-
S. B. Cenko (NASA/GSFC), M. M. Kasliwal (OCIW/Princeton), D. A. Perley
(Caltech), D. Jewitt (UCLA), A. V. Filippenko (UC Berkeley), A. Horesh
(Weizmann Institute), A. De Cia (Weizmann Institute), A. Rubin (Weizmann
Institute), A. Gal-Yam (Weizmann Institute), O. Yaron (Weizmann Institute), I.
Arcavi (LCOGT/KITP), Y. Cao (Caltech), and P. E. Nugent (LBNL/UCB) report on
behalf of a larger collaboration:
As part of the ongoing Intermediate Palomar Transient Factory survey, we report
the discovery of a new optical transient source, iPTF14yb, located at RA =
14:45:58.01, Dec: +14:59:35.4 (J2000.0). In an image obtained at the Palomar
48-inch Oschin Schmidt telescope beginning at 10:18 UT on 2014 February 26, we
measure an r-band magnitude of r = 18.42 +/- 0.05 mag. In subsequent P48
imaging, the source faded rapidly, with a measured magnitude of r = 20.4 +/-
0.2 mag at 13:08 UT on 2014 February 26.
Nothing was detected at this location (r > 20.5 mag) in an image obtained at
09:05 UT on 2014 February 26 (i.e., 1.2 hours prior to discovery). A
coaddition of previous (i)PTF imaging of this location from 2009-2012 with P48
reveals no sources at this location to a limit of r > 22.7 mag.
We obtained a target-of-opportunity spectrum with the Low Resolution Imaging
Spectrometer (LRIS) mounted on the 10 m Keck 1 telescope beginning at 15:27 UT
on 2014 February 26 (i.e., 5.2 hours after discovery). Our spectrum covers the
wavelength range from the atmospheric cutoff at ~ 3200 A to 10000 A.
Super-imposed on a relatively flat continuum, we detect a number of absorption
features at a common redshift of z = 1.98 (preliminary wavelength calibration),
including Mg II, Fe II, Mg I, and Ly-alpha.
Given the rapid temporal evolution, the large distance and luminosity, and the
observed spectrum, iPTF14yb resembles the optical afterglow of a gamma-ray
burst. We have triggered radio and X-ray observations to confirm this
hypothesis, and encourage additional follow-up at all wavelengths (including
archival searches of this location).
- ATEL 5924
S. B. Cenko (NASA/GSFC), M. M. Kasliwal (OCIW/Princeton),
D. A. Perley (Caltech), D. Jewitt (UCLA), A. V. Filippenko (UC
Berkeley),
A. Horesh (Weizmann Institute), A. De Cia (Weizmann Institute),
A.
Rubin (Weizmann Institute), A. Gal-Yam (Weizmann Institute), O.
Yaron
(Weizmann Institute), I. Arcavi (LCOGT/KITP), Y. Cao (Caltech),
and
P. E. Nugent (LBNL/UCB) report on behalf of a larger
collaboration:
As part of the ongoing Intermediate Palomar Transient Factory survey, we
report the discovery of a new optical transient source, iPTF14yb, located
at RA = 14:45:58.01, Dec: +14:59:35.4 (J2000.0). In an image obtained
at the Palomar 48-inch Oschin Schmidt telescope beginning at 10:18 UT on
2014 February 26, we measure an r-band magnitude of r = 18.42 +/- 0.05
mag. In subsequent P48 imaging, the source faded rapidly, with a measured
magnitude of r = 20.4 +/- 0.2 mag at 13:08 UT on 2014 February 26.
Nothing was detected at this location (r > 20.5 mag) in an image obtained
at 09:05 UT on 2014 February 26 (i.e., 1.2 hours prior to discovery).
A coaddition of previous (i)PTF imaging of this location from 2009-2012
with P48 reveals no sources at this location to a limit of r > 22.7 mag.
