Proposal Number: 4001
PI Last Name: Zelati
Title:LATE TIME NUSTAR OBSERVATION OF THE LONGEST MAGNETAR OUTBURST TO DATE
Abstract:The magnetar 1E 1547.0-5408 underwent a powerful outburst in 2009 January. Follow-up X-ray observations caught the source at a flux a factor of about 20-30 larger than the quiescent value over the past 5 years. Emission was detected up to at least 200 keV at the outburst peak. The hard X-ray flux decayed by a factor of about 3 over the first year of the outburst. Hard X-ray emission was detected in a deep NuSTAR observation in 2016 April, more than 7 years after the outburst onset. Extrapolation of the light curve indicates that this episode represents the longest magnetar outburst ever observed. We ask for a 85-ks NuSTAR observation of 1E 1547−5408 to characterize its current spectral and timing properties.

Proposal Number: 4004
PI Last Name: Reeves
Title:THE REMARKABLY COOL HARD X-RAY SPECTRUM OF THE QSO, 1H 0419-577
Abstract:The origin of the hard X-ray excess and coronal emission are key to our understanding of AGN. The nearby (z=0.104) luminous QSO, 1H 0419-577, shows a strong hard X-ray excess and our NuSTAR AO-1 observation surprisingly revealed one of the most extreme high energy cut-offs observed to date from any AGN. If its origin is due to thermal Comptonization, then this implies a remarkably low corona temperature of kT~14 keV. Here we propose simultaneous 3x50 ks NuSTAR and 3x15 ks XMM-Newton observations of 1H 0419-577 to understand the nature and variability of the corona and its response to the illuminating XUV continuum. This will reveal the true form of the X-ray emission produced from close to the central black hole.

Proposal Number: 4016
PI Last Name: Reeves
Title:A MULTI WAVELENGTH VIEW OF THE ULTRA FAST OUTFLOW IN PDS 456
Abstract:PDS456, the most luminous nearby quasar, is the prototype ultra fast outflow. With NuSTAR and XMM-Newton, we established the presence of a fast (0.3c), wide angle accretion disk wind, with sufficient power to provide significant mechanical feedback into its host galaxy. In a subsequent analysis of archival HST observations, we have found evidence for a fast, 0.3c UV counterpart of the wind, which may make PDS 456 the fastest BAL QSO known to date. We have now been approved a further 2x3 orbit HST/COS observations for 2018, to confirm the fast nature of the UV wind and its variability. Here, we request simultaneous X-ray coverage to be coordinated with HST, via 2x80 ks NuSTAR + XMM-Newton observations, which will reveal the wind structure and variability from the UV to hard X-rays.

Proposal Number: 4020
PI Last Name: Staubert
Title:MONITORING THE CYCLOTRON LINE ENERGY IN HERCULES X-1: IS THERE A TURN-UP AFTER THE LONG DECAY?
Abstract:We propose to continue the study of the long-term evolution of the cyclotron line energy in Her X-1. The long-term decay of Ecyc discovered in data taken between 1993 and 2012, was confirmed by a precise measurement by NuSTAR in August 2015, firmly establishing a decay by 5 keV over the last 20 yrs. However, the last observing campaign in 2016, had provided evidence that the decay has ended. This was confirmed by the latest NuSTAR observation in August 2017. It is now the question whether we will (at some time) see a new increase, similar to the one that was observed between 1990 and 1993. It is likely that we see a change in the structure of the local B-field. We propose to continue the monitoring of Her X-1 during Cycle-4 with two observations of 30 ks each (about half a year apart).

Proposal Number: 4024
PI Last Name: Zoghbi
Title:PROBING THE CHANGING REVERBERATION ECHOES
Abstract:Recent data have led to a breakthrough in AGN studies through the detection of relativistic reverberation. These echoes are caused by the delayed response of the reflected emission to a primary illuminating source, providing a powerful tool to probe regions close to the black hole in an unprecedented manner. The properties of the echoes are constant on days timescale, but change over the years. The characteristic timescale of the change, which would suggest a geometry change, is unknown. Here, we propose to observe SW J2127.4 for 350 ks to address this question. With several exposures separated by weeks to months, we will constrain this characteristic timescale and probe changes in the geometry of the system, providing unprecedented details about the disk-corona at the horizon scales.

Proposal Number: 4029
PI Last Name: Rauw
Title:NON-THERMAL X-RAYS FROM MASSIVE COLLIDING WIND BINARIES
Abstract:We propose to measure the hard non-thermal X-ray emission of the colliding wind massive binaries Cyg OB2 #8A and #9, located in the same NuSTAR field of view. Both systems display synchrotron radio emission, indicating the presence of relativistic electrons accelerated in the wind interaction zone. As a result of inverse Compton scattering, a hard non-thermal X-ray emission is expected. NuSTAR is the first mission able to detect this emission and to constrain its properties. The proposed measurements will have a deep impact on the understanding of colliding winds in massive binaries and of the role of such systems in particle acceleration in general.

Proposal Number: 4033
PI Last Name: Turner
Title:MEASURING HARD X-RAY LIGHT ECHOS IN NGC 4051
Abstract:X-ray reprocessing signatures appear in the timing and spectral characteristics of AGN. Especially valuable is the direct measurement of the reverberation delay of the reprocessor in response to X-ray continuum variations: extraction of the shape of the transfer function gives the location and extent of the circumnuclear gas. This is only possible in long observations of rapidly variable, bright AGN. To this end, we request a 300 ks NuSTAR exposure with 160 ks of XMM data, comprising the first joint observation of NGC 4051. NuSTAR opens up the critical window above 10 keV that is dominated by the undiluted light echo from the X-ray reprocessor. The proposed campaign will allow us to directly map the reverberating gas close to the black hole.

Proposal Number: 4034
PI Last Name: Lehmer
Title:A MEASUREMENT OF THE 0.3-30 KEV SPECTRUM OF THE LOW-METALLICITY GALAXY VV114
Abstract:We propose for a 30 ks XMM and 200 ks NuSTAR observation of VV114, a unique low-metallicity galaxy (0.3 Zsol), with high-SFR (SFR = 38 Msol/yr). We will measure ho the shape and normalization of the 0.3-30 keV spectral energy distribution of VV114 compares with more typical solar-metallicity galaxies in the nearby Universe that have SEDs characterized by NuSTAR (e.g., M83, NGC 253, NGC 3256, and NGC 3310). Our observations will provide an important benchmark for how the X-ray SED varies with metallicity, and thus how the X-ray SEDs of galaxies are expected to vary with redshift. This will allow for more informed bandpass and bolometric corrections to high-redshift galaxy studies and population synthesis models, and will inform studies of X-ray heating of the early Universe IGM.

