Accepted NuSTAR Programs through NICER Cycle 01

Proposal Number: 02096
PI Last Name: Neilsen
Title: A NICER CATALOG OF WINDS AND VARIABILITY IN GRS 1915+105
Abstract: GRS 1915+105 is a black hole binary displaying unique variability, strong winds, jets, and BH spin. The source was extensively monitored with RXTE; NICER provides improved constraints on the disk and lines owing to its soft X-ray sensitivity and resolution. Even after two decades of monitoring, critical questions remain unanswered. What is the relationship between winds, jets, and rapid variability in this system? NICER is the only mission capable of building a legacy catalog of observations to answer this question, but a broader sample is required. We propose 35 weekly exposures of 2.7 ks in Cycle 1, enabling the first measurement of intra-state wind variability, a more nuanced view of accretion/ejection physics around black holes, and a legacy archive of variability in GRS 1915+105.

Proposal Number: 02122
PI Last Name: Nynka
Title: LONG-TERM NICER MONITORING OF MAGNETAR X-RAY OUTBURSTS
Abstract: We propose a monitoring program using the soft X-ray instrument NICER to monitor the evolution of magnetar outbursts, two ToO triggers of 80ks each. With a coordinated NuSTAR observations (40ks), we will monitor the evolution of the pulse profile and spectrum over the decay phase of a magnetar outburst to provide crucial insight into the magnetic energy dissipation process in magnetars

Proposal Number: 02131
PI Last Name: Stevens
Title: COMPARING EMISSION MECHANISMS OF LOW-FREQUENCY QPOS IN BLACK HOLES AND NEUTRON STARS
Abstract: The best laboratory for strong-field gravity is the inner 100s of kilometers around compact objects in low-mass X-ray binaries. The X-ray emission varies rapidly, notably in quasi-periodic oscillations (QPOs), which may be produced by general relativistic effects. Low-frequency QPOs from black holes and neutron stars share similar temporal and spectral properties, indicating that they have similar emission mechanisms, even though neutron stars have a surface and strong magnetic field in addition to general relativistic effects. With these proposed observations, we will use phase-resolved spectroscopy of two types of low-frequency QPOs to constrain and compare the emission mechanisms, to better understand accretion flows in the strong gravity regime.

Accepted NuSTAR Programs through NICER Cycle 02

Proposal Number: 03104
PI Last Name: Ludlam
Title: UNDERSTANDING ACCRETION DISKS IN ULTRA-COMPACT X-RAY BINARIES
Abstract: Ultra-compact X-ray binaries (UCXBs) are a subclass of low-mass X-ray binaries that contain a degenerate stellar companion in a short orbit (<80 mins). The accretion disk in these systems differ in chemical composition from typical LMXBs due to a lack of hydrogen and overabundance of higher Z elements. These systems exhibit multiple emission lines in their reflection spectrum from O and Fe. These multiple emission features offer the opportunity to learn more about the properties of the compact object and accretion disks in these systems. We request 10 ks NICER observations and joint 30 ks NuSTAR observations of two UCXBs to reveal the entire reflection spectrum from low-E oxygen features to the Compton hump at higher energy to enhance our understanding of accretion in these systems.

Proposal Number: 03107
PI Last Name: Neilsen
Title: THE OBSCURED STATE: WINDS AND THE END OF GRS 1915+105?
Abstract: GRS 1915+105 is a black hole binary known for its unique variability, strong winds, jets, and BH spin. After 23 years of monitoring, NICER has detected a huge change in this iconic source: the X-ray flux has dropped by 100x! Is this the approach to quiescence? Spectra suggest a large obscuring shroud, but what is this obscuring gas? The obscured state is highly variable, with flares that reveal strong winds and highly-ionized absorption. We propose to study its long-term evolution with 35 weekly exposures of 2.7 ks in Cycle 2. NICER is the only mission capable of frequently monitoring this important new state. We request 3x25 ks NuSTAR to constrain scattering and wind photoionziation. These observations will also continue to grow our NICER legacy archive of variability in GRS 1915+105.

Proposal Number: 03126
PI Last Name: Nowak
Title: JOINT NICER, NUSTAR, AND EVENT HORIZON TELESCOPE OBSERVATIONS OF 3C 273 AND 3C 279
Abstract: The Event Horizon Telescope (EHT) is effectively an Earth-sized, interferometric mm-band telescope array with 20 muas spatial resolution that is conducting ground-breaking observations of supermassive black hole (SMBH) systems. The mm emission size resolved by EHT in SMBH are consistent with those inferred from X-ray and gamma-ray variability studies. We propose joint NICER/NuSTAR observations of two blazars during the Spring 2020 EHT campaign: 3C 273 and 3C 279. The former is an EHT target, and the latter is a calibrator for M87 observations. NICER will provide large effective area, low background, and rapid timing capabilities in the soft X-ray, and the joint spectra will span 0.1-70 keV. These blazars have shown both long term and short term flaring variability.

