250 research outputs found
Discovery and Follow-up Observations of the Young Type Ia Supernova 2016coj
The Type Ia supernova (SN Ia) 2016coj in NGC 4125 (redshift z = 0.00452 ± 0.00006) was discovered by the Lick Observatory Supernova Search 4.9 days after the fitted first-light time (FFLT; 11.1 days before B-band maximum). Our first detection (prediscovery) is merely 0.6 ± 0.5 days after the FFLT, making SN 2016coj one of the earliest known detections of an SN Ia. A spectrum was taken only 3.7 hr after discovery (5.0 days after the FFLT) and classified as a normal SN Ia. We performed high-quality photometry, low- and high-resolution spectroscopy, and spectropolarimetry, finding that SN 2016coj is a spectroscopically normal SN Ia, but the velocity of Si II λ6355 around peak brightness (~12,600 km s^(-1)) is a bit higher than that of typical normal SNe. The Si II λ6355 velocity evolution can be well fit by a broken-power-law function for up to a month after the FFLT. SN 2016coj has a normal peak luminosity (M_B ≈ -18.9 ± 0.2 mag), and it reaches a B-band maximum ~16.0 days after the FFLT. We estimate there to be low host-galaxy extinction based on the absence of Na I D absorption lines in our low- and high-resolution spectra. The spectropolarimetric data exhibit weak polarization in the continuum, but the Si II line polarization is quite strong (~0.9% ± 0.1%) at peak brightness
Discovery and Follow-up Observations of the Young Type Ia Supernova 2016coj
The Type Ia supernova (SN Ia) 2016coj in NGC 4125 (redshift z = 0.00452 ± 0.00006) was discovered by the Lick Observatory Supernova Search 4.9 days after the fitted first-light time (FFLT; 11.1 days before B-band maximum). Our first detection (prediscovery) is merely 0.6 ± 0.5 days after the FFLT, making SN 2016coj one of the earliest known detections of an SN Ia. A spectrum was taken only 3.7 hr after discovery (5.0 days after the FFLT) and classified as a normal SN Ia. We performed high-quality photometry, low- and high-resolution spectroscopy, and spectropolarimetry, finding that SN 2016coj is a spectroscopically normal SN Ia, but the velocity of Si II λ6355 around peak brightness (~12,600 km s^(-1)) is a bit higher than that of typical normal SNe. The Si II λ6355 velocity evolution can be well fit by a broken-power-law function for up to a month after the FFLT. SN 2016coj has a normal peak luminosity (M_B ≈ -18.9 ± 0.2 mag), and it reaches a B-band maximum ~16.0 days after the FFLT. We estimate there to be low host-galaxy extinction based on the absence of Na I D absorption lines in our low- and high-resolution spectra. The spectropolarimetric data exhibit weak polarization in the continuum, but the Si II line polarization is quite strong (~0.9% ± 0.1%) at peak brightness
Limits to the fraction of high-energy photon emitting gamma-ray bursts
After almost 4 years of operation, the two instruments onboard the Fermi
Gamma-ray Space Telescope have shown that the number of gamma-ray bursts with
high energy photon emission above 100 MeV cannot exceed roughly 9% of the total
number of all such events, at least at the present detection limits. In a
recent paper (Zheng et al. 2012c), we found that GRBs with photons detected in
the Large Area Telescope (LAT) have a surprisingly broad distribution with
respect to the photon number above background. Extrapolation of our empirical
fit to numbers of photons below our quoted detection limit suggests that the
overall rate of such events could be determined by standard image co-adding
techniques. In this case, we have taken advantage of the excellent angular
resolution of the Swift mission to provide accurate reference points for 79 GRB
events which have eluded any previous correlations with high energy photons. We
find a small but significant signal. Guided by the power law fit obtained
previously for the number distribution of GRBs, the data suggests that only a
small fraction of GRBs are sources of high energy photons.Comment: 16 pages, 3 figures, 2 tables, accepted for publication in Ap
GRB 110709A, 111117A and 120107A: Faint high-energy gamma-ray photon emission from Fermi/LAT observations and demographic implications
Launched on June 11, 2008, the LAT instrument onboard the Gamma-ray
Space Telescope has provided a rare opportunity to study high energy photon
emission from gamma-ray bursts. Although the majority of such events (27) have
been iden tified by the Fermi LAT Collaboration, four were uncovered by using
more sensiti ve statistical techniques (Akerlof et al 2010, Akerlof et al 2011,
Zheng et al 2 012). In this paper, we continue our earlier work by finding
three more GRBs ass ociated with high energy photon emission, GRB 110709A,
111117A and 120107A. To s ystematize our matched filter approach, a pipeline
has been developed to identif y these objects in near real time. GRB 120107A is
the first product of this anal ysis procedure. Despite the reduced threshold
for identification, the number of GRB events has not increased significantly.
This relative dearth of events with low photon number prompted a study of the
apparent photon number distribution. W e find an extremely good fit to a simple
power-law with an exponent of -1.8 0.3 for the differential
distribution. As might be expected, there is a substa ntial correlation between
the number of lower energy photons detected by the GBM and the number observed
by the LAT. Thus, high energy photon emission is associ ated with some but not
all of the brighter GBM events. Deeper studies of the pro perties of the small
population of high energy emitting bursts may eventually yi eld a better
understanding of these entire phenomena.Comment: accepted to Ap
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