17769( 4) - 15-Sep-2025 16:11:40 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 17769 Version: 4 Check-in Time: 15-Sep-2025 16:11:40 STScI Edit Number: 2 Title The UVOIR portrait of PSR J0030+0451, the key millisecond pulsar ------------------------------------------------------------------------------------ Type Cycle GO 32 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. George G. Pavlov The Pennsylvania State University Y CoI: Dr. Oleg Y. Kargaltsev George Washington University N CoI: Dr. Bettina Posselt University of Oxford N CoI: Dr. Andreas Reisenegger Metropolitan University of Educational N Sciences CoI: Luis E. Rodriguez Pontificia Universidad Catolica de Chile N CoI: Denis Gonzalez-Caniulef Institut de Recherche en Astrophysique et N Planetologie ------------------------------------------------------------------------------------ Abstract PSR J0030+0451 is a nearby single radio, X-ray and gamma-ray millisecond pulsar, which has never been studied in the UV-optical-IR (UVOIR). This pulsar turned out to be the best target for measuring neutron star mass and radius with the X-ray NICER mission, using the effects of bending of photon trajectories in a strong gravitational field. Such measurements are very important for understanding the equation of state of the superdense matter in neutron star interiors, determined by strong interactions of hadrons. The mass and radius are obtained from the analysis of the pulsations of thermal soft X-ray emission coming from ``hot spots'' on the neutron star surface, heated by relativistic particles precipitating from the pulsar's magnetosphere along the magnetic field lines. The pulse shape (hence the inferred mass and radius) critically depend on the positions of the heated regions and the temperature distribution over the neutron star surface. To understand this distribution, one should analyze not only soft X-ray but also far-UV (FUV) pulsations. Such pulsations could be detected with HST, but one should know the average thermal FUV flux to determine the needed exposure. We propose a short exploratory program to estimate the average neutron star surface temperature from measuring UVOIR fluxes in three bands. The estimated temperature will be compared with the predictions of neutron star cooling/heating models, which will give us independent constraints on properties of the superdense matter. ------------------------------------------------------------------------------------ Observations Description ------------------------ To measure the FUV flux and estimate the neutron star temperature in PSR J0030+0451, we will employ ACS/SBC, the most sensitive detector in the FUV range. To eliminate the contribution of the geocoronal emission and maximize the FUV sensitivity, we will use the F125LP filter (cuts off geocoronal Ly-alpha) in the SHADOW parts of the orbit (1820 s for J0030), and the F140LP filter (cuts off all the geocoronal lines) in the rest of the orbit (500 s). We choose the ACS/SBC exposure time from the requirement that a temperature of T = 0.5E+5 K, which corresponds to the flux density of 10 nJy at 1438 A, to be 17769( 4) - 15-Sep-2025 16:11:40 - [ 2] detectable at >3 sigma level. From an analysis of archived ACS/SBC F125LP observations we found that two SHADOW orbits (shadow exposure of 3640 s) would be required. A similar estimate is obtained with the ACS ETC: S/N = 3.0 for an aperture circle radius of 0.2 arcsec; (S/N)_optimal = 5.3 (ETC Request ID: ACS.im.1930247). In the shorter non-shadow parts of the orbits (1000 s exposure) we will firmly detect the pulsar with the F140LP filter if its flux density exceeds 60 nJy (ACS.im.1930268). To minimize the effects of the SBC "thermal glow", we request the SBC observations to be taken in two one-orbit visits. We have checked that there are no bright objects in the SBC field of view that could violate the Bright Object Protection limit. As some old pulsars show a nonthermal power-law component in the optical, it is important to subtract its contribution into the FUV range from the detected FUV flux in order to measure the temperature. To do this, we need observations in two additional bands covering a broad wavelength range. Optimal filters for this goal are FWC3/UVIS F475X (3800 - 6000 A) and FWC3/IR F110W (0.9 - 1.4 microns). Thanks to the high sensitivity of these detector/filter combinations, 1 orbit in each band would detect very faint sources (or provide very low upper limits). In UVIS/ F475X we put the target in the UVIS2-C512C-CTE subarray near the chip readout to maximize the CTE. According to ETC (WFC3UVIS.im.1930279), we would detect 13 nJy (at 4850 A) for a flat f_nu continuum in 2232 s science exposure, using the WFC3-UVIS-DITHER-BOX , with S/N = 3.0 at r = 0.1 arcsec, (S/N)_optimal = 4.4. In WFC3/IR/F110W (lambda = 1.15 micron; exposure 2397 s) we will use the WFC3-IR-DITHER-BOX and readout parameters SAMP-SEQ = STEP100, NSAMP = 12. According to ETC (WFC3IR.im.1930295), we will detect a 22 nJy target with S/N = 3.0 at r = 0.15 arcsec, (S/N)_optimal = 3.5. We will use the optical image for astrometry based on the Gaia catalog, and then co-align the FUV and optical images for the FUV astrometry. ------------------------------------------------------------------------------------ 17769( 4) - 15-Sep-2025 16:11:40 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 PSRJ0030+045 STAR, NEUTRON STAR, RA=00H30M27.4216S +/- 0.01", J2000 