Proposal Number: 1021
PI Last Name: Kara
Title: UNDERSTANDING REFLECTION IN THE BARE SEYFERT I ARK 564
Abstract: A NuSTAR legacy is emerging through long observations of bare Seyfert galaxies that reveal an unprecedented look at relativistic reflection off an ionized accretion disc. We propose now to look at the Seyfert galaxy Ark 564 for 200 ks with NuSTAR and 50 ks with Suzaku in order to understand the reflection in this bright source. Ark~564 has been well-studied in the soft band, revealing a steep spectrum, strong soft excess, broad iron~K emission line and dramatic variability on the order of hours. It is very akin to two other well-known bare Seyferts, 1H0707-405 and IRAS 13224-3809, except it is an order of magnitude brighter. With this 200 ks observation, we will probe the geometry of the corona, through a complete spectral and timing analysis.

Proposal Number: 1022
PI Last Name: Li
Title: HARD X-RAY EMISSION FROM A NEARBY COSMIC RAY ACCELERATOR
Abstract: The presence of nonthermal synchrotron from radio to ~100keV in young shell-type SNRs is a strong evidence of CR acceleration by SNR blast wave. The existing radio/X-ray data are not sensitive to the hard X-ray tails of synchrotron spectrum, which is affected by many processes limiting the diffusive shock acceleration. NuSTAR's broad energy coverage and high angular resolution make it the best to study this hard X-ray tail via spatially resolved spectroscopy. We propose NuSTAR observations of the two nonthermal limbs of SN1006, a nearby clean CR accelerator, in order to perform spatially resolved spectral analysis combining radio, X-ray, GeV, and TeV data. We will distinguish different models limiting CR acceleration, search for high energy break and evidence of shock-cloud interaction.

Proposal Number: 1025
PI Last Name: Tomsick
Title: THE INNER ACCRETION DISK AROUND THE RAPIDLY ROTATING BLACK HOLE IN CYGNUS X-1
Abstract: We propose to observe Cygnus X-1 with NuSTAR (for 30 ks) and Suzaku (for 50 ks) in any spectral state in order to measure the reflection component and constrain the properties of the inner accretion disk, including the location of the inner radius, the geometry of the hard X-ray source, and the inclination. Observations made in the first two years of the NuSTAR mission have raised the interesting possibility that the inner disk inclination may differ from the orbital inclination, and this could occur if the black hole spin is misaligned. The proposed NuSTAR/Suzaku observation would be at the orbital phase where absorption due to stellar wind material is at a minimum, providing a clean measurement of the iron line profile and a significant improvement over the existing observations.

Proposal Number: 1036
PI Last Name: Miller
Title: REVEALING NEUTRON STAR X-RAY BINARY INNER ACCRETION FLOWS
Abstract: NuSTAR spectra of neutron star LMXBs can place interesting limits on the neutron star radii and equation of state. Early-phase observations of Serpens X-1 with NuSTAR strongly require three continuum components, and disk reflection. Importantly, the reflection spectrum placed interesting limits on the neutron star radius. We propose to build on these successes by observing GX 17+2, 4U 1636-53, and 4U 1705-44 for 20 ks each. These bright targets have advantageous properties that will be effective in constraining the emission mechanisms and geometry (inner disk extent, inclination) of the inner accretion flow. We will coordinate Swift exposures to support our NuSTAR observations.

Proposal Number: 1042
PI Last Name: Bianchi
Title: NGC3147, A COMPTON-THICK OR A TRUE TYPE 2 SEYFERT GALAXY?
Abstract: The general purpose of this proposal is to definitely exclude the Compton-thick hypothesis for NGC3147, one of the three True Type 2 Seyfert galaxies currently known. If the source is Compton-thick, the direct emission would pierce through the absorber in hard X-rays or, for even larger column densities, cold reflection should emerge over the ionized reflection above 10 keV. NuSTAR is the only instrument presently available which provides the high energy coverage and sensitivity needed to reveal the expected excess in the Compton-thick scenario. Our proposed 50 ks observation will definitely exclude the Compton-thick scenario for NGC3147, which will then be securely identified as a component of the very peculiar class of True Type Seyfert 2 galaxies.

Proposal Number: 1046
PI Last Name: Tagliaferri
Title: UNVEILING THE ORIGIN OF THE HARD TEV EMISSION IN BLLACS
Abstract: Some BLLacs are characterized by a hard intrinsic TeV spectrum irrespective of EBL absorption, locating the Compton peak above few TeV. This is difficult to reconcile with the typically softer spectrum of the synchrotron emission observed in these objects, for standard leptonic emission models and parameters. A different particle population might be responsible. We propose NuSTAR observations to pin down the synchrotron emission of these hard TeV electrons, either as a new hard component emerging in the hard X-ray band, or by constraining the synchrotron peak in the SED at the highest X-ray energies. The result can shed light on the origin of this hard TeV emission, as yet unexplained, and on the underlying acceleration mechanism.

Proposal Number: 1053
PI Last Name: Della Ceca
Title: PROBING COMCOMITANT STARBURST-AGN ACTIVITY: THE MOST LUMINOUS STARBURST IN THE LOCAL UNIVERSE
Abstract: The relative role of stellar emission and black-hole accretion, as mechanisms of energy production in the Universe, and their interconnection are two of the most debated topics of modern astrophysics. We propose here a 100 Ksec NuStar observation of IRAS00397-1312, the most luminous starburst in the local (z<0.3) Universe. The hard (E>10 keV) X-ray data will be unique to unveil the putative AGN component, never detected in the X-ray domain, and will allow us to delineate the intrinsic Lx and the column density of the obscuring matter. Complemented with the wealth of data at other wavelengths, the NuStar data will be fundamental to describe the circum-nuclear absorbing matter and to compare the AGN emission with the starburst emission.

Proposal Number: 1056
PI Last Name: Reeves
Title: SOLVING THE ORIGIN OF THE HARD X-RAY EXCESS IN THE SEYFERT 1, 1H 0419-577
Abstract: A key issue in the study of AGN is the origin of the hard X-ray excess. A recent study with Suzaku by Tatum et al. (2013) revealed that a majority of nearby type I AGN show a strong hard excess, requiring they are covered by Compton thick matter, with columns in excess of 10^24 cm^-2, in contrast to Unified models. Here we propose a 150 ks NuSTAR observation of the luminous Seyfert 1 galaxy, 1H 0419-577, one of the first AGN where a strong hard excess was reported. We will unequivocally determine the origin of the hard excess, namely; (i) a high covering Compton thick absorber, or (ii) two phase disc Comptonization, or (iii) a relativistically blurred reflector. This will be key to testing the validity of the AGN unified model and the true form of the X-ray continuum near the black hole.