We obtained a target-of-opportunity spectrum with the Low Resolution Imaging
Spectrometer (LRIS) mounted on the 10 m Keck 1 telescope beginning at 15:27
UT on 2014 February 26 (i.e., 5.2 hours after discovery). Our spectrum
covers the wavelength range from the atmospheric cutoff at ~ 3200 A to
10000 A. Super-imposed on a relatively flat continuum, we detect a number
of absorption features at a common redshift of z = 1.98 (preliminary wavelength
calibration), including Mg II, Fe II, Mg I, and Ly-alpha.
Given the rapid temporal evolution, the large distance and luminosity,
and the observed spectrum, iPTF14yb resembles the optical afterglow of
a gamma-ray burst. We have triggered radio and X-ray observations to confirm
this hypothesis, and encourage additional follow-up at all wavelengths
(including archival searches of this location).
- GCN Circular #15884
A.P. Beardmore, P.A. Evans and K.L. Page (U. Leicester) report on
behalf of the Swift-XRT team:
We have analysed 2.3 ks of XRT data for the PTF-detected transient /
possible GRB iPTF14yb, from 24.8 ks to 42.8 ks after the time of the
initial PTF observation. The data are entirely in Photon Counting (PC)
mode. An X-ray source is detected within the PTF error circle. The
refined XRT position is RA, Dec = 221.49179, +14.99396 which is
equivalent to:
RA (J2000): 14 45 58.03
Dec(J2000): +14 59 38.3
with an uncertainty of 3.7 arcsec (radius, 90% confidence). This
position is 2.9 arcsec from the PTF position. The source has a mean
count rate of 4.7e-02 ct/sec and shows marginal evidence for fading at
the 1.6-sigma level, with a decay slope of 1.14, however more data are
required to confirm this.
A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.15 (+0.51, -0.30). The
best-fitting absorption column is consistent with the Galactic value
of 1.5 x 10^20 cm^-2 (Kalberla et al. 2005). The counts to observed
(unabsorbed) 0.3-10 keV flux conversion factor deduced from this
spectrum is 3.3 x 10^-11 (3.5 x 10^-11) erg cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
Galactic foreground: 1.5 x 10^20 cm^-2
Intrinsic column: 0 (+6.2, -0) x 10^21 cm^-2 at z=1.98
Photon index: 2.15 (+0.51, -0.30)
The ROSAT (PSPC) All Sky Survey 3-sigma upper limit at the position of
this source is 0.056 ct/sec, which, given the spectrum above,
corresponds to 0.03 ct/sec in the XRT; hence the source was not seen at
the current flux level at the time of the RASS.
The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00033157.
This circular is an official product of the Swift-XRT team.
- ATEL 5927
Peter Garnavich and Jason Wiggins (Notre Dame)
We observed the field of the GRB afterglow-like transient iPTF14yb (Cenko
et al, GCN 15883; Cenko et al, ATEL 5924) with the KPNO-4m plus Mosaic-1.1
camera. Images were obtained in the Sloan-r filter beginning 12:55 UT on
Feb 27 which is 26.6 hours after the first detection. A faint source at
the position of the transient is seen in all four exposures. We estimate
a r-band magnitude of 22.24+/-0.10 mag based on nearby stars in the SDSS
catalog.
The late-time power-law decay slope is between 0.75 and 0.90 depending
on the actual time of the burst. If the burst occurred near 9:54 UT on
Feb 26 (20 minutes before the iPTF detection), then a single power-law
with index of 0.79 fits the iPTF and KPNO-4m photometry.
- GCN Circular #15886
Antonino Cucchiara (ORAU/GSFC), Nat Butler (ASU), Alan M. Watson (UNAM),
Alexander Kutyrev (GSFC), William H. Lee (UNAM), Michael G. Richer (UNAM),
Chris Klein (UCB), Ori Fox (UCB), J. Xavier Prochaska (UCSC), Josh Bloom (UCB),
Eleonora Troja (GSFC), Owen Littlejohns (ASU), Enrico Ramirez-Ruiz (UCSC),
Jos� A. de Diego (UNAM), Leonid Georgiev (UNAM), Jes�s Gonz�lez (UNAM),
Carlos Rom�n-Z��iga (UNAM), Neil Gehrels (GSFC), and Harvey Moseley (GSFC)
report:
We observed the field of the transient iPTF14yb (Cenko et al., GCN 15883,
Beardmore et al.,
GCN 15884) with the Reionization and Transients Infrared Camera (RATIR;
www.ratir.org)
on the1.5m Harold Johnson Telescope at the Observatorio Astron�mico Nacional on
Sierra San Pedro M�rtir from 2014/02 27.28 to 2014/02 27.54 UTC (20.53 to 26.68
hours
after the reported time of discovery), obtaining a total of 3.91 hours exposure
in the
r and i bands and 1.64 hours exposure in the Z, Y, J, and H bands.