Proposal Number: 03145
PI Last Name: Earnshaw
Title: A BROADBAND STUDY OF A NEARBY ULX IN NGC 4190
Abstract: We propose to observe NGC 4190 ULX-1, one of the last remaining nearby ULXs without broad- band X-ray data and an excellent target for both NICER and NuSTAR due to its persistently high flux (> 10^−12 ergs/s/cm2) and isolation from other X-ray sources. Quasi-simultaneous observations for 50 ks with NICER and 80 ks with NuSTAR will allow us to constrain the broadband spectrum of the source and to search for pulsations and other timing features in both the NICER and NuSTAR data, in one of the best available opportunities to grow the small sample of ULXs with sufficient data for in-depth timing analysis.

Proposal Number: 03151
PI Last Name: Espinoza-Galeas
Title: NICER MONITORING OF ETA CARINAE AFTER THE 2020 PERIASTRON PASSAGE
Abstract: We are requesting 104 ksec of observation time in NICER AO2 to monitor the X-ray emission from the super-luminous massive colliding wind binary ETA CARINAE through its next X-ray minimum and recovery. This proposal is the next step of monitoring campaign of X- ray telescopes started with RXTE, followed by Swift and continued by NICER through Cycle 1. The proposed NICER monitoring program in Cycle 2 will give us unprecedented observations to compare the changes during its X-ray recovery. We also request a NuSTAR observation to study the connections between the thermal emission and non-thermal emission by comparing the 30-50 keV X-ray spectrum with NICER soft X-ray spectra. Our proposed NICER program will also provide context for our approved CHANDRA ACIS observations.

Proposal Number: 03155
PI Last Name: Borghese
Title: PROMPT NICER AND NUSTAR STUDY OF MAGNETAR OUTBURSTS
Abstract: Magnetars are a small class of neutron stars believed to be powered by their huge magnetic fields. They go through long stretches of quiescence, interrupted by periods of activity in the form of short X-ray bursts, giant flares and yearly-timescale X-ray outbursts. Multi-band observations of these transient events yield the largest amount of information on magnetars emission, allowing to test the theoretical models on a variety of phenomena and source states. We propose a joint NICER (50 ks) and NuSTAR (110 ks) ToO program (1 trigger of 4 observations over a few months) aimed at gathering new physical insights on magnetars surface and crust, magnetic field configuration and magnetospheres.

Accepted NuSTAR Programs through NICER Cycle 03

Proposal Number: 04118
PI Last Name: Wang
Title: RELATIVISTIC REFLECTION AND REVERBERATION MAPPING IN A BLACK HOLE BINARY
Abstract: Black hole astrophysics can be regarded as a fundamental tool in studying the accretion and ejection physics in the strongest gravity regime in the Universe. Reflection spectroscopy studies the time-averaged energy spectrum, providing constraints on properties in the accretion disk and the corona, but degeneracies take place in problems such as the truncation level of the disk. Reverberation mapping is a timing technique revealing the disk-corona geometry in the innermost regions, which could help break degeneracies. With recent cutting-edge developments in physical spectral-timing models, the main goal in this proposal is to find clues on the state transition mechanism, and the coupling between the disk, corona and jet in black hole binaries.

Proposal Number: 04135
PI Last Name: Ghosh
Title: PROBING THE ACCRETING PULSAR CANDIDATE NGC 1042 ULX1
Abstract: We propose to observe one bright and isolated ULX in the galaxy NGC 1042, simultaneously with broadband coverage by NICER and NuSTAR for the first time. Motivated by a marginal detection of pulsation in one archival XMM data with poor statistics, we want to confirm the pulsation with new NICER data. Our primary aim is to detect the pulsation of ULX1 central compact object with high confidence and study the spectral properties of the source in broad energy band. The detailed spectral study of this ULX will quantify both the soft and hard spectral components which was not possible previously because of unavailability of high S/N ratio data with broadband coverage. Therefore, we propose to obtain simultaneous observations with 50 ks of NICER and 100 ks of NuSTAR exposure for NGC 1042 ULX1.

