0 Assigned ID: 7871 ----- Attempting Submission 1 (Thu Sep 17 00:03:34 GMT 2026) ----- 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 Request is for two observations separated by 25-40 days, if possible. -1273294432 ----- Attempting Submission 1 (Fri Oct 16 03:10:10 GMT 2026) ----- Both warning are about flash levels. Please contact me if this is an issue. Luminous X-ray Sources Below 0.3 keV in Galaxies: A New Population An exciting new class of luminous X-ray emitters with little to no detectable emission above 0.3 keV has recently been discovered within galaxies observed with early ACIS-S data, dubbed `hypersoft' X-ray sources. Within the narrow 0.15-0.3 keV bandpass these sources emit up to 1e38 erg/s with bolometric luminosities potentially exceeding 1e39 erg/s. We propose to utilize the very soft response of HRC-I coupled with a far UV HST/UVIS/F225W exposure of the nearby galaxy M94 which has previously been observed to harbor luminous hypersoft sources to determine the sources' temperatures and therefore the crucial bolometric correction. We also request ACIS-S observations of a very hot Milky Way dwarf with a known blackbody temperature to translate X-ray hardness ratios into temperatures. Our observations are designed to mimic the WFC3/UVIS/F225W observations of previous HST programs (11583; PI: Bregman, 18091; PI: Irwin) of the galaxies NGC 4697 and NGC 3379 as closely as possible, except that we break the 5-orbit F225W observation into two visits of 3 and 2 orbits, separated by 25-40 days if possible. We use the UVIS-CENTER aperture and CR-SPLIT=NO to match Programs 11583/18091, and remove cosmic rays by combining the dithered frames. Visit 01 (3 orbits) uses the WFC3-UVIS-DITHER-LINE-3PT pattern with two exposures of 1242 s at each of its three dither points, for 6 exposures and 7452 s in total. Visit 02 (2 orbits) uses the WFC3-UVIS-DITHER-BOX pattern with a single exposure of 1232 s at each of its four points, for 4 exposures and 4928 s in total. In both visits two exposures are obtained per orbit. Exposure durations were packed to fill each orbit using the Orbit Planner's Auto-Adjust. Because the exposures are long (more than 348 s), buffer dumps are hidden during the following exposure, maximizing on-target time. Since Program 11583 did not increase the flash level, we did not add post-flash either, so the APT diagnostic that the FLASH level may be too low is expected. Professor Jimmy Irwin has 33 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. Stellar Populations and the Interstellar Medium 6 false false false false false false false true SECONDARY CHANDRA 28620162 false SUPPORTED GALAXY SPIRAL YES This object was generated by the targetselector and retrieved from the SIMBAD database. SIMBAD listed proper motion for this target. When retrieving targets with PM from SIMBAD, APT requests the coordinates be calculated with an epoch of the year 2000. Do not modify this epoch. Always review coordinates using the Target Confirmation tool, which graphically displays the PM. J2000 J2000 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 POS-TARG DITHER 0.135 LINE false false 3 46.84 WFC3-UVIS-DITHER-LINE-3PT 2 false /Users/jimmyirwin/Documents/OP-cache/M94_HST-v01.xml Timing link suitability includes constraints ([02 After 01 by 25.0 to 40.0 days]) The scheduling data was generated by CASM 34.2. CASM was run in Phase II mode. (Tic-Visit :proposal-id 18486 :visit-id "01" :proposal-version -1 :trans-version "20260828" :date "13-Oct-2026 23:24:57.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 3 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 1732464 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18486 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18486 :visit-id "01" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2620 :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 3001 :pcs-gap 0 ) (Tic-Orbit :proposal-id 18486 :visit-id "01" :orbit-number 2 :pcs-time 380 :si-vis-utilization 2620 :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 3001 :pcs-gap 0 ) (Tic-Orbit :proposal-id 18486 :visit-id "01" :orbit-number 3 :pcs-time 380 :si-vis-utilization 2620 :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 3001 :pcs-gap 0 ) true 3 0 /Users/jimmyirwin/Documents/OP-cache/M94_HST-v02.xml Timing link suitability includes constraints ([02 After 01 by 25.0 to 40.0 days]) The scheduling data was generated by CASM 34.2. CASM was run in Phase II mode. (Tic-Visit :proposal-id 18486 :visit-id "02" :proposal-version -1 :trans-version "20260828" :date "13-Oct-2026 23:23:53.0" :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 18486 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18486 :visit-id "02" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2620 :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 3001 :pcs-gap 0 ) (Tic-Orbit :proposal-id 18486 :visit-id "02" :orbit-number 2 :pcs-time 380 :si-vis-utilization 2620 :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 3001 :pcs-gap 0 ) true 2 0