For the source reported by Cenko et al. (GCN 15883), in comparison with the
SDSS DR9 and 2MASS, we obtain the following detections and upper limit
(3-sigma):
r 22.28 +/- 0.09
i 22.02 +/- 0.09
Z 21.98 +/- 0.24
Y 22.12 +/- 0.35
J 21.88 +/- 0.35
H > 21.59
These magnitudes are in the AB system and are not corrected for Galactic
extinction in the direction of the transient.
Our photometry indicates that the transient is fading in r band according to a
single power law with temporal index alpha=1.04. This behavior is also typical
of a long gamma-ray burst type transient as suggested by Cenko et al. (GCN
+15883)
We thank the staff of the Observatorio Astron�mico Nacional in San Pedro
M�rtir.
- GCN Circular #15887
K. Varela, J. F. Graham, J. Greiner, (all MPE Garching) and D. A.
Kann (TLS Tautenburg) report on behalf of the GROND team:
We observed the iPTF-detected GRB optical afterglow-like transient
iPTF14yb (Cenko et al. GCN 15883) simultaneously in g'r'i'z'JHK
with the GROND instrument (Greiner et al. 2008, PASP 120, 405)
mounted at the 2.2m MPG telescope at La Silla Observatory (Chile).
Observations started at 08:09 UT on February 27th 2014
(approximately 22 hours after initial detection). We clearly
detect the source in the g'r'i'z' bands at the following (AB)
magnitudes and errors:
g = 22.37 +/- 0.04
r = 22.11 +/- 0.03
i = 22.07 +/- 0.06
z = 22.11 +/- 0.03
We do not detect the source in the JHK bands above our 3-sigma AB
limits given below:
J > 21.6
H > 21.0
K > 19.7
The values we measure are comparable with the concurrent RATIR
observations (Cucchiara et al., GCN 15886). Given magnitudes are
calibrated against SDSS field stars (g'r'i'z') as well as 2MASS
field stars (JHK) and are not corrected for the expected Galactic
foreground extinction corresponding to a reddening of E_(B-V)=0.03
mag in the direction of the burst (Schlegel et al. 1998).
Given the unusually flat spectral slope of 0.25 +/- 0.07 (after
correcting for Galactic extinction) apparent in our photometry
and the flat spectra noted in Cenko et al. (GCN 15883) with the
present data we cannot distinguish between a powerlaw or a thermal
spectrum. Deep NIR imaging is encouraged to allow this distinction.