Proposal Number: 04152
PI Last Name: Sridhar
Title: ILLUMINATING THE ACCRETION DISK-CORONAE OF BLACK HOLES DURING THEIR FADING PHASE WITH NICER
Abstract: We request 40 ks of NICER and 60 ks of NuSTAR time to trigger ToO observations to obtain high signal-to-noise spectra from the relatively under-explored fading phases of a non-failed outburst of transient black hole. Our principal goal is to track the evolving properties of the accretion-corona system viz., inner disk truncation, disk density, coronal geometry, and disk inclination as the outburst enters the returning hard-intermediate to quiescent-hard state. This will be achieved with a suite of relativistic reflection and reverberation models to investigate the implications of accretion physics on the origin of hysteresis in the hardness-intensity diagram.

Proposal Number: 04155
PI Last Name: Conners
Title: THE PROPERTIES AND EVOLUTION OF ACCRETION DISKS IN BLACK HOLE BINARIES
Abstract: We propose simultaneous NICER and NuSTAR ToO observations of any one of the 19 listed transient black hole X-ray binaries. We request a total of 8 ks of NICER time, split into four 2 ks exposures, each simultaneous with a 20 ks NuSTAR exposure (total of 80 ks NuSTAR time), and each spaced about a week apart.

Proposal Number: 04163
PI Last Name: Homan
Title: BROADBAND SPECTRA OF THE ULTRA-COMPACT X-RAY BINARY 4U 1820-30
Abstract: The modeling of neutron-star LMXB X-ray spectra often suffers from a lack of coverage at either the low or high energy end. NICER spectra offer great low-energy coverage, with the potential to obtain excellent constraints on the thermal components, including parameters such as the inner disk radius and size of the boundary layer. However, this still requires additional coverage above 10 keV. Here we request three 20 ks NICER/NuSTAR ToO observations of the ultra-compact neutron-star LMXB 4U 1820-30, a bright source with large spectral variations. The observations will be triggered to observe the source at select locations in its spectral range, with the goal of improving our understanding of the evolution of the various spectral components and the underlying changes in the accretion flow.

Proposal Number: 04181
PI Last Name: Mastroserio
Title: MEASURING BLACK HOLE SPIN AND MASS THROUGH X-RAY REFLECTION SPECTRA AND REVERBERATION LAGS
Abstract: X-ray reflection in accreting black holes probes the inner region of the accretion disc, and proper modelling of the spectral and timing properties of this emission enables measurement of the black hole mass and spin. The unique combination of NICER s soft and NuSTAR's hard coverage provide the broad bandpass, high count rates and energy and timing resolution required to constrain models of the time averaged energy spectrum and the reverberation lag energy spectrum on different timescales. We propose to observe any black hole transient, known or unknown, exceeding 30 mCrab during the bright hard state for 30 ks with simultaneous NICER and NuSTAR observation in order to access unprecedented characterisation of black hole spin and mass.

Accepted NuSTAR Programs through NICER Cycle 04

Proposal Number: 05065
PI Name: Riley Connors
Title: NICER CONSTRAINTS ON BLACK HOLE BINARY ACCRETION PHYSICS
Abstract: A number of open questions persist in our understanding of the accretion flow properties of outbursting black hole binaries: principally the inner disk radius location, the disk density, iron abundance and inclination, and black hole spin. The superior spectral/timing resolution of NICER, and the high energy coverage provided by NuSTAR, present a golden opportunity to get constraints on these key quantities. We propose simultaneous NICER and NuSTAR ToO observations of any one of the 18 listed transient black hole X-ray binaries. We request a total of 8 ks of NICER time, split into four 2ks exposures, each simultaneous with a 20 ks NuSTAR exposure (total of 80 ks NuSTAR time), to be spaced within a week of one another.

Proposal Number: 05076
PI Name: Teruaki Enoto
Title: MAGNETAR OUTBURSTS AS A CLUE FOR UNDERSTANDING MAGNETIC ENERGY DISSIPATION AND FAST RADIO BURSTS
Abstract: Magnetar X-ray outburst is sporadic dissipation of magnetic energy via short bursts, giant flares, and persistent emission enhancement. The physics underlying this process is still an open question. Follow-up NICER observations of transient magnetars have provided clues for this question, as shown by recent successful NICER ToO programs: the radio-loud XTE J1810-197, the Galactic fast radio burst (FRB) source SGR 1935+2154, high-B pulsar / magnetar Swift J1818.0-1607, a new source SGR 1830-0645, and the long-term active Swift J1555.2-5402. Prompt X-ray observation is becoming more and more critical after discovering the FRBs from the Galactic magnetar SGR~1935+2154 in 2020. Here we propose NICER ToO observations of magnetar outbursts in soft X-rays.

