Please note that I will be travelling from New Zealand to the UK on Tuesday and Wednesday. I therefore request that all Co-Is should be cc'd in communications to ensure a quick turnaround. -674552526 Assigned ID: 1647 ----- Attempting Submission 1 (Sun Mar 18 06:09:55 GMT 2018) ----- STIS TIME-TAG EXPOSURE GENERATES HEAVY DATA VOLUME STIS TIME-TAG EXPOSURE GENERATES HEAVY DATA VOLUME The current Swift/UVOT flux in the UVW2 filter (approx 1900A) is about 6e-14. For the standard ETC calculations, I have adopted a flat spectrum with this flux for both FUV and NUV. In addition, I have carried out an additional instrument safety check via the ETC calculation STIS.sp.1168846 . Here, I have extrapolated the UVW2 flux to the FUV, assuming a Million degree temperature blackbody SED and no reddening. APT gives one warning per visit because the BUFFER-TIMES are quite short, so that there are more than 30 buffer-dumps required per visit. We request that this should be permitted: the BUFFER-TIMES have been set based on the ETC calculations (the safety check one, in the case of the FUV), with a little bit of additional slack. This should ensure that there will be no data loss even allowing for the fact that the source is variable. RESUBMISSION: * removed incorrect mention of "July" window from changed observing description (request is simply for visit 1 to be as soon as possible) * added "after visit 1 by 30 - 60 days" timing requirement for visit 2 I have changed the grating for the second visit from E140M to G140L for the first 3 FUV orbits and from E230M to G230L for the final 2 NUV orbits. I have also changed the slit from the 0.2x0.2 to the 52x0.2 for the second visit. The buffer times have been adjusted slightly but there are still more than 30 buffer dumps for the visit. 1271293537 ----- Attempting Submission 1 (Wed Mar 28 00:12:21 GMT 2018) ----- HST Phase II Proposal 15454 (maxi-j1824-phase2.apt) successfully submitted. Receipt: # 15454-1 ----- Attempting Submission 2 (Wed Mar 28 03:12:36 GMT 2018) ----- ----- Attempting Submission 3 (Thu Jun 14 20:25:15 GMT 2018) ----- The current Swift/UVOT flux in the UVW2 filter (approx 1900A) is about 6e-14. For the standard ETC calculations, I have adopted a flat spectrum with this flux for both FUV and NUV. In addition, I have carried out an additional instrument safety check via the ETC calculation STIS.sp.1168846 . Here, I have extrapolated the UVW2 flux to the FUV, assuming a Million degree temperature blackbody SED and no reddening. APT gives one warning per visit because the BUFFER-TIMES are quite short, so that there are more than 30 buffer-dumps required per visit. We request that this should be permitted: the BUFFER-TIMES have been set based on the ETC calculations (the safety check one, in the case of the FUV), with a little bit of additional slack. This should ensure that there will be no data loss even allowing for the fact that the source is variable. I have changed the grating for the second visit from E140M to G140L for the first 3 FUV orbits and from E230M to G230L for the final 2 NUV orbits. I have also changed the slit from the 0.2x0.2 to the 52x0.2 for the second visit. The buffer times have been adjusted slightly but there are still more than 30 buffer dumps for the visit. On March 11, MAXI/GSC detected a new X-ray transient, MAXI J1820+070. Since then, the system has become one of the brightest and least reddened black-hole X-ray binaries ever seen and is currently the target of an extensive multi-wavelength campaign. However, there is one critical gap in this campaign: the ultraviolet band. Here, we propose to rectify this omission by obtaining two epochs of FUV and NUV spectroscopy of the system with HST/STIS. Remarkably, even though MAXI~J1820+070 is already UV bright, it still appears to be in the so-called ``hard'' state at the moment. This presents us with the unique opportunity to obtain the first-ever hard-state UV observations of any BH binary. This, in turn, will allow us to use the most sensitive disk wind signatures -- which are located in the UV band -- to test for the presence of a disk wind in both the hard and soft states. We therefore propose to obtain two epochs, one scheduled as early as possible to catch the system in the hard state, the other scheduled roughly 1 month later, to catch the system in the soft state. In addition to the search for disk wind signatures, our data will also be