2,305 research outputs found
Growth of human gliomas in immune-deficient mice: a possible model for pre-clinical therapy studies.
Thirteen gliomas from 55 neurosurgical specimens, derived from 25 adults and 30 children, have been successfully grown as subcutaneous xenografts in immune-deprived or nude mice. Only 2 of the 30 paediatric specimens implanted (6.7%), a medulloblastoma and an astrocytoma Grade III, have grown compared with 11 of the 25 adult specimen (44%) which were mostly astrocytomas Grade III. Tumour growth usually occurred several months after implantation, and karyotypic analysis confirmed their human origin in all cases. The histopathology of xenografted tumours correlated with the original surgical material, both after initial implantation and when tumours had been passaged several times. Observations on tumour growth in various types of immune-deprived mice indicated that, within certain limits, the immunological competence of the host mouse did not relate to take rates of primary implants, but could affect the take rate of passaged tumours
GRB 090426: The Environment of a Rest-Frame 0.35-second Gamma-Ray Burst at Redshift z=2.609
We present the discovery of an absorption-line redshift of z = 2.609 for GRB
090426, establishing the first firm lower limit to a redshift for a gamma-ray
burst with an observed duration of <2 s. With a rest-frame burst duration of
T_90z = 0.35 s and a detailed examination of the peak energy of the event, we
suggest that this is likely (at >90% confidence) a member of the short/hard
phenomenological class of GRBs. From analysis of the optical-afterglow spectrum
we find that the burst originated along a very low HI column density sightline,
with N_HI < 3.2 x 10^19 cm^-2. Our GRB 090426 afterglow spectrum also appears
to have weaker low-ionisation absorption (Si II, C II) than ~95% of previous
afterglow spectra. Finally, we also report the discovery of a blue, very
luminous, star-forming putative host galaxy (~2 L*) at a small angular offset
from the location of the optical afterglow. We consider the implications of
this unique GRB in the context of burst duration classification and our
understanding of GRB progenitor scenarios.Comment: Submitted to MNRA
Precursors prior to Type IIn supernova explosions are common: precursor rates, properties, and correlations
There is a growing number of supernovae (SNe), mainly of Type IIn, which
present an outburst prior to their presumably final explosion. These precursors
may affect the SN display, and are likely related to some poorly charted
phenomena in the final stages of stellar evolution. Here we present a sample of
16 SNe IIn for which we have Palomar Transient Factory (PTF) observations
obtained prior to the SN explosion. By coadding these images taken prior to the
explosion in time bins, we search for precursor events. We find five Type IIn
SNe that likely have at least one possible precursor event, three of which are
reported here for the first time. For each SN we calculate the control time.
Based on this analysis we find that precursor events among SNe IIn are common:
at the one-sided 99% confidence level, more than 50% of SNe IIn have at least
one pre-explosion outburst that is brighter than absolute magnitude -14, taking
place up to 1/3 yr prior to the SN explosion. The average rate of such
precursor events during the year prior to the SN explosion is likely larger
than one per year, and fainter precursors are possibly even more common. We
also find possible correlations between the integrated luminosity of the
precursor, and the SN total radiated energy, peak luminosity, and rise time.
These correlations are expected if the precursors are mass-ejection events, and
the early-time light curve of these SNe is powered by interaction of the SN
shock and ejecta with optically thick circumstellar material.Comment: 15 pages, 20 figures, submitted to Ap
Highly Variable Extinction and Accretion in the Jet-driving Class I Type Young Star PTF 10nvg (V2492 Cyg, IRAS 20496+4354)
We report extensive new photometry and spectroscopy of the highly variable
young stellar object PTF 10nvg including optical and near-infrared time series
data as well as mid-infrared and millimeter data. Following the previously
reported 2010 rise, during 2011 and 2012 the source underwent additional
episodes of brightening and dimming events including prolonged faint states.