Proposal Number: 1064
PI Last Name: Piconcelli
Title: THE CENTRAL ENGINE OF A HOT DOG
Abstract: Hot dust-obscured galaxies (Hot DOGs) are a very rare population of high-z, hyper-luminous (~1e14 Lsun) sources recently discovered in the WISE all-sky survey. Given their extraordinary luminosities they may represent a rapid, dust-enshrouded AGN/host galaxy evolutionary phase leading to the formation of the most massive systems. Our XMM observation of W1835+4355 (a Hot DOG at z~2.3) provided the first X-ray spectrum of this outstanding class of objects and revealed a buried but intrinsically luminous quasar. We propose here a 150 ks NuSTAR observation of this intriguing source to deepen our understanding of the physical properties of the nuclear region by a direct measurement of the absorber column density and X-ray luminosity of the AGN continuum, responsible for its huge energy output.

Proposal Number: 1084
PI Last Name: Tomsick
Title: SEARCHING FOR A CYCLOTRON LINE FROM THE SLOWLY ROTATING NEUTRON STAR IN IGR J16320-4751
Abstract: Thus far during the NuSTAR mission, there have been observations of many bright X-ray binaries, but studies of intermediate-brightness systems have lagged behind. One intermediate source class is the INTEGRAL High-Mass X-ray Binaries. With their hard spectra, the sensitivity of NuSTAR provides a large improvement in the >10 keV measurements of these sources with moderate exposure times. We propose a 50 ks observation of IGR J16320-4751, which is a slowly rotating (1300s) accreting pulsar. The slow rotation rates may be related to high neutron star magnetic fields now or sometime in the evolution of these systems, and a main goal of the proposed observation is to search for a cyclotron line that would provide a direct measurement of the magnetic field strength.

Proposal Number: 1085
PI Last Name: Hodges-Kluck
Title: A HARD X-RAY MAP OF THE NEARBY RADIO GALAXY FORNAX A
Abstract: Radio lobes produced by AGN can strongly impact their environment, so it is important to understand the energetics of these systems. Radio synchrotron emission tells us the slope of the energy distribution, but the energy and magnetic field strength are degenerate. This degeneracy is broken if one also has the inverse Compton flux produced by scattering of CMB photons, which is visible in the hard X-rays. There are few systems with detected IC lobes and even fewer where one can measure changes in the spectral index as a function of position. We will make a hard X-ray spectral index map in the best target for this type of work, Fornax A, to map the particle energy and field strength in young and old plasma.

Proposal Number: 1088
PI Last Name: Nardini
Title: NUCLEAR OBSCURATION IN THE AGN MERGER NGC 6240
Abstract: We propose to monitor the hard X-ray behavior of the Compton-thick AGN pair in the galaxy merger NGC 6240 with NuSTAR. Together with the existing 30-ks observation performed in March 2014, this series of three 20-ks snapshots will allow us to probe the source variability on timescales ranging from a few months to almost two years. Recent results from the Swift/BAT survey suggest a strong energy dependence of the excess variance, peaking around 20 keV. If driven by column density changes, the different spectral states would bring further insights on the structure and dynamics of the gas in proximity of the black holes. In any case, the increased total exposure will make it possible to perform a comprehensive analysis and take into account the dual AGN nature of the hard X-ray source.

Proposal Number: 1092
PI Last Name: Fuerst
Title: IDENTIFYING THE COMPACT OBJECT IN 4U 1700-37
Abstract: We propose to observe the HXMB 4U 1700-37 for 40ks to identify the nature of its compact object. NuSTAR's exceptional coverage of the hard X-ray band will allow us to search for a cyclotron line, which would unambiguously identify the compact object as neutron star. Indications for such a line have been seen in BeppoSAX and Suzaku data, but the ultimate evidence is missing. The NuSTAR data will also allow us to perform the most sensitive search for pulsations in the iron line band to date. With a mass estimate of 2.5 solar masses, this would be one of the most massive accreting neutron stars known. Accepted contemporaneous Hubble observations will additionally allow us to study the structure of the dense stellar wind and investigate its connection to the observed X-ray variability.

Proposal Number: 1093
PI Last Name: Bamba
Title: DISCOVERING THE MOST POWERFUL COSMIC-RAY ACCELERATOR, N132D IN THE LARGE MAGELLANIC CLOUD
Abstract: A supernova remnant (SNR) in the Large Magellanic Cloud, N132D can be the most efficient particle accelerating SNR with very bright and hard GeV and TeV gamma-rays. However, we need synchrotron X-ray information to understand the origin of the gamma-ray emission. Thanks to the NuSTAR spectroscopy and imaging above 10 keV, we will detect synchrotron X-rays buried by bright thermal X-rays for the first time, and judge the origin of gamma-rays to be leptonic or hadronic. Estimation of the maximum energy and injected total energy to accelerated particles will be carried out with wide-band spectroscopy from radio to TeV. We expect NuSTAR will show us that N132D is the most efficient accelerating SNR ever found, up to 10^51 erg, which implies that N132D may be a hypernova remnant.

Proposal Number: 1094
PI Last Name: Grefenstette
Title: PROTOSTAR FLARES FROM RHO OPH: EXTENDING OUR REACH INTO THE HARD X-RAYS
Abstract: Bright X-ray flares, presumed to be analogous to the magnetic flares in the solar corona, are common on Young Stellar Objects (YSO) as well as on nearby magnetic red dwarfs. Using NuSTAR to extend the spectral coverage above that provided by Chandra and XMM-Newton is particularly important in that it allows us to understand the influence of the flares on the protostellar system as well as identifying deeply shrouded YSOs. The main core of the rho Ophiuchi cloud complex, well observed by both Chandra and XMM-Newton, makes an ideal target for NuSTAR in terms of the brightness, number, and spatial extent of the expected flaring targets.