Proposal Number: 05079
PI Name: Alice Borghese
Title: FOLLOWING A NEW MAGNETAR OUTBURST WITH NICER AND NUSTAR
Abstract: Isolated neutron stars powered by the instabilities and decay of their huge magnetic field, magnetars are characterized by a distinctive high-energy flaring phenomenology: short bursts of X-/gamma-rays, often accompanied by enhancements of the persistent X-ray luminosity, referred to as outbursts. Magnetar-like activity was discovered from isolated neutron stars with a broad range of magnetic field strengths. Moreover, the recent detection of a FRB-like burst from a Galactic magnetar has strengthened the belief that at least a sub-group of FRBs can be powered by magnetars. Here, we propose to follow two new outbursts from a known or a new source with NICER and NuSTAR to gather new physical insights on magnetar surface, field configuration and magnetosphere.

Proposal Number: 05094
PI Name: Kaya Mori
Title: CHARACTERIZING X-RAY EMISSION OF A WHITE DWARF PULSAR CANDIDATE DISCOVERED IN THE ZTF OPTICAL SURVEY
Abstract: We propose to observe a white dwarf (WD) pulsar candidate ZTF J185139.81+171430.3 with NICER and NuSTAR. The first WD pulsar system, AR Sco, is one of the rare astrophysical manifestations on how a magnetically interacting binary system can accelerate particles in the magnetosphere and generate broad-band non-thermal synchrotron radiation from radio to X-ray band. ZTF observations revealed a 12.37-minute highly-modulated, coherent periodicity from our target. This is a unique feature previously detected from AR Sco. Alternatively, the source could be an AM CVn star or an accreting intermediate polar with unusually high optical modulation. The proposed NICER + NuSTAR observations will explore the nature of this peculiar CV by investigating its X-ray spectral and timing properties.

Proposal Number: 05099
PI Name: Federico Garcia
Title: LF-QPOS IN BH-LMXBS: EXPLORING THE ROLE OF COMPTONISATION WITH NICER AND NUSTAR
Abstract: BH LMXBs show prominent low-frequency QPOs in their power-density spectra, with fractional amplitudes that increase with energy and complex lag spectra. The question about their physical origin remains unanswered. Quasi-simultaneous observations with NICER and NuSTAR in the soft and hard X-ray bands will allow us to probe the radiative mechanism that modulates the energy-dependent timing properties of these LF QPOs. This information is crucial to unveil the physical mechanism that produces these QPOs, both dynamically, either connected to Lense-Thirring Precession or through instabilities in the hot accretion flow, and radiatively, via Compton amplification in the corona where the observed spectral-timing properties are imprinted onto the X-ray emission.

Proposal Number: 05104
PI Name: PI: Alessio Marino
Title: INVESTIGATING THE ACCRETION-EJECTION INTERPLAY IN THE NS X-RAY BINARY 4U 1820-30 WITH NICER
Abstract: The persistent neutron star X-ray binary 4U 1820-30 displays a 170 d accretion cycle, evolving between phases of high and low X-ray luminosity. Over this cycle, dramatic changes are observed in both the X-ray spectral-timing properties (related to the accretion flow) and the radio spectral shape (related to the jet). Interestingly, the jet evolution seems to be triggered by the accretion rate rather than the spectral state. The aim of the proposal is to progressively track the spectral and timing evolution of the accretion flow over a cycle with a NICER+NuSTAR monitoring campaign. 9 NICER observations of 10 ks each, 3 of them paired with 20 ks NuSTAR visits, are requested. This campaign will be coupled with radio and IR observations to trace the accretion/ejection coupling mechanism.

Proposal Number: 05106
PI Name: Filioop D'Ammando
Title: NICER AND NUSTAR FOLLOW-UP OBSERVATIONS OF GAMMA-RAY FLARING BLAZARS
Abstract: There are many open questions related to the nature of the high-energy emission and the physics of jets which need to be addressed, such as the radiative processes producing the high-energy emission, the parameters of the emitting region(s) and the jet composition. Radiative models need to be tested against MWL simultaneous SED. We propose to trigger 1 ToO observation with NICER and NuSTAR if gamma-ray flaring activity from a blazar is detected by Fermi-LAT and a high X-ray flux has been confirmed by a rapid Swift follow-up observation. The goal is the study of the broadband SED and MWL light curves for putting constraints on the physics of relativistic jets from super-massive black holes, and on the acceleration and radiation mechanisms at work in such extreme environments.

Proposal Number: 05118
PI Name: Jingyi Wang
Title: RELATIVISTIC REFLECTION AND REVERBERATION MAPPING IN A BLACK HOLE BINARY
Abstract: Black hole astrophysics can be regarded as a fundamental tool in studying the accretion and ejection physics in the strongest gravity regime in the Universe. Reflection spectroscopy studies the time-averaged flux-energy spectrum, providing constraints on properties in the accretion disk and the corona, but degeneracies take place in problems such as the truncation level of the disk. Reverberation mapping is a timing technique revealing the disk-corona geometry in the innermost regions, which could help break degeneracies. With recent cutting-edge developments in physical spectral-timing models, the main goal in this proposal is to find clues on the state transition mechanism, and the coupling between the disk, corona and jet in black hole binaries.

