23 research outputs found
Spatial coincidence between ultra-high energy cosmic rays and TeV gamma rays in the direction of GRB 980425/SN 1998bw
Gamma-ray bursts (GRBs) have long been suspected as possible ultra-high
energy cosmic ray (UHECR) accelerators. In this brief note, I report that GRB
980425/SN 1998bw falls within the region of interest (ROI) with the highest
significance in an all-sky blind search for magnetically-induced effects in the
arrival directions of UHECRs conducted by the Pierre Auger Collaboration with
events detected up to to 2018 August 31. There is also report in the literature
of delayed TeV emission in archival Fermi-LAT observations from the direction
of GRB 980425/SN 1998bw. The combined probability that two distinct cosmic ray
acceleration signatures in two different multimessenger experiments may appear
at the same spatial location by chance is estimated to be between and 0.0157.Comment: 3 pages, 1 figure, Research Notes of the AA
Secondary GeV-TeV emission from ultra-high-energy cosmic rays accelerated by GRB 221009A
The origin of ultra-high-energy cosmic rays (UHECRs) remains elusive.
Gamma-ray bursts (GRBs) are among the best candidates able to meet the
stringent energy requirements needed for particle acceleration to such high
energies. If UHECRs were accelerated by the central engine of GRB 221009A, it
might be possible to detect secondary photons and neutrinos as the UHECRs
travel from the source to the Earth. Here we attempt to interpret some of the
early publicly available data connected to this burst. If the reported early
GeV-TeV detection was produced by secondary emission from UHECRs it probably
indicates that UHECRs reached energies eV and that GRB 221009A
exploded inside a magnetic void with intergalactic magnetic field (IGMF)
strength G. In order to understand the entire energy
deposition mechanism, we propose to search existing and future Fermi-LAT data
for secondary emission arriving over larger spatial scales and longer
time-scales. This strategy might help clarify the origin of UHECRs, constrain
the intergalactic magnetic field (IGMF) strength along this line of sight and
start to quantify the fraction of magnetic voids around GRBs.Comment: 2 pages, submitted to MNRAS, catching up with GCN Circular
references, included reference to delay formulatio
The Smith Cloud and its dark matter halo: Survival of a Galactic disc passage
The current velocity of the Smith Cloud indicates that it has undergone at
least one passage of the Galactic disc. Using hydrodynamic simulations we
examine the present day structure of the Smith Cloud. We find that a dark
matter supported cloud is able to reproduce the observed present day neutral
hydrogen mass, column density distribution and morphology. In this case the
dark matter halo becomes elongated, owing to the tidal interaction with the
Galactic disc. Clouds in models neglecting dark matter confinement are
destroyed upon disc passage, unless the initial cloud mass is well in excess of
what is observed today. We then determine integrated flux upper limits to the
gamma-ray emission around such a hypothesised dark matter core in the Smith
Cloud. No statistically significant core or extended gamma-ray emission are
detected down to a 95% confidence level upper limit of ph
cm s in the 1-300 GeV energy range. For the derived distance of
12.4 kpc, the Fermi upper limits set the first tentative constraints on the
dark matter cross sections annihilating into and
for a high-velocity cloud.Comment: 10 pages, 8 figures. Submitted to MNRA
Sensitivity Projections for Dark Matter Searches with the Fermi Large Area Telescope
The nature of dark matter is a longstanding enigma of physics; it may consist
of particles beyond the Standard Model that are still elusive to experiments.
Among indirect search techniques, which look for stable products from the
annihilation or decay of dark matter particles, or from axions coupling to
high-energy photons, observations of the -ray sky have come to
prominence over the last few years, because of the excellent sensitivity of the
Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope mission. The
LAT energy range from 20 MeV to above 300 GeV is particularly well suited for
searching for products of the interactions of dark matter particles. In this
report we describe methods used to search for evidence of dark matter with the
LAT, and review the status of searches performed with up to six years of LAT
data. We also discuss the factors that determine the sensitivities of these
searches, including the magnitudes of the signals and the relevant backgrounds,
considering both statistical and systematic uncertainties. We project the
expected sensitivities of each search method for 10 and 15 years of LAT data
taking. In particular, we find that the sensitivity of searches targeting dwarf
galaxies, which provide the best limits currently, will improve faster than the
square root of observing time. Current LAT limits for dwarf galaxies using six
years of data reach the thermal relic level for masses up to 120 GeV for the
annihilation channel for reasonable dark matter density profiles.