Proposal Number: 1108
PI Last Name: Garcia
Title: OBSERVING THE STRONG-FIELD REGION OF THE AGN IN MRK 509
Abstract: We propose combined Suzaku 50 ks and NuSTAR 200 ks observations of the bright Seyfert 1 galaxy Mrk 509 for the purpose of making a detailed study of the spectrum of radiation reflected from the accretion disk. Our chief aim is to constrain both the spin of the black hole and the properties of the corona that illuminates the disk. The combination of NuSTAR's high-sensitivity in the hard X-ray band, the soft-band coverage of Suzaku, and our state-of-the-art relativistic reflection models will allow us to break degeneracies between different scenarios currently proposed to explain the broadband spectrum of this exceptionally bright and much-studied source.

Proposal Number: 1113
PI Last Name: Pottschmidt
Title: DOES THE CYCLOTRON LINE OF 4U 1626-67 SHOW AN EMISSION WING?
Abstract: Observing the accreting pulsar 4U 1626-67 with NuSTAR for 80 ks will allow us to constrain the shape of the cyclotron line at ~37 keV in spectra of at least eight pulse phasebins. If the line is asymmetric this study will confirm the first such case and provide crucial input for understanding the accretion columns of high B-field pulsars.

Proposal Number: 1126
PI Last Name: Ng
Title: HARD X-RAY EMISSION OF CLASS II MILLISECOND PULSARS
Abstract: Millisecond pulsars (MSPs) are old neutron stars spun up by accretion from companion stars. The recent launch of the Fermi Gamma-ray Space Telescope has greatly increased the MSP sample and identified a new subclass, known as Class II, MSPs that show aligned pulse profiles in different energy bands. This could represent a new radio emission mechanism in the outer magnetosphere. We suggest that the radio waves could inverse-Compton scatter with energetic particles to produce hard X-ray emission, and we developed a model to account for the high-energy emission. To directly test this model, we propose NuSTAR observations to measure the hard X-ray spectra of several Class II MSPs. The results will also offer predictions to the low-frequency radio spectra for a comparison with on-going studies.

Proposal Number: 1130
PI Last Name: Markowitz
Title: COMPLEX CIRCUMNUCLEAR STRUCTURE IN RADIO-LOUD AGN: VARIABLE ABSORPTION IN MKN 6
Abstract: We request two quasi-simultaneous NuSTAR + Suzaku-XIS pointings of the radio-loud Sy 1.5 Mkn 6 to understand the complexity of its accreting circumnuclear gas structures. A series of high-quality, broadband X-ray spectra, including coverage above 10 keV, are needed to properly quantify the variable and complex line of sight absorbers. These new observations, in conjunction with radio and previous X-ray observations, will be a unique opportunity to understand accretion modes in the innermost regions of a radio-loud AGN that has recently undergone a merger.

Proposal Number: 1134
PI Last Name: Tombesi
Title: REVEALING THE BLACK HOLE WIND IN THE ULTRALUMINOUS INFRARED GALAXY IRAS F11119+3257 WITH NUSTAR
Abstract: Recent Herschel observations have identified powerful molecular outflows in ultraluminous infrared galaxies (ULIRGs), indicating that AGN feedback can indeed have a strong impact on star formation and galaxy evolution. Theoretical models describing the formation of such large-scale outflows require the existence of a putative inner accretion disk wind. Recently, we found the first observational evidence of such wind in a ULIRG, IRAS F11119+3257, in the form of blue-shifted Fe XXV/XXVI absorption lines with velocity of 0.25c in a Suzaku observation obtained in 2013. Here, we request a 100ks NuSTAR observation to independently confirm the Fe K absorber at E=8.5 keV and hard excess at E>10 keV. Only NuSTAR allows the continuous coverage of the critical E=7 30 keV energy band.

Proposal Number: 1136
PI Last Name: Papitto
Title: THE HARD X-RAY EMISSION IN A ROTATION-POWERED RADIO PULSAR STATE OF THE TRANSITIONAL MS PULSAR BINARY XSS J12270-4859
Abstract: We propose a 80 ks NuSTAR observation of the transitional ms pulsar XSS J12270-4859 during its first radio pulsar phase ever discovered, aimed at constraining the physical mechanism producing its X-ray emission (e.g. the intrabinary shock between the pulsar wind and the mass lost by the companion), at deriving the first broad-band spectral energy distribution from radio to gamma-rays, and at understanding if transitional pulsars represent unique few cases or instead are representative of the whole class of ms pulsar binaries.

Proposal Number: 1137
PI Last Name: Degenaar
Title: HOW NEUTRON STARS ACCRETE AT LOW EDDINGTON RATES
Abstract: Little is known about the properties of accretion flows around neutron stars accreting at <1E-2 of the Eddington limit. Here we propose to exploit the unprecedented sensitivity of NuSTAR at >10 keV to observe the remarkable neutron star low-mass X-ray binary IGR J17062-6143, which accretes persistently at ~1E-3 of the Eddington limit. With a 75 ks observation we will test the emission mechanism, geometry and origin of the poorly understood hard X-ray emission, which will yield important new insight into the morphology of low-level accretion flows around neutron stars.

Proposal Number: 1138
PI Last Name: Enoto
Title: QUIESCENT HARD X-RAYS OF THE FASTEST SPINING SGR/AXP 1E 1547.0-5408
Abstract: We propose a 80 ks NuSTAR observation of the fast spinning (2.07 s) SGR/AXP 1E 1547.0-5408. During a transient outburst in 2009, this magnetar exhibited a distinctive hard power-law in the ~10-100 keV band. Even at the present quiescent state (~0.4 mCrab), this source is still bright enough for NuSTAR to detect the hard X-rays. A good determination of its spectral index and intensity enables us to establish a broad-band spectral correlation with the pulsar poloidal field. We also search for evidence of free precession already suggested from the previous Suzaku observation. This will provide second evidence for a strong toroidal field inside magnetars.

Proposal Number: 1139
PI Last Name: Nowak
Title: NUSTAR OBSERVATIONS OF THE LOW LUMINOSITY AGN NGC 4258
Abstract: Given the unique constraints we have on the mass, distance, and inclination of the low luminosity active galactic nuclei (LLAGN) NGC 4258, and it's unique position as a bridge source between bright Seyferts (accreting at 10% of the Eddington luminosity) and likely Advection Dominated Accretion Flow (ADAF) systems (accreting at <10^-6 Eddington luminosity), we propose a 150 ksec NuSTAR observation of this source. We will study the historically variable narrow Fe line, and model the continuum spectrum with partial covering powerlaw models. We will search for evidence of spectral curvature in the hard X-rays. This will be the first observation with statistics sufficient to perform such a study.