V = 29 1 PULSAR DEC=+04D51'39.72" +/- 0.01" Reference Frame: ICRS Extended: NO ------------------------------------------------------------------------------------------------------------------------------------ 17769( 4) - 15-Sep-2025 16:11:40 - [ 4] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type WFC3-IR-DITHER-BOX-MIN Pattern_Purpose DITHER Number_Of_Points 4 Point_Spacing 0.572 Line_Spacing 0.365 Coordinate_Frame POS-TARG Pattern_Orient 18.528 Angle_Between_Sides 74.653 Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 2 Primary_Pattern Secondary_Pattern Pattern_Type WFC3-UVIS-DITHER-BOX Pattern_Purpose DITHER Number_Of_Points 4 Point_Spacing 0.173 Line_Spacing 0.112 Coordinate_Frame POS-TARG Pattern_Orient 23.884 Angle_Between_Sides 81.785 Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ 17769( 4) - 15-Sep-2025 16:11:40 - [ 5] Visit: 01 (fuv1) 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 PSRJ0030+04 ACS/SBC ACCUM SBC F125LP 1 1820 S SHADOW; GS ACQ SCENARIO 51 (1820 S) BASE1O3 ------------------------------------------------------------------------------------------------------------------------------------ 2 PSRJ0030+04 ACS/SBC ACCUM SBC F140LP 1 500 S (500 51 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 | ------------------------------------------------------------------------------------------------------------------------------------ PSRJ0030+0451 1 ACS/SBC ACCUM SBC F125LP none none none none 1 N/A PSRJ0030+0451 2 ACS/SBC ACCUM SBC F140LP none none none none 1 N/A 17769( 4) - 15-Sep-2025 16:11:40 - [ 6] Visit: 02 (blue-uvis) 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 PSRJ0030+04 WFC3/UVI ACCUM UVIS2-C51 F475X 1 558 S PATTERN 2 1 51 S 2C-CTE (2232 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 | ------------------------------------------------------------------------------------------------------------------------------------ PSRJ0030+0451 1 WFC3/UVI ACCUM UVIS2-C5 F475X 1 none none none 1 N/A S 12C-CTE PSRJ0030+0451 1 WFC3/UVI ACCUM UVIS2-C5 F475X 2 none none none 1 N/A S 12C-CTE PSRJ0030+0451 1 WFC3/UVI ACCUM UVIS2-C5 F475X 3 none none none 1 N/A S 12C-CTE PSRJ0030+0451 1 WFC3/UVI ACCUM UVIS2-C5 F475X 4 none none none 1 N/A S 12C-CTE 17769( 4) - 15-Sep-2025 16:11:40 - [ 7] Visit: 03 (nir) 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 PSRJ0030+04 WFC3/IR MULTIAC IR F110W SAMP-SEQ=STEP100, NSAMP=12 1 DEF PATTERN 1 1 51 CUM (2396.929 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 | ------------------------------------------------------------------------------------------------------------------------------------ PSRJ0030+0451 1 WFC3/IR MULTIAC IR F110W 1 none none none 1 N/A CUM PSRJ0030+0451 1 WFC3/IR MULTIAC IR F110W 2 none none none 1 N/A CUM PSRJ0030+0451 1 WFC3/IR MULTIAC IR F110W 3 none none none 1 N/A CUM PSRJ0030+0451 1 WFC3/IR MULTIAC IR F110W 4 none none none 1 N/A CUM 17769( 4) - 15-Sep-2025 16:11:40 - [ 8] Visit: 04 (fuv2) Visit Requirements: On Hold Comments: Additional Comments: We request this visit to be separated in time from the identical visit fuv1 (01) to minimize the "thermal glow" of the detector. 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 PSRJ0030+04 ACS/SBC ACCUM SBC F125LP 1 1820 S SHADOW; GS ACQ SCENARIO 51 (1820 S) BASE1O3 ------------------------------------------------------------------------------------------------------------------------------------ 2 PSRJ0030+04 ACS/SBC ACCUM SBC F140LP 1 500 S (500 51 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 | ------------------------------------------------------------------------------------------------------------------------------------ PSRJ0030+0451 1 ACS/SBC ACCUM SBC F125LP none none none none 1 N/A PSRJ0030+0451 2 ACS/SBC ACCUM SBC F140LP none none none none 1 N/A 17769( 4) - 15-Sep-2025 16:11:40 - [ 9] Visit: 05 (nir) 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 PSRJ0030+04 WFC3/IR MULTIAC IR F110W SAMP-SEQ=STEP100, NSAMP=12 1 DEF PATTERN 1 1 51 CUM (2396.929 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 | ------------------------------------------------------------------------------------------------------------------------------------ PSRJ0030+0451 1 WFC3/IR MULTIAC IR F110W 1 none none none 1 N/A CUM PSRJ0030+0451 1 WFC3/IR MULTIAC IR F110W 2 none none none 1 N/A CUM PSRJ0030+0451 1 WFC3/IR MULTIAC IR F110W 3 none none none 1 N/A CUM PSRJ0030+0451 1 WFC3/IR MULTIAC IR F110W 4 none none none 1 N/A CUM 17769( 4) - 15-Sep-2025 16:11:40 - [ 10] Summary Form for Proposal 17769 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures IR, SBC, UVIS2-C512C-CTE ------------------------------------------------------------------------------------------------------------------------------------ Configurations ACS/SBC, WFC3/IR, WFC3/UVIS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM, MULTIACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters NSAMP=12, SAMP-SEQ=STEP100 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements GS ACQ SCENARIO BASE1O3, PATTERN 1 1, PATTERN 2 1, SHADOW ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F110W, F125LP, F140LP, F475X ------------------------------------------------------------------------------------------------------------------------------------ Target Names PSRJ0030+0451 ------------------------------------------------------------------------------------------------------------------------------------