16839( 6) - 10-Oct-2022 00:10:07 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 16839 Version: 6 Check-in Time: 10-Oct-2022 00:10:07 STScI Edit Number: 1 Title Transient LMXBs in Globular Clusters ------------------------------------------------------------------------------------ Type Cycle GO 29 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Jeroen Homan Eureka Scientific Inc. Y CoI: Dr. David A. Pooley Eureka Scientific Inc. N CoI: Dr. Craig Heinke University of Alberta N CoI: Dr. Maureen van den Berg Harvard University Y ------------------------------------------------------------------------------------ Abstract Since the discovery of globular cluster LMXBs in the 1970s, it was long assumed there was only one luminous LMXB per cluster. Deep Chandra observations of globular clusters have revealed that they contain numerous quiescent LMXB systems, any of which could go into outburst. Past Chandra studies have shown that globular clusters can indeed harbor multiple transients and that more quiescent LMXBs are hiding under the sensitivity limits of even relatively deep Chandra exposures. Here we propose a Chandra program to precisely localize new transients in globular clusters, with the aim of gaining better insight into globular cluster LMXB populations. As part of this effort we further request HST observations to identify the optical counterparts of these transients. ------------------------------------------------------------------------------------ Observations Description ------------------------ * General background for the program The goal of this joint Chandra/HST Target-of-Opportunity (ToO) proposal is to measure accurate coordinates of the next two X-ray transients in a globular cluster with Chandra, and to use HST subsequently to look for their optical counterparts inside the Chandra positional error circles. The Chandra error circle is large enough (about 0.6" radius) that it likely contains multiple globular-cluster stars. Comparison of the photometry that is extracted from the observations requested here with photometry from archival HST data reveals highly variable objects in the error circle, and hence the identity of the true counterpart. Our choice for the ACS/WFC is driven by the existence of a large body of archival globular-cluster images taken with this camera. We have been allocated time to do Chandra/HST follow-up for two X-ray transients. For the HST component we were granted 4 HST orbits in total (2 orbits per transient). * The first trigger (September 2022) Early September 2022, MAXI and subsequently Swift detected an outburst of an X-ray transient in the globular cluster M15. This X-ray transient has not been confidently identified with any of the known low-mass X-ray binaries in the cluster. We have triggered our Chandra ToO program to obtain an accurate X-ray position of the source. The Chandra observations will be performed on **September 19, 2022**. We have triggered the HST component of our program to search for the optical counterpart. 16839( 6) - 10-Oct-2022 00:10:07 - [ 2] * Visit 1 Our program for Visit 1 to observe M15 consists of observations in the F435W and F814W filters as there are already archival ACS data in these filters that we can use for comparison. The observations are organized in a 4-point dither-box pattern to improve the resolution. We aim for a S/N>10 for a star of mag 25 (F435W, F814W). We also include short observations to get photometry of bright stars, and of stars near bright stars. To fit all observation in one orbit, we make use of subarrays (aperture WFC1B-1K). The positional uncertainty on the X-ray transient fits well within this field-of-view. *** Note added on Oct 9 2022: M15 was observed on Oct 3. The observations in orbit 1 of Visit 1 (named Visit-Transient1) were successful, but the observations in orbit 2 failed. The observations in orbit 2 will be repeated, see Visit-Transient1_repeat. ------------------------------------------------------------------------------------ 16839( 6) - 10-Oct-2022 00:10:07 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 M15-TRANSIEN STELLAR CLUSTER, RA=21H29M58.1240S +/- 0.4", J2000 