Breakthrough? China's and India's Transition from Production to Innovation

▪ Abstract GRS 1915+105—the first stellar-scale, highly relativistic jet source identified—is a key system for our understanding of the disc-jet coupling in accreting black hole systems. Comprehending the coupling between inflow and outflow in this source not only is important for X-ray binary systems but has a broader relevance for studies of active galactic nuclei and gamma-ray bursts. In this paper, we present a detailed review of the observational properties of the system, as established in the decade since its discovery. We attempt to place it in context by a detailed comparison with other sources, and construct a simple model for the disc-jet coupling, which may be more widely applicable to accreting black hole systems.

GRS 1915+105 and the Disc-Jet Coupling in Accreting Black Hole Systems

We present a catalogue of low-mass X-ray binaries. The catalogue is an updated version of the catalogue of van Paradijs (1995). This new catalogue contains 150 sources, 31 new low-mass X-ray binaries in addition to the 119 sources listed in van Paradijs' catalogue. The aim of this catalogue is to help the reader gain easy access to the recent literature (up to about August 2000) on individual sources, and to provide of some basic information on the X-ray sources and their counterparts in other wavelength ranges (UV, optical, IR, and radio). In cases where there is some doubt about the low-mass nature of the X-ray binary, this is mentioned. In an appendix we list the Anomalous X-ray Pulsars (AXPs), which nowadays are no longer thought to be low-mass X-ray binaries.

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A catalogue of low-mass X-ray binaries

A Model for Variable Extragalactic Radio Sources

With the advent of more sensitive all-sky instruments, the transient Universe is being probed in greater depth than ever before. Taking advantage of available resources, we have established a comprehensive database of black hole (and black hole candidate) X-ray binary (BHXB) activity between 1996 and 2015 as revealed by all-sky instruments, scanning surveys, and select narrow-field X-ray instruments aboard the INTErnational Gamma-Ray Astrophysics Laboratory (INTEGRAL), Monitor of All-Sky X-ray Image (MAXI), Rossi X-ray Timing Explorer (RXTE), and Swift telescopes; the Whole-sky Alberta Time-resolved Comprehensive black-Hole Database Of the Galaxy or WATCHDOG. Over the past two decades, we have detected 132 transient outbursts, tracked and classified behavior occurring in 47 transient and 10 persistently accreting BHs, and performed a statistical study on a number of outburst properties across the Galactic population. We find that outbursts undergone by BHXBs that do not reach the thermally dominant accretion state make up a substantial fraction ($\sim$ 40%) of the Galactic transient BHXB outburst sample over the past $\sim20$ years. Our findings suggest that this "hard-only" behavior, observed in transient and persistently accreting BHXBs, is neither a rare nor recent phenomenon and may be indicative of an underlying physical process, relatively common among binary BHs, involving the mass-transfer rate onto the BH remaining at a low level rather than increasing as the outburst evolves. We discuss how the larger number of these "hard-only" outbursts and detected outbursts in general have significant implications for both the luminosity function and mass-transfer history of the Galactic BHXB population.

https://iopscience.iop.org/article/10.3847/0067-0049/222/2/15/pdf

Watchdog: a comprehensive all-sky database of galactic black hole x-ray binaries

We report X-ray observations of the Galactic X-ray transient source GRS 1915+105 with the pointed proportional counters of the Indian X-ray Astronomy Experiment (IXAE) onboard the Indian satellite IRS-P3, which show remarkable richness in temporal variability. The observations were carried out on 1997 June 12-29 and August 7-10, in the energy range of 2-18 keV and revealed the presence of very intense X-ray bursts. All the observed bursts have a slow exponential rise, a sharp linear decay, and broadly can be put in two classes: irregular and quasi-regular bursts in one class, and regular bursts in the other. The regular bursts are found to have two distinct timescales and to persist over extended durations. There is a strong correlation between the preceding quiescent time and the burst duration for the quasi-regular and irregular bursts. No such correlation is found for the regular bursts. The ratio of average flux during the burst time to the average flux during the quiescent phase is high and variable for the quasi-regular and irregular bursts, while it is low and constant for the regular bursts. We present a comprehensive picture of the various types of bursts observed in GRS 1915+105 in the light of the recent theories of advective accretion disks. We suggest that the peculiar bursts that we have seen are characteristic of the change of state of the source. The source can switch back and forth between the low-hard state and the high-soft state near critical accretion rates in a very short timescale, giving rise to the irregular and quasi-regular bursts. The fast timescale for the transition of the state is explained by invoking the appearance and disappearance of the advective disk in its viscous timescale. The periodicity of the regular bursts is explained by matching the viscous timescale with the cooling timescale of the postshock region. A test of the model is presented using the publicly available 13-60 keV RXTE/PCA data for irregular and regular bursts concurrent with our observations. It is found that the 13-60 keV flux relative to the 2-13 keV flux shows clear evidence for state change between the quiescent phase and the burst phase. The value of this ratio during burst is consistent with the values observed during the high-soft state seen on 1997 August 19, while its value during quiescent phase is consistent with the values observed during the low-hard state seen on 1997 May 8.

