Monitoring M31 for BHXNe During A01-13 we found ~28 Black Hole X-ray Novae (BHXNe) in M31 using Chandra, and with HST follow-up have estimated orbital periods for 12 of these. Observations are under way with HST to attempt to estimate additional periods. Preliminary results indicate these orbital periods are shorter than in the Galaxy and also shorter nearer the nucleus, indicating that some BHXN are formed via tidal capture. Continued observations can confirm or refute this. We propose to continue this program concentrating our HST resources on a single transient which is >1e38 erg/s or <1 from the nucleus. Only uninterrupted monitoring can yield the duty cycles and long-term light curves of BHXNe (and other variables) in M31. This is a target of opportunity. We will trigger based on the discovery of a bright X-ray transient with Chandra. The first observation will be made within ~3 weeks of the Chandra detection (2 orbits); a follow-up observation will be made 6 months later (also 2 orbits). The target co-ordinates will be updated at the time of the trigger 12 false false 0.0 0.0 false false false SUPPORTED UNIDENTIFIED X-RAY EMITTER New M31 transient. J2000 J2000 UNIDENTIFIED X-RAY EMITTER Position to be ubdated ~3 weeks before observation; the location will be within 8' of the current position. J2000 J2000 ACS/WFC Imaging No No F435W ACS/WFC Imaging No No F435W POS-TARG DITHER 0.265 LINE 0.187 false false 69.05 4 20.67 ACS-WFC-DITHER-BOX 1 false The scheduling data was generated by CASM 20.2. CASM was run in Phase II mode. 1371597732000 259.8936447538321 (Tic-Visit :proposal-id 13111 :visit-id "01" :proposal-version -1 :trans-version "20120802" :date "18-Oct-2012 16:15:33.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "27" :si-bright-earth-limb-angle 20.0 :data-volume 1136896 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 13111 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 13111 :visit-id "01" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2676 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3010 :pcs-gap 0 ) (Tic-Orbit :proposal-id 13111 :visit-id "01" :orbit-number 2 :pcs-time 222 :si-vis-utilization 2788 :al-overhead-at-end 0 :internal-dur-at-end 347 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3010 :pcs-gap 0 ) false 2 0 The scheduling data was generated by CASM 22.0. CASM was run in Phase II mode. /private/var/folders/tc/ydsxjyy102b9cplf304tbl300005f2/T/OPVisit292277720860378046.xml (Tic-Visit :proposal-id 13111 :visit-id "02" :proposal-version -1 :trans-version "20140319" :date "21-May-2014 06:40:48.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "27" :si-bright-earth-limb-angle 20.0 :data-volume 1136896 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 13111 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 13111 :visit-id "02" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2676 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3010 :pcs-gap 0 ) (Tic-Orbit :proposal-id 13111 :visit-id "02" :orbit-number 2 :pcs-time 222 :si-vis-utilization 2788 :al-overhead-at-end 0 :internal-dur-at-end 347 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3010 :pcs-gap 0 ) true 2 0