V = 16 T GLOBULAR CLUSTER DEC=+12D10'2.37" +/- 0.4" Reference Frame: ICRS Extended: NO Comments: Our target is a to-be-identified star in the globular cluster M15. The counterpart that we aim to identify is expected to have a magnitude in F435W m(F435W) >~ 16. ------------------------------------------------------------------------------------------------------------------------------------ 16839( 6) - 10-Oct-2022 00:10:07 - [ 4] TARGET LIST Generic Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Selection Criteria | Flux data No | Name | Description | | ------------------------------------------------------------------------------------------------------------------------------------ 2 GCTRANSIENT2 STAR, X-RAY TRANSIENT SECOND TRIGGER OF GLOBULAR-CLUSTER V = 19 X-RAY TRANSIENT PROGRAM Comments: next X-ray transient discovered in a Galactic globular cluster, whose position can only be accurately determined with Chandra ------------------------------------------------------------------------------------------------------------------------------------ 16839( 6) - 10-Oct-2022 00:10:07 - [ 5] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type ACS-WFC-DITHER-BOX Pattern_Purpose DITHER Number_Of_Points 4 Point_Spacing 0.262 Line_Spacing 0.192 Coordinate_Frame POS-TARG Pattern_Orient 18.39 Angle_Between_Sides 68.14 Center_Pattern YES ------------------------------------------------------------------------------------------------------------------------------------ 16839( 6) - 10-Oct-2022 00:10:07 - [ 6] Visit: 01 (Visit-Transient1) Visit Requirements: ORIENT 60D TO 120 D; TOO RESPONSE TIME 25.0D On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 M15-TRANSIE ACS/WFC ACCUM WFC1B-1K F435W 1 15 S (60 PATTERN 1 1 NT S) ------------------------------------------------------------------------------------------------------------------------------------ 2 M15-TRANSIE ACS/WFC ACCUM WFC1B-1K F435W 1 324 S PATTERN 1 2 NT (1296 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 M15-TRANSIE ACS/WFC ACCUM WFC1B-1K F814W 1 10 S (40 PATTERN 1 3 NT S) ------------------------------------------------------------------------------------------------------------------------------------ 4 M15-TRANSIE ACS/WFC ACCUM WFC1B-1K F435W 1 220 S (880 PATTERN 1 4 NT S) ------------------------------------------------------------------------------------------------------------------------------------ 5 M15-TRANSIE ACS/WFC ACCUM WFC1B-1K F814W CR-SPLIT=2 1 168 S (672 PATTERN 1 5 NT S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ M15-TRANSIENT 1 ACS/WFC ACCUM WFC1B-1K F435W 1 none none none 1 N/A M15-TRANSIENT 1 ACS/WFC ACCUM WFC1B-1K F435W 2 none none none 1 N/A M15-TRANSIENT 1 ACS/WFC ACCUM WFC1B-1K F435W 3 none none none 1 N/A M15-TRANSIENT 1 ACS/WFC ACCUM WFC1B-1K F435W 4 none none none 1 N/A M15-TRANSIENT 2 ACS/WFC ACCUM WFC1B-1K F435W 1 none none none 1 N/A M15-TRANSIENT 2 ACS/WFC ACCUM WFC1B-1K F435W 2 none none none 1 N/A M15-TRANSIENT 2 ACS/WFC ACCUM WFC1B-1K F435W 3 none none none 1 N/A M15-TRANSIENT 2 ACS/WFC ACCUM WFC1B-1K F435W 4 none none none 1 N/A M15-TRANSIENT 3 ACS/WFC ACCUM WFC1B-1K F814W 1 none none none 1 N/A M15-TRANSIENT 3 ACS/WFC ACCUM WFC1B-1K F814W 2 none none none 1 N/A M15-TRANSIENT 3 ACS/WFC ACCUM WFC1B-1K F814W 3 none none none 1 N/A M15-TRANSIENT 3 ACS/WFC ACCUM WFC1B-1K F814W 4 none none none 1 N/A M15-TRANSIENT 4 ACS/WFC ACCUM WFC1B-1K F435W 1 none none none 2 N/A M15-TRANSIENT 4 ACS/WFC ACCUM WFC1B-1K F435W 2 none none none 2 N/A M15-TRANSIENT 4 ACS/WFC ACCUM WFC1B-1K F435W 3 none none none 2 N/A M15-TRANSIENT 4 ACS/WFC ACCUM WFC1B-1K F435W 4 none none none 2 N/A M15-TRANSIENT 5 ACS/WFC ACCUM WFC1B-1K F814W 1 none none 1 2 N/A M15-TRANSIENT 5 ACS/WFC ACCUM WFC1B-1K F814W 1 none none 2 2 N/A M15-TRANSIENT 5 ACS/WFC ACCUM WFC1B-1K F814W 2 none none 1 2 N/A M15-TRANSIENT 5 ACS/WFC ACCUM WFC1B-1K F814W 2 none none 2 2 N/A M15-TRANSIENT 5 ACS/WFC ACCUM WFC1B-1K F814W 3 none none 1 2 N/A 16839( 6) - 10-Oct-2022 00:10:07 - [ 7] Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ M15-TRANSIENT 5 ACS/WFC ACCUM WFC1B-1K F814W 3 none none 2 2 N/A M15-TRANSIENT 5 ACS/WFC ACCUM WFC1B-1K F814W 