1,723,707 research outputs found
Nustar Results and Future Plans for Magnetar and Rotation-Powered Pulsar Observations
Get PDFThe Nuclear Spectroscopic Telescope Array (NuSTAR) is the first focusing hard X-ray mission in orbit and operates in the 3–79 keV range. NuSTAR's sensitivity is roughly two orders of magnitude better than previous missions in this energy band thanks to its superb angular resolution. Since its launch in 2012 June, NuSTAR has performed excellently and observed many interesting sources including four magnetars, two rotation-powered pulsars and the cataclysmic variable AE Aquarii. NuSTAR also discovered 3.76-s pulsations from the transient source SGR J1745–29 recently found by Swift very close to the Galactic center, clearly identifying the source as a transient magnetar. For magnetar 1E 1841–045, we show that the spectrum is well fit by an absorbed blackbody plus broken power-law model with a hard power-law photon index of ∼ 1.3. This is consistent with previous results by INTEGRAL and RXTE. We also find an interesting double-peaked pulse profile in the 25–35 keV band. For AE Aquarii, we show that the spectrum can be described by a multi-temperature thermal model or a thermal plus non-thermal model; a multi-temperature thermal model without a non-thermal component cannot be ruled out. Furthermore, we do not see a spiky pulse profile in the hard X-ray band, as previously reported based on Suzaku observations. For other magnetars and rotation-powered pulsars observed with NuSTAR, data analysis results will be soon availableUnited States. National Aeronautics and Space Administration (NASA Contract No. NNG08FD60C)United States. National Aeronautics and Space Administration (NASA grant NNX10AI72G)United States. National Aeronautics and Space Administration (NASA Grant NNX13AI34G)United States. Dept. of Energy (Lawrence Livermore National Laboratory Contract DE- AC52-07NA27344
First NuSTAR Observations of Mrk 501 within a Radio to TeV Multi-Instrument Campaign
No full textVK: BIBCODE: 2015ApJ...812...65F; DOI: 10.1088/0004-637X/812/1/65; eprintid: arXiv:1509.04936We report on simultaneous broadband observations of the TeV-emitting blazar Markarian 501 between 2013 April 1 and August 10, including the first detailed characterization of the synchrotron peak with Swift and NuSTAR. During the campaign, the nearby BL Lac object was observed in both a quiescent and an elevated state. The broadband campaign includes observations with NuSTAR, MAGIC, VERITAS, the Fermi Large Area Telescope, Swift X-ray Telescope and UV Optical Telescope, various ground-based optical instruments, including the GASP-WEBT program, aswell as radio observations by OVRO, Metsähovi, and the F-Gamma consortium. Some of the MAGIC observations were affected by a sand layer from the Saharan desert, and had to be corrected using event-by-event corrections derived with a Light Detection and Ranging (LIDAR) facility.This is the first time that LIDAR information is used to produce a physics result with Cherenkov Telescope data taken during adverse atmospheric conditions, and hence sets a precedent for the current andfuture ground-based gamma-ray instruments. The NuSTAR instrument provides unprecedented sensitivity in hard X-rays, showing the source to display a spectral energy distribution (SED) between 3 and 79 keV consistent with a log-parabolic spectrum and hard X-ray variability onhour timescales. None (of the four extended NuSTAR observations) show evidence of the onset of inverse-Compton emission at hard X-ray energies. We apply a single-zone equilibrium synchrotron self-Compton(SSC) model to five simultaneous broadband SEDs. We find that the SSC model can reproduce the observed broadband states through a decrease inthe magnetic field strength coinciding with an increase in the luminosity and hardness of the relativistic leptons responsible for the high-energy emission.Peer reviewe
StrayCats II: A catalog of NuSTAR Stray Light Observations
No full textIn addition to being the first focusing hard X-ray space observatory, NuSTAR is also sensitive to sources from 1- to 3-degrees from the optical axis that pass through the telescope structure to shine on the detectors. When a bright source falls into this region of the sky, a characteristic stray light pattern is observed on the detectors and the instrument can be used as a classical collimated instrument. For bright (mostly Galactic) X-ray sources, this provides additional data suitable both for spectroscopy (including above the fiducial 78 keV cutoff caused by the NuSTAR optics) and timing/variability studies. Most of these sources have multiple epochs spanning a variety of source behaviors. StrayCats v1 included all SL sources through mid-2021. StrayCats v2 (released May 2022) updates this catalog through Jan 2022 and now includes long-term lightcurves, hardness ratios, and source extraction regions for most entries in the catalog