The observed high-amplitude variations are largely consistent with extinction
changes having a 220 day quasi-periodic signal. Spectral evolution includes not
only changes in the spectral slope but correlated variation in the prominence
of TiO/VO/CO bands and atomic line emission, as well as anticorrelated
variation in forbidden line emission which, along with H_2, dominates optical
and infrared spectra at faint epochs. Neutral and singly-ionized atomic species
are likely formed in an accretion flow and/or impact while the origin of
zero-velocity atomic LiI 6707 in emission is unknown. Forbidden lines,
including several rare species, exhibit blueshifted emission profiles and
likely arise from an outflow/jet. Several of these lines are also seen
spatially offset from the continuum source position, presumably in a shocked
region of an extended jet. CARMA maps resolve on larger scales a spatially
extended outflow in mm-wavelength CO. We attribute the observed photometric and
spectroscopic behavior in terms of occultation of the central star as well as
the bright inner disk and the accretion/outflow zones that renders shocked gas
in the inner part of the jet amenable to observation at the faint epochs. We
discuss PTF 10nvg as a source exhibiting both accretion-driven (perhaps
analogous to V1647 Ori) and extinction-driven (perhaps analogous to UX Ori or
GM Cep) high-amplitude variability phenomena.Comment: accepted to AJ - in press (74 pages
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The Factory and the Beehive. I. Rotation Periods for Low-mass Stars in Praesepe
Stellar rotation periods measured from single-age populations are critical for investigating how stellar angular momentum content evolves over time, how that evolution depends on mass, and how rotation influences the stellar dynamo and the magnetically heated chromosphere and corona. We report rotation periods for 40 late-K to mid-M star members of the nearby, rich, intermediate-age (~600 Myr) open cluster Praesepe. These rotation periods were derived from ~200 observations taken by the Palomar Transient Factory of four cluster fields from 2010 February to May. Our measurements indicate that Praesepe's mass-period relation transitions from a well-defined singular relation to a more scattered distribution of both fast and slow rotators at ~0.6 M ☉. The location of this transition is broadly consistent with expectations based on observations of younger clusters and the assumption that stellar spin-down is the dominant mechanism influencing angular momentum evolution at 600 Myr. However, a comparison to data recently published for the Hyades, assumed to be coeval to Praesepe, indicates that the divergence from a singular mass-period relation occurs at different characteristic masses, strengthening the finding that Praesepe is the younger of the two clusters. We also use previously published relations describing the evolution of rotation periods as a function of color and mass to evolve the sample of Praesepe periods in time. Comparing the resulting predictions to periods measured in M35 and NGC 2516 (~150 Myr) and for kinematically selected young and old field star populations suggests that stellar spin-down may progress more slowly than described by these relations
Swift J2058.4+0516: Discovery of a Possible Second Relativistic Tidal Disruption Flare?
We report the discovery by the Swift hard X-ray monitor of the transient
source Swift J2058.4+0516 (Sw J2058+05). Our multi-wavelength follow-up
campaign uncovered a long-lived (duration >~ months), luminous X-ray (L_X,iso ~
3 x 10^47 erg s^-1) and radio (nu L_nu,iso ~ 10^42 erg s^-1) counterpart. The
associated optical emission, however, from which we measure a redshift of
1.1853, is relatively faint, and this is not due to a large amount of dust
extinction in the host galaxy. Based on numerous similarities with the recently
discovered GRB 110328A / Swift J164449.3+573451 (Sw J1644+57), we suggest that
Sw J2058+05 may be the second member of a new class of relativistic outbursts
resulting from the tidal disruption of a star by a supermassive black hole. If
so, the relative rarity of these sources (compared with the expected rate of
tidal disruptions) implies that either these outflows are extremely narrowly
collimated (theta < 1 degree), or only a small fraction of tidal disruptions
generate relativistic ejecta. Analogous to the case of long-duration gamma-ray
bursts and core-collapse supernovae, we speculate that rapid spin of the black
hole may be a necessary condition to generate the relativistic component.
Alternatively, if powered by gas accretion (i.e., an active galactic nucleus
[AGN]), Sw J2058+05 would seem to represent a new mode of variability in these
sources, as the observed properties appear largely inconsistent with known
classes of AGNs capable of generating relativistic jets (blazars, narrow-line
Seyfert 1 galaxies).Comment: Minor typos correcte
Exploring the Optical Transient Sky with the Palomar Transient Factory
The Palomar Transient Factory (PTF) is a wide-field experiment designed to
investigate the optical transient and variable sky on time scales from minutes
to years. PTF uses the CFH12k mosaic camera, with a field of view of 7.9 deg^2
and a plate scale of 1 asec/pixel, mounted on the the Palomar Observatory
48-inch Samuel Oschin Telescope. The PTF operation strategy is devised to probe
the existing gaps in the transient phase space and to search for theoretically
predicted, but not yet detected, phenomena, such as fallback supernovae,
macronovae, .Ia supernovae and the orphan afterglows of gamma-ray bursts. PTF
will also discover many new members of known source classes, from cataclysmic
variables in their various avatars to supernovae and active galactic nuclei,
and will provide important insights into understanding galactic dynamics
(through RR Lyrae stars) and the Solar system (asteroids and near-Earth
objects). The lessons that can be learned from PTF will be essential for the
preparation of future large synoptic sky surveys like the Large Synoptic Survey
Telescope. In this paper we present the scientific motivation for PTF and
describe in detail the goals and expectations for this experiment.Comment: 15 pages, 6 figures, submitted to PAS
Slow-Speed Supernovae from the Palomar Transient Factory: Two Channels
Since the discovery of the unusual prototype SN 2002cx, the eponymous class
of low-velocity, hydrogen-poor supernovae has grown to include at most another
two dozen members identified from several heterogeneous surveys, in some cases
ambiguously. Here we present the results of a systematic study of 1077
hydrogen-poor supernovae discovered by the Palomar Transient Factory, leading
to nine new members of this peculiar class. Moreover we find there are two
distinct subclasses based on their spectroscopic, photometric, and host galaxy
properties: The "SN 2002cx-like" supernovae tend to be in later-type or more
irregular hosts, have more varied and generally dimmer luminosities, have
longer rise times, and lack a Ti II trough when compared to the "SN
2002es-like" supernovae. None of our objects show helium, and we counter a
previous claim of two such events. We also find that these transients comprise
5.6+17-3.7% (90% confidence) of all SNe Ia, lower compared to earlier
estimates. Combining our objects with the literature sample, we propose that
these subclasses have two distinct physical origins.Comment: 49 pages, 36 figures, submitted to Ap
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