13939( 2) - 27-Oct-2014 15:37:52 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 13939 Version: 2 Check-in Time: 27-Oct-2014 15:37:52 STScI Edit Number: 0 Title The nature of the transient X-ray binary Swift J1910.2-0546 ------------------------------------------------------------------------------------ Type Cycle GO 22 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Nathalie Degenaar University of Michigan Y CoI: Dr. Mark Reynolds University of Michigan N CoI: Dr. Jon Matthew Miller University of Michigan N CoI: Ashley King University of Michigan N CoI: Dr. Dipankar Maitra Wheaton College N CoI: Dr. Edward M. Cackett Wayne State University N CoI: Dr. Rudy Wijnands Universiteit van Amsterdam N ------------------------------------------------------------------------------------ Abstract Swift J1910.2-0546 is a newly discovered transient X-ray binary that exhibited a ~1 yr long outburst in 2012-2013. Owing to its low hydrogen column density and fair proximity, it is one of the few sources for which X-ray/UV quiescent studies are feasible. This provides the opportunity to verify the nature of the compact primary (black hole versus neutron star), and to investigate the properties of the quiescent accretion flow. Such a study would provide an important perspective to understand the intriguing outburst phenomena observed for this source. To this end, we request a 45 ks Chandra/ACIS-S observation and 2 orbits of HST/WFC3-UVIS time for Swift J1910.2-0546. ------------------------------------------------------------------------------------ Observations Description ------------------------ UV emission from quiescent LMXBs is thought to be the prime tracer of the quiescent accretion stream that provides important insight into the physics of quiescent accretion flows. Such studies are highly challenging, however, given that most LMXBs are located in the Galactic plane and hence their intrinsically faint UV emission further suffers from substantial interstellar extinction. Owing to its low extinction, Swift J1910.2-0546 is one of the few LMXBs for which quiescent UV studies are feasible. To make a direct comparison with other LMXBs studied in quiescence in the UV band (see e.g., Hynes & Robinson 2012, ApJ 749, 3), we chose to perform near-UV photometry (~2000-4000 A). The most sensitive imaging instrument in this range is the WFC3/UVIS. To obtain the spectral-energy distribution, we propose to use three filters (similar to those used in studies of other LMXBs): F225W (lambda_c~2359 A), F275W (lambda_c~2704 A), and F336W (lambda_c~3355 A). We propose to perform the science exposures in sequences of F336W-F275W-F225W-F336W, so that we can average over possible variability (and are able to search for such variability if the source is bright enough). We used the online WFC3/UVIS exposure time calculator (v. 22.2). Our target is located at ~6.9 kpc and the reddening is E(B-V)=0.66. A recent XMM-Newton/OM 13939( 2) - 27-Oct-2014 15:37:52 - [ 2] observation (dd 2014 October 5; PI Degenaar) did not detect the source in the UV band, providing an upper limit of <1E-17 erg/cm2/s/A (measured at lambda_c ~ 2298 A). The faintest quiescent LMXBs observed in the UV have luminosities of ~1E31 erg/s (Hynes & Jones 2012). At the distance of our target this translates into a flux of ~3E-18 erg/cm2/s/A. Based on UV studies of other quiescent LMXBs (e.g., Hynes & Jones 2012), we model our point source as a blackbody with a temperature of 10, 000 K, where we normalized the continuum flux to our lowest expected level of 3E-18 erg/cm2/s/A. We impose a S/N ratio of 25 at this minimum flux level. We use dither patterns (2 dithers for exposures <1000s, 3 dithers for longer exposures) and lamp flashes are applied to ensure that the minimum background for proper CTE is reached (12 e-/pixel). The exposure times range from ~700-2000 s per filter. A total of two orbits are required, which are combined into a single visit (only one instrument is used). Our target is a transient X-ray source, but its outburst recurrence time is very low: only one outburst (in 2012-2013) has