We present detailed timing and spectral studies of the black hole candidate MAXI J0637$-$430 during its 2019-2020 outburst using observations with the {\em Neutron Star Interior Composition Explorer (NICER)} and the {\em Neil Gehrels Swift Observatory}. We find that the source evolves through the soft-intermediate, high-soft, hard-intermediate and low-hard states during the outburst. No evidence of quasi-periodic oscillations is found in the power density spectra of the source. Weak variability with fractional rms amplitude $<5\%$ is found in the softer spectral states. In the hard-intermediate and hard states, high variability with the fractional rms amplitude of $>20\%$ is observed. The $0.7-10$ keV spectra with {\em NICER} are studied with a combined disk-blackbody and nthcomp model along with the interstellar absorption. The temperature of the disc is estimated to be $0.6$ keV in the rising phase and decreased slowly to $0.1$ keV in the declining phase. The disc component was not detectable or absent during the low hard state. From the state-transition luminosity and the inner edge of the accretion flow, we estimate the mass of the black hole to be in the range of 5$-$12 $M_{\odot}$, assuming the source distance of $d<10$ kpc.
The X-ray transient MAXI J1631-479 went into outburst on 2018 December 21 and remained active for about seven months. Owing to various constraints it was monitored by NICER only during the decay phase of the outburst for about four months. The NICER observations were primarily in the soft state with a brief excursion to the hard intermediate state. While the soft state spectrum was dominated by thermal disk emission, the hard intermediate state spectrum had maximum contribution from the thermal Comptonization. Almost all intermediate-state power spectra had a Type-C low frequency quasi-periodi…
We present a detailed timing analysis of the bright black hole X-ray binary MAXI J1820+070 (ASASSN-18ey), during its first detected outburst lasting from March 2018 until October 2019 based on Swift/XRT window timing mode observations, corresponding UVOT data and NICER observations. The light curves clearly show four outbursts, with the source remaining in the hard state during its first outburst, while the rise of the second outburst corresponds with the transition to the soft state. A similar double outburst of GX339-4 has been observed in 2004. Here it is followed by two hard-state only out…
We present the earliest available soft X-ray observations of XTE J1810-187, the prototypical transient magnetar, obtained 75--84 days after its 2018 outburst with the Neutron Star Interior Composition Explorer (NICER). Using a series of observations covering eight days we find that its decreasing X-ray flux is well-described by either a blackbody plus power-law or a two-blackbody spectral model. The 2-10 keV flux of the source varied from (1.206+/-0.007)x10^{-10} to (1.125+/-0.004)x10^{-10} erg s^{-1} cm^{-2}, a decrease of about 7% within our observations and 44% from that measured 7-14 days …
We present a comprehensive spectral and temporal study of the black hole X-ray transient MAXI J1820+070 during its outbursts in 2018 using Swift/XRT, NICER, NuSTAR and AstroSat observations. The Swift/XRT and NICER spectral study shows a plateau in the light curve with spectral softening (hardness changes from $\sim$ $2.5$ to $2$) followed by a gradual decline without spectral softening during the first outburst. Also, spectral modelling suggests that the first outburst is in the low/hard state throughout with a truncated disk whereas the thermal disk emission dominates during the second outbu…
We report on the coherent timing analysis of the 182 Hz accreting millisecond X-ray pulsar Swift J1756.9$-$2508 during its 2018 outburst as observed with the Neutron Star Interior Composition Explorer (NICER). Combining our NICER observations with Rossi X-ray Timing Explorer observations of the 2007 and 2009 outbursts, we also studied the long-term spin and orbital evolution of this source. We find that the binary system is well described by a constant orbital period model, with an upper limit on the orbital period derivative of $|\dot P_b| < 7.4\times 10^{-13}$ s s$^{-1}$. Additionally, we im…
