A Silver Anniversary Observation of the X-ray Emitting SN1978K in NGC 1313

We describe the results of a 2003 Chandra ACIS-I observation of SN1978K. The spectrum shows little flux below 0.6 keV, in contrast to the 2002 ACIS-S observation that showed flux to 0.4 keV. Fitting the ACIS-I spectrum alone leads to two solutions depending upon the value of the column density. A joint fit using a dual thermal plasma model applied to the ACIS-I and a contemporaneous XMM spectrum, which if fit alone also leads to a two-column solution, yields a single column density fit. The fitted temperature of the joint fit for the soft component remains constant with the errors from previous Chandra, XMM, and ASCA data. The hard temperature recovers from its 2000-2002 decline and corresponds to an increase in the column density during that time. The hard (2-10 keV) light curve is confirmed to be declining. The derived number density represents a lower limit of 1e5 depending upon the adopted filling factor of the emitting volume, leading to an estimated mass cooling rate of 0.1-0.15 solar masses per year.Comment: accepted A

Full-depth Coadds of the WISE and First-year NEOWISE-Reactivation Images

The Near Earth Object Wide-field Infrared Survey Explorer (NEOWISE) Reactivation mission released data from its first full year of observations in 2015. This data set includes ~2.5 million exposures in each of W1 and W2, effectively doubling the amount of WISE imaging available at 3.4 and 4.6 microns relative to the AllWISE release. We have created the first ever full-sky set of coadds combining all publicly available W1 and W2 exposures from both the AllWISE and NEOWISE-Reactivation (NEOWISER) mission phases. We employ an adaptation of the unWISE image coaddition framework (Lang 2014), which preserves the native WISE angular resolution and is optimized for forced photometry. By incorporating two additional scans of the entire sky, we not only improve the W1/W2 depths, but also largely eliminate time-dependent artifacts such as off-axis scattered moonlight. We anticipate that our new coadds will have a broad range of applications, including target selection for upcoming spectroscopic cosmology surveys, identification of distant/massive galaxy clusters, and discovery of high-redshift quasars. In particular, our full-depth AllWISE+NEOWISER coadds will be an important input for the Dark Energy Spectroscopic Instrument (DESI) selection of luminous red galaxy and quasar targets. Our full-depth W1/W2 coadds are already in use within the DECam Legacy Survey (DECaLS) and Mayall z-band Legacy Survey (MzLS) reduction pipelines. Much more work still remains in order to fully leverage NEOWISER imaging for astrophysical applications beyond the solar system.Comment: coadds available at http://unwise.me, zoomable full-sky rendering at http://legacysurvey.org/viewe