Proposal Number: 4037
PI Last Name: Ichikawa
Title:HOW RAPID DOES AGN DIE? UNVEILING THE DRASTIC AGN LUMINOSITY DROP WITHIN 10^4 YEARS
Abstract:We propose the NuSTAR 3-70 keV observation of a nearby dying active galactic nculeus (AGN) candidate Arp 187. The scientific goal is to constrain the X-ray luminosity of Arp 187 down to low-luminosity regime with < 10^42 erg/s. Our ALMA and VLA images reveal the radio-jet lobe. The optical spectrum also indicates a clear AGN signature originated from the narrow line region with 1 kpc. However, Arp 187 shows neither AGN torus nor radio-jet core emission. From these contradictory results, Arp 187 hosts either an obscured AGN or a dying AGN which dropped its luminosity rapidly over >100 times within 10^4 yrs. The broadband NuSTAR spectra above 10 keV are crucial to break the degeneracy between the obscuration and the intrinsic AGN luminosity drops.

Proposal Number: 4045
PI Last Name: Nowak
Title:USING NUSTAR TO ASSESS THE MASS, SPIN, DISTANCE, AND FE LINE OF 4U 1957+11
Abstract:We propose three, 35 ksec observations of 4U 1957+11, potentially the most rapidly spinning Galactic black hole. With the existing 50 ksec observation, we plan to perform a simultaneous fit to the spectra using modern disk atmosphere models, where we attempt to describe the spectra with a common mass, distance, spin, and system inclination. These results will be compared to and used to 'normalize' a similar fit to existing RXTE spectra. The posterior probably estimates from these fits will be combined with theoretical models of disk color correction factors to make a prediction of the likely range of the black hole system parameters, and help verify that it is indeed a maximally spinning black hole.

Proposal Number: 4048
PI Last Name: Toba
Title:REVEALING THE BLACK HOLE IN THE DUST OBSCURED GALAXY WITH EXTREME RED COLOR
Abstract:We propose the hard X-ray observation with NuSTAR for a curious Dust Obscured Galaxy (DOG). DOGs have been considered as a subset of high-redshift (z~2) ULIRGs and a crucial population for understanding the co-evolution of galaxies and SMBHs. However, the properties of BHs in DOGs have been poorly understood observationally due to the absence of high-sensitivity hard X-ray telescopes. Recently, we discovered a peculiar DOG (ULIRG) whose spectroscopic redshift (z=0.89) is much lower than the typical redshift of DOGs (z~2) and has an extremely red color. Its extreme MIR color and its SED imply the presence of heavily obscured, Compton-thick AGN. The observation proposed here will allow to shed light on the BH properties for ULIRG with extremely red color.

Proposal Number: 4060
PI Last Name: Ingram
Title:TESTING RELATIVISTIC PRECESSION AROUND THE ACCRETING BLACK HOLE IN GRS 1915+105 WITH NUSTAR AND NICER
Abstract:We propose a 30 ks ToO, contemporaneous with a pre-approved 30 ks NICER ToO, to observe a low frequency quasi-periodic oscillation (QPO) from the accreting black hole (BH) GRS 1915+105. We will use QPO phase-resolved spectroscopy to test for QPO phase dependent changes in the shape of the reflection spectrum and disc temperature indicative of relativistic precession. The unique combination of NICER and NuSTAR will allow the first joint analysis of disc, iron line and reflection hump modulations. We will trigger from MAXI, plus Swift/XRT pointings, and aim to supplement our core science goals with multi-wavelength observations.

Proposal Number: 4061
PI Last Name: Brandt
Title:IDENTIFYING INTRINSICALLY X-RAY WEAK AGNS WITH NUSTAR
Abstract:Luminous X-ray emission is considered a universal property of AGNs. There are few intrinsically X-ray weak AGNs reliably identified so far. Such systems may exist preferentially in BAL quasars, where it is challenging to ascribe the observed X-ray weakness to absorption vs. intrinsic X-ray weakness. Via stacking analysis, our exploratory 21-32 ks NuSTAR observations have demonstrated the unique capability of NuSTAR to discover a significant fraction of intrinsically X-ray weak AGNs among BAL quasars. Thus we propose to obtain 90 and 100 ks additional observations for PG 1254 and PG 1001, respectively, to identify intrinsically X-ray weak AGNs individually and constrain the fraction of such objects among the luminous BAL quasar population.

Proposal Number: 4078
PI Last Name: Yamaguchi
Title:THE SUPERNOVA REMNANT 3C 397: CONSTRAINING PHYSICS OF TYPE IA SUPERNOVAE IN THE SINGLE-DEGENERATE SCENARIO
Abstract:We propose joint NuSTAR-XMM observations of 3C 397, a Type Ia supernova remnant (SNR) likely originating from a near-Chandrasekhar-mass white dwarf in a single-degenerate progenitor system. Suzaku observations of this SNR detected strong emission of the Fe-peak elements (Cr, Mn, Fe, Ni) and indicated remarkably high mass ratios of Mn/Fe and Ni/Fe. Under the auspices of this proposal, we will reveal the spatial distribution of these elements to constrain the properties of the progenitor and the supernova explosion mechanism. NuSTAR is particularly suitable for this study, thanks to the highest sensitivity to Ni K-alpha emission at 7.6 keV among currently operating X-ray missions. XMM-Newton provides a perfect complement to NuSTAR, by enabling clear detection of Cr and Mn lines.

Proposal Number: 4085
PI Last Name: Margutti
Title: DETAILED MAPPING OF EXTREME MASS LOSS WITH COORDINATED NUSTAR-XMM OBSERVATIONS
Abstract: Contrary to expectations from current stellar evolutionary models, recent observations uncovered the ejection of shells of material by massive stars in the years before the supernova (SN) explosion. The physical mechanism behind the impulsive mass ejection synchronized with the stellar core-collapse is unclear. Here we propose a coordinated NuSTAR-XMM effort to map the evolution of the broad-band X-ray spectrum of 1 nearby (d<50 Mpc) strongly interacting SN and enable progress. Our program has the immediate goal to characterize the medium around strongly interacting SN, which originate from stellar progenitors with the most extreme mass loss before explosion.

Proposal Number: 4096
PI Last Name: Neilsen
Title: NUSTAR-NICER OBSERVATIONS OF BLACK HOLE TRANSIENTS
Abstract:ith its excellent hard X-ray sensitivity, spectral resolution, and timing, NuSTAR has revolutionized our view of black hole accretion, particularly through studies of Compton scattering and relativistic reflection. But we still have yet to attain a fully self-consistent model of the accretion flow, in part because of the difficulty of constraining seed photons: thermal emission from cool, faint disks. With the launch of NICER in June 2017, we took a great step forward. NICER is to soft X-rays what NuSTAR is to hard X-rays, and together they can produce incredibly tight constraints on the geometry of the inner disk, corona, and their interactions. We propose 5x20 ks coordinated observations of a black hole transient with NuSTAR and NICER to exploit these groundbreaking capabilities.