First Nustar Observations Of Mrk 501 Within A Radio To Tev Multi-Instrument Campaign
Get PDFWe report on simultaneous broadband observations of the TeV-emitting blazar Markarian 501 between 2013 April 1 and August 10, including the first detailed characterization of the synchrotron peak with Swift and NuSTAR. During the campaign, the nearby BL Lac object was observed in both a quiescent and an elevated state. The broadband campaign includes observations with NuSTAR, MAGIC, VERITAS, the Fermi Large Area Telescope, Swift X-ray Telescope and UV Optical Telescope, various ground-based optical instruments, including the GASP-WEBT program, as well as radio observations by OVRO, Metsähovi, and the F-Gamma consortium. Some of the MAGIC observations were affected by a sand layer from the Saharan desert, and had to be corrected using event-by-event corrections derived with a Light Detection and Ranging (LIDAR) facility. This is the first time that LIDAR information is used to produce a physics result with Cherenkov Telescope data taken during adverse atmospheric conditions, and hence sets a precedent for the current and future ground-based gamma-ray instruments. The NuSTAR instrument provides unprecedented sensitivity in hard X-rays, showing the source to display a spectral energy distribution (SED) between 3 and 79 keV consistent with a log-parabolic spectrum and hard X-ray variability on hour timescales. None (of the four extended NuSTAR observations) show evidence of the onset of inverse-Compton emission at hard X-ray energies. We apply a single-zone equilibrium synchrotron self-Compton (SSC) model to five simultaneous broadband SEDs. We find that the SSC model can reproduce the observed broadband states through a decrease in the magnetic field strength coinciding with an increase in the luminosity and hardness of the relativistic leptons responsible for the high-energy emission
Multiwavelength Study Of Quiescent States Of Mrk 421 With Unprecedented Hard X-Ray Coverage Provided By Nustar In 2013
Get PDFWe present coordinated multiwavelength observations of the bright, nearby BL Lacertae object Mrk 421 taken in 2013 January–March, involving GASP-WEBT, Swift, NuSTAR, Fermi-LAT, MAGIC, VERITAS, and other collaborations and instruments, providing data from radio to very high energy (VHE) γ-ray bands. NuSTAR yielded previously unattainable sensitivity in the 3–79 keV range, revealing that the spectrum softens when the source is dimmer until the X-ray spectral shape saturates into a steep power law, with no evidence for an exponential cutoff or additional hard components up to ~80 keV. For the first time, we observed both the synchrotron and the inverse-Compton peaks of the spectral energy distribution (SED) simultaneously shifted to frequencies below the typical quiescent state by an order of magnitude. The fractional variability as a function of photon energy shows a double-bump structure that relates to the two bumps of the broadband SED. In each bump, the variability increases with energy, which, in the framework of the synchrotron self-Compton model, implies that the electrons with higher energies are more variable. The measured multi band variability, the significant X-ray-to-VHE correlation down to some of the lowest fluxes ever observed in both bands, the lack of correlation between optical/UV and X-ray flux, the low degree of polarization and its significant (random) variations, the short estimated electron cooling time, and the significantly longer variability timescale observed in the NuSTAR light curves point toward in situ electron acceleration and suggest that there are multiple compact regions contributing to the broadband emission of Mrk 421 during low-activity states
Precise measurement of the cosmic X-ray background with NuSTAR
No full textIn the first X-ray astronomical observations in the early 60s, isotropic X-ray radiation was discovered - the cosmic X-ray background (CXB). According to the generally accepted paradigm, the CXB is composed of the radiation of numerous active galactic nuclei, and its broadband spectrum contains information about the growth history of supermassive black holes in the Universe. Despite the long history of X-ray studies and the rapid development of observational technology, the measurement of the exact characteristics of the CXB is associated with significant uncertainties. We measured the CXB spectrum in the energy range from 3 to 20 keV using the NuSTAR observations of selected extragalactic fields with a total exposure of 7 Ms. Our method uses spatial modulation of the CXB signal on the NuSTAR detectors through the telescope's side aperture. A record statistical measurement accuracy of less than one percent has been achieved, with an insignificant contribution of systematic noise. The observed differences in the intensity of the CXB in different directions on the sky are consistent with the expected dispersion of the CXB due to variations in the population of point sources, which opens up new possibilities for studying the angular fluctuations of the CXB on a scale of several square degrees
