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Observations of the X-ray binary system Her X-1 by the AstroSat Soft X-ray Telescope (SXT) were carried out in 2020 through 2023 with the goals of measuring X-ray spectrum changes with the 35-day disk precession phase and measuring eclipses at different 35-day phases. Her X-1 exhibits a regular flux modulation with a period of ≃35 days with different intensity levels at various 35-day phases (called "states"). The four multi-day long observations were scheduled to cover most of these states. Each 35-day phase was determined using monitoring observations with the Swift Burst Alert Telescope (BAT). Nine eclipses were observed in the range of 35-day phases, with at least one eclipse during each observation. Data with dips were separated from data without dips. The variation in X-ray spectral parameters vs. 35-day phase shows the following: eclipse parameters are nearly constant, showing that the scattering corona does not change with 35-day phase; dips show an increase in covering fraction but not column density compared to non-dip data; the1 keV line normalization behaves similarly to the powerlaw normalization, consistent with an origin near the powerlaw emission region, likely the magnetospheric accretion flow from the inner disk onto the neutron star; and the blackbody normalization (area) is large ( ∼ 3 × 10 5 km2) during the Main High and Short High states, consistent with the inner edge of the accretion disk. [ABSTRACT FROM AUTHOR]

The high-mass X-ray binary system 4U 0114 + 65 was observed by Nustar in October 2019 and by XMM-Newton in August 2015. Here we performed spectral and timing analysis of the Nustar observation and carry out timing analysis on the XMM-Newton data. We measured the spin period of the neutron star from both observations and found a spin-up rate |$\dot{p}$| = 1.54 ± 0.38 × 10−6 |$\mathrm{s\, s}^{-1}$|. During the Nustar observation, two flares occurred, one shortly after the start of the observation and the other near the end separated by a long period of low/quiescent state. The large and sudden flares mostly resulted from accretion of corotating interaction region (CIR) material. A common spectral model to high mass X-ray binaries (HMXBs), powerlaw with high energy cutoff and absorption at low energy, gave a good fit to both flaring and quiescent states. A fluorescent iron line was not required in fitting any of the states. On the other hand, very tentative evidence of Cyclotron Resonant Scattering Feature (CRSF) at ∼17 keV was found during fitting using cyclabs model; however, fitting improvement was not significant enough to confirm its detection, plus a very narrow width (<1 keV) was obtained for the line and its first harmonic. Visual inspection of the spectra showed a deficiency of emission near the expected first and second harmonic. Another important feature visually noticed in the spectra is the presence of hard tail above 50 keV. This could be explained by the shocked material bounding the CIR. [ABSTRACT FROM AUTHOR]

Hercules X-1/HZ Hercules (Her X-1/HZ Her) is an X-ray binary monitored by multiple X-ray missions since the last century. With the abundance of long-term observations, we present a complete set of orbital lightcurves of Her X-1/HZ Her during the six states of the 35 day cycle in multiple energy bands. These illustrate in detail the changing lightcurve caused by the rotating twisted-tilted accretion disk surrounding the neutron star. The orbital lightcurves during the main high state are analyzed in 0.05 35 day phase intervals. These show the regular occurrence of pre-eclipse dips that march to earlier orbital phases as the 35 day phases increase. From the multiband lightcurves, we derive the time-average orbital phase dependence of column density for photoelectric absorption and energy-independent transmission as a function of 35 day phase. The X-ray lightcurves during low states are similar in shape to the optical low-state lightcurve, but X-ray leads optical by ≃0.04â€"0.08 in orbital phase. [ABSTRACT FROM AUTHOR]

LSQ14bdq and SN 2006oz are superluminous, hydrogen-poor, SNe with double-humped light curves. We show that a Quark-Nova (QN; explosive transition of the Neutron Star - NS - to a quark star -QS) occurring in a massive binary, experiencing two Common Envelope (CE) phases, can quantitatively explain the light curves of LSQ14bdq and SN 2006oz. The more massive component (A) explodes first as a normal SN, yielding a NS which ejects the hydrogen envelope of the companion when the system enters its first CE phase. During the second CE phase, the NS spirals into and inflates the second He-rich CE. In the process it gains mass and triggers a QN, outside of the CO core, leaving behind a QS. The first hump in our model is the QN shock re-energizing the expanded He-rich CE. The QN occurs when the He-rich envelope is near maximum size (~1000 RΘ) and imparts enough energy to unbind and eject the envelope. Subsequent merging of the QS with the CO core of component B, driven by gravitational radiation, turns the QS to a black hole. The ensuing black hole accretion provides sufficient power for the second brighter and long lasting hump. Our model suggests a possible connection between SLSNe-I and type Ic-BL SNe which occur when the QN is triggered inside the CO core. We estimate the rate of QNe in massive binaries during the second CE phase to be ~5 × 10-5 of that of core-collapse SNe. [ABSTRACT FROM AUTHOR]