Proposal Number: 05131
PI Name: Joseph Neilsen
Title: THE OBSCURED STATE OF GRS 1915+105
Abstract: GRS 1915+105 is a black hole binary known for its unique variability, strong winds, jets, and BH spin. After 20+ years in outburst, NICER detected a huge change in this iconic source: the X-ray flux dropped by 100x! Spectra suggest a large obscuring shroud, but what is this obscuring gas? The "obscured" state is highly variable, with flares that reveal strong winds and highly-ionized absorption. We propose to study its long-term evolution with 35 weekly exposures of 2.7 ks in Cycle 4. NICER is the only mission capable of frequently monitoring this important new state. We also request a 25 ks NuSTAR ToO to constrain scattering and wind photoionziation. These observations will also grow a NICER legacy archive of obscured variability in GRS 1915+105.

Proposal Number: 05140
PI Name: Guglielmo Mastroserio
Title: MEASURING BLACK HOLE SPIN AND MASS THROUGH X-RAY REFLECTION SPECTRA AND REVERBERATION LAGS
Abstract: X-ray reflection in accreting black holes probes the inner region of the accretion disc, and proper modelling of the spectral and timing properties of this emission enables measurement of the black hole mass and spin. The unique combination of NICER s soft and NuSTAR's hard coverage provide the broad bandpass, high count rates and energy and timing resolution required to constrain models of the time averaged energy spectrum and the reverberation lag energy spectrum on different timescales. We propose to observe any black hole transient, known or unknown, exceeding 30 mCrab during the bright hard state for 30 ks with simultaneous NICER and NuSTAR observation in order to access unprecedented characterisation of black hole spin and mass.

Proposal Number: 05172
PI Name: Javier Garcia
Title: THE PROPERTIES AND EVOLUTION OF ACCRETION DISKS IN BLACK HOLE BINARIES
Abstract: We request 10ks of NICER and 100ks of NuSTAR time to trigger Target of Opportunity (ToO) observations of a new or known black hole transient during the end of the outburst, after the source has entered the low-hard state. We aim to obtain high signal-to-noise data during this fainter phase in order to measure the level of disk truncation using X-ray reflection spectroscopy. We will also provide measurements for the disk inclination, ionization and iron abundance. These observations will provide crucial constraints to support a large-scale data analysis program for these sources.

Accepted NuSTAR Programs through NICER Cycle 05

Proposal Number: 06057
PI Name: Fiamma Capitanio
Title: THE FIRST X-RAY POLARIMETRY AND SPECTROSCOPY OBSERVATIONS OF TRANSIENT BLACK HOLE X-RAY BINARIES
Abstract: We propose 3 joint NICER+NuSTAR ToOs observations of transient black hole X-ray binaries (TBHXBs), to be taken in coordination with the Imaging X-ray Polarimetry Explorer(IXPE), a NASA-ASI mission launched on December 9, 2021. As the first year, the second year IXPE observing plan includes 3 ToOs of TBHXB in outburst. Each ToO includes one long (# 300 ks) exposure in the hard state and another in the soft state. In fact, until now IXPE has not had an opportunity to observe a complete outburst of a TBHXB because of the lack of bright standard outbursts occurred within the visibility windows. We propose (for each ToO) two 30 ks NICER+NuSTAR exposures during the hard state IXPE observation and one 20 ks NICER+NuSTAR exposure during the soft state IXPE observation. This will provide, as demonstrated by the IXPE first year results, an unprecedented combination of X-ray polarimetry, high resolution broad-band spectroscopy and timing; yielding novel and unique information on the coronal geometry, the black hole spin and the role of jets in these sources.

Proposal Number: 06078
PI Name: Yuhan Yao
Title: NICER+NUSTSR OBSERVATIONS OF TIDAL DISRUPTION EVENTS: OPENING A NEW CHAPTER IN BLACK HOLE SUPER-EDDINGTON ACCRETION
Abstract: Tidal disruption events (TDEs) offer great opportunities to study the physics of black hole accretion in the super-Eddington regime. The field of X-ray TDE study is still so young such that each object reveals new and unexpected phenomena. We propose high-cadence NICER monitoring on two X-ray bright TDEs to address: (1) how often and on what timescales does corona formation happen; (2) does the thick-to-thin disk transition happen in TDEs other than AT2021ehb; (3) what is the fraction of TDEs that launch on-axis relativistic jets. We also ask for one epoch of NuSTAR observation for one TDE that is sufficiently bright in the hard X-ray. The NICER+NuSTAR spectrum will allow us to study the geometry of the super-Eddington accreting inflow and the powering of the outflow/jet.