We studied the outburst evolution and timing properties of the recently discovered X-ray transient MAXI J1348-630 as observed with NICER. We produced the fundamental diagrams commonly used to trace the spectral evolution, and power density spectra to study the fast X-ray variability. The main outburst evolution of MAXI J1348-630 is similar to that commonly observed in black hole transients. The source evolved from the hard state, through hard- and soft-intermediate states, into the soft state in the outburst rise, and back to the hard state in reverse during the outburst decay. At the end of t…
We present the observational results from a detailed timing analysis of the black hole candidate Swift J1658.2-4242 during its 2018 outburst with the observations of Hard X-ray Modulation Telescope (Insight-HXMT), Neutron Star Interior Composition Explorer (NICER) and AstroSat in 0.1-250keV. The evolution of intensity, hardness and integrated fractional root mean square (rms) observed by Insight-HXMT and NICER are presented in this paper. Type-C quasi-periodic oscillations (QPOs) observed by NICER (0.8-3.5Hz) and Insight-HXMT (1-1.6Hz) are also reported in this work. The features of the QPOs a…
Timing and spectral analysis of the 2025 outburst of 4U 1630$-$47 with \textit{NICER}
Kapteyn Astronomical Institute, University of Groningen（格罗宁根大学卡普坦天文研究所）；Department of Physics, College of Science, Southern University of Science and Technology（南方科技大学理学院物理系）；Department of Astronomy, School of Physics and Technology, Wuhan University（武汉大学物理科学与技术学院天文学系）
The prolific thermonuclear X-ray bursts from the outburst of the newly discovered millisecond pulsar MAXI~J1816--195 observed by Insight-HXMT and NICER
Spectral Analysis of the 2019 and 2022 Outbursts of SAX J1808.4-3658
Montana State University（蒙大拿州立大学）；Kavli Institute for the Physics and Mathematics of the Universe (WPI), The University of Tokyo（东京大学宇宙学前沿研究机构（WPI））；RTX（RTX公司）
We report on X-ray and radio observations of the ultra-compact X-ray binary 4U 1543-624 taken in August 2017 during an enhanced accretion episode. We obtained NICER monitoring of the source over a $\sim10$ day period during which target-of-opportunity observations were also conducted with Swift, INTEGRAL, and ATCA. Emission lines were measured in the NICER X-ray spectrum at $\sim0.64$ keV and $\sim6.4$ keV that correspond to O and Fe, respectively. By modeling these line components, we are able to track changes in the accretion disk throughout this period. The innermost accretion flow appears …
We study the properties of the type-C quasi-periodic oscillation (type-C QPO) of MAXI J1348-630 during its 2019 outburst and reflare with NICER. This is the first time that the evolution of the properties of type-C QPOs is studied during an outburst reflare. We found that the properties of the type-C QPO during the reflare are similar to those of type-C QPOs observed in other black-hole systems during outburst. This suggests that the physical processes responsible for type-C QPOs are the same in a reflare and in an outburst. We also found that the FWHM of a high-frequency broadband component o…
We present a detailed X-ray spectral and variability study of the full 2018 outburst of MAXI J1727-203 using NICER observations. The outburst lasted approximately four months. Spectral modelling in the 0.3-10 keV band shows the presence of both a soft thermal and a hard Comptonised component. The analysis of these components shows that MAXI J1727-203 evolved through the soft, intermediate and hard spectral states during the outburst. We find that the soft (disc) component was detected throughout almost the entire outburst, with temperatures ranging from ~0.4 keV, at the moment of maximum lumin…
Timing and Spectral Analysis of the 2024 Outburst of 2S 1553$-$542 with NuSTAR and NICER
University of Groningen（格罗宁根大学）；Wuhan University（武汉大学）；Shanghai Astronomical Observatory, Chinese Academy of Sciences（中国科学院上海天文台）；Guizhou Minzu University（贵州民族大学）
Return of 4U~1730--22 after 49 years silence: the spectral properties of the 2021/2022 outbursts observed by NICER and Insight-HXMT and the soft-to-hard state transition caused by the propeller effect
In November 2019, MAXI detected an X-ray outburst from the known Be X-ray binary system RX J0209.6-7427 located in the outer wing of the Small Magellanic Cloud. We followed the outburst of the system with NICER which led to the discovery of X-ray pulsations with a period of 9.3 s. We analyzed simultaneous X-ray data obtained with NuSTAR and NICER allowing us to characterize the spectrum and provide an accurate estimate of its bolometric luminosity. During the outburst the maximum broadband X-ray luminosity of the system reached $1-2\times10^{39}$ erg/s, thus exceeding by about one order of mag…