Proposal Number: 1143
PI Last Name: Acero
Title: MEASURING THE SHAPE OF THE SYNCHROTRON CUT-OFF IN THE VELA JR. SNR
Abstract: The X-ray synchrotron emission in SNRs provides insights into the population of accelerated particles as well as on the mechanism of acceleration itself. The electron population emitting in X-rays is in the spectral cutoff region and its shape can provide important constraints on the limiting factor of the acceleration. However, there are currently poor observational constraints on the curvature of this cutoff because the leverage arm of "soft" (0.5-10 keV) X-ray telescopes is too narrow. We propose the first broad-band study of a synchrotron filament using the hard X-ray focusing telescope NuSTAR. To study the acceleration in a simple context, we target an isolated filament in the large diameter SNR Vela , allowing to isolate the physical processes taking place at the shock front.

Proposal Number: 1150
PI Last Name: Uchiyama
Title: HARD X-RAY IMAGING OF SYNCHROTRON-DOMINATED SNR RXJ1713.7-3946
Abstract: RX J1713.7-3946 is the strongest synchrotron X-ray and TeV gamma-ray emitter among galactic SNRs, and therefore an excellent SNR to compare the spectral shapes of the synchrotron X-ray and TeV gamma-ray emissions in great details. Our recent study with Chandra has revealed the presence of unresolved very hard X-ray sources along time-variable synchrotron X-ray filaments. The properties of the hard point-like sources challenge the standard perception of shock acceleration. Here we propose NuSTAR observations of SNR RX J1713.7-3946 to measure hard X-ray spectra of diffuse synchrotron X-rays and the very hard point-like source. The NuSTAR measurements can constrain the key parameters of shock acceleration such as diffusion coefficient at shocks.

Proposal Number: 1156
PI Last Name: Natalucci
Title: INVESTIGATION OF ACCRETION MODES AND MAGNETIC FIELD IN THE TRANSIENT HMXB IGR J16418 4532
Abstract: The detection of cyclotron absorption features in Supergiant Fast X-ray Transients (SFXT) is a powerful tool to unveil the physical processes driving their accretion modes. We propose a 40 ks observation by NuSTAR of the candidate SFXT IGR J16418 4532. The recent discovery by NuSTAR of a CSRF in the SFXT IGR J17544 2619 (Bhalerao et al. 2014) has motivated us to build upon this result by exploring the role of the magnetic field to characterize the accretion mode in these objects. A 40ks observation by NuSTAR will allow a sensitive cyclotron line search and a detailed study of the high energy spectrum of IGR J16418 4532 in two distinct accretion modes, characterized by low intensity and flaring emission.

Proposal Number: 1161
PI Last Name: Miller
Title: A NU SPIN ON GRS 1915+105 WITH NUSTAR
Abstract: We request two 20 ks observations of the well-known microquasar GRS 1915+105. GRS 1915+105 is extremely variable, and new exposures are guaranteed to expand upon the early-phase observation in the "low/hard" or"plateau" state. Additional observations can help to test our disk reflection-based spin constraint, as well as prior spin constraints in "high/soft" states based on the disk continuum. Recent work suggests that the continuum in the high/soft state may be strongly affected by wind absorption; the improved resolution and sensitivity of NuSTAR over RXTE will be essential to making a robust test of the spectrum. Last, additional exposures can potentially detect Lense-Thirring precession through phase-resolved spectroscopy of the QPOs.

Proposal Number: 1162
PI Last Name: Hornschemeier
Title: MONITORING THE X-RAY BINARY POPULATIONS OF THE M31 DISK WITH NUSTAR
Abstract: We propose a 100 ks NuSTAR exposure for each of three fields along the M31 disk as a first step in long-term monitoring of X-ray Binary (XRB) populations to LX~6e36 erg/s (4-25 keV) in an environment similar to the Milky Way (MW). These three pointings will follow ~3-12 months after the initial NuSTAR observations planned during early 2015 to connect XRB variability from hour to year-long timescales. We will (1) study individual XRBs similar to those seen in the MW but with slightly different environments and star formation histories and (2) establish a baseline for long-term monitoring. NuSTAR observations are critical as the different XRB accretion states are distinguishable at E>10 keV and only subtly different at 0.5-10 keV.

Proposal Number: 1166
PI Last Name: van der Horst
Title: NUSTAR OBSERVATIONS OF THE MAGNETAR SGR 1806-20
Abstract: Magnetars are young isolated neutron stars with bright persistent X-ray emission and bursting behavior in hard X-rays/soft gamma-rays, caused by their extremely high magnetic fields. Here we propose to monitor one of the most prolific bursting magnetars, SGR 1806-20, with NuSTAR over the course of one year, to study the low-level bursting behavior of this source, its broad-band persistent X-ray emission, and the connection between these two properties. This will allow us to characterize the spectral and temporal properties of any low-level bursting activity, study the effect of low-level bursting activity on the erratic timing behavior of the source, track any change in torque, and characterize the hard X-ray spectral and temporal properties of SGR 1806-20.

Proposal Number: 1176
PI Last Name: Croston
Title: PHYSICAL CONDITIONS IN THE LOBES OF A POWERFUL RADIO GALAXY
Abstract: The energetic impact of radio-loud AGN is widely accepted to have crucial effects on the growth of the most massive galaxies. A very important method of assessing the energetics of a particular source involves combining radio and X-ray observations to measure magnetic field strengths in the lobes using synchrotron and inverse-Compton observations. With soft X-ray observations this method is model-dependent because the electrons responsible for the inverse-Compton emission emit synchrotron radiation below the observable radio band. NuSTAR offers us the chance to subject the inverse-Compton model to a critical test and make the first model-independent measurement of field strength and field variation. Our target is the brightest inverse-Compton source in the sky, Pictor A.

Proposal Number: 1177
PI Last Name: Madsen
Title: OBSERVATION OF TWO YOUNG PWNE: G11.2-0.3 AND SNR B0540-69
Abstract: We propose observations of two pulsar-wind nebulae in shell remnants, B0504-69 for 50ks and G11.2-0.3 for 100ks, to expand our understand of the PWN and PSR spectra respectively above 10keV. These two targets are bright and allow us in a relatively short amount of time to probe the possibility of spectral breaks between 10 and 80 keV, like those observed by NuSTAR in the Crab and G21.5-0.9. In addition to using the timing properties of NuSTAR to separate the PWN from the PSR, we will also be imaging G11.2-0.3 above 10 keV for the first time.

