0 ----- Attempting Submission 1 (Wed Aug 31 13:51:02 GMT 2022) ----- HST Phase II Proposal 17245 successfully submitted. Receipt: # 17245-1 ----- Attempting Submission 2 (Wed Aug 31 21:09:39 GMT 2022) ----- Millisecond pulsars (MSPs) are the fastest spinning compact stars known to date. They can appear as radio pulsars powered by the rotation of the NS magnetic field or accreting X-ray pulsars powered by the accretion of mass transferred by a companion star. The accreting millisecond X-ray pulsar SAX J1808.4-3658 has revealed an abrupt increase in intensity beginning in 19 August 2022, indicating the onset of a new outburst. This activity has never been observed since the last outburst in 2019. During the outburst this source emits X-ray pulsations at the neutron star spin period, which have been already detected with NICER. Ultraviolet millisecond pulsations have also been detected from SAX J1808.4-3658 during its 2019 outburst with HST/STIS, representing the first discovery of this kind in accreting MSPs. For the first time in forty years of pulsar studies, we might have witnessed that electrons are accelerated to relativistic energies by the rotation of the neutron star magnetosphere even during the accretion phase. To probe the nature of this new phenomenon, we require disruptive activation time to observe SAX J1808.4-3658 with HST STIS/NUV-MAMA instrument combination to study UV pulses during the 2022 outburst. The detection of UV pulsations close to the peak of the outburst, when the mass accretion rate is maximum, would allow us to probe the UV pulse emission mechanism over a range of mass accretion rates spanning 2-3 orders of magnitude. We ask to observe SAX J1808.4-3658 with HST during its 2022 outburst. This visit will consist in one HST orbits 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 \AA setting for this observation to achieve continuous wavelength coverage between 1570 \AA and 3180 \AA, with the 52X0.2 slit. The TIME-TAG mode of STIS will provide a maximum time resolution of 125 $\mu$s, fast enough to resolve pulsations at 2.5 ms (NS pulse period) in the Near-UV band. We will use precise and updated ephemeris of the 2022 outburst measured by the timing analysis of X-ray NICER data to study the pulses in NUV band. 0 false SUPPORTED STAR ACCRETION DISK BINARY PULSAR LMXB NEUTRON STAR PULSAR J2000 1661979904520 /tmp/OPVisit9516467807517827015.xml The scheduling data was generated by CASM 30.3. CASM was run in Phase II mode. (Tic-Visit :proposal-id 17245 :visit-id "01" :proposal-version -1 :trans-version "20220630" :date "31-Aug-2022 23:05:04.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "24" :si-bright-earth-limb-angle 20.0 :data-volume 296128 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 17245 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 17245 :visit-id "01" :orbit-number 1 :pcs-time 393 :si-vis-utilization 2804 :al-overhead-at-end 0 :internal-dur-at-end 440 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3200 :pcs-gap 0 ) true 1 0