Proposal Number: 4099
PI Last Name: Xu
Title: THE BRIGHT HARD STATE OF A TRANSIENT BLACK HOLE BINARY IS THE ACCRETION DISK TRUNCATED?
Abstract: We propose to undertake a 60 ks NuSTAR target-of-opportunity observation of a new or known black hole transient during a bright, hard outburst phase. The goals of this program are to 1) determine whether the accretion disk is truncated in the bright hard state via modeling the disk reflection spectrum 2) test an apparent anti-correlation between winds and jets in soft and hard states by making a very sensitive search for winds in a hard state 3) searching for quasi-periodic oscillations (QPOs) in the power spectrum and compare with theoretical models. This observation will be supported by a network of ground-based observatories, and X-ray monitoring.

Proposal Number: 4100
PI Last Name: Privon
Title:DOES A MONSTER LURK IN THE ATOMS FOR PEACE GALAXY?
Abstract:AGN feedback is a key component of the standard paradigm for the merger-driven transformation of blue late-type galaxies into red early-type galaxies. AGNs have been argued to show large (>3 dex) fluctuations in luminosity on 10^4-10^5 year timescales, which will influence the transfer of energy/momentum for clearing the interstellar medium. The prototypical merger remnant NGC 7252 has an extended [O III] nebulae which is consistent with AGN photoionization. However, the AGN is presently undetected, suggesting it is either heavily obscured or has decreased in luminosity by >3 dex. We propose NuSTAR observations to perform a sensitive search for active BH accretion. NGC 7252 contains the lowest luminosity light echo discovered and is a key probe of AGN variability at lower luminosities.

Proposal Number: 4101
PI Last Name: Tomsick
Title: THE SPIN RATES OF BLACK HOLES IN X-RAY BINARIES
Abstract: With its measurements of the reflection components from accretion disks in black hole (BH) binaries, NuSTAR has made significant progress in constraining BH spins. Determining BH spins is important for probing regions of strong gravity, investigating connections between spin and relativistic jets, and for comparing the X-ray binary spin distributions to those inferred for the BH-BH inspiral events. To continue this work, we propose a 50 ks TOO observation of any BH transient that has not been previously observed by NuSTAR. We will use Swift/XRT monitoring to trigger the NuSTAR observation if a BH transient shows evidence that it is making a transition from the hard state to the intermediate state.

Proposal Number: 4107
PI Last Name: Boissay Malaquin
Title:INVESTIGATION ON FAIRALL 51 WITH NUSTAR AND CHANDRA/HETG
Abstract:We propose an observation of the particularly intriguing polar-scattered Seyfert 1 Fairall 51 with NuSTAR (120 ks), divided in two periods of 60 ks separated by about 8 months, to be coordinated with our two Guaranteed Time Observations (GTO) with Chandra/HETG (120 ks each, so 240 ks of total exposure). Timing and spectral analyses of these joint observations will put constraints on the characteristics of reflection from both the accretion disk near the black hole and from more distant material, on the presence and origin of a possible broad iron line, on the spin of the black hole, on the inclination angle, on the physical properties of the hot corona, on the structure and properties of the warm absorbers, and on the origin of the potential soft excess.

Proposal Number: 4127
PI Last Name: Nardini
Title:EDGE-ON DISK OR RELATIVISTIC WIND? THE CASE OF PG 1402+261
Abstract:We propose a simultaneous observation with NuSTAR (150 ks) and XMM (75 ks) of the radio-quiet Narrow-Line Seyfert 1 galaxy PG 1402+261 (z=0.164), which showed significant spectral complexity at 6-9 keV in a previous XMM snapshot. This can be interpreted as either a very strong, extremely broadened FeK emission line from the accretion disk, or the signature of a high-column, high-ionization disk wind. By pinpointing the intensity and shape of the continuum beyond this puzzling feature, NuSTAR will allow us to distinguish between the two scenarios or disentangle their relative contribution. Indeed, PG 1402+261 is a high-luminosity (and possibly more extreme) equivalent of other NLS1s where both strong reflection and ultra-fast outflows have been recently revealed.

Proposal Number: 4129
PI Last Name: Tanaka
Title:NUSTAR REVEALS PARTICLE ACCELERATION UP TO THE KNEE IN HESS J1641-463
Abstract:We propose a 100-ks observation of an unidentified TeV gamma-ray source, HESS J1641-463. This source has the hardest spectrum ever detected in the TeV band. The hard spectrum is best interpreted as neutral pion decay emission with the parent proton spectrum extending up to PeV energies. If so, in the NuSTAR band, we can expect synchrotron radiation from secondary electrons which are decay products of charged pions generated at the same time as neutral pions. Probing the highest energy end of the proton spectrum through the emission, we can obtain conclusive evidence that HESS J1641-463 is indeed accelerating particles up to PeV energies.

Proposal Number: 4133
PI Last Name: Van Den Eijnden
Title:THE MAGNETIC FIELD OF THE YOUNGEST ACCRETING NEUTRON STAR
Abstract:No direct measurements currently exist of the magnetic field of an accreting neutron star at its birth. We propose to use the unparalleled NuSTAR hard X-ray sensitivity to observe the youngest known accreting neutron star low-mass X-ray binary, the puzzling Cir X-1 with an age of 5000 years. With a 60 ks observation in the source's low flux state, we will constrain Cir X-1's accretion geometry, aiming for a first estimate of the magnetic field in this very young neutron star, and characterise its ill-understood persistent low flux state.

Proposal Number: 4139
PI Last Name: Lanzuisi
Title:THE HIGH-ENERGY CUT-OFF IN HIGH-Z/HIGH-L QSO
Abstract:We propose NuSTAR observations of two bright (FX>5 10^-13 cgs, LX>10^46 erg/s) radio-quiet QSOs at z>2, plus short XMM exposures for each of them: our total time request is 320k NuSTAR and 70ks XMM. By looking at rest-frame energies up to 300 keV, our goal is to measure unambiguously the presence of spectral cut-offs at rest-frame energies up to E_c=500 keV. This is not possible for local targets, where NuSTAR is just sensitive to E_c<250 keV. The two brightest sources of a sample of four have been successfully observed in Cycle 3. These observations allowed to measure for the first time E_c in distant, luminous QSOs. The proposed observations will allow to build a a small but unique sample of high-z, high-LX QSOs with accurate E_c measurements, to test current coronal models.

Proposal Number: 4147
PI Last Name: Enoto
Title:MAGNETIC ENERGY DISSIPATION IN MAGNETAR OUTBURSTS OBSERVED BY NUSTAR AND NICER
Abstract:We propose NuSTAR ToO observations (total 80 ks) of magnetar outbursts coordinated with the new soft X-ray timing instrument NICER. The evolution of the pulse profile and spectrum over the decay phase of a magnetar outburst provide crucial insight into the magnetic energy dissipation process in magnetars. Simultaneous coverage of the NICER (0.2-12 keV) and NuSTAR (3-79 keV) bands is essential for understanding the soft-thermal surface radiation and non-thermal magnetospheric emission. With the unprecedented sensitivity in the soft X-ray band of NICER, a pre-approved ToO can constrain the thermal evolution in the soft X-ray band. The addition of NuSTAR will allow simultaneous tracking of the hard X-ray flux -- a crucial element to understand the physics of magnetars.