been detected so far in the history of X-ray astronomy. The maximum UV flux reached during that outburst was ~18 mag at lambda_c~2246 A (~3E-16 erg/cm2/s/A; Degenaar et al. 2014, ApJ 784, 122). The probability that the source goes into outburst in the next year is very low. Nevertheless, should the source go into outburst, that will be readily picked up by all-sky monitors such as Swift/BAT (15-50 keV) and MAXI (2-20 keV), which cover the position of our target every day. The rise of accretion outbursts in transient LMXBs typically takes a few days. ------------------------------------------------------------------------------------ 13939( 2) - 27-Oct-2014 15:37:52 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 SWIFT-J1910. STAR, ACCRETION DISK, RA=19H10M22.8000S, J2000 <1E-17 erg/cm/s/A at lambda_c ~ 2298 A 2-0546 LMXB, X-RAY TRANSIENT DEC=-05D47'58.00" Reference Frame: Other: SIMBAD Comments: This object was generated by the targetselector and retrieved from the SIMBAD database. ------------------------------------------------------------------------------------------------------------------------------------ 13939( 2) - 27-Oct-2014 15:37:52 - [ 4] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 2 Primary_Pattern Secondary_Pattern Pattern_Type WFC3-UVIS-DITHER-LINE-3PT Pattern_Purpose DITHER Number_Of_Points 3 Point_Spacing 0.135 Line_Spacing Coordinate_Frame POS-TARG Pattern_Orient 46.84 Angle_Between_Sides Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 3 Primary_Pattern Secondary_Pattern Pattern_Type WFC3-UVIS-DITHER-LINE Pattern_Purpose DITHER Number_Of_Points 2 Point_Spacing 0.145 Line_Spacing Coordinate_Frame POS-TARG Pattern_Orient 46.84 Angle_Between_Sides Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ 13939( 2) - 27-Oct-2014 15:37:52 - [ 5] Visit: 01 Visit Requirements: 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 SWIFT-J1910 WFC3/UVI ACCUM UVIS F336W FLASH=11 1 349 S (698 PATTERN 3 1 .2-0546 S S) ------------------------------------------------------------------------------------------------------------------------------------ 2 SWIFT-J1910 WFC3/UVI ACCUM UVIS F225W FLASH=11 1 541 S PATTERN 2 2 .2-0546 S (1623 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 SWIFT-J1910 WFC3/UVI ACCUM UVIS F275W FLASH=11 1 577 S PATTERN 2 3 .2-0546 S (1731 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 SWIFT-J1910 WFC3/UVI ACCUM UVIS F336W FLASH=11 1 349 S (698 PATTERN 3 4 .2-0546 S 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 | ------------------------------------------------------------------------------------------------------------------------------------ SWIFT-J1910.2-0546 1 WFC3/UVI ACCUM UVIS F336W 1 none none none 1 N/A S SWIFT-J1910.2-0546 1 WFC3/UVI ACCUM UVIS F336W 2 none none none 1 N/A S SWIFT-J1910.2-0546 2 WFC3/UVI ACCUM UVIS F225W 1 none none none 1 N/A S SWIFT-J1910.2-0546 2 WFC3/UVI ACCUM UVIS F225W 2 none none none 1 N/A S SWIFT-J1910.2-0546 2 WFC3/UVI ACCUM UVIS F225W 3 none none none 1 N/A S SWIFT-J1910.2-0546 3 WFC3/UVI ACCUM UVIS F275W 1 none none none 2 N/A S SWIFT-J1910.2-0546 3 WFC3/UVI ACCUM UVIS F275W 2 none none none 2 N/A S SWIFT-J1910.2-0546 3 WFC3/UVI ACCUM UVIS F275W 3 none none none 2 N/A S SWIFT-J1910.2-0546 4 WFC3/UVI ACCUM UVIS F336W 1 none none none 2 N/A S SWIFT-J1910.2-0546 4 WFC3/UVI ACCUM UVIS F336W 2 none none none 2 N/A S 13939( 2) - 27-Oct-2014 15:37:52 - [ 6] Summary Form for Proposal 13939 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures UVIS ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFC3/UVIS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters FLASH=11 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PATTERN 2 2, PATTERN 2 3, PATTERN 3 1, PATTERN 3 4 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F225W, F275W, F336W ------------------------------------------------------------------------------------------------------------------------------------ Target Names SWIFT-J1910.2-0546 ------------------------------------------------------------------------------------------------------------------------------------