4 none none 1 2 N/A M15-TRANSIENT 5 ACS/WFC ACCUM WFC1B-1K F814W 4 none none 2 2 N/A 16839( 6) - 10-Oct-2022 00:10:07 - [ 8] Visit: 02 (Visit-Transient2) Visit Requirements: ON HOLD ; TOO RESPONSE TIME 25.0D On Hold Comments: Target of Opportunity Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 GCTRANSIENT ACS/WFC ACCUM WFC1 F606W FLASH=25 1 30 S (30 2 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 GCTRANSIENT ACS/WFC ACCUM WFC1 F606W 1 340 S (340 2 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 GCTRANSIENT ACS/WFC ACCUM WFC1 F606W 1 340 S PATTERN 1 3 2 (1360 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 GCTRANSIENT ACS/WFC ACCUM WFC1 F814W FLASH=25 1 30 S (30 2 S) ------------------------------------------------------------------------------------------------------------------------------------ 5 GCTRANSIENT ACS/WFC ACCUM WFC1 F814W 1 340 S (340 2 S) ------------------------------------------------------------------------------------------------------------------------------------ 6 GCTRANSIENT ACS/WFC ACCUM WFC1 F814W 1 340 S PATTERN 1 6 2 (1360 S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ GCTRANSIENT2 1 ACS/WFC ACCUM WFC1 F606W none none none none 1 N/A GCTRANSIENT2 2 ACS/WFC ACCUM WFC1 F606W none none none none 1 N/A GCTRANSIENT2 3 ACS/WFC ACCUM WFC1 F606W 1 none none none 1 N/A GCTRANSIENT2 3 ACS/WFC ACCUM WFC1 F606W 2 none none none 1 N/A GCTRANSIENT2 3 ACS/WFC ACCUM WFC1 F606W 3 none none none 1 N/A GCTRANSIENT2 3 ACS/WFC ACCUM WFC1 F606W 4 none none none 1 N/A GCTRANSIENT2 4 ACS/WFC ACCUM WFC1 F814W none none none none 2 N/A GCTRANSIENT2 5 ACS/WFC ACCUM WFC1 F814W none none none none 2 N/A GCTRANSIENT2 6 ACS/WFC ACCUM WFC1 F814W 1 none none none 2 N/A GCTRANSIENT2 6 ACS/WFC ACCUM WFC1 F814W 2 none none none 2 N/A GCTRANSIENT2 6 ACS/WFC ACCUM WFC1 F814W 3 none none none 2 N/A GCTRANSIENT2 6 ACS/WFC ACCUM WFC1 F814W 4 none none none 2 N/A 16839( 6) - 10-Oct-2022 00:10:07 - [ 9] Visit: 03 (Visit-Transient1_repeat) Visit Requirements: ORIENT 60D TO 120 D; TOO RESPONSE TIME 25.0D On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 M15-TRANSIE ACS/WFC ACCUM WFC1B-1K F435W 1 208 S (832 PATTERN 1 1 NT S) ------------------------------------------------------------------------------------------------------------------------------------ 2 M15-TRANSIE ACS/WFC ACCUM WFC1B-1K F814W CR-SPLIT=2 1 168 S (672 PATTERN 1 2 NT S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ M15-TRANSIENT 1 ACS/WFC ACCUM WFC1B-1K F435W 1 none none none 1 N/A M15-TRANSIENT 1 ACS/WFC ACCUM WFC1B-1K F435W 2 none none none 1 N/A M15-TRANSIENT 1 ACS/WFC ACCUM WFC1B-1K F435W 3 none none none 1 N/A M15-TRANSIENT 1 ACS/WFC ACCUM WFC1B-1K F435W 4 none none none 1 N/A M15-TRANSIENT 2 ACS/WFC ACCUM WFC1B-1K F814W 1 none none 1 1 N/A M15-TRANSIENT 2 ACS/WFC ACCUM WFC1B-1K F814W 1 none none 2 1 N/A M15-TRANSIENT 2 ACS/WFC ACCUM WFC1B-1K F814W 2 none none 1 1 N/A M15-TRANSIENT 2 ACS/WFC ACCUM WFC1B-1K F814W 2 none none 2 1 N/A M15-TRANSIENT 2 ACS/WFC ACCUM WFC1B-1K F814W 3 none none 1 1 N/A M15-TRANSIENT 2 ACS/WFC ACCUM WFC1B-1K F814W 3 none none 2 1 N/A M15-TRANSIENT 2 ACS/WFC ACCUM WFC1B-1K F814W 4 none none 1 1 N/A M15-TRANSIENT 2 ACS/WFC ACCUM WFC1B-1K F814W 4 none none 2 1 N/A 16839( 6) - 10-Oct-2022 00:10:07 - [ 10] Summary Form for Proposal 16839 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures WFC1, WFC1B-1K ------------------------------------------------------------------------------------------------------------------------------------ Configurations ACS/WFC ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=2, FLASH=25 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ON HOLD , ORIENT 60D TO 120 D, PATTERN 1 1, PATTERN 1 2, PATTERN 1 3, PATTERN 1 4, PATTERN 1 5, PATTERN 1 6, TOO RESPONSE TIME 25.0D ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F435W, F606W, F814W ------------------------------------------------------------------------------------------------------------------------------------ Target Names GCTRANSIENT2, M15-TRANSIENT ------------------------------------------------------------------------------------------------------------------------------------