/pdf/different-types-of-x-ray-bursts-from-grs-1915-105-and-their-1e2pbt95h1.pdf

Different types of X-ray bursts from GRS 1915+105 and their origin

Three different types of very intense, quasi-regular X-ray bursts have been observed from the Galactic superluminal X-ray transient source GRS 1915+105 with the pointed proportional counters of the Indian X-Ray Astronomy Experiment on board the Indian satellite IRS-P3. The observations were carried out from 1997 June 12 to 29 in the energy range of 2-18 keV and revealed the presence of persistent quasi-regular bursts with different structures. Only one of the three types of bursts is regular in occurrence, revealing a stable profile over extended durations. The regular bursts have an exponential rise with a timescale of about 7-10 s and a sharp linear decay in 2-3 s. The X-ray spectrum becomes progressively harder as the burst evolves, and it is the hardest near the end of the burst decay. The profile and energetics of the bursts in this black hole candidate source are distinct from both the type I and type II X-ray bursts observed in neutron star sources. We propose that the sharp decay in the observed burst pattern is a signature of the disappearance of matter through the black hole horizon. The regular pattern of the bursts can be produced by material influx into the inner disk that is due to oscillations in a shock front far away from the compact object.

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Quasi-regular X-Ray Bursts from GRS 1915+105 Observed with the IXAE: Possible Evidence for Matter Disappearing into the Event Horizon of the Black Hole

The X-ray pulsar 4U 1907+09 was observed in the 2-18 keV energy band with the Indian X-Ray Astronomy Experiment (IXAE) during 1996 August and again in 1998 June. From the timing measurements, the spin-down rate of the neutron star is measured to be +0.23 ± 0.01 s yr-1. A straight-line fit to the historical pulse period data indicates that the pulsar has been in a monotonic phase of spin-down since its discovery. The day-to-day pulse profile indicates some variations during its 8.4 day binary period. The average profile obtained from these observations shows a double-pulse shape with a pronounced asymmetric primary separated by a dip from a relatively weaker but broad secondary. These profiles show a closer resemblance to the pulse shape obtained with the recent observations with the Rossi X-Ray Timing Explorer (RXTE) during 1996 February, as compared to the earlier observations carried out six to 13 years earlier. A secondary flare of 88 mcrab intensity was detected during the IXAE observations in 1996 August. A detailed analysis of the flare data shows the presence of transient 14.4 s oscillations, which may be quasi-periodic during the flaring activity but have a period different from the earlier reported oscillations of 18.2 s as detected by RXTE during the flare of 1996 February. These results, therefore, strengthen the evidence for the presence of a transient accretion disk around the neutron star during the flare, which may be responsible for the continuous slowing down of the pulsar. The studies of such transient quasi-periodic oscillations during flaring activities of 4U 1907+09 thus provide opportunities for understanding the transient behavior of the accretion disk and its physical characteristics.

Pulse Characteristics of the X-Ray Pulsar 4U 1907+09

Indian remote sensing satellite (IRS)-1C - the beginning of a new era

A new survey for pulsating, chemically peculiar A- and F-type stars in the northern hemisphere has been initiated using the 1-m telescope at Uttar Pradesh State Observatory in Naini Tal. The survey is primarily structured to reveal high-overtone pulsations in chemically peculiar A{F stars, but it is also revealing low-overtone Scuti-type pulsations in stars with peculiar colours. This paper describes the scope and methods of the survey. Preliminary observations of 28 candidate stars are presented and the discovery of three new pulsators, HD 12098, HD 13038 and HD 13079, is announced. Null results for the remaining 25 stars are also discussed.

https://www.aanda.org/articles/aa/pdf/2001/21/aa1188.pdf

K. Kasturirangan

Papers

Different types of X-ray bursts from GRS 1915+105 and their origin

Quasi-regular X-Ray Bursts from GRS 1915+105 Observed with the IXAE: Possible Evidence for Matter Disappearing into the Event Horizon of the Black Hole

Pulse Characteristics of the X-Ray Pulsar 4U 1907+09

Indian remote sensing satellite (IRS)-1C - the beginning of a new era

The Naini Tal { Cape survey for pulsations in chemically peculiar A-type stars I. Methods and preliminary results