Proposal Number: 4149
PI Last Name: Walton
Title:EXTREME DISK REFLECTION IN THE AGN IRAS 09149-6206
Abstract:Previous X-ray observations of the AGN in IRAS 09149-6206 show evidence for some of the strongest reflection from the accretion disk observed among local, Compton-thin AGN. The unusually high reflection fraction indicates an extreme accretion geometry in which the intrinsic continuum emission experiences strong gravitational light bending, resulting in a broadband X-ray spectrum dominated by reflection from the inner accretion disk. We request a coordinated broadband X-ray observation of this remarkable source with XMM (70ks) and NuSTAR (100ks). The quality of the data will enable us to robustly confirm the strong reflection, and utilize the full potential of the latest models to measure the black hole spin.

Proposal Number: 4154
PI Last Name: Strohmayer
Title:NICER + NUSTAR: BROAD-BAND SPECTROSCOPY OF X-RAY BURSTS FROM 4U 1636-536
Abstract:Type I X-ray bursts are brief (10 - 100 s) energetic flashes powered by nuclear burning of material accreted onto the surface of a neutron star. They strongly irradiate the accretion environment, inducing a wide range of interesting physical processes. For example, X-ray reprocessing (often termed ``reflection'') from the accretion disk produces emission features in the soft X-ray band. The latter provides unique clues to disk structure and dynamics. A broadband X-ray observation could trace all these features in detail, and study how the accretion disk responds to an X-ray burst. The combination of NICER and NuSTAR will provide a unique broadband view of the impact of bursts on accretion disk dynamics. We propose a 100 ks simultaneous observation of the prolific bursting source 4U 1636-53

Proposal Number: 4157
PI Last Name: Petrucci
Title:NUSTAR/XMM MONITORING OF THE EXTREME NARROW LINE SEYFERT MRK 359
Abstract:We propose to perform a unique NuSTAR/XMM monitoring with 5 repeated observations of 50 ks spaced by a 2-3 days of the extreme Radio-Quiet Narrow line Seyfert 1 galaxy Mrk 359. This will permit 1) to correctly disentangle the different spectral components present in this energy band, and 2) to reveal their complex interdependences and variability behavior. This study will allow us i) to constrain the physical parameters of the Comptonizing coronae responsible for the bulk of the X-ray emission ; ii) to investigate the nature of the soft X-ray excess and differentiate between multiple origins; iii) to put firm conclusions on the distance, nature and geometry of the reflecting material(s). Such monitorings appear as the best strategy to reach these goals.

Proposal Number: 4159
PI Last Name: Degenaar
Title:LINKING JET SUPPRESSION TO ACCRETION GEOMETRY
Abstract:The strong connection between the X-ray and radio properties of low-mass X-ray binaries (LMXBs) reflects a direct link between the accretion inflow and outflow. Most of our current knowledge on this is based on LMXBs in hard X-ray states. However, neutron star LMXBs in soft X-ray states reveal intriguing differences in their radio properties that can provide new information about the destruction of jets. We propose a single NuSTAR observation of each of the two neutron star LMXBs GX 9+9 (40 ks) and GX 9+1 (20 ks), which persistently accrete in a soft state. Through broad-band and reflection modeling we aim to explain their very weak radio emission compared to other neutron stars that accrete at similar X-ray luminosities.

Proposal Number: 4160
PI Last Name: Wilms
Title:SIMULTANEOUS NUSTAR-EROSITA OBSERVATIONS OF NGC 7793-P13
Abstract:The study of ultraluminous X-ray sources (ULXs) has been revolutionized by the detection of pulsations from three objects, indicating that they contain neutron stars that radiate apparent luminosities of up to 500 L_Edd. They therefore pose an immense challenge to our understanding of accretion physics. In order to study the soft emission from these objects, we have been approved a 60 ks eROSITA observation of the pulsating ULX NGC 7793-P13. We ask for a simultaneous 40 ks NuSTAR observation, with the aim of constraining the spectral and timing behavior of the source and providing crucial cross-calibration information.

Proposal Number: 4161
PI Last Name: Degenaar
Title:TESTING DISK TRUNCATION FOR ACCRETING NEUTRON STARS
Abstract:It is commonly assumed that the accretion disk in low-mass X-ray binaries (LMXBs) moves significantly away from the black hole or neutron star when the X-ray luminosity decays below ~E-2 of the Eddington limit (Ledd). However, there is virtually no observational data to test this key aspect of accretion disk physics. Using a single 60-ks NuSTAR ToO observation and 11 ks of Swift/XRT monitoring, we propose to exploit the proximity and strong reflection features of the neutron star LMXB 4U 1608-52 to measure the location of its inner disk at a luminosity of ~E-3 Ledd. Comparing this with our previous NuSTAR observation obtained at E-2 Ledd, where we found the disk very close to the neutron star, we can directly test the disk truncation paradigm.

Proposal Number: 4170
PI Last Name: Uchida
Title:EXTENDED HARD X-RAY EMISSION DISCOVERED IN THE MIDDLE-AGED SUPERNOVA REMNANT W44
Abstract:We propose a NuSTAR observation of the southern part of a middle-aged supernova remnant W44, from which we have found a previously unknown hard diffuse emission. The emitting region is located near the shell interacting with a molecular cloud, implying a nonthermal bremsstrahlung radiation in dense environments. The XMM spectrum is well fitted with a harder power law than that of a nearby pulsar wind nebula. The measured photon index is roughly consistent with the nonthermal bremsstrahlung scenario. The energy band covered by NuSTAR is essential to disentangle possible emission mechanisms of the mysterious south faint structure. The 100-ks NuSTAR spectrum is enough to support or reject the scenario. This observation will open a new window to nonthermal phenomena in W44.

Proposal Number: 4172
PI Last Name: Li
Title:ENLARGING THE POPULATION OF NON-THERMAL X-RAY PULSARS
Abstract:We propose to observe theoretically-selected gamma-ray pulsars to search for their hard X-ray counterparts. Enlarging the yet very small population of hard X-ray pulsators is essential to understand their individual multi-frequency behaviors, as well as their global properties.

