186 research outputs found
Detection of polarized quasi-periodic microstructure emission in millisecond pulsars
Microstructure emission, involving short time scale, often quasi-periodic,
intensity fluctuations in subpulse emission, is well known in normal period
pulsars. In this letter, we present the first detections of quasi-periodic
microstructure emission from millisecond pulsars (MSPs), from Giant Metrewave
Radio Telescope (GMRT) observations of two MSPs at 325 and 610 MHz. Similar to
the characteristics of microstructure observed in normal period pulsars, we
find that these features are often highly polarized, and exhibit quasi-periodic
behavior on top of broader subpulse emission, with periods of the order of a
few s. By measuring their widths and periodicities from single pulse
intensity profiles and their autocorrelation functions, we extend the
microstructure timescale - rotation period relationship by more than an order
of magnitude down to rotation periods 5 ms, and find it to be consistent
with the relationship derived earlier for normal pulsars. The similarity of
behavior is remarkable, given the significantly different physical properties
of MSPs and normal period pulsars, and rules out several previous speculations
about the possible different characteristics of microstructure in MSP radio
emission. We discuss the possible reasons for the non-detection of these
features in previous high time resolution MSP studies along with the physical
implications of our results, both in terms of a geometric beam sweeping model
and temporal modulation model for micropulse production.Comment: 6 pages, 4 figures, 1 table. Accepted for publication in ApJ Letter
Dusty, Self-obscured Transients from Stellar Coalescence
We discuss the central role that dust condensation plays in shaping the
observational appearance of outflows from coalescing binary systems. As
binaries begin to coalesce, they shock-heat and expel material into their
surroundings. Depending on the properties of the merging system, this material
can expand to the point where molecules and dust form, dramatically increasing
the gas opacity. We use the existing population of Luminous Red Novae (LRNe) to
constrain the thermodynamics of these ejecta, then apply our findings to the
progressive obscuration of merging systems in the lead in to their coalescence.
Compact progenitor stars near the main sequence or in the Hertzsprung gap along
with massive progenitor stars have sufficiently hot circumstellar material to
remain unobscured by dust. By contrast, more extended, low-mass giants should
become completely optically obscured by dust formation in the circumbinary
environment. We predict that 30--50\% of stellar coalescence transients for
solar-mass stars will be dusty, infrared-luminous sources. Of these, the
optical transients may selectively trace complete merger outcomes while the
infrared transients trace common envelope ejection outcomes.Comment: v2, published in AAS Journal
Single pulse polarization study of pulsars B0950+08 and B1642-03: micropulse properties and mixing of orthogonal modes
We present the results of a high-time resolution polarization study of single
pulses from pulsars B0950+08 and B1642-03. Single pulses from pulsar B0950+08
sometimes show isolated micropulses without any significant associated subpulse
emission. Assuming that the properties of such micropulses represent the
intrinsic nature of micropulse emission, we characterize the width and
polarization properties of these `intrinsic' microstructures. Most of the
`intrinsic' micropulses (~90%) follow common characteristic polarization
properties, while the average width of these micropulses is consistent with the
general micropulse population from this pulsar. Single pulses from these
pulsars show a diverse range of polarization properties, including
depolarization and mixing of two orthogonal modes resulting in polarization
position angle jumps. We present a superposition model of the two orthogonal
modes which can explain depolarization, the observed position angle jumps, and
associated changes in other polarization parameters.Comment: 12 pages, 18 figures, Accepted for publication in the Monthly Notices
of the Royal Astronomical Society (MNRAS
Infrared spectroscopy of SWIFT J0850.8-4219: Identification of the second red supergiant X-ray binary in the Milky Way
High mass X-ray binaries hosting red supergiant (RSG) donors are a rare but
crucial phase in massive stellar evolution, with only one source previously
known in the Milky Way. In this letter, we present the identification of the
second Galactic RSG X-ray binary SWIFT J0850.8-4219. We identify the source
2MASS 08504008-4211514 as the likely infrared counterpart with a chance
coincidence probability . We present a m spectrum of the counterpart, exhibiting features characteristic of
late-type stars and an exceptionally strong He I emission line, corroborating
the identification. Based on i) the strength of the CO(2,0) band, ii)
strong CN bandheads and absent TiO bandheads at m and iii)
equivalent width of the Mg I m line, we classify the counterpart to
be a K3K5 type RSG with an effective temperature of K,
located at a distance of kpc. We estimate the source X-ray
luminosity to be erg s, with a hard photon
index (), arguing against a white dwarf accretor but consistent
with a magnetized neutron star in the propeller phase. Our results highlight
the potential of systematic NIR spectroscopy of Galactic hard X-ray sources in
completing our census of the local X-ray binary population.Comment: 6 pages, 4 figures, 1 table. Submitted to MNRAS letters. Comments
welcome
The Whisper and the Bang: Cosmic Fireworks in the Lives of Compact Binaries
Compact binaries, comprising of a white dwarf, neutron star or black hole in a tight orbit around another star are produced from binary evolution through a complex range of astrophysical processes -- ranging from eruptive mass loss episodes ('the whisper') to spectacular explosions ('the bang') that have shaped the universe as we see it today. In pursuit of a complete road-map of the explosive lives of high mass and low mass stars in compact binaries, I undertook two major experiments.