Proposal Number: 1181
PI Last Name: Lanz
Title: NGC1266: A LOCAL COMPTON-THICK AGN IN A QUENCHING GALAXY
Abstract: NGC1266 is a nearby lenticular galaxy hosting a massive molecular outflow likely driven by its AGN. The turbulence injected into the ISM by the outflow may account for the suppression its star formation by a factor of 50-150. Recent ALMA and CARMA measurements of the dense gas tracers H13CN and CS show its nuclear region lies behind a column of N(H2)~3x10^24 cm^-2. Current XMM-Newton and Chandra observations of NGC1266 cannot conclusively differentiate between a moderately bright (LX~10^42 erg/s) Compton-thick AGN or a ultra-compact central starburst with a top-heavy IMF. We propose to observe NGC1266 using NuSTAR to measure the hard X-ray properties of its central source and thereby conclusively determine which of these mechanisms is responsible for the feedback observed in this galaxy.

Proposal Number: 1200
PI Last Name: Young
Title: M81: ACCRETION GEOMETRY AT LOW EDDINGTON RATES
Abstract: We propose to observe the Low-Luminosity Active Galactic Nucleus of M81 for 200 ksec with NuSTAR and for 100 ksec with Suzaku. In low accretion rate AGN, where does the optically thick part of the accretion disk stop? Does it go in to within a few gravitational radii of the black hole, as in higher accretion rate Seyfert galaxies, or does it stop hundreds of gravitational radii from the black hole? Using NuSTAR and Suzaku spectra we will measure the strengths of the Compton reflection hump, Fe K alpha, Fe XXV and Fe XXVI lines. This will determine whether the Fe K alpha line is produced by reflection off the optically thick outer disk, or is produced in the optically thin inner flow. We will measure the reflection fraction and constrain the source geometry and disk transition radius.

Proposal Number: 1202
PI Last Name: Margutti
Title: THE UNPRECEDENTED METAMORPHOSIS OF SN2014C: FROM A H-STRIPPED EXPLOSION TO A STRONGLY INTERACTING SN
Abstract: Mass loss in evolved massive stars is one of the least understood yet fundamental aspects of stellar evolution. HOW and WHEN do massive stars lose their H-envelopes? This central question motivates this proposal. We request NuSTAR observations to map the unique situation of the interaction of a H-stripped SN2014C with a H-rich shell ejected by its progenitor star, as part of our radio-to-gamma-ray follow-up. Our goal is to constrain the density and proximity of the ejected material, and hence the mass-loss history of the progenitor star. Unlike all the other H-stripped SNe, the radio and X-ray emission of SN14C is still increasing at t>300 days, giving us the unprecedented opportunity to map the density profile of the ejected material and constrain the epoch of its ejection in fine detail.

Proposal Number: 1208
PI Last Name: Lopez
Title: PROBING THE HIGHEST ENERGY ELECTRONS ACCELERATED BY THE SUPERBUBBLE 30 DOR C WITH NUSTAR
Abstract: We propose to observe the superbubble (SB) 30 Dor C with NuSTAR for 200 ks to probe particle acceleration within the region. SBs are plausible candidates for sites of cosmic-ray acceleration, yet observational evidence of diffuse non-thermal X-ray emission in SBs has remained controversial. Portions of 30 Dor C have been imaged off axis serendipitously by NuSTAR in its monitoring of nearby SN 1987A, and these data demonstrate that electrons are accelerated to TeV energies in the SB shell. However, at the off axis position of 30 Dor C, vignetting dramatically reduces the throughput of the instrument, and robust background subtraction is not possible. Thus, we request new observations close to the optical axis that are specifically designed to probe the hard X-ray emission of 30 Dor C.

Proposal Number: 1216
PI Last Name: Wolff
Title: NUSTAR OBSERVATIONS OF THE SYMBIOTIC BINARY GX 1+4
Abstract: We propose a 50 ks NuSTAR observation of the symbiotic X-ray binary GX 1+4. This source was one of the first sources found in the direction of the galactic center. This source is an accreting X-ray pulsar with a hard spectrum and it can sometimes reach many tens of mCrab (2-60 keV) in brightness. Little is known for certain about this source, in particular the neutron star magnetic field strength and the physics of the formation of its X-ray spectrum are not well understood. We will analyze the NuSTAR spectrum and place constraints on the magnetic field strength by comparing the observed spectrum with a Becker & Wolff model for the radiation-dominated, radiative shock in the magnetically funneled accretion flow.

Proposal Number: 1217
PI Last Name: Iwasawa
Title: FIRE UNDER ICE: ULIRG IRAS F00183-7111
Abstract: We propose a 100 ks NuSTAR observation of the ultra-luminous infrared galaxy IRAS F00183-7111 at z=0.327. The mid-IR spectrum of this galaxy is characterized by deep silicate absorption and the previous X-ray observation showed that a Compton thick AGN is present in the ULIRG and dominates the large output. We aim at detecting absorbed primary emission of the obscured nucleus and a measurement of the hard X-ray spectrum above 10 keV.

Proposal Number: 1219
PI Last Name: Hickox
Title: SUPERORBITAL VARIATION OF LMC X-4: EXPLORING THE INNER ACCRETION FLOW WITH NUSTAR AND SUZAKU
Abstract: We propose for a series of four 20ks observations with NuSTAR and Suzaku XIS of the binary X-ray pulsar LMC X-4. This source shows 13.5 s pulsations, a 1.4 d orbital period, and a long-period (~30 d) superorbital cycle due to a warped, precessing accretion disk. This disk is heated by the pulsed hard X-ray beam from the neutron star, and observations of this thermal emission can provide a unique probe of the inner accretion flow near the magnetosphere. However this requires sensitivity and timing resolution across the full X-ray band (from below 1 keV to above 20 keV), and full sampling of a full superorbital cycle. We will take advantage of NuSTAR's exquisite high-energy sensitivity in concert with Suzaku to yield the clearest picture to date of the inner accretion flow.

