Current Issue : October-December Volume : 2025 Issue Number : 4 Articles : 5 Articles
We explain an analysis strategy for ultrafast X-ray photon correlation spectroscopy, a technique enabled by X-ray free electron lasers to probe nanoand atomic-scale dynamics in complex systems on nanosecond timescales or faster. Central to the technique is the methodology for extracting contrast in coherent X-ray diffraction patterns, known as speckle patterns. Guided by simulations, we analyze common challenges and examine errors encountered in contrast extraction. A method for accurately determining contrast amid shot noise across a wide range of count rates is presented....
NinjaSat is an X-ray CubeSat designed for agile, long-term continuous observations of bright X-ray sources, with the size of 6U ( 112 . 7 × 237 . 1 × 340 . 5 mm 3 ) and a mass of 8 kg. NinjaSat is capable of pointing at X-ray sources with an accuracy of less than 0 . ◦1 ( 2 σ confidence le v el ) with three-axis attitude control. The satellite bus is a commercially a v ailable NanoAvionics M6P, equipped with two non-imaging gas X-ray detectors co v ering an energy range of 2–50 keV. A total effective area of 32 cm 2 at 6 keV is capable of observing X-ray sources with a flux of approximately 10 −10 erg cm −2 s −1 . The arrival time of each photon can be tagged with a time resolution of 61 μs. The two radiation belt monitors continuously measure the fluxes of protons above 5 MeV and electrons above 200 keV trapped in the geomagnetic field, alerting the X-ray detectors when the flux e x ceeds a threshold. T he NinjaSat project started in 2020. Fabrication of the scientific payloads was completed in 2022 August, and satellite integration and tests were completed in 2023 July. NinjaSat was launched into a Sun-synchronous polar orbit at an altitude of about 530 km on 2023 No v ember 11 b y the SpaceX Transporter-9 mission. After about three months of satellite commissioning and pa yload v erification, w e observed the Crab Nebula on 2024 February 9 and successfully detected the 33.8262 ms pulsation from the neutron st ar. W ith this observation, NinjaSat met the minimum success criterion and stepped f orw ard to scientific observations as initially planned. By the end of 2024 November, w e successfully observ ed 21 X-ra y sources using NinjaSat. T his achie v ement demonstrates that, with careful target selection, we can conduct scientific observations effectively using CubeSats, contributing to time-domain astronomy....
We report on X-ray limits on observations of FRB 20190520B during simultaneous observations with the Green Bank Telescope and the Chandra X-ray Observatory. FRB 20190520B is an outlier in the fast radio burst (FRB) population due to its excess source-local dispersion, its association with compact persistent radio emission, and its high line-of-sight magnetic field variability. One radio burst was detected during the overlapping observing time, and no X-ray emission was detected. We find line-of-sight density and burst duration limits on FRB 20190520B’s X-ray luminosity, interpreting the nondetection in the context of known X-ray populations that might serve as progenitors for FRB 20190520B. We place a direct limit on the presence of a massive black hole (MBH) in this system, limiting mass and the Eddington ratio λE to MBH 4.3 10 ( ) M 3 E 1 (in a low-density line-of-sight limit) and MBH 1.8 10 ( ) M 4 E 1 (high-density limit). These limits are both inconsistent with the scenario derived by Anna-Thomas et al. in which the FRB is viewed through a MBH wind; however, the model is still allowed if the wind luminosity has an X-ray emission fraction of less than 8%. Our observations would have been sensitive to the brightest ∼15% of the ultraluminous X-ray source (ULX) population and the brightest flares from soft gamma-ray repeaters, but the nondetection is consistent with expectations for SGR 1806-20–like flares, most ULX hypernebula models, and X-ray binaries....
Fifty years after the very first sounding rocket measurement of cosmic X-ray polarization, the Imaging X-ray Polarimetry Explorer (IXPE) mission has effectively opened a new window into the X-ray sky. Prior to launch of IXPE, an extensive calibration campaign was carried out to fully characterize the response of this new type of instrument. Specifically, the polarization-sensitive detectors were intensively calibrated in Italy, where they were developed and built. The X-ray optics, which collect and focus X rays onto the detectors, were built and calibrated in the U.S. A key question was whether the telescope (optics + detectors) calibrations could be synthesized from the individual component calibrations, avoiding time consuming and costly end-to-end calibrations for a flight program with a fixed schedule. The data presented here are from a calibration of the flight spare telescope utilizing the flight spare detector and flight spare mirror assembly combined. These data show that the presence of the mirror module does not affect the polarization response of the detectors (within the required calibration accuracy) and that the angular resolution of the telescopes could be accurately determined. Thus, the original extensive stand-alone ground calibration data of all the flight detectors and all the flight optic can be utilized in full to derive the flight telescopes calibrations....
The X-ray light curves of gamma-ray bursts (GRBs) display complex features, including plateaus and flares, that challenge theoretical models. Here, we study the properties of flares that are observed in the early afterglow phase (up to a few thousand seconds). We split the sample into two groups: bursts with and without an X-ray plateau. We find that the distributions of flare properties are similar in each group; specifically, the peak time (tpk) of the flares and the ratio of the flare width to the flare peak time (wtpk), which is found to be ≈1, regardless of the presence of a plateau. We discuss these results in view of the different theoretical models aimed at explaining the origin of the plateau. These results are difficult to explain by viewing angle effects or late-time energy injection, but do not contradict the idea that GRBs with X-ray plateaus have a low Lorentz factor, on the order of tens. For these GRBs, the dissipation processes that produce the flares naturally occur at smaller radii compared to GRBs with higher Lorentz factors, while the flares maintain a similar behavior. Our results therefore provide independent support for the idea that many GRBs have a Lorentz factor of a few tens rather than a few hundreds....
Loading....