International audienceA very low latency search pipeline has been developed for the LIGO S6 and Virgo VSR2 science runs, targeting signals from coalescing compact binary systems with total mass from 2 to 35 solar masses. The goal of this search is to provide both single-detector triggers and multi-detector coincident triggers with a latency of a few minutes, the former for online detector monitoring and the latter to allow searching for electromagnetic counterparts to possible gravitational wave candidates. The features and current performance of this low latency search pipeline are presented