VizieR Online Data Catalog: ULXs with multiepoch Spitzer/IRAC obs. (Lau+, 2019)

In order to search for mid-IR ultraluminous X-ray (ULX) counterparts, we utilized imaging data taken in the SPitzer InfraRed Intensive Transient Survey (SPIRITS; Kasliwal+ 2017, J/ApJ/839/88) as well as archival Spitzer Post Basic Calibrated (PBCD) imaging data from the Spitzer Heritage Archive. SPIRITS is a program that has been going in since 2014 and has been renewed for Spitzer Cycle 14 (until 2019 November 30). Additionally, many of the nearby ULX host galaxies have previous imaging observations with Spitzer from as long ago as 2004.

As part of SPIRITS, we performed follow-up ground-based near-IR J, H, and/or Ks imaging observations with the Multi-object Spectrometer for Infra-red Exploration (MOSFIRE) on Keck I, FourStar on the Magellan 6.5m Baade Telescope, and the Wide Field Infrared Camera (WIRC) on the Palomar 200 inch Telescope.

In a dedicated IR ULX follow-up program, the ULX Holmberg II X-1 was observed with the NIRC2 instrument on Keck II with the laser guide star adaptive optics (LGSAO) system on 2018 November 28. See Section 2.4.

In order to investigate possible correlations between mid-IR/X-ray variability in ULXs from our Spitzer DDT program (PID-13163), we conducted contemporaneous observations with the X-ray Telescope (XRT) on the Neil Gehrels Swift Observatory of five ULXs: Holmberg II X-1, Holmberg IX X-1, NGC 925 ULX1, NGC 925 ULX2, and NGC 253 ULX1. See Section 2.5.

(4 data files).