Proposal Number: 4174
PI Last Name: Hemphill
Title:THE FIRST NUSTAR OBSERVATION OF 4U 1907+09
Abstract:The persistent X-ray pulsar and cyclotron line source 4U 1907+09 has not been observed in nearly a decade. Recently, several X-ray pulsars have been shown to exhibit a secular decay in their cyclotron line energy on timescales of months to years. 4U 1907+09 is a prime candidate to search for this kind of behavior, due to its persistent flux level and its two cyclotron lines well within the NuSTAR band. It is additionally of interest due to its moderate X-ray flux, which likely places it in the 'low sub-critical' accretion regime, an important area for testing new developments in the modeling of X-ray spectra from accreting pulsars.

Proposal Number: 4175
PI Last Name: Okon
Title:EXPLORATION OF NONTHERMAL BREMSSTRAHLUNG FROM SUB-RELATIVISTIC PARTICLES ACCELERATED IN SUPERNOVA REMNANT W28
Abstract:We propose a 100-ks NuSTAR observation of Supernova Remnant W28. In Suzaku data, we detected the FeI Ka line, which can probably be attributed to K-shell ionization of Fe in an ambient molecular cloud by sub-relativistic particles accelerated in W28. In the hard X-ray band, nonthermal bremsstrahlung from the same population of the particles is expected. A NuSTAR observation enables us to detect nonthermal bremsstrahlung, which is direct evidence of sub-relativistic particles accelerated in W28. Furthermore, we can determine whether the particles are electrons or protons based on the equivalent width of the FeI Ka line with respect the nonthermal bremsstrahlung continuum. Also, the flux and slope of the bremsstrahlung can constrain the amount and spectrum of the particles.

Proposal Number: 4179
PI Last Name: Hailey
Title:NUSTAR OBSERVATION OF POLARS - PROBING THE X-RAY POINT SOURCE POPULATION IN THE GALACTIC RIDGE
Abstract:The proposed NuSTAR observations are the first crucial steps to resolve one of the long-standing problems in high-energy astrophysics - the source populations that comprise the Galactic ridge X-ray emission (GRXE). Broad-band X-ray spectroscopy of six nearby polars (highly magnetized cataclysmic variables) with modest exposure (20 ksec per source) will test our hypothesis that the GRXE is dominated by a large number of polars whose mean white dwarf mass is consistent with those of intermediate polars and CVs (observed by SDSS) at 0.8-0.9 solar mass.

Proposal Number: 4181
PI Last Name: Pradhan
Title:UNVEILING THE ACCRETION PHYSICS AND GEOMETRY IN OAO 1657-415 WITH NUSTAR
Abstract:We propose a 80 ks observation of the accreting X-ray pulsar, OAO 1657-415, in the brightest phase of its orbital cycle (phase 0.65-0.75), with a major aim of investigating the much debated cyclotron line at ~36 keV with NuSTAR, which provides unprecedented sensitivity for such studies. Its large effective area will permit detailed spin phase-resolved spectral analysis and possible variations of CRSF energy with luminosity, for the first time for OAO 1657-415, helping us understand accretion physics/geometry. The magnetic field strength will also allow us to investigate the contribution of magnetic/centrifugal gating to dips/flares. Through deep spectral studies, we will characterize the frequent flares. Intensity/energy-resolved pulse profiles will map hard X-ray beaming and clumpy winds.

Proposal Number: 4185
PI Last Name: Satyapal
Title:WISE DISCOVERY OF THE LARGEST SAMPLE OF OBSCURED DUAL AGNS: A NUSTAR FOLLOW-UP
Abstract:Despite decades of searching, observationally confirmed cases of dual AGNs are extremely rare, and most have been discovered serendipitously. Using the all-sky WISE survey, we identified a population of over 200 interacting galaxies that display extreme red mid-IR colors thus far exclusively associated in extragalactic sources with powerful AGNs, despite showing no signatures of activity in the optical. We were recently awarded 340ks of Chandra time to observe the 15 brightest MIR-selected dual AGN candidates with separations of a few kpc, of which 8 display two nuclear X-ray point sources consistent with dual AGNs.We propose follow-up NuSTAR observations of our sample to constrain the intrinsic absorption of the systems and determine the AGN bolometric luminosity.

Proposal Number: 4191
PI Last Name: Jiang
Title:CONFIRMING THE ULTRA-FAST OUTFLOW IN NLS1 WKK 4438
Abstract:A 75ks Suzaku observation and a 20ks Nustar short look of the Narrow-Line Seyfert 1 (NLS1) WKK 4438 show tantalizing evidence of a broad blueshifted Fe absorption line at 10 keV in addition to the Fe K emission line at 6.4keV. It corresponds to a highly ionized ultra-fast outflow (UFO) with velocity faster than 0.3c. A 100ks NuSTAR observation will be able to confirm the existence of such a strong outflowing wind. From our proposed observation, we will be able to study the inner structure of the AGN including the high accretion rate disk and the origin of the X-ray UFO.

Proposal Number: 4202
PI Last Name: Vincentelli
Title:NEUTRON STARS MULTI-LAMBDA FAST VARIABILITY: PROBING DISK-JET CONNECTION
Abstract:Fast optical-infrared photometry applied to black hole X-ray binaries has now revealed its great potential and has shown to be one of the best ways to probe the jet in its innermost regions. Nonetheless Neutron Star X-ray binaries, which are clearly dominated by the jet at IR wavelength, have not been studied yet with such approach. Here we propose participate to a simultaneous multiwavelength campaign of the Neutron Star Low Mass X-ray binary 4U 1728-34. We ask to perform 6 (20 ks apiece) pointings to be matched by 6 XMM/VLT observations with the aim of studying the simultaneous IR/X-ray fast variability of this system. This data will allow us to study the disc-jet interaction in different accretion regimes and to search for, and investigate the differences between jet properties in blac

Proposal Number: 4210
PI Last Name: Bellm
Title:NUSTAR CAN DISCOVER SPECTRAL COMPONENTS IN THE AFTERGLOWS OF ULTRA-LONG GRBS
Abstract:Ultra-long Gamma-Ray Bursts (ULGRBs) produce a gamma-ray transient more than several thousand seconds long followed by a decaying X-ray afterglow. Much remains uncertain about these recently-discovered events, most notably whether they are an extreme tail of normal long GRBs or represent a new class entirely. Our NuSTAR TOO observations of the afterglow of ULGRB 130925A unveiled a rich and unexpected phenomenology that may point towards the origin of these mysterious events. NuSTAR's sensitivity and wide bandpass makes it the best instrument available to constrain multiple spectral components in GRB afterglows. We request one NuSTAR TOO for an ULGRB discovered in Cycle 4 to characterize its afterglow spectrum.

Proposal Number: 4221
PI Last Name: Sobolewska
Title:COMPTON THICK ENVIRONMENT OF YOUNG RADIO SOURCES CONSTRAINED WITH NUSTAR
Abstract:We propose to observe with NuSTAR two young radio sources: PKS 2021+614 and PKS 1511+0518 (300-400 years old, linear radio size 7-16 pc). Our ongoing studies of young radio sources indicate that the X-ray obscured sources (including the two proposed targets) have smaller radio structures than the X-ray unobscured sources with the same 5 GHz radio power. This has far reaching implications for the initial evolution of AGN radio jets and AGN/galaxy co-evolution. Confirming and exploring this result requires hard X-ray observations (>10 keV). Among the current X-ray telescopes operating at energies >10 keV, only NuSTAR has capabilities required to detect and study our targets.