- GCN Circular #15888
K. Hurley, on behalf of the Interplanetary Network,
S. Golenetskii, R. Aptekar, V. Pal'shin, D. Frederiks,
D. Svinkin, and T. Cline on behalf of the Konus-Wind team,
I. G. Mitrofanov, D. Golovin, M. L. Litvak, and A. B. Sanin,
on behalf of the HEND-Odyssey GRB team,
W. Boynton, C. Fellows, K. Harshman, H. Enos, and R. Starr, on
behalf of the GRS-Odyssey GRB team,
A. von Kienlin, X. Zhang, A. Rau, V. Savchenko, E. Bozzo, and C.
Ferrigno, on behalf of the INTEGRAL SPI-ACS GRB team,
S. Barthelmy, J. Cummings, N. Gehrels, H. Krimm, and D. Palmer, on behalf of
the Swift-BAT team, and
V. Connaughton, M. S. Briggs, C. Meegan, and V. Pelassa, on behalf of the Fermi
GBM team, report:
We have examined IPN data for the period 2014-02-26T09:05:00 to
2014-02-26T10:18:00, when the optical transient source iPTF14yb was
discovered (Cenko et al. GCN 15883). During this time, Konus, Swift,
INTEGRAL, RHESSI, Odyssey, and MESSENGER were operating and returning
data, although in the presence of increased solar activity. Suzaku was
off. We have identified one event, at 2014-02-26T10:02:57 (36177 s),
observed by Odyssey, INTEGRAL (SPI-ACS) and Konus (in the waiting
mode), whose duration is ~15 s, and whose localization is consistent
with iPTF14yb. Specifically, the Odyssey-INTEGRAL triangulation
annulus is centered at RA, Dec = 206.305 degrees (13 h 45 m 13.2 s),
-7.925 degrees (-7 o 55 ' 29 "), with radius 27.577 +/- 0.607 degrees
(3 sigma). iPTF14yb lies 0.157 degrees from the center line of the
annulus. The probability that the transient lies within the annulus by
chance is roughly 0.005. At the time of this event, the optical
transient was below the horizon for Swift, and no emission consistent
with a GRB was seen in the data. Fermi was in the SAA. The RHESSI and
MESSENGER backgrounds were high and variable due to solar activity,
making the identification of this burst uncertain in their data.
If this is indeed the GRB counterpart to iPTF14yb, this would appear to
be the first GRB to be discovered on the basis of its optical
counterpart.
This triangulation can be improved. Detailed spectral and temporal
information on this burst will be presented in a forthcoming GCN
Circular.
- ATEL 5929
J. Vinko (U Szeged, UT Austin), J. M. Silverman (UT Austin),
D. Pooley (SHSU), T. Szalai (U Szeged), E. L. Robinson, J. C. Wheeler
(UT Austin)
We observed the field around the GRB afterglow candidate iPTF14yb (Cenko
et al. ATel #5924) with the DIAFI instrument mounted on the 2.7 m Harlan
J. Smith Telescope at McDonald Observatory, Texas. A series of CCD frames
using Sloan-g and Sloan-r filters were collected on Feb.27 08:25 UT. The
transient has been successfully detected on all frames.
Photometry of this source using nearby field stars from SDSS DR10 resulted
in the following magnitude estimates: g' = 22.29 +/- 0.08, r' = 22.03 +/-
0.10. These magnitudes are consistent with the nearly contemporaneous photometry
by Garnavich & Wiggins (ATel #5927).
Provided the light curve can be fit by a single power-law, the moment of
outburst and the power-law index is MJD 56714.416 (Feb 25, 9:59 UT) and
-0.79, respectively. These values are in perfect agreement with the ones
in ATel #5927.
The DIAFI image and the light curve can be accessed at the following http
URL:
http://www.as.utexas.edu/~vinko/ptf14yb_sdss.png
http://www.as.utexas.edu/~vinko/ptf14yb_lc.jpg
- GCN Circular #15889
S. Golenetskii, R.Aptekar, D. Frederiks, V. Pal'shin,
P. Oleynik, M. Ulanov, D. Svinkin, and T. Cline on behalf
of the Konus-Wind team, report:
The long-duration GRB 140226A
(IPN trangulation: Hurley et al., GCN 15888),
which is a possible counterpart to the optical
transient source iPTF14yb (Cenko et al. GCN 15883),
was detected by Konus-Wind in the waiting mode
against the high solar particle background.
The light curve shows a single pulse, which peaked
at T0=3D36177 s UT (10:02:57) and had a duration of ~15 s.
As observed by Konus-Wind, the burst had a fluence of
(5.6 =B1 1.1)x10^-6 erg/cm2 and a 2.944-s peak energy flux,
measured from T0 of (8.6 =B1 1.7)x10^-7 erg/cm2
(both in the 20 - 10000 keV energy range).
Modeling the KW 3-channel time-integrated spectrum
(from T0-6.263 s to T0+5.513 s) by a power law
with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
yields alpha =3D -1.1 =B1 0.1, and Ep =3D 414 =B1 79 keV.
All the quoted errors are estimated at 1 sigma confidence level.