Revisiting the 2021 Outburst of the BHC MAXI J1803-298 Using NICER, NuSTAR, and Insight-HXMT Data
South-Western Institute for Astronomy Research, Yunnan University（西南天体物理研究所，云南大学）；Indian Center for Space Physics（印度空间物理中心）；Institute of Astronomy, National Tsing Hua University（国立清华大学天文研究所）
The millisecond pulsar MAXI J1816-195 was recently discovered in an outburst by MAXI in 2022 May. We study different properties of the pulsar using data from NuSTAR and NICER observations. The unstable burning of accreted material on the surface of neutron stars induces thermonuclear (Type-I) bursts. Several such thermonuclear bursts have been detected by MAXI J1816-195 during its outburst. We investigate the evolution of the burst profile with flux and energy using NuSTAR and NICER observations. During the NuSTAR observation, a total of four bursts were detected from the source. The duration …
The neutron star low-mass X-ray binary SWIFT J1749.4-2807 is the only known eclipsing accreting millisecond X-ray pulsar. In this manuscript we perform a spectral characterization of the system throughout its 2021, two-week-long outburst, analyzing 11 NICER observations and quasi-simultaneous XMM-Newton and NuSTAR single observations at the outburst peak. The broadband spectrum is well-modeled with a black body component with a temperature of $\sim$0.6 keV, most likely consistent with a hot spot on the neutron star surface, and a Comptonisation spectrum with power-law index $Γ\sim 1.9$, arisin…
We report on NICER observations of the Magnetar SGR~1935+2154, covering its 2020 burst storm and long-term persistent emission evolution up to $\sim90$ days post outburst. During the first 1120~seconds taken on April 28 00:40:58 UTC we detect over 217 bursts, corresponding to a burst rate of $>0.2$ bursts s$^{-1}$. Three hours later the rate is at 0.008 bursts s$^{-1}$, remaining at a comparatively low level thereafter. The $T_{90}$ burst duration distribution peaks at 840~ms; the distribution of waiting times to the next burst is fit with a log-normal with an average of 2.1 s. The 1-10 keV bu…
GRS 1915+105 is a transient black hole X-ray binary consistently emitting 10-100% of the Eddington luminosity in the X-ray band during the last three decades until mid-2018 when the source luminosity suddenly decreased by an order of magnitude. This phase was followed by a change to a state with even lower average X-ray fluxes never seen before during the outburst but presenting renewed flaring activity at different wavelengths. Nevertheless, the mean fluxes were still in decline. GRS 1915+105 has the longest orbital period known among low-mass X-ray binaries, the largest accretion disk size, …
Probing the emission geometry of the X-ray pulsar 2S 1417$-$624 during a weak outburst with NICER, IXPE, and NuSTAR
Institut für Astronomie und Astrophysik, Universität Tübingen（蒂宾根大学天文与天体物理研究所）；Research Center of Astronomy, QingHai University（青海大学天文研究中心）；Department of Physics and Astronomy, QingHai University（青海大学物理与天文系）；Key Laboratory of Particle Astrophysics, Institute of High Energy Physics, Chinese Academy of Sciences（中国科学院高能物理研究所粒子天体物理重点实验室）；University of Chinese Academy of Sciences, Chinese Academy of Sciences（中国科学院大学）
We study the timing and spectral properties of the X-ray pulsar 2S 1417--624 during the recent outburst in January 2021 based on the Neutron Star Interior Composition Explorer (NICER) observation. We also used some early data from the 2018 outburst to compare different temporal and spectral properties. The evolution of the spin period and pulsed flux is studied with Fermi/GBM during the outburst and the spin-up rate is found to be varied between $\simeq(0.8-1.8)\times 10^{-11}$ Hz s$^{-1}$. The pulse profile shows energy dependence and variability. The pulse profile shows multiple peaks and di…
We report the results of eROSITA and NICER observations of the June 2020 outburst of the Be/X-ray binary pulsar RX J0529.8-6556 in the Large Magellanic Cloud, along with the analysis of archival X-ray and optical data from this source. We find two anomalous features in the system's behavior. First, the pulse profile observed by NICER during maximum luminosity is similar to that observed by XMM-Newton in 2000, despite the fact that the X-ray luminosity was different by two orders of magnitude. By contrast, a modest decrease in luminosity in the 2020 observations generated a significant change i…