Proposal Number: 4222
PI Last Name: Wik
Title:TOWARD A BETTER CENSUS OF BLACK HOLES AND NEUTRON STARS IN THE DISK OF M31
Abstract:The sensitivity and spatial resolving power of NuSTAR have allowed the study of individual neutron stars and black holes in other galaxies at hard energies for the first time, but they are nearly all more luminous than the population of sources probed in detail in the Milky Way. With a NuSTAR legacy survey of M31, we have finally detected sources at these lower luminosities, allowing a direct comparison of M31's neutron star and black hole accretors to the Milky Way's in the crucial window above 10 keV. We propose 4 additional pointings of M31 to increase the number of 10^37 erg/s detected at hard energies to ensure the shape of the luminosity function is more robust to low number fluctuations. Also, we will classify the brightest sources, which is only possible with hard band data.

Proposal Number: 4223
PI Last Name: Shaw
Title:THE NATURE OF THE CATACLYSMIC VARIABLE POPULATION IN THE GLOBULAR CLUSTER NGC 6397
Abstract:Globular clusters (GCs) are efficient sites for the formation of compact binary systems through close stellar encounters. Cataclysmic variables (CVs) in globular clusters exhibit vastly different properties to their Galactic field counterparts, leading to the suggestion that the majority of CVs in GCs are formed as products of these encounters. The unusual properties of GC CVs are thought to be evidence of belonging to the magnetic class of CVs. The X-ray spectrum of magnetic CVs is dominated by a high temperature (>10keV) thermal plasma component, requiring telescopes with hard X-ray capabilities to measure. We propose a 100ks observation of the CVs in NGC 6397 with NuSTAR, allowing us to constrain the nature of a GC CV population for the first time.

Proposal Number: 4227
PI Last Name: Younes
Title:NUSTAR OBSERVATION OF THE MAGNETAR 1RXS J170849.0-400910
Abstract:Magnetars are young isolated neutron stars with bright broad-band 0.5-200 keV persistent X-ray emission, caused by the decay of the extremely high internal and external magnetic field. Here we propose a simultaneous NuSTAR+XMM-Newton observation of one of the brightest magnetars, 1RXS~J170849.0$-$400910. This source shows the most drastic changes in pulse profile shape with energy as well as the most complex spectral variations with phase. The proposed observation will allow us to perform broad-band high-sensitivity fine-resolution phase-resolved spectroscopy, crucial to disentangle the contribution from different spectral components in each phase bin. Such analysis would be the ultimate test for the currently available theoretical models for X-ray emission production in magnetars.

Proposal Number: 4229
PI Last Name: Hemphill
Title:IS THE CYCLOTRON LINE ENERGY IN 4U 1538-522 INCREASING WITH TIME?
Abstract:The persistent X-ray pulsar 4U 1538-522 has been observed by nearly every X-ray satellite since its discovery by Uhuru. Recently, an increase of ~1.5 keV in its cyclotron line energy was reported by Hemphill et al. (2016), based on an analysis of the RXTE and Suzaku data. However, the increased line energy is only seen by a single satellite (Suzaku), as no other missions at the time were capable of measuring the line with sufficient precision. We request a 40 ks NuSTAR observation to confirm and constrain this trend. A NuSTAR observation in AO4 would also allow us to apply newly-developed physical models for the X-ray spectra of accreting neutron stars, shedding light on the physical processes that drive sub-critical accretion on neutron stars.

Proposal Number: 4230
PI Last Name: Corbet
Title:PROPERTIES & CAUSES OF SUPERORBITAL PERIODS IN SUPERGIANT X-RAY BINARIES
Abstract:Five wind-accreting supergiant high-mass X-ray binaries are now known to exhibit superorbital periods. Unlike systems that possess persistent accretion disks, the cause of this modulation is unknown, although several models have been proposed. We were awarded NuSTAR time on one of these systems (IGR J16493-4348) in Cycle 1 to compare superorbital maximum and minimum. Surprisingly, we see differences from an RXTE study of the superorbital modulation in 2S 0114+650. We now request NuSTAR observations at superorbital maximum and minimum of the three other known members of this class so we can determine global modulation properties and disentangle the effects of inclination angle and orbital period. Determining the superorbital mechanism may yield insights into supergiant wind properties.

Proposal Number: 4231
PI Last Name: Ajello
Title:BL LAC OBJECTS AT THE HIGHEST REDSHIFTS
Abstract:For a long time high-redshift BL Lac objects were deemed not to exist. Fermi showed us that there is relevant population of BL Lacs with redshift beyond 1.0. Some of them belong to the HSP class and are among the hardest gamma-ray sources detected by Fermi showing emission up and beyond 100 GeV. This makes them the most luminous BL Lacs ever detected and rates them among the most powerful accelerators in the Universe. We plan to observe the extreme BL Lac 2FHL J2146.6-1345 simultaneously with NuSTAR, XMM-Newton, and SARA. This will provide unprecedented coverage of the synchrotron peak from nIR to hard X-ray allowing us: to understand the nature and the energetic of this object, to answer long-standing questions on the blazar sequence and to use it as probe of the extragalactic background.

Proposal Number: 4245
PI Last Name: Wik
Title:MAPPING THE TEMPERATURE STRUCTURE ACROSS TWO SHOCKS IN THE MASSIVE MERGING CLUSTER ABELL 2146
Abstract:The galaxy cluster A2146 is undergoing a major merger and hosts two huge, bright Mach 2 shock fronts, which provide a unique opportunity to measure the electron-ion thermal equilibration timescale along with other key transport phenomena. We propose to characterize the heating mechanism of the electrons by measuring the temperatures behind the two shocks in A2146. Such measurements are extremely difficult for other observatories due to the high temperatures involved; we have pioneered a method combining Chandra and NuSTAR data to do this, and the upstream shock in A2146 is the best remaining target for this test. We will also constrain the highest temperatures throughout the cluster and search for dark matter lines and non-thermal emission.

Proposal Number: 4251
PI Last Name: Ricci
Title:DRILLING THROUGH THE DUST OF IRAS 08572+3915: CHARACTERIZING THE POWER SOURCE OF THIS JWST EARLY RELEASE SCIENCE TARGET
Abstract:Galaxy mergers are thought to trigger strong accretion onto supermassive black holes, during a phase in which the system is heavily obscured. However, the dynamics of this process, and of the possible feedback from the active galactic nucleus, are still largely unknown. We propose here a joint NuSTAR/XMM-Newton (200/112ks) observation of the most energetic, embedded galactic nucleus in the local Universe, which will be observed by JWST as part of an approved Early Release Science proposal. The combination of state-of-the-art X-ray observations and high spatial resolution IR spectroscopy will allow us to define the energy budget of the system, to assess the impact of AGN activity in its surrounding, and to study in unprecedented detail this fundamental phase of black hole growth.