Proposal Number: 1220
PI Last Name: Braito
Title: PROBING THE ABSORPTION AND CONTINUUM VARIABILITY IN THE SEYFERT 2 NGC4507
Abstract: X-ray monitoring of bright Seyfert that show changes in the amount of X-ray absorption, are the key programs in assessing the nature and location of the X-ray absorbing media present in the central regions of AGN. We propose a monitoring (5x30ks) of the obscured and bright AGN NGC4507. NGC4507 shows dramatic changes of its X-ray emission altering from transmission to reflection dominated states and a strong variability of its X-ray flux in the 14-195keV band. NuSTAR sensitivity over the 3-79 keV energy range offers a unique tool to investigate the X-ray emission of NGC4507, allowing us to decouple any possible ambiguity on the variability of the intrinsic emission and amount of absorption. This will be the first monitoring on short timescale of this AGN in the hard X-ray band.

Proposal Number: 1222
PI Last Name: Fuerst
Title: LUMINOSITY DEPENDENCE OF THE CYCLOTRON LINE IN GX 301-2
Abstract: We propose to observe the HMXB GX301-2 for 30ks around orbital phase 0.75-0.85 to measure the luminosity dependence of its cyclotron line. This observation will allow us to understand the accretion geometry of GX301-2 and provide a missing link between archival observations. A first NuSTAR observation was performed in October 2014 around orbital phase 0.5 during which the source was in an anomalous low state. The new data will allow us to compare a higher luminosity observation to this very low luminosity data and compare spectral changes as function of luminosity and orbital phase to investigate the accretion geometry. Additionally they will allow us to perform time- and phase-resolved spectral analysis to study short term changes in the X-ray production region.

Proposal Number: 1232
PI Last Name: Bogdanov
Title: THE REDBACK BINARY PSR J1723-2837: A LABORATORY FOR PULSAR WIND AND SHOCK PHYSICS
Abstract: The class of so-called "redback" millisecond pulsar binaries typically exhibit non-thermal X-ray emission that originates in an intra-binary shock produced by the interaction of the energetic pulsar wind with material from the close companion star. We propose a 79-ks NuSTAR observation of the redback PSR J1723-2837 to establish for the first time its hard X-ray properties up to ~60 keV thereby constraining the broad-band variability pattern and spectrum of the shock. As the brightest known object of its kind in X-rays, PSR J1723-2837 offers the best opportunity to study key unknowns regarding the characteristics of millisecond pulsar winds and the physics of shocks.

Proposal Number: 1236
PI Last Name: Wood
Title: NUSTAR OBSERVATIONS OF THE PUZZLING ROTATION-POWERED PULSAR PSR J1813-1246
Abstract: PSR J1813-1246 is a 48-ms rotation powered pulsar found by Fermi in gamma-rays and recently found to be pulsing in X-rays below 10 keV, using XMM. The X-ray pulses are advanced 90 degrees in phase relative to the gamma-rays, and the X-ray spectrum appears to be extremely hard. This phase offset is modeled by invoking a substantial physical separation of the X-ray and gamma-ray emitting regions. Further understanding and model refinement requires observations of the spectrum and light curve at energies above 10 keV. NuSTAR is uniquely qualifited to perform this observation, having the requisite sensitivity, energy coverage and time resolution. We propose a 50 ks observation, designed to address the puzzling nature of the source.

Proposal Number: 1241
PI Last Name: Yukita
Title: BINARIES IN THE M31 BULGE: A HARD X-RAY VIEW OF OLD STELLAR POPULATIONS
Abstract: We propose a 100 ks NuSTAR observation of the M31 bulge to investigate the resolved point source population at E >10 keV. This observation will allow us to investigate, for the first time, source populations in an older stellar environment at harder energies outside our own galaxy. Our primary objectives are (1) to explore the previously detected, luminous, E > 10 keV emission by Swift BAT with NuSTAR's better PSF, (2) to investigate the nature and accretion states of the resolved point sources, and (3) to compare and examine hard X-ray point sources in the different stellar environments (disk vs. bulge).

Proposal Number: 1243
PI Last Name: Armus
Title: HEARTS OF DARKNESS: PROBING THE MOST OBSCURED LIRGS IN THE LOCAL UNIVERSE WITH NUSTAR
Abstract: A detailed study of low-redshift LIRGs is critical for our understanding of the cosmic evolution of galaxies and black holes, since LIRGs comprise the bulk of the cosmic far-infrared background and dominate the star-formation between 0.5 < z < 1. Among the 254 galaxies that are part of the Great Observatories All-Sky LIRG Survey (GOALS), there are a dozen highly obscured galaxies those with extremely deep 9.7-micron silicate features, implying A_V > 30-80 mags. We propose to observe 4 of these sources with NuSTAR to search for buried AGN, measure the hard X-ray spectrum, and characterize the the nature of the obscuring circum-nuclear, interstellar medium on scales of 10-100 pc.

Proposal Number: 1250
PI Last Name: Becerra Gonzalez
Title: SEARCHING FOR COSMOLOGICAL PROBES WITH NUSTAR
Abstract: We wish to exploit the unique capabilities of NuSTAR supported by simultaneous observations by the Swift and Fermi-LAT to search for the most powerful BL Lac objects. NuSTAR observations of a carefully chosen sample of high-peaked BL Lacs at 3-79keV will provide strong constraints on the high-energy portion of the electron distribution in the primary jet emitting region. Since these are the same electrons responsible for the very high energy (VHE, E>100 GeV) gamma-ray emission, it will allow testable predictions of the VHE emission. This will identify the best sources to observe with atmospheric Cherenkov telescopes for the goal of constraining the extragalactic background light (EBL) and the intergalactic magnetic field (IGMF).

Proposal Number: 1259
PI Last Name: Markowitz
Title: UNDERSTANDING CORE EMISSION IN THE NEARBY RADIO-LOUD AGN CENTAURUS A
Abstract: Centaurus A, the nearest radio-loud AGN, offers a complexity of X-ray emitting components, and we seek to accurately constrain the high-energy power-law continuum shape. Our group has a Chandra-LETG observation scheduled for May 2015, to study the diffuse plasma. We request a 20 ks NuSTAR observation simultaneous to the LETG observation. We will use the Chandra observation to assess the impact of variable point sources (particularly the core) on the NuSTAR spectrum. We will also use the NuSTAR+Swift spectra to correctly model continuum components in the LETG spectrum.

