17587( 6) - 23-Jan-2024 15:54:59 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 17587 Version: 6 Check-in Time: 23-Jan-2024 15:54:59 STScI Edit Number: 3 Title Fast Variability of the Inner Accretion Flow in Transitional Millisecond Pulsars: a Multi-Wavelength Campaign to Unveil Mode Switching ------------------------------------------------------------------------------------ Type Cycle GO 31 ------------------------------------------------------------------------------------ Investigators Contact? PI: Giulia Illiano INAF, Osservatorio Astronomico di Roma Y CoI: Dr. Arianna Miraval Zanon Agenzia Spaziale Italiana (ASI) Science Y Data Center (ASDC) CoI: Francesco Coti Zelati Institute of Space Sciences (CSIC-IEEC) Y CoI: Dr. Alessandro Papitto INAF, Osservatorio Astronomico di Roma N CoI: Dr. Filippo Ambrosino INAF, Osservatorio Astronomico di Roma N CoI: Dr. Alessio Marino Institute of Space Sciences (CSIC-IEEC) N CoI: Dr. Nanda Rea Institute of Space Sciences (CSIC-IEEC) N CoI: Dr. Domitilla De Martino Osservatorio Astronomico di Capodimonte N (OAC) CoI: Maria Cristina Baglio INAF - Osservatorio Astronomico di Brera N ------------------------------------------------------------------------------------ Abstract Transitional millisecond pulsars exhibit a peculiar X-ray sub-luminous disk state that features characteristics of both rotation-powered radio pulsars and accretion-powered X-ray pulsars. In this state, switching between two distinct intensity levels, dubbed high and low modes, is observed in both X-rays and optical/UV bands. For the prototype PSR J1023+0038, it was suggested that fast variations of the inner accretion flow might be at the origin of the observed mode-switching phenomenon. To better understand the physical mechanisms driving these transitions, we are organizing the first high-time resolution multi-wavelength campaign on the robust candidate transitional millisecond pulsar 3FGL J1544.6-1125, exploiting recently approved high-time resolution observations with the quintuple-beam imager HiPERCAM, at the 10.4m GTC, and ToO observing programs with XMM-Newton and NuSTAR. High-time resolution UV observations have never been performed on this source, but we expect, given its brightness, to allow a similar study as performed for PSR J1023+0038. We will investigate the timescales of mode-switching in 3FGL J1544.6-1125, assessing their compatibility with the proposed model for PSR J1023+0038. We will model broadband spectral energy distributions, separately extracted during the high and low modes. Such analyses are pivotal in refining and constraining the considered model, enhancing our efforts to understand this intriguing phenomenon. We found a candidate pulsed signal with the fast optical photometer TNG/SiFAP2. The proposed observing campaign also aims at confirming the hint of detection or put stringent upper limits on the fractional amplitude. ------------------------------------------------------------------------------------ Observations Description ------------------------ We ask to observe 3FGL J1544.6-1125 in the time interval: 2024-02-08, 04:30-06:30 UTC (60348.18750000 - 60348.27083333 MJD) 17587( 6) - 23-Jan-2024 15:54:59 - [ 2] This visit will consist in one HST orbit during which we will carry out time-resolved NUV TIME-TAG spectroscopy with the STIS/NUV-MAMA/G230L instrument/grating combination. We will use the 2376 A setting for this observation to achieve continuous wavelength coverage between 1570 A and 3180 A, with the 52X0.2 slit. The TIME-TAG mode of STIS will provide a maximum time resolution of 125 micro-s, fast enough to resolve high/low mode transitions and to search for pulsations at millisecond periods in the Near-UV band. We will observe simultaneously with 10.4m Gran Telescopio Canarias and X-ray telescopes. ------------------------------------------------------------------------------------ 17587( 6) - 23-Jan-2024 15:54:59 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 3FGLJ1544.6- STAR, ACCRETION DISK, RA=15H44M39.3674S, J2000 V = 19 1125 BINARY PULSAR, NEUTRON DEC=-11D28'4.68" STAR, PULSAR Reference Frame: ICRS Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 2000.0 0.0013437601399236528 -0.012541 0.0 ------------------------------------------------------------------------------------------------------------------------------------ 17587( 6) - 23-Jan-2024 15:54:59 - [ 4] Visit: 01 Visit Requirements: BETWEEN 08-FEB-2024:04:30:00 AND 08-FEB-2024:06:30:00 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 3FGLJ1544.6 STIS/CCD ACQ 50CCD MIRROR 1 7 S (7 S) -1125 ------------------------------------------------------------------------------------------------------------------------------------ 2 3FGLJ1544.6 STIS/NUV TIME-TA 52X0.2 G230L 2376 BUFFER-TIME=1165 1 2130 S -1125 -MAMA G see below (2121 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 | ------------------------------------------------------------------------------------------------------------------------------------ 3FGLJ1544.6-1125 1 STIS/CCD ACQ 50CCD MIRROR none none none none 1 N/A 3FGLJ1544.6-1125 2 STIS/NUV TIME-TA 52X0.2 G230L 2376 none none none none 1 2121.0 S -MAMA G 17587( 6) - 23-Jan-2024 15:54:59 - [ 5] Summary Form for Proposal 17587 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures 50CCD, 52X0.2 ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD, STIS/NUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ, TIME-TAG ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters BUFFER-TIME=1165 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements BETWEEN 08-FEB-2024:04:30:00 AND 08-FEB-2024:06:30:00 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements G230L, MIRROR ------------------------------------------------------------------------------------------------------------------------------------ Target Names 3FGLJ1544.6-1125 ------------------------------------------------------------------------------------------------------------------------------------