Proposal Number: 4253
PI Last Name: Marchesi
Title:HEAVILY OBSCURED AGN: THE PHYSICS BEHIND THE OBSCURATION
Abstract:The X-ray spectral analysis of Compton thick (CT-, i.e., having intrinsic obscuration NH>1E24 cm^-2) active galactic nuclei (AGN) is key to understand the physics of the obscuring material surrounding accreting supermassive black holes. We propose to target with a combined NuSTAR/XMM-Newton observation three candidate CT-AGN selected from the BAT 100-month survey. Thanks to the excellent count statistics, we will be able to assess if these sources are in fact CT-AGN. We will also constrain several spectral parameters (e.g., relative importance of the scattered component versus the direct one, geometry of the obscuring torus, equivalent width of the Iron emission line). This analysis will refine our knowledge on the true intrinsic fraction of CT-AGN and their contribution to the CXB.

Proposal Number: 4261
PI Last Name: Perez
Title:OPTIMIZING SENSITIVITY TO STERILE NEUTRINO DARK MATTER IN THE GALACTIC CENTER
Abstract:A compelling dark-matter candidate is the keV-mass sterile neutrino, which can be tested by X-ray line signals from their radiative decays. NuSTAR observations have been used to place strong constraints on their properties. For example, the proposing team exploited archival NuSTAR observations of the Galactic Center, using 0-bounce photons to search for diffuse emission from dark matter. Here we propose dedicated NuSTAR observations (100 ks) just off the Galactic plane. Relative to our previous work, there is only a slight reduction in the dark-matter signal, while there is a large reduction in the background and attendant systematic uncertainties. We project that these observations, analyzed by our proven team, will lead to unprecedented ensitivity to sterile neutrino dark matter.

Proposal Number: 4270
PI Last Name: Principe
Title:X-RAY FLARES FROM YOUNG STARS AND THE SUN: BRIDGING THE GAP WITH NUSTAR+CHANDRA
Abstract:It is widely accepted that the coronae of pre-main sequence (pre-MS) stars constitute scaled-up versions of the solar corona. However, the potential hard (10-100 keV) non-thermal emission components of pre-MS flares, and the link between such emission and the softer thermal emission accessible to Chandra and XMM, remain unstudied. We propose a 90 ks NuSTAR observation simultaneous to our approved Chandra gratings observation of V773 Tau, one of the brightest and most energetically flaring pre-MS X-ray sources. By elucidating the connection between hard, non-thermal X-ray emission and softer, thermal emission, these observations will provide an essential test of models invoking scaled-up solar magnetic activity to explain the origin of X-ray emission from pre-MS stars.

Proposal Number: 4273
PI Last Name: Koss
Title:USING THE SPECTRAL CURVATURE TO FIND COMPTON-THICK AGN AMONG THE FAINTEST SWIFT BAT SOURCES
Abstract:We propose Nustar observations of 15 candidate Compton-thick (CT) AGN using a new metric, the spectral curvature (SC) above 10 keV, to identify CT AGN in low-quality Swift BAT X-ray data from the deepest 105-month all sky maps. Our initial survey of the 70-month data found that the majority of SC selected AGN are indeed CT (7/9). The proposed sensitive, broadband X-ray observations will allow us to confirm their reflection-dominated nature, study the iron line morphology, and constrain the absorbing column and reflection. The shape of the X-ray background requires a significant population of heavily obscured AGN and this flux-limited sample will improve our understanding of this important population by providing detailed study of some of the nearest examples.

Proposal Number: 4274
PI Last Name: Vulic
Title:THE GIANT ELLIPTICAL GALAXY HIDING IN OUR BACKYARD: THE RESOLVED X-RAY BINARY POPULATION IN MAFFEI 1
Abstract:As NuSTAR enters its sixth year of operations, it has yet to perform a deep observation of an elliptical galaxy to study the low-mass X-ray binary (LMXB) population associated with older stellar ages. Maffei 1 is the nearest giant elliptical galaxy at 3.4 Mpc and as such provides a unique environment to investigate the accreting black hole (BH) and neutron star (NS) populations in the sensitive E>10 keV bandpass. Due to its proximity, it is the only elliptical where the resolved X-ray binary (XRB) population can be studied at hard X-ray energies until a next generation hard X-ray telescope is flown. We request a 200 ks NuSTAR observation of the giant elliptical galaxy Maffei 1 to study the formation channels of NS and BH populations both in globular cluster (GC) and field environments.

Proposal Number: 4278
PI Last Name: Reynolds
Title:CONSTRAINING THE RELATIVISTIC OUTFLOW IN THE MICRO-QUASAR GRS 1758-258
Abstract:We propose a 50 ks observation of the Galactic microquasar GRS 1758-258 with NuSTAR, to obtain a high quality hard X-ray spectrum in the low-hard state. An observation with Suzaku has revealed the presence of a relativistic wind (v ~ 0.1c). Here we aim to utilize the excellent hard X-ray sensitivity of NuSTAR to constrain the properties of this outflow, and how it relates to the observed accretion flow geometry. As this system is known to power large radio jets, its study will aid our understanding of the conditions necessary for the formation of relativistic outflows and how these relate to the accretion geometry in the low-hard state.

Proposal Number: 4284
PI Last Name: Hamaguchi
Title:DETECTION OF NON-THERMAL X-RAY EMISSION FROM GAMMA2 VELORUM
Abstract:Our NuSTAR observations of two massive colliding wind binary systems presented clear evidence of high-energy, non-thermal emission, which probably originate from inverse-Compton (IC) of stellar photons by high-energy electrons accelerated at the wind-wind colliding (WWC) shocks. However, the observed emission is nearly constant unlike the WWC thermal emission, and this is not expected from the standard IC mechanism. To understand the emission mechanism, we need more colliding wind binary systems with different stellar parameters. We propose two NuSTAR observations of another colliding wind binary system, gamma2 Velorum, which shows signatures of WWC X-ray activity and has a GeV gamma-ray counterpart, to detect high-energy non-thermal emission.

Proposal Number: 4285
PI Last Name: Glesener
Title:INVESTIGATION OF IMPULSIVE HEATING OF ACTIVE REGIONS IN THE SOLAR CORONA
Abstract:Our goal is to investigate the solar coronal heating problem, specifically the role of small solar flares in explaining how the Sun s corona is consistently heated to millions of degrees. To this aim, we will observe solar active regions with long enough integrations to detect faint signatures of small flares and will quantify their contributions to the heating of these particular regions. We will also combine NuSTAR measurements with those from novel solar-observing telescopes operating the extreme ultraviolet X-ray range to obtain the most sensitive measurements to date of flare heating of the corona. With these coordinated observations we will search for the weak high-temperature (>5MK) and non- thermal emission expected from impulsive energy release models.