critical for reconstructing the disk SED, allow us to search for stochastic and (quasi-)periodic variability and inter-band time-lags, yield abundance estimates that will tell us the evolutionary history of the system and provide a direct estimate of the reddening and extinction towards the source. We will visit V404 Cyg three times with HST. The first and third visit will each consist of 5 consecutive HST orbits, during which we will carry out time-resolved far-UV spectroscopy with the COS/G140L instrument/grating combination. We will use the 1105 A setting for all of these observations to achieve continuous wavelength coverage between 1121 A and 2148 A. The TIME-TAG mode of COS will provide sufficient time resolution to capture variability on the dynamical time-scale within the accretion disk. COS is preferred to STIS in the far-UV despite due to its much higher sensitivity in this waveband. The second visit will consist of 2 consecutive HST orbits, during which we will obtain time-resolved near-UV spectroscopy with the STIS/NUV-MAMA/G230L instruments/detector/grating combination. This gives continuous wavelength coverage between 1570 A and 3180 A, again at a time resolution sufficient to resolve fast flickering. Recent near-UV photometry obtained by Swift/UVOT shows that F_lambda,NUV ~ 1-5 x 1e-16 erg/cm^2/ s/A. (Motta et al. 2015b), where the near-UV measurement corresponds to the UVW1 or UVW2 filters, which have central wavelength of 2600 A and 1900 A, respectively. Since the intrinsic SED is likely to be blue, but subject to considerable reddening, far-UV and near-UV fluxes will probably be comparable. Based on these numbers, and allowing for overheads, we then estimate that 10 HST orbits of far-UV spectroscopy will yield a combined spectrum with S/N ~ 5-15 per resolution element at 1500 A. Similarly, our 2 orbits of near-UV spectroscopy will yield a combined spectrum with S/N ~ 5-15 per resolution element at 2800 A. There are no safety concerns for the COS or STIS detectors. In the near-UV, the existing Swift/UVOT observations show that the system is nowhere near bright enough to threaten detector damage. No empirical data exists so far in the far-UV, but even the most extreme plausible extrapolation from the near-UV to the far-UV -- assuming that both near-UV and far-UV emission lie on the Rayleigh-Jeans tail of the disk spectrum (F_lambda ~ lambda^{-4}) -- yields local and global count rates that remain well below the bright object limits. We will use an imaging target acquisition with Mirror B as the best compromise between efficiency and instrument safety. With this set-up, a 1 min ACQ/IMAGE target acquisition exposure yields S/N ~ 30-60 depending on the detailed SED shape, and the count rate in the brightest pixel never exceeds 8 c/s, well below the bright object limit. The observations should ideally take place as soon as possible, in order to ensure that we catch the system before it decays too much. We also request that the near-UV visit should take place between the two far-UV visits and that all three visits should take place as close in time as possible. This will allow us to construct a near-simultaneous global SED. Several of us are leaders/members of ongoing monitoring campaigns at other wavelengths, so we can rely on existing/approved programs to obtain (near-)simultaneous coverage across the entire frequency range. In order to facilitate the scheduling of the HST program, we are not requesting any of these auxiliary observations to be formally linked to the HST observations. Instead, we will simply make a best effort to achieve obtain the widest possible range of auxiliary observations as close as possible to the time of the HST observations. We finally note that, given the strong variability currently seen at all wavelengths and on all time-scales (e.g. Ferrigno et al. 2015; Motte et al. 2015ab; Hynes et al. 2015; Hardy et al. 2015; Tetarenko et al. 2015), it is impossible to predict with certainty whether the system is likely to be detectable in the far-UV in early July. We are therefore happy to work with STScI to mitigate the risk of a non-detection. For example, it may be possible to implement a ``dead-man's switch'', whereby the HST observations will only be executed if Swift/UVOT near-UV photometry closer to the HST scheduling window indicates a significant likelihood of success. 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