arXiv subjects

Bruce Grossan

Publications and source records attributed to Bruce Grossan.

21 records · Page 2Linked to original sources

arXiv2004

High Resolution Mid-Infrared Observations of Low-Luminosity AGN with the Keck Telescope and LWS

We present high-resolution Keck LWS SiC filter (10.5-12.9 micron) mid-IR (MIR) images and photometry of a sample of nearby LLAGN. All MIR images show extended emission on small scales (e.g. 90% maximum widths 18 - 106 pc) deep within the nucleus. Because the profile of this small-scale emission is inconsistent with the near-IR stellar emission profile, we conclude the MIR emission is not from the stellar population. Because strong starburst emission is not reported for our objects, we eliminate this origin as well, and conclude that the extended component of the MIR emission is most likely due to a warm dust structure deep in the nucleus, consistent with the gross details of a Unified Model Torus. Because MIR and X-ray flux measurements are very insensitive to the effects of pure dust extinction, the ratio of MIR and X emission can be used as a discriminator of emission processes that is insensitive to dust extinction. X and MIR emission are known to be correlated in quasars and Seyfert galaxies. Our LLAGN objects follow this correlation with small scatter down to extremely low luminosity, suggesting that the same continuum emission mechanisms are present in LLAGN as in Seyferts and quasars. This result suggests that weak UV emission (relative to other bands) in LLAGN compared to Seyferts and quasars could be due to dust extinction; it then follows that modifications to standard AGN continuum emission models for LLAGN (e.g. ADAF accretion) are not required.

astro-ph↗

arXiv1998

An IR Search for Extinguished Supernovae in Starburst Galaxies

IR and Radio band observations of heavily extinguished regions in starburst galaxies suggest a very high SN rate associated with such regions. Optically measured supernova (SN) rates may therefore underestimate the total SN rate by factors of up to 10, due to the high extinction to SNe in starburst regions. The IR/radio SN rates come from a variety of indirect means, however, which suffer from model dependence and other problems. We describe a direct measurement of the SN rate from a regular patrol of starburst galaxies done with K' band imaging to minimize the effects of extinction. A collection of K' measurements of core-collapse SNe near maximum light is presented. Results of a preliminary SN search using the MIRC camera at the Wyoming IR Observatory (WIRO), and an improved search using the ORCA optics are described. A monthly patrol of starburst galaxies within 25 Mpc should yield 1.6 - 9.6 SNe/year. Our MIRC search with low-resolution (2.2" pixels) failed to find extinguished SNe, limiting the SN rate outside the nucleus (at > 15" radius) to less than 3.8 Supernova Rate Units (SRU or SNe/century/10^10 L(solar); 90% confidence). The MIRC camera had insufficient resolution to search nuclear starburst regions, where SN activity is concentrated, explaining why we found no heavily obscured SNe. We conclude that high-resolution, small field SN searches in starburst nuclei are more productive than low resolution, large-field searches, even for our large galaxies. With our ORCA high-resolution optics, we could limit the total SN rate to < 1.3 SRU at 90% confidence in 3 years of observations, lower than the most pessimistic estimate.

astro-ph↗

arXiv1997

A Search for Gamma-Ray Burst Optical Emission with the Automated Patrol Telescope

The Automated Patrol Telescope (APT) is a wide-field (5 X 5 deg.s), modified Schmidt capable of covering large gamma-ray burst (GRB) localization regions to produce a high rate of GRB optical emission measurements. Accounting for factors such as bad weather and incomplete overlap of our field and large GRB localization regions, we estimate our search will image the actual location of 20-41 BATSE GRB sources each year. Long exposures will be made for these images, repeated for several nights, to detect delayed optical transients (OTs) with light curves similar to those already discovered. The APT can also respond within about 20 sec. to GRB alerts from BATSE to search for prompt emission from GRBs. We expect to image more than 2.4 GRBs/yr. during gamma-ray emission. More than 5.1 will be imaged/yr. within about 20 sec. of emission. The APT's 50 cm aperture is much larger than other currently operating experiments used to search for prompt emission, and the APT is the only GRB dedicated telescope in the Southern Hemisphere. Given the current rate of about 25% OTs per X/gamma localization, we expect to produce a sample of about 10 OTs for detailed follow-up observations in 1-2 years of operation.

astro-ph↗