Proposal Number: 4288
PI Last Name: Hamaguchi
Title:MONITORING THE EXTREMELY HARD X-RAY EMISSION FROM ETA CARINAE TOWARD PERIASTRON
Abstract:The massive stellar binary system, eta Carinae, drives strong shocks by collision of winds from two stars. From NuSTAR observations of the star performed between 2014-2017, we found definitive evidence for extremely hard, non-thermal X-ray emission. Our current best explanation of this component is the inverse-Compton (IC) of seed stellar photons that are scattered by GeV electrons accelerated by the 1st-order Fermi mechanism at the WWC shocks. However, this emission did not brighten before periastron in 2014, though it is expected from the standard IC mechanism. To understand the emission mechanism, we propose another NuSTAR observation of eta Carinae in AO4 when the thermal X-ray emission is expected to increase gradually toward the next periastron passage.

Proposal Number: 4294
PI Last Name: Wolff
Title:NUSTAR OBSERVATIONS OF THE BE BINARY SYSTEM X PERSEI
Abstract:We propose a 60 ks NuSTAR observation of the low luminosity accretion-powered pulsar X Persei. Several previous studies have shown that this source has both a softer power law spectral component (3-20 keV) and also a hard X-ray spectral component ($>$ 30 keV). Work by Coburn et al. who studied RXTE data, and Maitra et al., who studied Suzaku data, concluded there is a possible cyclotron resonant scattering feature in the range 29-39 keV. However, Doroshenko et al. have challenged this conclusion in their study of INTEGRAL data. Our NuSTAR observation will settle key questions for this source: 1) does the X-ray spectrum really have a soft and hard component, and, 2) is there a cyclotron resonant scattering feature anywhere in the NuSTAR energy band.

Proposal Number: 4298
PI Last Name: Zakamska
Title:X-RAY OBSERVATIONS OF AN OBSCURED QUASAR WITH OUTFLOWS AT PEAK GALAXY FORMATION EPOCH
Abstract:We discovered a population of powerful L>1e47 erg/s red quasars at z=2-3 which show unprecedented signatures of fast v>3000 km/s outflows in their [OIII]5007A lines. These objects may be signposts of the 'blow-out' phase of quasar feedback onto quasar host galaxy, at the epoch when quasars may have made the strongest impact on galaxy formation. Here we propose NuStar+XMM observations of one of these objects, a target from our approved JWST Early Release Science program. These data will allow us to determine the physical properties of the corona and the intrinsic accretion luminosity; constrain wind driving mechanisms; and provide a 'gold standard' spectrum for studies of the obscured high-redshift quasar population, which remains the single most elusive key target of X-ray astronomy.

Proposal Number: 4299
PI Last Name: Brumback
Title:A DEFINITIVE INVESTIGATION OF THE MAGNETIZED ACCRETION FLOW IN THE X-RAY PULSAR HER X-1 WITH NUSTAR AND XMM
Abstract:We propose a series of four 20 ks observations with NuSTAR and XMM of the Galactic binary X-ray pulsar Hercules X-1, which has a 35 day superorbital period caused by a warped, precessing accretion disk. The hard beam from the neutron star heats this disk and the corresponding reprocessed, thermal emission provides a unique opportunity for observation of magnetic-dominated accretion. Our proposed analysis requires good spectral and timing resolution across the full energy band (<1 keV to >20 keV) in order to constrain both the soft emission from the disk and the pulsar beam. For the first time, we will track a complete precession of Her X-1's accretion disk with full hard X-ray coverage to gain the clearest picture to date of the structure and kinematics of the magnetized accretion flow.

Proposal Number: 4301
PI Last Name: Marcotulli
Title:CHASING THE MOST POWERFUL BLAZARS
Abstract:We request a total of 200 ksec of NuSTAR observations for 4 high-z blazars (z>3.1). These sources are among the only nine quasar detected in gamma-rays beyond z = 3.1 by the Fermi-LAT but lack sensitive hard X-ray spectral measurements. The NuSTAR observations will allow us to accurately measure the rising part of the inverse Compton spectrum. Combined with existing gamma-ray observations, the X-rays will be fundamental to determining the jet power, the underlying electron population responsible for the emission and to measuring spectral curvature in the X-ray continuum.

Proposal Number: 4302
PI Last Name: Irwin
Title:HARD X-RAY EMISSION FROM A NEW TYPE OF VIOLENTLY FLARING OBJECT
Abstract:We have recently discovered a new class of violently flaring soft X-ray point source in nearby galaxies that increase their luminosities by two orders of magnitude to >1e40 ergs/s on time scales of a few seconds before returning to their pre-flare luminosities, apparently unscathed. These sources might be intermediate-mass black holes, exhibiting beamed emission, or be experiencing a type of explosive emission mechanism onto neutron stars or stellar-mass black holes that has not been observed in our Galaxy. We propose a 60 ksec NuSTAR observation of the source with the highest X-ray flux and shortest flare recurrence rate to put the first constraints on hard X-rays emitted by these sources during a flare, and determine how fast the rise time of the flare is in both soft and hard X-rays.

Proposal Number: 4305
PI Last Name: Kara
Title:THE COOLEST CORONA IN THE EDDINGTON-LIMITED AGN ARK 564
Abstract:Ark 564 is a luminous accreting supermassive black hole that has revealed several extraordinary qualities in soft X-rays: it is the brightest NLS1 from 0.3-10 keV, is one of the most highly variable AGN, has a very steep spectrum and strong soft excess. In NuSTAR AO1, we were awarded 200 ks to study this source above 20 keV for the first time, and discovered that Ark 564 is as exceptional in hard X-rays as it is in soft. Ark 564 has a coronal temperature of 15 2 keV, one of the lowest ever observed, and also shows an iron K line complex that is so highly ionised that it resembles more closely a black hole binary than an AGN. We now propose for an additional 500 ks of NuSTAR observations, simultaneous with 200 ks of XMM-Newton time and 100 ks of NICER time (through NICER Baseline Mission

Proposal Number: 4307
PI Last Name: Steiner
Title:LMC X-3 AS A WINDOW INTO ACCRETION-DISK STRUCTURE WITH NUSTAR AND NICER
Abstract:LMC X-3 is unique among stellar black holes in that it is a transient system (varying by orders of magnitude in intensity), and yet it is also persistently bright and nearly always in a very soft, thermal state. By virtue of its extreme thermal dominance, it is the ideal system with which to examine the structure of the thermal disk. NICER and NuSTAR offer a uniquely powerful capability in this respect to empirically establish the structure of slim disks.