Proposal Number: 06113
PI Name: Adam Ingram
Title: THE FIRST X-RAY POLARIMETRY AND SPECTROSCOPY OBSERVATIONS OF GRS 1915+105
Abstract: We propose three 30ks NICER exposures contemporaneous with three 20ks NuSTAR exposures of the black hole (BH) X-ray binary (XRB) GRS 1915+105, to be taken during a six-day long Imaging X-ray Polarimetry Explorer (IXPE) target of opportunity (ToO) observation of the source. The IXPE ToO will be triggered when the source resumes behaviour for which a detection of X-ray polarisation can reasonably be expected, and we will trigger this companion program in response. The high spectral resolution and broad band pass provided by NICER+NuSTAR coverage will be vital for breaking degeneracies in polarization models.

Proposal Number: 06127
PI Name: Guillem Marti-Devesa
Title: WIND-WIND INTERACTION AND PARTICLE ACCELERATION IN THE KLEINMANN STAR TRAPEZIUM SYSTEM
Abstract: Binary stellar systems with shocked, powerful winds have been suggested as particle accelerators (i.e. colliding-wind binaries, or CWB). Therefore, CWBs are potential gamma-ray sources detectable by the Fermi-LAT, yet only eta Car and g2 Vel have been identified as such. Those two systems posses very different geometrical and wind conditions and, consequently, any new gamma-ray emitting CWB identified will clarify the conditions required for particle acceleration in stellar binaries. The Kleinmann Star is a system composed of two CWBs recently associated with a gamma-ray source, but their orbital periods and the variable conditions in the shocked winds are unknown. The proposed monitoring with NICER will characterise them and allow to establish this unique system as a particle accelerator.

Proposal Number: 06141
PI Name: Jingyi Wang
Title: RELATIVISTIC REFLECTION AND REVERBERATION MAPPING IN A BLACK HOLE BINARY
Abstract: Black hole astrophysics can be regarded as a fundamental tool in studying the accretion and ejection physics in the strongest gravity regime in the Universe. Reflection spectroscopy studies the time-averaged flux-energy spectrum, providing constraints on properties in the accretion disk and the corona, but degeneracies take place in problems such as the truncation level of the disk. Reverberation mapping is a timing technique revealing the disk-corona geometry in the innermost regions, which could help break degeneracies. With recent cutting-edge developments in physical spectral-timing models, the main goal in this proposal is to find clues on the state transition mechanism, and the coupling between the disk, corona and jet in black hole binaries.

Proposal Number: 06143
PI Name: James Steiner
Title: NICER, NUSTAR, AND IXPE SPECTRO-POLARIMETRIC CONSTRAINTS ON THE SOFT STATE OF CYGNUS X-1
Abstract: A groundbreaking recent study of the hard state of Cygnus X-1 with IXPE, NICER and NuSTAR provided the first robust soft X-ray polarimetric detection of an accreting black hole. The spectro-polarimetric results yielded unprecedented constraints on the jet, corona, and accretion disk geometry. This was anchored in the broadband X-ray spectral data from NICER and NuSTAR being modeled in conjunction with IXPE's polarimetric data. If Cyg X-1 transitions to its soft state, an approved 600ks IXPE campaign will be triggered. To achieve equivalent constraints on the soft state's accretion geometry as with the hard state campaign, we request an accompanying 5ks per day for 12 days with NICER, and 3 x 20ks observations with NuSTAR during the IXPE run, 60ks apiece for NICER and NuSTAR.

Proposal Number: 06148
PI Name: Renee Ludlam
Title: UNVEILING THE ORIGIN OF FE L EMISSION IN SERPENS X-1
Abstract: Serpens X-1 is a persistently accreting neutron star low-mass X-ray binary that exhibits multiple emission line components in its reflection spectrum. The detection of multiple emission line components (e.g., Fe K and Fe L) in the reflection spectrum provides the opportunity to test different theories about where the emission arises in the disk and challenge our current understanding of accretion. Therefore, we request a 30 ks NICER observation with a contemporaneous 30 ks NuSTAR observation in order to test the emission radius of the Fe K line and lower-energy Fe L blend. We demonstrate that the requested observations are necessary to test the different ideas with respect to emission radii and enhance our understanding of accretion.