Proposal Number: 1267
PI Last Name: Bachetti
Title: TIMING AND SPECTRAL STUDIES OF THE ULTRALUMINOUS X-RAY SOURCES IN M82.
Abstract: M82 X-2 is the first ultraluminous X-ray source (ULX) found to harbor a pulsar, and so a neutron star (NS). Its luminosity is ~10 times the theoretical limits for accretion onto NSs, and investigating its nature is of extreme importance to understand the accretion process. The same galaxy harbors another remarkable source: M82 X-1 is one of the brightest ULXs known, and recent evidence strongly suggested a nature of intermediate-mass black hole. We propose a 2.5-d observation of M82 during AO-1. The primary goal is to track the timing of M82 X-2, and constrain its long-term spin evolution and its orbital evolution. If this source is too faint, we will take advantage of it and study the broadband spectrum of M82 X-1 that would normally be too strongly contaminated by X-2.

Proposal Number: 1272
PI Last Name: Nelson
Title: A REFLECTION ON SYMBIOTIC STARS - USING REFLECTED X-RAYS TO CONSTRAIN PROPERTIES OF THE WHITE DWARF AND ACCRETION DISK
Abstract: Symbiotic stars are powered by a white dwarf accreting from a late type giant mass donor. We now know that many symbiotic stars are medium energy (2-10 keV) X-ray sources, but some stand out as luminous, hard sources detected in the INTEGRAL and Swift/BAT surveys. The X-rays likely originate in the accretion disk boundary layer, and so we expect reflection from the white dwarf surface and the disk. The highest temperature plasma present allows us to set a lower limit to their white dwarf mass, probably to values not too far from the Chandrasekhar limit. We therefore propose NuSTAR observations of three X-ray luminous symbiotic systems, T CrB, RT Cru and V648 Car, to (1) confirm the presence of an accretion disk via the presence of reflection, and (2) constrain the white dwarf mass.

Proposal Number: 1273
PI Last Name: Risaliti
Title: A HARD X-RAY VIEW OF QUASAR 2S INSIDE ULIRGS
Abstract: We propose NuSTAR observations of four ULIRGs with extreme properties: they all host a deeply buried quasar, revealed by mid-IR spectra, but do now show significant X-ray emission below 10~keV, suggesting complete obscuration of the central source. NuSTAR can pierce into the gas and dust screen, revealing for the first time examples of the long-sought quasar 2s in the local Universe. In one case a good quality spectrum is granted based on a previous Suzaku observation; in the other cases we may detect the AGN component for the first time. Confirming the presence of powerful quasars inside ULIRGs would be an important step towards a complete understanding of galaxy and AGN co-evolution.

Proposal Number: 1274
PI Last Name: Bauer
Title: WHEN IN THE MAJOR MERGER SEQUENCE IS (OBSCURED) BLACK HOLE GROWTH TRIGGERED?
Abstract: With the unrivaled 10-30 keV sensitivity provided by NuSTAR, we propose a snapshot program to observe a volume-limited sample of 13 luminous infrared galaxies spread across the galaxy major merger sequence. When combined with archival NuSTAR data, these observations stand to place the strongest constraints to date on the timing of SMBH growth during galaxy evolution, effectively probing the potential accretion signatures from even Compton-thick AGN (going where Chandra could not).

Proposal Number: 1279
PI Last Name: Lutovinov
Title: OBSERVATIONS OF SUPERGIANT X-RAY BINARY SYSTEMS: SEARCH OF THE CLUE FOR THE SFXT MECHANISMS
Abstract: We propose two 40~ks NuSTAR observations of two persistent wind accreting X-ray pulsars in high-mass X-ray binaries (HMXB), IGR J18027-2016 and 4U1909+07, which have similar orbital periods and optical companions with supergiant fast X-ray transient IGR J17544-2619. The observations are aimed at (i) detecting cyclotron resonance scattering spectral features (CRSF), (ii) pulsar timing measurements. The properties of the sources will be compared with those of IGR J17544-2619 in order to determine the physical parameters (or their combination) responsible for different variability character observed in these two classes of accreting neutron stars.

Proposal Number: 1281
PI Last Name: Grinberg
Title: REFLECTION AND THE INNER ACCRETION FLOW IN NEUTRON STAR LOW MASS X-RAY BINARIES: THE CASE OF GX 354-0
Abstract: We propose a 60ks NuSTAR observation of GX 354-0 that will allow us to self-consistently model the reflection in this low mass neutron star X-ray binary and to test relativistic reflection models in the low spin limit. We will put constraints on the non-reflection origin of the observed iron line and obtain further estimates of the neutron star parameters by employing NuSTAR s timing capabilities to measure the kHz QPO present in the source.

Proposal Number: 1285
PI Last Name: Ajello
Title: CHASING THE MOST POWERFUL BLAZARS
Abstract: MeV blazars, that have larger-than-average jet powers, accretion luminosities and black hole masses,are best studied in the hard X-ray domain where they display extremely hard X-ray continua. Observations in this domain probe the acceleration mechanism, the bulk Lorentz factor, and the emission process. We propose to observe with NuSTAR the 3 most luminous MeV blazars detected by Fermi that do not have any observation between 10 keV and 100 MeV. We will complement the NuSTAR exposure with observations with Fermi, Swift and GROND to obtain an high-quality simultaneous SED for all these sources. Moreover, optical spectroscopy will be performed for 2 targets lacking a kinematic measurement of the black hole mass. All this will greatly enhance our knowledge of this elusive source class

Proposal Number: 1289
PI Last Name: Wilms
Title: THE HARD TAIL OF THE CANONICAL SOFT STATE BLACK HOLE LMC X-3
Abstract: We propose a 30 ks observation of the canonical soft state black hole LMC X-3. Our aim is to perform the first high signal to noise ratio observation of the hard tail of this source to confirm its non-thermal nature and to study the transition between the hard tail and the thermal component.

Proposal Number: 1290
PI Last Name: Gotthelf
Title: HIGH ENERGY X-RAY SPECTROSCOPY OF THE EXCEPTIONAL MILLISECOND PULSAR PSR B1821-24
Abstract: PSR B1821-24 in M28 is the most energetic and X-ray luminous "recycled" millisecond pulsar known. It exhibits hard, purely non-thermal emission, nearly all of it contained within two very narrow pulses. Extensive hard X-ray observations with RXTE have detected this object only up to ~15 keV owing to the overwhelming background of this non-imaging telescope. We propose a deep NuSTAR observation of PSR B1821-24 to characterize its >15 keV emission for the first time. This will provide fresh insight into the high-energy emission processes that operate in millisecond pulsars, which in turn may improve our understanding of particle acceleration mechanisms in pulsar magnetospheres, in general.