With projected discoveries of additional dwarfs, these limits could extend to
about 250 GeV. With as much as 15 years of LAT data these searches would be
sensitive to dark matter annihilations at the thermal relic cross section for
masses to greater than 400 GeV (200 GeV) in the ()
annihilation channels.Comment: Updated with a few additional and corrected references; otherwise,
text is identical to previous version. Submitted on behalf of the Fermi-LAT
collaboration. Accepted for publication in Physics Reports, 59 pages, 34
figures; corresponding author: Eric Charles ([email protected]
The Rapidly Flaring Afterglow of the Very Bright and Energetic GRB 070125
We report on multiwavelength observations, ranging from X-ray to radio wave bands, of the IPN-localized gamma-ray burst GRB 070125. Spectroscopic observations reveal the presence of absorption lines due to O I, Si II, and C IV, implying a likely redshift of z = 1.547. The well-sampled light curves, in particular from 0.5 to 4 days after the burst, suggest a jet break at 3.7 days, corresponding to a jet opening angle of ~7.0°, and implying an intrinsic GRB energy in the 1-10,000 keV band of around EÎł = (6.3â6.9) Ă 1051 ergs (based on the fluences measured by the gamma-ray detectors of the IPN). GRB 070125 is among the brightest afterglows observed to date. The SED implies a host extinction of AV \u3c 0.9 mag . Two rebrightening episodes are observed, one with excellent time coverage, showing an increase in flux of 56% in ~8000 s. The evolution of the afterglow light curve is achromatic at all times. Late-time observations of the afterglow do not show evidence for emission from an underlying host galaxy or supernova. Any host galaxy would be subluminous, consistent with current GRB host galaxy samples. Evidence for strong Mg II absorption features is not found, which is perhaps surprising in view of the relatively high redshift of this burst and the high likelihood for such features along GRB-selected lines of sight
The Rapidly Flaring Afterglow of the Very Bright and Energetic GRB 070125
We report on multi-wavelength observations, ranging from the X-ray to radio
wave bands, of the IPN-localized gamma-ray burst GRB 070125. Spectroscopic
observations reveal the presence of absorption lines due to O I, Si II, and C
IV, implying a likely redshift of z = 1.547. The well-sampled light curves, in
particular from 0.5 to 4 days after the burst, suggest a jet break at 3.7 days,
corresponding to a jet opening angle of ~7.0 degrees, and implying an intrinsic
GRB energy in the 1 - 10,000 keV band of around E = (6.3 - 6.9)x 10^(51) erg
(based on the fluences measured by the gamma-ray detectors of the IPN network).
GRB 070125 is among the brightest afterglows observed to date. The spectral
energy distribution implies a host extinction of Av < 0.9 mag. Two
rebrightening episodes are observed, one with excellent time coverage, showing
an increase in flux of 56% in ~8000 seconds. The evolution of the afterglow
light curve is achromatic at all times. Late-time observations of the afterglow
do not show evidence for emission from an underlying host galaxy or supernova.
Any host galaxy would be subluminous, consistent with current GRB host-galaxy
samples. Evidence for strong Mg II absorption features is not found, which is
perhaps surprising in view of the relatively high redshift of this burst and
the high likelihood for such features along GRB-selected lines of sight.Comment: 50 pages, 9 figures, 5 tables Accepted to the Astrophysical Journa
The 2001 Superoutburst of WZ Sagittae
We report the results of a worldwide campaign to observe WZ Sagittae during
its 2001 superoutburst. After a 23-year slumber at V=15.5, the star rose within
2 days to a peak brightness of 8.2, and showed a main eruption lasting 25 days.
The return to quiescence was punctuated by 12 small eruptions, of ~1 mag
amplitude and 2 day recurrence time; these "echo outbursts" are of uncertain
origin, but somewhat resemble the normal outbursts of dwarf novae. After 52
days, the star began a slow decline to quiescence.
Periodic waves in the light curve closely followed the pattern seen in the
1978 superoutburst: a strong orbital signal dominated the first 12 days,
followed by a powerful /common superhump/ at 0.05721(5) d, 0.92(8)% longer than
P_orb. The latter endured for at least 90 days, although probably mutating into
a "late" superhump with a slightly longer mean period [0.05736(5) d]. The
superhump appeared to follow familiar rules for such phenomena in dwarf novae,
with components given by linear combinations of two basic frequencies: the
orbital frequency omega_o and an unseen low frequency Omega, believed to
represent the accretion disk's apsidal precession. Long time series reveal an
intricate fine structure, with ~20 incommensurate frequencies. Essentially all
components occurred at a frequency n(omega_o)-m(Omega), with m=1, ..., n. But
during its first week, the common superhump showed primary components at n
(omega_o)-Omega, for n=1, 2, 3, 4, 5, 6, 7, 8, 9 (i.e., m=1 consistently); a
month later, the dominant power shifted to components with m=n-1. This may
arise from a shift in the disk's spiral-arm pattern, likely to be the
underlying cause of superhumps.
The great majority of frequency components ... . (etc., abstract continues)Comment: PDF, 54 pages, 4 tables, 21 figures, 1 appendix; accepted, in press,
to appear July 2002, PASP; more info at http://cba.phys.columbia.edu
Preprint typeset using L ATEX style emulateapj v. 14/09/00 THE MERGER IN ABELL 576: A LINE OF SIGHT BULLET CLUSTER?
Using a combination of Chandra and XMM observations, we confirmed the presence of a significant velocity gradient along the NE/EâW/SW direction in the intracluster gas of the cluster Abell 576. The results are consistent with a previous ASCA SIS analysis of this cluster. The error weighted average over ACIS-S3, EPIC MOS 1 & 2 spectrometers for the maximum velocity difference is>3.3Ă10 3 km s â1 at the 90 % confidence level, similar to the velocity limits estimated indirectly for the âbullet â cluster (1E0657-56). The probability that the velocity gradient is generated by standard random gain fluctuations with Chandra and XMM is <0.1%. The regions of maximum velocity gradient are in CCD zones that have the lowest temporal gain variations. It is unlikely that the velocity gradient is due to Hubble distance differences between projected clusters (probability ⌠<0.01%). We mapped the distribution of elemental abundance ratios across the cluster and detected a strong chemical discontinuity using the abundance ratio of silicon to iron, equivalent to a variation from 100 % SN Ia iron mass fraction in the Westâ Northwest regions to 32 % in the Eastern region. The âcenter â of the cluster is located at the chemical discontinuity boundary, which is inconsistent with the radially symmetric chemical gradient found in some regular clusters, but consistent with a cluster merging scenario. We predict that the velocity gradient as measured will produce a variation of the CMB temperature towards the East of the core of the cluster that will be detectable by current and near-future bolometers. The measured velocity gradient opens for the possibility that this cluster is passing through a near line-of-sight merger stage where the cores have recently crossed