Proposal Number: 06190
PI Name: Henric Krawczynski
Title: X-RAY SPECTROPOLARIMETRIC OBSERVATIONS OF THE PERSISTENT HIGH MASS X-RAY BINARIES CYG X-3 AND LMC X-1
Abstract: We propose NICER and NuSTAR observations accompanying simultaneous Imaging X-ray Polarimetry Explorer (IXPE) observations of the two persistent black holes Cyg~X-3 and LMC X-1. We will complement the 600 ksec IXPE observations of each source with 8 x 5 ksec NICER snapshots (40 ksec per source) and one 20 ksec NuSTAR snapshot per source. The NICER and NuSTAR observations will reveal the relative contributions of the different emission components (multi-temperature disk emission, coronal emission, reflected emission) to the IXPE signal. The two legacy data sets acquired with the three satellites will allow us to measure the black hole inclinations, to refine the black hole spin estimates, and to constrain the geometries and locations of the accretion disk coronae.

Proposal Number: 06196
PI Name: Justin Vandenbroucke
Title: PROBING THE AGN NEUTRINO CONNECTION USING MULTIMESSENGER OBSERVATIONS WITH NICER AND ICECUBE
Abstract: Multimessenger astronomy is a powerful new method for understanding astrophysical processes. This was illustrated in 2017 when IceCube reported a high-energy neutrino found to be coincident with a very-high-energy flaring blazar (detected by Fermi and MAGIC). Since then, various multimessenger studies involving neutrinos and photon data have occurred, but the associations between neutrinos and active galactic nuclei (AGN) remain uncertain. We propose a monitoring program for two AGN, NGC1068 and PKS1502+106, using NICER and NuSTAR to study the X-ray-neutrino connection. This analysis will make use of both model-dependent and model-independent approaches using observed X-ray and IceCube non-public data and will also serve as a trigger for real-time follow-up using IceCube.

Proposal Number: 06197
PI Name: Joseph Neilsen
Title: THE OBSCURED STATE OF GRS 1915+105
Abstract: GRS 1915+105 is a black hole binary known for its unique variability, strong winds, jets, and BH spin. After 20+ years in outburst, NICER detected a huge change in this iconic source: the X-ray flux dropped by 100x! Spectra suggest a large obscuring shroud, but what is this obscuring gas? The "obscured" state is highly variable, with flares that reveal strong winds and highly-ionized absorption. We propose to study its long-term evolution with 35 weekly exposures of 2.7 ks in Cycle 5. NICER is the only mission capable of frequently monitoring this important new state. We also request a 25 ks NuSTAR ToO to constrain scattering and wind photoionziation. These observations will also grow a NICER legacy archive of obscured variability in GRS 1915+105.

Proposal Number: 06203
PI Name: Paul Draghis
Title: TRACKING TWO FUTURE BLACK HOLE OUTBURST WITH NICER AND NUSTAR
Abstract: We propose monitoring two future, previously unobserved BH transients with fluxes above 50 mCrab by dedicating 45 ks of NICER time over 15 observations spread throughout each of the two outbursts. By pairing a 30 ks NuSTAR observation with a NICER observation, we can obtain a precise spin measurement for each BH. The NICER monitoring campaign will probe the effects of the evolution of the outburst on the spin measurement. This project will test the assumptions and hypotheses of BH spin measurements in X-ray binaries, and will serve as a legacy for NICER and NuSTAR. In the future, this treatment will maximize the number of new BHs observed and, together with gravitational wave observations, will allow developing a unifying understanding of stellar-mass black hole formation and evolution.

Accepted NuSTAR Programs through NICER Cycle 06

Proposal number: 7082
PI last name: Enoto
Title: PROMPT AND HIGH-CADENCE X-RAY FOLLOW-UP OF TRANSIENT MAGNETARS FOR UNDERSTANDING THE MAGNETAR-FRB CONNECTION
Abstract: The phenomenon of Fast Radio Bursts (FRBs) is one of the most tantalizing mysteries in astronomy. However, the mechanism of how magnetars initiate FRBs is poorly understood. In October 2022, this magnetar exhibited FRBs and short X-ray bursts again. During this magnetar outburst, ToO observations and time series analyses with NICER and NuSTAR revealed a pair of glitches that occurred before and after FRBs, associated with a burst forest, providing valuable insights into this mystery. Hence, this proposal aims to prompt and high-cadence X-ray monitoring during an outburst of transient magnetars to investigate their X-ray behaviours and to search for glitches similar to those of SGR 1935+2154 and also for FRB-associated X-ray bursts.

