0 Assigned ID: 2555 ----- Attempting Submission 1 (Wed Dec 17 18:50:56 GMT 2014) ----- 0 ----- Attempting Submission 1 (Fri Jan 02 04:05:24 GMT 2015) ----- A fast X-ray transient was discovered by Chandra in the Chandra Deep Field-South field on 2014 October 01. The transient lasted only a few ks in duration, reaching a 0.5-8 keV luminosity of ~1e45 erg/s (assuming z=0.3 from nearest galaxy), with no detection in ~4.5 Ms of previous data nor in a subseqent ~1.2 Ms of exposure. No optical transient down to R_AB~26.5 (2 sigma limit) has been found yet in three epochs (~0.05, 17, and 28 days after discovery). At this point, the observations appear inconsistent with all known Galactic phenomena, tidal disruption events, low-z gamma-ray bursts (GRB), and most types of supernovae (SNe). The transient could still be: 1) a SN from a SN1987A-like blue supergiant (BSG) progenitor, which are known to produce very late rising SNe; 2) a SN with little or no 56Ni due to fallback; 3) a highly extinguished or high-z GRB; or 4) a new type of transient. We request 1 orbit with HST to firmly confirm/rule out all known SNe light curves. If no counterpart is found, a high-z GRB or a new class of X-ray transient are all that remain. Importantly, the detection in the small CDF-S field may imply up to a factor of 100 higher rate than Swift/BAT. TBD UNRESOLVED STELLAR POPULATIONS AND GALAXY STRUCTURE Default false false false false false SUPPORTED UNIDENTIFIED X-RAY EMITTER CDFS-XT1 is an X-ray transient with no optical counterpart detected as yet. Two potential host galaxies lie within the error Chandra error circle, with R=27.3 and 27.5 respectively. As stated in the proposal, we wish to obtain a F110W image to enable image subtraction against previous F110W images of the field to probe as for a transient signature down to the level indicated. J2000 WFC3/IR Imaging No No F110W POS-TARG DITHER 0.572 LINE 0.365 false false 74.653 4 18.528 WFC3-IR-DITHER-BOX-MIN 1 false /private/var/folders/35/spdt8sqd3nq6406_62fcysx80000gn/T/OPVisit3150613145474580356.xml 1420171161536 The scheduling data was generated by CASM 22.2. CASM was run in Phase II mode. (Tic-Visit :proposal-id 14043 :visit-id "01" :proposal-version -1 :trans-version "20140605" :date "01-Jan-2015 22:59:21.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "30" :si-bright-earth-limb-angle 20.0 :data-volume 1044528 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 14043 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 14043 :visit-id "01" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2840 :al-overhead-at-end 0 :internal-dur-at-end 519 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3241 :pcs-gap 0 ) true 1 0