0 Assigned ID: 6745 ----- Attempting Submission 1 (Thu Apr 10 21:51:39 GMT 2025) ----- FLASH level may be too low for this exposure or a short subexposure. See extended explanation in the diagnostic browser FLASH level may be too low for this exposure or a short subexposure. See extended explanation in the diagnostic browser I have not increased the flash level to match the set-up of a previous observation, please let me know if it is better to increase the flash level or not. -1462295107 ----- Attempting Submission 1 (Thu Jul 31 18:02:14 GMT 2025) ----- I have not increased the flash level to match the set-up of a previous observation, please let me know if it is better to increase the flash level or not. An Exciting New Population of Luminous Point Sources in Nearby Galaxies An exciting new class of X-ray emitters with no detectable emission above 0.3 keV has recently been discovered within galaxies observed with early archival Chandra ACIS-S data, dubbed 'hypersoft' X-ray sources. Within the narrow 0.15-0.3 keV X-ray bandpass these sources emit up to 1e38 erg/s with bolometric luminosities potentially as high as 1e40 erg/s. The estimated blackbody temperatures of these source are constrained to be below 21 eV (250,000 K), making them strong EUV, and potentially FUV emitters detectable with HST. The available X-ray data indicate the sources are not persistent over ~5 year time scales. Previous WFC3/UVIS/F225W observations of large, nearby elliptical galaxies taken in 2009 have found FUV-bright point sources in those galaxies that we suggest are the FUV tails of hypersoft X-ray sources. We propose WFC3/UVIS/F225W re-observations of two of those nearby large elliptical galaxies known to possess hypersoft X-ray sources to search for variable FUV-bright sources that have turned off (or on) since the initial 2009 F225W observations that would be strong evidence for a new, unrecognized very high bolometric luminosity class of objects in galaxies. Our observations are designed to mimic the WFPC3/UVIS/F225W observations of HST program (11583; PI: Bregman) of the galaxies NGC4697 and NGC3379 as much as possible. We plan for four exposures (to eliminate cosmic rays) covering two orbits each for each of the galaxies in the F225W filter. This led to individual exposure times of ~1220 seconds (and four exposures per galaxy). We choose the pattern type as WFC3-UVIS-DITHER-BOX, with UVIS-CENTER as the aperture, and CR-SPLIT=NO to match Program 11583. Since Program 11583 did not increase the flash level, we did not either. Professor Jimmy Irwin has 32 years X-ray and optical data analysis experience, and has been awarded Hubble and Chandra time in previous cycles. Professor Irwin is an expert in X-ray populations of galaxies, transient X-ray sources, and hot gas in galaxies and clusters of galaxies. Dr. Rosanne Di Stefano is an expert on supersoft X-ray sources, and has authors several seminal papers in this field. Mr. Mustafa Muhibullah is a graduate student at the University of Alabama working on hypersoft X-ray sources. He was the PI of a successful Chandra archival proposal in Cycle 25 to study hypersoft X-ray sources. Galaxies 6 false true false false true false false false false false SUPPORTED GALAXY ELLIPTICAL YES This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 J2000 GALAXY ELLIPTICAL YES This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 J2000 WFC3/UVIS Imaging No No F225W WFC3/UVIS Imaging No No F225W POS-TARG DITHER 0.173 LINE 0.112 false false 81.785 4 23.884 WFC3-UVIS-DITHER-BOX 1 false /Users/jimmyirwin/Documents/OP-cache/Cycle33_PhaseII-v01.xml The scheduling data was generated by CASM 33.1. CASM was run in Phase II mode. 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CASM was run in Phase II mode. (Tic-Visit :proposal-id 18091 :visit-id "02" :proposal-version -1 :trans-version "20250624" :date "29-Jul-2025 11:56:58.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 1154976 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18091 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18091 :visit-id "02" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2594 :al-overhead-at-end 116 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2974 :pcs-gap 0 ) (Tic-Orbit :proposal-id 18091 :visit-id "02" :orbit-number 2 :pcs-time 380 :si-vis-utilization 2594 :al-overhead-at-end 116 :internal-dur-at-end 668 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2974 :pcs-gap 0 ) true 2 0