In the first two parts of this thesis, I describe the largest volume-limited supernova classification experiment undertaken till date, using the Zwicky Transient Facility optical time domain survey. I present the identification of a new class of 'ultra-stripped' supernovae that form neutron stars in compact binary systems, that are likely direct progenitors of merging neutron stars detectable in LIGO/Virgo. Using the systematic sample of supernovae, I identify a class of helium shell explosions on low mass white dwarfs that likely represent the final fates of helium accreting white dwarfs. In the third part of this thesis, I present the development of Palomar Gattini-IR (PGIR), the first wide-field infrared survey capable of studying the dynamic infrared sky from timescales of seconds to years. I present a systematic search for nova eruptions in the Milky Way using PGIR, and show that optical surveys have systematically missed a large fraction of dust obscured novae to derive the first quantitative estimate of the Galactic nova rate. I present the first infrared constraints on the second-timescale emission from a Galactic Fast Radio Burst identified with a dust obscured Galactic magnetar.
This thesis helps set the stage for a systematic exploration of the local stellar graveyard using i) the Vera Rubin Observatory to probe the lowest luminosity stellar deaths in the local universe and ii) the upcoming assemblage of infrared surveys to study variability in Galactic compact objects in conjunction with the rich landscape of X-ray and radio sky surveys. By mapping out the demographics of explosive phenomena, it helps us interpret the astrophysical populations detectable with current and future gravitational wave observatories.</p
RNO 54: A Previously Unappreciated FU Ori Star
We present evidence in support of the hypothesis that the young stellar
object RNO 54 is a mature-stage FU Ori type source. The star was first
cataloged as a ``red nebulous object" in the 1980s but appears to have
undergone its outburst prior to the 1890s. Present-day optical and
near-infrared spectra are consistent with those of other FU Ori type stars,
both in the details of spectral line presence and shape, and in the overall
change in spectral type from an FGK-type in the optical, to the M-type
presented in the near-infrared. In addition, the spectral energy distribution
of RNO 54 is well-fit by a pure-accretion disk model with parameters: yr, , and
, though we believe
is likely close to its upper range of in order
to produce a K that is consistent with the optical to
near-infrared spectra. The resulting is .
To find these values, we adopted a source distance pc and extinction
mag, along with disk inclination deg based on consideration of
confidence intervals from our initial disk model, and in agreement with
observational constraints. The new appreciation of a well-known source as an FU
Ori type object suggests that other such examples may be lurking in extant
samples.Comment: to appear in AAS Journal
Detection of Polarized Quasi-periodic Microstructure Emission in Millisecond Pulsars
Microstructure emission, involving short timescale, often quasi-periodic, intensity fluctuations in subpulse emission, is well known in normal period pulsars. In this Letter, we present the first detections of quasi-periodic microstructure emission from millisecond pulsars (MSPs), from Giant Metrewave Radio Telescope observations of two MSPs at 325 and 610 MHz. Similar to the characteristics of microstructure observed in normal period pulsars, we find that these features are often highly polarized and exhibit quasi-periodic behavior on top of broader subpulse emission, with periods of the order of a few μs. By measuring their widths and periodicities from single pulse intensity profiles and their autocorrelation functions, we extend the microstructure timescale–rotation period relationship by more than an order of magnitude down to rotation periods ~5 ms, and find it to be consistent with the relationship derived earlier for normal pulsars. The similarity of behavior is remarkable, given the significantly different physical properties of MSPs and normal period pulsars, and rules out several previous speculations about the possible different characteristics of microstructure in MSP radio emission. We discuss the possible reasons for the non-detection of these features in previous high time resolution MSP studies along with the physical implications of our results, both in terms of a geometric beam sweeping model and temporal modulation model for micropulse production
Revealing the geometry of gravitational wave event GW 170817 with radio observations
GW 170817 marks the first gravitational wave detection of a binary neutron-star (BNS) merger by the Advanced LIGO and the Advanced VIRGO detectors. This is also the first gravitational wave event from which the electromagnetic (EM) emission was seen all the way from gamma-rays to radio bands. We detected it in radio bands 16 days after the detection [2]
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