The accreting millisecond pulsar XTE J1807-294 is studied through a pulse-shape modeling analysis. The model includes blackbody and Comptonized emission from the one visible hot spot and makes use of the Oblate Schwarzschild approximation for ray-tracing. We include a scattered light contribution, which accounts for flux scattered off an equatorial accretion disk to the observer including time delays in the scattered light. We give limits to mass and radius for XTE J1807-294 and compare these to limits determined for SAX J1808-3658 and XTE J1814-334 previously determined using similar methods. The resulting allowed region for mass-radius curves is small but consistent with a mass-radius relation with nearly constant radius (~12 km) for masses between 1 and 2.5 solar masses. [ABSTRACT FROM AUTHOR]

Titanium-rich subluminous supernovae are rare and challenge current SN nucleosynthesis models. We present a model in which ejecta from a standard supernova is impacted by a second explosion of the neutron star (a quark nova), resulting in spallation reactions that lead to 56Ni destruction and 44Ti creation under the right conditions. Basic calculations of the spallation products shows that a delay between the two explosions of ~5 days reproduces the observed abundance of 44Ti in Cas A and explains its low luminosity as a result of the destruction of 56Ni. Our results could have important implications for light curves of subluminous as well as superluminous supernovae. [ABSTRACT FROM AUTHOR]

We present new analysis of the birth rate of AXPs and SGRS and their associated SNRs. Using Kolmogorov-Smirnov statistics together with parametric fits based on a robust estimator, we find a birth rate of ~1/(1000 years) for AXPs/SGRs and their associated SNRs. These high rates suggest that all massive stars (greater than ~(23-32)Mʘ) give rise to remnants with magnetar-like fields. Observations indicate a limited fraction of high magnetic fields in these progenitors; thus our study is suggestive of magnetic field amplification. Dynamo mechanisms during the birth of the neutron stars require spin rates much faster than either observations or theory indicate. We propose that massive stars produce neutron stars with normal (~1012 G) magnetic fields, which are then amplified to 1014-1015 G after a delay of hundreds of years. The amplification is speculated to be a consequence of color ferromagnetism and to occur with a delay after the neutron star core reaches quark deconfinement density (i.e., the quarknova scenario). The delayed amplification allows one to interpret simultaneously the high birth rate and high magnetic fields of AXPs/SGRs and their link to massive stars. [ABSTRACT FROM AUTHOR]

The most luminous Supernova SN2006gy (more than 100 times brighter than a typical supernova) has been a challenge to explain by standard models. For example, pair-instability supernovae which are luminous enough seem to have too slow a rise, and core-collapse supernovae do not seem to be luminous enough. We present an alternative scenario involving a Quark Nova (an explosive transition of the newly born neutron star to a quark star) in which a second explosion (delayed) occurs inside the ejecta of a normal supernova. The reheated supernova ejecta can radiate at higher levels for longer periods of time primarily due to reduced adiabatic-expansion losses, unlike the standard supernova case. We find an encouraging match between the resulting light curve and that observed in the case of SN2006gy suggesting that we might have at hand the first ever signature of a Quark Nova. Successful application of our model to SN2005gj and SN2005ap is also presented. [ABSTRACT FROM AUTHOR]

This paper shows that the collision of the ejecta of an exploding neutron star (the Quark-Nova or QN) with the preceding Type II Supernova (SNII) ejecta synthesizes p-nuclei, r-process-like and s-process-like isotopes. The QN ejecta, rich in A > 130 r-process isotopes, spallates against the 56 Ni nuclei in the inner supernova ejecta, producing secondary nuclides in the A > 130 and A < 130 mass ranges. This secondary nuclide yield includes r-process-like and s-process-like isotopes, and all 35 p-nuclei. This model suggests that heavy-ion spallation, in the context of a QN-SNII interaction (dual-shock Quark-Nova or dsQN), could play a role in heavy-isotope nucleosynthesis as a secondary process. [ABSTRACT FROM AUTHOR]