Proposal Number: 1291
PI Last Name: Corbet
Title: PROPERTIES AND CAUSE OF SUPERORBITAL PERIODS IN SUPERGIANT X-RAY BINARIES
Abstract: There are now at least 5 supergiant High-Mass X-ray Binaries where superorbital periods have been found - predominantly at energies above 15 keV. Curiously, these periods increase monotonically with orbital period. We propose to obtain two NuSTAR observations of IGR J16493-4348 to determine the detailed spectral properties and their changes over its superorbital period. Suggested driving mechanisms for the modulation include pulsations in the primary star, 3 body systems, and precession of the primary with an equatorial wind. To allow detailed modeling to proceed, good characterization of the modulation properties in hard X-rays is first required. We will also determine whether a previously claimed cyclotron feature at ~30 keV is present.

Proposal Number: 1292
PI Last Name: Marcu
Title: CENTAURUS X-3: IMPROVING THE CONTINUUM MODELING OF ACCRETING PULSARS
Abstract: We propose a NuSTAR observation of the accreting pulsar Cen X-3 in order to perform a spectral analysis of the currently unexplained feature that has been seen ~10 keV in the spectra of a number of these types of sources. This would be the first detailed study of the feature. NuSTAR is currently the best instrument for the scientific objectives of this project because it allows high precision broadband spectral measurements, particularly at energy where the feature has been observed. Our objectives are to constrain the parameters of the feature by applying empirical continuum models and also determine how both the boradband spectrum and the feature can be described with newly implemented physical models.

Proposal Number: 1295
PI Last Name: Wik
Title: UNAMBIGUOUSLY DETECTING NON-THERMAL AND SHOCKED GAS IN ABELL 2163
Abstract: Since the first non-thermal detections of inverse Compton (IC) emission in galaxy clusters at hard X-ray energies, we have yet to unambiguously confirm IC in follow-up observations. Claims of large IC fluxes from the 10' extent of Abell 2163, a massive merging cluster at z=0.2, give it the best chance of confirming a previous IC detection with NuSTAR. Additionally, recently available deep XMM data indicate extreme temperature variations (10-20 keV), the hottest of which are likely due to shocks. However, the XMM spectra suffer from variable Galactic absorption across the cluster, which can be avoided with NuSTAR's harder energy band. We will definitively confirm or refute the previously estimated IC flux and constrain the high kT makeup of this dynamic cluster.

Proposal Number: 1296
PI Last Name: Homan
Title: THE SUPER-EDDINGTON ACCRETION FLOW IN GX 5-1
Abstract: We propose three short (25 ks) observations of the super-Eddington neutron-star low-mass X-ray binary GX 5-1. The properties of super-Eddington accretion flows onto neutron stars are still poorly understood. The aim of our observations is to test proposed models for the spectral evolution in this type of source, by simultaneously constraining the continuum and reflection features (in particular the Fe line) in the spectrum. NuSTAR is uniquely capable of doing so. By observing GX 5-1 we also complete NuSTAR's coverage of neutron-star low-mass X-ray binaries across the entire luminosity range of this class, allowing for a detailed comparison between subclasses.

Proposal Number: 1299
PI Last Name: Stierwalt
Title: CAN DWARF-DWARF GALAXY INTERACTIONS TRIGGER THE GROWTH OF AGN?
Abstract: We propose NuSTAR observations of 4 AGN candidates hosted by dwarf galaxies with a close dwarf galaxy companion to determine whether dwarf-dwarf interactions can trigger the growth of an active massive black hole. Super massive black holes (SMBHs) are thought to play an important role in galaxy evolution, but their formation mechanisms are not well understood. Massive black holes in today's dwarf galaxies offer a unique window into not only the typical masses of early black holes and the properties of the galaxies that host them, but also how these seeds may have formed. Mergers among massive galaxies are observed to fuel central AGN but whether or not this process happens at lower mass scales in dwarf-dwarf interactions is unknown. In fact, two of the three confirmed AGN in dwarf galaxies

Proposal Number: 1301
PI Last Name: Roberts
Title: EXPLORING THE ENERGETICS OF THE INTRABINARY SHOCK IN THE REDBACK SYSTEM PSR J2129-0429
Abstract: We propose a NuStar observation of PSR J2129-0429, a redback millisecond pulsar which is at an earlier stage of the recycling process than PSR J1023+0038. This will help determine if a very hard X-Ray spectrum out to 10s of keV is an ubiquitous feature of redback systems. It will also let us explore the potential effect of synchrotron cooling as a function of orbital phase, which may clarify the role of the companions magnetic field in determining the geometry and emission properties of the shock.

Proposal Number: 1302
PI Last Name: Zhang
Title: HARD X-RAY MORPHOLOGY AND SPECTROSCOPY OF THE INTERACTION SITE BETWEEN THE SUPERNOVA REMNANT IC 443 AND MOLECULAR CLOUD
Abstract: IC 443 is the best target to study SNR-MC interaction to its brightness and proximity. Yet, its complexity with several unidentified soft X-ray (<10 keV) sources as well as their unknown relationship with the GeV emission requires high-resolution hard X-ray (>10 keV) observation for a broadband SED study. Previous INTEGRAL observation was not able to resolve the hard X-ray source 1SAX J0618.0+2227 detected in the SNR-MC interaction site. Our simulation show that NuSTAR will able to resolve the hard X-ray source and obtain high resolution spectroscopy. It will be the first confirmation of hard X-ray emission due to SNR-MC interaction and sternly constrain the model parameters.This will also shed light on understanding of other hard X-ray sources in the other SNR-MC interaction systems.

Proposal Number: 1303
PI Last Name: Hickox
Title: THE SEARCH FOR EXTREME ABSORPTION IN ``TYPICAL'' WISE-SELECTED OBSCURED QUASARS
Abstract: One of the major science drivers of NuSTAR is to uncover the growth of supermassive black holes that are hidden behind large columns of gas and dust, and a particular focus is the powerful obscured quasars that have previously proven difficult to detect and characterize. Here we propose to observe a sample of four quasars, selected based on mid-IR photometry from WISE and SDSS, that represent the "typical" obscured quasar population and complement previous studies of specific quasar subsets with more complicated selection effects. These 126 ks total observations will use NusTAR's high-energy sensitivity to provide the best measurements of heavy obscuration in "typical" mid-IR selected quasars, and constrain their contributions to the hard cosmic X-ray background.