We study different timing and spectral properties of the new Galactic X-ray transient Swift J1728.9-3613 using NICER and Swift, discovered by the Burst Alert Telescope (BAT) on the Neil Gehrels Swift Observatory. The source went through multiple transitions to different spectral states during the outburst, and the complete evolution created a q-shaped track in the hardness intensity diagram. A partial hysteresis is also observed in the RMS-intensity diagram, which is another well-defined phenomenon of black hole transients. In SIMS, power density spectra were dominated by broadband noise compo…
Probing accretion dynamics and spin evolution in the X-ray pulsar RX J0520.5-6932 during its 2024 Outburst
Inter-University Centre for Astronomy and Astrophysics (IUCAA)（大学间天文学与天体物理学中心）；Raman Research Institute（拉曼研究所）；Indian Institute of Science Education and Research (IISER) Mohali（印度科学教育与研究学院穆扎法尔纳加尔分校）；School of Physics & Astronomy, University of Southampton（南安普顿大学物理与天文学院）；Indian Institute of Astrophysics（印度天体物理研究所）；Universitá degli Studi di Cagliari, Dipartimento di Fisica（卡利亚里大学物理系）；Max-Planck-Institut für extraterrestrische Physik（马克斯·普朗克地外物理研究所）；National Astronomical Observatories, Chinese Academy of Sciences（中国科学院国家天文台）；School of Astronomy and Space Science, University of Chinese Academy of Sciences（中国科学院大学天文与空间科学学院）
Flux Dependence of the 1\,keV Soft X-ray Feature in SAX J1808.4-3658 with \textit{NICER}
Montana State University（蒙大拿州立大学）；University of Leicester（莱斯特大学）；Inter-University Centre for Astronomy and Astrophysics（大学间天体物理中心）；The University of Tokyo（东京大学）
Systematic assessment of disk truncation in the black hole X-ray binary Swift J1727.8-1613 using NICER
Anton Pannekoek Institute for Astronomy, University of Amsterdam（阿姆斯特丹大学安东·潘内库克天文学研究所）；Department of Physics, Villanova University（维拉诺瓦大学物理系）；Dr. Karl Remeis-Observatory and Erlangen Centre for Astroparticle Physics, Friedrich-Alexander-Universität Erlangen-Nürnberg（弗里德里希-亚历山大埃尔朗根-纽伦堡大学卡尔·雷梅斯天文台与埃尔朗根高能粒子物理中心）；Astronomical Institute of the Czech Academy of Sciences（捷克科学院天文研究所）；Department of Physics, Stanford University（斯坦福大学物理系）；Kavli Institute for Particle Astrophysics and Cosmology, Stanford University（斯坦福大学卡弗里粒子天体物理学与宇宙学研究所）；NASA Goddard Space Flight Center（美国宇航局戈达德太空飞行中心）；School of Mathematics, Statistics and Physics, Newcastle University（纽卡斯尔大学数学、统计与物理学院）
MAXI J1535-571 is a black-hole X-ray binary that in 2017 exhibited a very bright outburst which reached a peak flux of up to 5 Crab in the 2-20 keV band. Given the high flux, several X-ray space observatories obtained unprecedented high signal-to-noise data of key parts of the outburst. In our previous paper we studied the corona of MAXI J1535-571 in the hard-intermediate state (HIMS) with Insight-HXMT. In this paper we focus on the study of the corona in the soft-intermediate state (SIMS) through the spectral-timing analysis of 26 NICER detections of the type-B quasi-periodic oscillations (QP…
The newly discovered galactic black hole candidate (BHC) MAXI~J1348-630 showed two major outbursts in 2019, just after its discovery. Here, we provide a detailed spectral and temporal analysis of the less-studied second outburst using archive data from multiple satellites, namely Swift, MAXI, NICER, NuSTAR and AstroSat. The outburst continued for around two and a half months. Unlike the first outburst from this source, this second outburst was a `failed' one. The source did not transition to soft or intermediate spectral states. During the entire outburst, the source was in the hard state with…
We conducted a spectral and temporal analysis of X-ray data from the Be X-ray binary pulsar SXP 15.6 located in the Small Magellanic Cloud based on NuSTAR, NICER and Swift observations during the 2021 outburst. We present for the first time the broadband X-ray spectra of the system based on simultaneous NuSTAR and NICER observations. Moreover we use monitoring data to study the spectral and temporal properties of the system during the outburst. Comparison of the evolution of the 2021 outburst with archival data reveals a consistent pattern of variability with multiple peaks occurring at time i…