All the presented results are preliminary.
The K-W light curve of this burst is available at
http://www.ioffe.rssi.ru/LEA/GRBs/GRB140226A/
- GCN Circular #15891
A.P. Beardmore (U. Leicester) reports on behalf of the Swift-XRT team:
The Swift-XRT has continued to observe the source GRB 140226A /
iPTF14yb (Cenko et al., GCN Circ. 15883; Cucchiara et al., GCN
Circ. 15886; Varela et al., GCN Circ. 15887; Hurley et al., GCN
Circ. 15888) and has now accumulated 9.1ks of data in Photon Counting
(PC) mode. The X-ray light curve shows that the source announced by
Beardmore et al. (GCN Circ. 15884) has faded, with a powerlaw decay
index of 1.47 +0.29 -0.25 (with respect to the Konus-Wind T0;
Golenetskii et al., GCN Circ. 15889).
Taken together with the fading optical source and IPN localisation,
the decaying X-ray source confirms the GRB origin of the object.
The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00033157.
- GCN Circular #15892
Antonino Cucchiara (ORAU/GSFC),Nat Butler (ASU), Alan M. Watson (UNAM),=20
Alexander Kutyrev (GSFC), William H. Lee (UNAM), Michael G. Richer (UNAM)=
,=20
Chris Klein (UCB), Ori Fox (UCB), J. Xavier Prochaska (UCSC), Josh Bloom =
(UCB),=20
Eleonora Troja (GSFC), Owen Littlejohns (ASU), Enrico Ramirez-Ruiz (UCSC)=
,=20
Jos=E9 A. de Diego (UNAM), Leonid Georgiev (UNAM), Jes=FAs Gonz=E1lez (UN=
AM),=20
Carlos Rom=E1n-Z=FA=F1iga (UNAM), Neil Gehrels (GSFC), and Harvey Moseley=
(GSFC) report:
We observed again the field of the GRB-like transient iPTF14yb (Cenko et =
al., GCN 15883,=20
Beardmore et al., GCN 15884, 15891) with the Reionization and Transients =
Infrared Camera
(RATIR; www.ratir.org) on the 1.5m Harold Johnson Telescope at the Observ=
atorio Astron=F3mico=20
Nacional on Sierra San Pedro M=E1rtir from 2014/02 28.34 to 2014/02 28.5=
3 UTC (roughly 46=20
to 50 hours after the reported time of discovery), obtaining a total of 2=
.63 hours exposure=20
in the r and i bands and 1.12 hours exposure in the Z, Y, J, and H bands.
For the source within the Cenko et al. (GCN 15883) error circle, in compa=
rison with the=20
SDSS DR9 and 2MASS, we obtain the following detections and upper limits:
r 23.28 +/- 0.32
i 22.51 +/- 0.20
Z > 22.11
J > 21.73
The detections are at the 2-sigma level and the upper limits at the
3-sigma level.
These magnitudes are in the AB system and are not corrected for Galactic
extinction in the direction of the GRB.
Our photometry indicates that the transient is still fading in r band wit=
h a similar
decay index (within the systematic errors) as reported by Cucchiara et al=
. (GCN=20
15886).
We thank the staff of the Observatorio Astron=F3mico Nacional in San Pedr=
o=20
M=E1rtir.
- GCN Circular #15893
A.Volnova (IKI), A. Pozanenko (IKI), I. Korobtsev (ISTP), E. Klunko
(ISTP), M. Eselevich (ISTP), report on behalf of larger GRB follow-up
collaboration:
We observed the field of transient iPTF14yb (Cenko et al., GCN 15883,
Beardmore et al., GCN 15884, 15891) of possible GRB 140226A (Hurley et
al., GCN 15888) with AZT-33IK telescope of Mondy observatory on Feb. 27
between (UT) 18:59:34 - 19:59:36. On a stacked R-filter image of 30 x
120 s we marginally detected iPTF14yb source with S/N ~2, and
photometry of the source R = 23.0 at Feb. 27.81221 (mid).