Proposal number: 7126
PI last name: Mastroserio
Title: MEASURING BLACK HOLE SPIN AND MASS THROUGH X-RAY REFLECTION AND REVERBERATION LAGS
Abstract: X-ray reflection in accreting black holes probes the inner region of the accretion disc, and proper modelling of the spectral and timing properties of this emission enables measurement of the black hole mass and spin. The unique combination of NICER s soft and NuSTAR's hard coverage provides the broad bandpass, high count rates and energy and timing resolution required to constrain models of the time-averaged energy spectrum and the reverberation lag energy spectrum on different timescales. We propose to observe any black hole transient, known or unknown, exceeding 50 mCrab during the bright hard state for 50 ks with simultaneous NICER and NuSTAR observation in order to access unprecedented characterization of black hole spin and mass.

Proposal number: 7133
PI last name: Corcoran
Title: FIRST NICER OBSERVATIONS OF WR 140 NEAR PERIASTRON: HOT GAS, ORGANICS AND THE RELIC
Abstract: We propose observing the X-ray variability of the "standard" colliding wind long-period binary WR 140 near periastron passage with NICER, when the X-ray spectrum varies greatly and dust forms. NICER observations are needed to provide measurement of the variation of the soft spectrum, which could not be done by previous RXTE or Swift observations. The proposed observations will provide key information on variations in X-ray temperature, flux and absorption column for comparison to detailed models, and monitor the appearance of the soft "relic" component seen in previous Suzaku and XMM-Newton snapshots. This will be the first time that WR 140's periastron passage will be monitored by NICER. We also ask for joint observations with NuSTAR to monitor the non-thermal emission.

Proposal number: 7141
PI last name: Guolo
Title: NICER+NUSTAR OBSERVATIONS OF TIDAL DISRUPTION EVENTS: PROBING THE REAL-TIME FORMATION OF JETS AND X-RAY CORONAE
Abstract: Tidal disruption events (TDEs) offer excellent opportunities to study the physics of black hole accretion, including the real-time formation of jets and X-ray coronae. The field of X-ray TDE study is still so young that each object reveals new and unexpected phenomena. We propose high-cadence NICER monitoring on one X-ray bright TDE showing hard X-ray emission: i) if triggered in a relativistic/jetted TDE, we aim to probe the physical properties of nascent jet; ii) if triggered in a non-relativistic TDE, we aim to probe the accretion state transitions, the real-time formation of a hard X-ray corona and search for reflection features akin to AGN. The NICER+NuSTAR broad-band spectrum will allow us to study the geometry of the super-Eddington accreting inflow and the powering of the outflow

Proposal number: 7164
PI last name: Fukumura
Title: BROADER PERSPECTIVES OF ACCRETION DISK AND MULTI-ION UFOS IN MAXI J1810-222
Abstract: We propose a multi-epoch, joint ToO program of BH XRB, MAXI J1810-222, to study a physical link between multi-ion ultra-fast outflows (UFOs) and yet-to-be explored reflection features with NICER (for soft X-ray UFOs) and NuSTAR (for Fe K and reflection) during an outburst. Being triggered by MAXI/GSC daily monitoring, we aim to unpack a concealed nature of powerful disk winds and disk reflection by systematically modeling and analyzing multi-epoch NICER+NuSTAR spectra. Our study is conducted by a physically-motivated wind model in the context of magnetic-driving in conjunction with state-of-the-art reflection spectroscopy to further understand a broadband X-ray phenomenology of this XRB for which NICER (30ks x3) and NuSTAR (20ks x3) play indispensable roles.

Proposal number: 7170
PI last name: Nathan
Title: RESOLVING A QUASI PERIODIC OSCILLATION IN GRS1915+105 UPON ITS RETURN TO AN UNOBSCURED STATE
Abstract: Before 2018, the black hole X-ray binary GRS1915+105 was extremely bright in X-rays, and at times showed powerful type-C quasi-periodic oscillations (QPOs). We propose a joint 30 ks NICER and 30 ks NuSTAR observation of a QPO in GRS1915+105 if the source leaves its current X-ray obscured state. We will apply state-of-the-art phase resolving techniques to test for the presence of a precessing corona via its effects on the flux reflected from the accretion disc.

Proposal number: 7174
PI last name: Airapetian
Title: SEARCHING FOR SUPERFLARES AND ERUPTION EVENTS FROM AN INFANT SUN, EK DRA
Abstract: Recent missions have revealed that young solar-like planet hosts produce frequent superflares, which may have profound effects on the ability of terrestrial planets to retain their atmospheres. Observations also suggest that superflares are associated with filament or prominence eruptions that signify coronal mass ejections (CMEs). X-ray and EUV emission from superflares and dynamic pressure exerted by CMEs on exoplanets influence atmospheric chemistry and heating. In order to develop theoretical models of such events and assess their impact on habitable environments, we propose to perform a multi-wavelength campaign to observe various forms of magnetic activity of a young (~ 100 Myr) solar analog, EK Dra known to produce frequent flares and filament eruptions.