Supernovae in the nuclear regions of starburst galaxies

The feasibility of using near-infrared observations to discover supernovae in the nuclear and circumnuclear regions of nearby starburst galaxies is investigated. We provide updated estimates of the intrinsic core-collapse supernova rates in these regions. We discuss the problem of extinction, and present new estimates of the extinction towards 33 supernova remnants in the starburst galaxy M 82. This is done using H I and H_2 column density measurements. We estimate the molecular to atomic hydrogen mass ratio to be 7.4 +- 1.0 in M 82. We have assembled near-infrared photometric data for a total of 13 core-collapse supernovae, some unpublished hitherto. This constitutes the largest database of IR light curves for such events. We show that the IR light curves fall into two classes, ``ordinary'' and ``slow-declining''. Template JHKL light curves are derived for both classes. For ordinary core-collapse supernovae, the average peak JHKL absolute magnitudes are -18.4, -18.6, -18.6, and -19.0 respectively. The slow-declining core-collapse SNe are found to be significantly more luminous than the ordinary events, even at early times, having average peak JHKL absolute magnitudes of -19.9, -20.0, -20.0, and -20.4 respectively. We investigate the efficiency of a computerised image subtraction method in supernova detection. We then carry out a Monte Carlo simulation of a supernova search using K-band images of NGC 5962. The effects of extinction and observing strategy are discussed. We conclude that a modest observational programme will be able to discover a number of nuclear supernovae.Comment: 19 pages, 7 figures; accepted in MNRA

The Core-Collapse Supernova Rate in Arp299 Revisited

We present a study of the CCSN rate in nuclei A and B1 of the luminous infrared galaxy Arp299, based on 11 years of Very Large Array monitoring of their radio emission at 8.4 GHz. Significant variations in the nuclear radio flux density can be used to identify the CCSN activity in the absence of high-resolution very long baseline interferometry observations. In the case of the B1-nucleus, the small variations in its measured diffuse radio emission are below the fluxes expected from radio supernovae, thus making it well-suited to detect RSNe through flux density variability. In fact, we find strong evidence for at least three RSNe this way, which results in a lower limit for the CCSN rate of 0.28 +/- 0.16 per year. In the A-nucleus, we did not detect any significant variability and found a SN detection threshold luminosity which allows only the detection of the most luminous RSNe known. Our method is basically blind to normal CCSN explosions occurring within the A-nucleus, which result in too small variations in the nuclear flux density, remaining diluted by the strong diffuse emission of the nucleus itself. Additionally, we have attempted to find near-infrared counterparts for the earlier reported RSNe in the Arp299 nucleus A, by comparing NIR adaptive optics images from the Gemini-N telescope with contemporaneous observations from the European VLBI Network. However, we were not able to detect NIR counterparts for the reported radio SNe within the innermost regions of nucleus A. While our NIR observations were sensitive to typical CCSNe at 300 mas from the centre of the nucleus A, suffering from extinction up to A_v~15 mag, they were not sensitive to such highly obscured SNe within the innermost nuclear regions where most of the EVN sources were detected. (abridged)Comment: 12 pages, 4 figures and 7 tables. Accepted for publication in MNRA

Supernovae and radio transients in M 82

We present optical and near-infrared (IR) photometry and near-IR spectroscopy of SN 2004am, the only optically detected supernova (SN) in M 82. These demonstrate that SN 2004am was a highly reddened type II-P SN similar to the low luminosity type II-P events such as SNe 1997D and 2005cs. We show that SN 2004am was located coincident with the obscured super star cluster M 82-L, and from the cluster age infer a progenitor mass of 12 +7/-3 Msun. In addition to this, we present a high spatial resolution Gemini-N K-band adaptive optics image of the site of SN 2008iz and a second transient of uncertain nature, both detected so far only at radio wavelengths. Using image subtraction techniques together with archival data from the Hubble Space Telescope, we are able to recover a near-IR transient source co-incident with both objects. We find the likely extinction towards SN 2008iz to be not more than Av ~ 10. The nature of the second transient remains elusive and we regard an extremely bright microquasar in M 82 as the most plausible scenario.Comment: 14 pages, 8 figures, accepted for publication in MNRA

On the nature of the progenitors of three type II-P supernovae: 2004et, 2006my and 2006ov

The pre-explosion observations of the type II-P supernovae 2006my, 2006ov and 2004et, are re-analysed. In the cases of supernovae 2006my and 2006ov we argue that the published candidate progenitors are not coincident with their respective supernova sites in pre-explosion Hubble Space Telescope observations. We therefore derive upper luminosity and mass limits for the unseen progenitors of both these supernovae, assuming they are red supergiants: 2006my (log L/Lsun = 4.51; mass < 13Msun) and 2006ov (log L/Lsun = 4.29; mass < 10Msun). In the case of supernova 2004et we show that the yellow-supergiant progenitor candidate, originally identified in Canada France Hawaii Telescope images, is still visible ~3 years post-explosion in observations from the William Herschel Telescope. High-resolution Hubble Space Telescope and Gemini (North) adaptive optics late-time imagery reveal that this source is not a single yellow supergiant star, but rather is resolved into at least three distinct sources. We report the discovery of the unresolved progenitor as an excess of flux in pre-explosion Isaac Newton Telescope i'-band imaging. Accounting for the late-time contribution of the supernova using published optical spectra, we calculate the progenitor photometry as the difference between the pre- and post-explosion, ground-based observations. We find the progenitor was most likely a late K to late M-type supergiant of 8 +5/-1 Msun. In all cases we conclude that future, high-resolution observations of the supernova sites will be required to confirm these results.Comment: 43 pages (pre-print format), 12 figures, 10 tables. Significant revision following referee's comments. Accepted for publication in MNRA

The Role of Emotions in Service Encounters

This article advances our understanding of the influence of affect in consumers’ responses to brief, non-personal service encounters. This study contributes to the services marketing literature by examining for mundane service transactions the impact of customer-displayed emotion and affect on assessments of the service encounter and the overall experience. Observational and perceptual data from customers were matched with frontline employees in 200 transaction-specific encounters. The results of this study suggest that consumers’ evaluations of the service encounter correlate highly with their displayed emotions during the interaction and post-encounter mood states. Finally, the findings indicate that frontline employees’ perceptions of the encounter are not aligned with those of their customers. The managerial implications of these findings are briefly discussed