arXiv subjects

Michal J. Michalowski

Publications and source records attributed to Michal J. Michalowski.

21 records · Page 2Linked to original sources

arXiv2013

The Burst Cluster: Dark Matter in a Cluster Merger Associated with the Short Gamma Ray Burst, GRB 050509B

We have identified a merging galaxy cluster with evidence of two distinct sub-clusters. The X-ray and optical data suggest that the subclusters are moving away from each other after closest approach. This cluster merger was discovered from observations of the well localized short-duration gamma-ray burst (GRB), GRB 050509B. The Swift/Burst Alert Telescope (BAT) source position is coincident with a cluster of galaxies ZwCl 1234.0+02916. The subsequent Swift/X-Ray Telescope (XRT) localization of the X-ray afterglow found the GRB coincident with 2MASX J12361286+2858580, a giant red elliptical galaxy in the cluster. Deep multi-epoch optical images were obtained to constrain the evolution of the GRB afterglow, including a 27480s exposure in the F814W band with Hubble Space Telescope Advanced Camera for Surveys (ACS), among the deepest imaging ever obtained towards a known galaxy cluster in a single passband. We perform a weak gravitational lensing analysis, including mapping the total mass distribution of the merger system. Combined with Chandra X-ray Observatory and Swift/XRT observations, we investigate the dynamical state of the merger to probe the nature of the dark matter component. Our weak gravitational lensing measurements reveal a separation of the X-ray centroid of the western subcluster from the center of the mass and galaxy light distributions, similar to that of the famous "Bullet cluster". We conclude that the "Burst cluster" is another candidate merger system for determining the nature of dark matter and for studying the environment of short GRBs. We discuss connections between the cluster dynamical state and/or matter composition and compact object mergers, the leading model for the origin of short GRBs. Finally, we present results from a weak lensing survey based on archival Very Large Telescope (VLT) images in the areas of 5 other short GRBs.

astro-ph.CO↗

arXiv2008

NGC 2770 - a supernova Ib factory?

NGC 2770 has been the host of three supernovae of Type Ib during the last 10 years, SN 1999eh, SN 2007uy and SN 2008D. SN 2008D attracted special attention due to the serendipitous discovery of an associated X-ray transient. In this paper, we study the properties of NGC 2770 and specifically the three SN sites to investigate whether this galaxy is in any way peculiar to cause a high frequency of SNe Ib. We model the global SED of the galaxy from broadband data and derive a star-formation and SN rate comparable to the values of the Milky Way. We further study the galaxy using longslit spectroscopy covering the major axis and the three SN sites. From the spectroscopic study we find subsolar metallicities for the SN sites, a high extinction and a moderate star-formation rate. In a high resolution spectrum, we also detect diffuse interstellar bands in the line-of-sight towards SN 2008. A comparison of NGC 2770 to the global properties of a galaxy sample with high SN occurance (at least 3 SN in the last 100 years) suggests that NGC 2770 is not particularly destined to produce such an enhancement of observed SNe observed. Its properties are also very different from gamma-ray burst host galaxies. Statistical considerations on SN Ib detection rates give a probability of ~1.5% to find a galaxy with three Ib SNe detected in 10 years. The high number of rare Ib SNe in this galaxy is therefore likely to be a coincidence rather than special properties of the galaxy itself. NGC 2770 has a small irregular companion, NGC 2770B, which is highly starforming, has a very low mass and one of the lowest metallicities detected in the nearby universe as derived from longslit spectroscopy. In the most metal poor part, we even detect Wolf-Rayet features, against the current models of WR stars which require high metallicities.

astro-ph↗

arXiv2007

Spatially resolved properties of the GRB 060505 host: implications for the nature of the progenitor

GRB 060505 was the first well-observed nearby possible long-duration GRB that had no associated supernova. Here we present spatially resolved spectra of the host galaxy of GRB 060505, an Sbc spiral, at redshift z=0.0889. The GRB occurred inside a star-forming region in the northern spiral arm at 6.5 kpc from the center. From the position of the emission lines, we determine a maximum rotational velocity for the galaxy of v~212km/s corresponding to a mass of 1.14x10^11 M_solar within 11 kpc from the center. By fitting single-age spectral synthesis models to the stellar continuum, we derive a very young age for the GRB site, confirmed by photometric and Halpha line measurements, of around 6 Myr which corresponds to the lifetime of a 32 M_solar star. The metallicity derived from several emission line measurements is lowest at the GRB site with 1/5 Z_solar but roughly solar in the rest of the galaxy. Using the 2dF galaxy redshift survey we can locate the host galaxy in its large scale (Mpc) environment. The galaxy lies in the foreground of a filamentary overdensity extending south west from the galaxy cluster Abell 3837 at z=0.0896. The properties of the GRB site are similar to those found for other long-duration GRB host galaxies with high specific star formation rate and low metallicity, which is an indication that GRB 060505 originated from a young massive star that died without making a supernova.

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