The photometry is based on SDSS J144600.66+145826.2 star assuming
R(Lupton transformation)= 17.624 +/- 0.018
- GCN Circular #15894
M. H. Siegel (PSU), F. E. Marshall (NASA/GSFC) and A. P. Beardmore (U. Leicester)
report on behalf of the Swift/UVOT team:
Swift/UVOT started observations of GRB140226A/iPTF14yb (Cenko et al., GCN Circ.
15833) 25718 s after the IPN trigger (Hurley et al., GCN Circ. 15888).
No optical counterpart is detected at the position of the iPTF or
XRT positions (Beardmore et al., GCN Circ 15884) in summed
exposures.
Preliminary 3-sigma upper limit using the UVOT photometric system
(Breeveld et al al. 2011, AIP Conf. Proc. 1358, 373) is:
Filter T_start (s) T_stop (s) Exp(s) Mag
uvm2 25718 43672 2180 >21.24
v 124093 136265 4877 >20.96
v 147705 154552 1822 >20.54
No correction has been made for the expected Galactic extinction
corresponding to E(B-V) = 0.02 in the direction of the burst (Schlegel et al. 1998).
- GCN Circular #15895
J. Gorosabel (IAA-CSIC/UPV-EHU), I. Ordonez, S. Perez-Hoyos, R. Hueso (UPV/EHU), J.J. Salamero, D. Cebrian, P. Martorell, R. Pidal (Obs. Guirguillano), report on behalf of the BEGIRA project:
"We carried out optical observations of the GRB140226A/iPTF14yb transient field (Cenko et al., GCN 15883, Beardmore et al., GCN 15884, 15891) with the 1.23m CAHA telescope. The observations were performed in the R-band on Feb 28.14668-28.19763 UT. The object is detected with a Vega magnitude of R~23 calibrated against the USNO-B1.0 catalog."
- GCN Circular #16037
A.Volnova (IKI), A. Pozanenko (IKI), I. Korobtsev (ISTP), E. Klunko
(ISTP), M. Eselevich (ISTP), report on behalf of larger GRB follow-up
collaboration:
We observed the field of transient iPTF14yb (Cenko et al., GCN 15883,
Beardmore et al., GCN 15884, 15891) a possible counterpart of GRB
140226A (Hurley et al., GCN 15888) with AZT-33IK telescope of Mondy
observatory on Feb. 28 between (UT) 19:22:46 - 21:52:52 R-filter. On a
stacked image of 75 x 120 s we clearly detected iPTF14yb source with a
magnitude of R =3D 22.86 =C2=B1 0.17 at Feb. 28.85959 (mid) or 2.44087 days
after GRB 140226A trigger (Hurley et al., GCN 15888).
The photometry is based on SDSS J144600.66+145826.2 star assuming
R(Lupton transformation)=3D 17.624 +/- 0.018.
- 1504.00673 from 6 Apr 15
S. Bradley Cenko et al.: iPTF14yb: The First Discovery of a GRB Afterglow Independent of a High-Energy Trigger
We report here the discovery by the Intermediate Palomar Transient Factory (iPTF) of iPTF14yb, a luminous ($M_{r}\approx-27.8$ mag),
cosmological (redshift 1.9733), rapidly fading optical transient. We demonstrate, based on probabilistic arguments and a comparison with the
broader population, that iPTF14yb is the optical afterglow of the long-duration gamma-ray burst GRB 140226A. This marks the first unambiguous
discovery of a GRB afterglow prior to (and thus entirely independent of) an associated high-energy trigger. We estimate the rate of
iPTF14yb-like sources (i.e., cosmologically distant relativistic explosions) based on iPTF observations, inferring an all-sky value of
$\Re_{\mathrm{rel}}=610$ yr$^{-1}$ (68% confidence interval of 110-2000 yr$^{-1}$). Our derived rate is consistent (within the large
uncertainty) with the all-sky rate of on-axis GRBs derived by the Swift satellite. Finally, we briefly discuss the implications of the
nondetection to date of bona fide "orphan" afterglows (i.e., those lacking detectable high-energy emission) on GRB beaming and the degree of
baryon loading in these relativistic jets.
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