A search for the `10 keV feature' in the NuSTAR spectra of accreting X-ray pulsars
No full textA peculiar characteristic exhibited by the accretion powered X-ray pulsars is called the '10 keV feature', which appears as a dip/hump/wiggle in the X-ray spectrum at around 10 keV. Using the NuSTAR archival observations of several bright accretion powered X-ray pulsars, we extensively searched for the 10 keV feature. Surprisingly, we found the occurrence of the 10 keV feature to be rare as opposed to previous reports
Follow-up of eROSITA discovered X-ray binaries with NuSTAR and XMM
No full textWe report on the first follow-up observations of galactic X-ray binary candidates identified in the ongoing SRG/eRosita all-sky survey, with NuSTAR (~60ks) and XMM-Newton (26ks and 27ks). This analysis is part of a project in the eROSTEP (eROsita view of STellar EndPoints) network, with a focus on search and identification of galactic X-ray binaries. Preliminary analysis of the broadband X-ray spectrum of eRASSU J084850 observed with NuSTAR shows that the continuum can be well described either with a comptonization spectrum, or emission from an accretion disk (diskbb) along with a reflection component. There is no significant evidence of a cyclotron resonant scattering feature and no pulsations are present in the lightcurve. The most likely optical counterpart of the source is identified as a Be star, UCAC2 13726137, ~3'' away, suggesting that the compact object is most likely a neutron star. Analysis of XMM data of eRASSU J061331 and eRASSU J161201 allowed better localization of both X-ray sources and their optical counterparts. In both cases, low counting statistics precluded detection of significant pulsations in the lightcurves from XMM. The XMM spectra are consistent with thermal emission from collisionally ionised plasma and there is no strong evidence for the presence of a power-law type continuum component. Moreover, their X-ray and optical behaviour appear more similar to chromospheric active stars than X-ray binaries. Further confirmation of this is pending
The first hard X-ray spectral catalogue of Blazars observed by NuSTAR
No full textBlazars are a peculiar class of active galactic nuclei (AGNs) that enlighten the sky at all wavelengths. The electromagnetic emission of these sources is jet-dominated resulting in a spectral energy distribution (SED) that has a typical double-humped shape. X-ray photons provide a wealth of information on the physics of each source as in the X-ray band we can observe the tail of SED first peak, the rise of the second one or the transition between the two. NuSTAR, thanks to its capability of focusing X-rays up to 79 keV provides broadband data particularly suitable to compute SEDs in a still poorly explored part of the spectrum. In the context of the Open Universe initiative we developed a dedicated pipeline, NuSTAR_Spectra, a shell-script that automatically downloads data from the archive, generates scientific products and carries out a complete spectral analysis. The script homogeneously extracts high level scientific products for both NuSTAR's telescopes and the spectral characterisation is performed testing two phenomenological models. The corresponding X-ray properties are derived from the data best-fit and the SEDs are also computed. The systematic processing of all blazar observations of the NuSTAR public archive allowed us to release the first hard X-ray spectroscopic catalogue of blazars (NuBlazar). The catalogue, updated to September 30th, 2021, includes 253 observations of 126 distinct blazars, 30 of which have been multiply observed
Investigating the candidate IPs IGR J15038-6021, IGR J18007-4146 with NuSTAR
No full textThe INTEGRAL hard X-ray sources IGR J18007-4146 and IGR J15039-6061 were identified as candidate CVs using Chandra observations alongside optical/IR counterpart photometry. For this study we obtained simultaneous XMM-Newton and NuSTAR observations and carried out timing and spectra analyses. For both sources, we confirm an intermediate polar (IP) classification and measure the WD spin period as well as the WD mass. Both sources are heavier than average WD in IP systems, suggesting that follow-up of hard X-ray sources is a productive way to discover massive WDs
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