- GCN Circular #16425
M. M. Kasliwal (Carnegie Observatories/Princeton), S. B. Cenko
(NASA/GSFC), and L. P. Singer (Caltech) report on behalf of the
intermediate Palomar Transient Factory (iPTF) collaboration:
Fermi GBM reported trigger 424934131 at 2014-06-20 05:15:28.02 UT.
Starting 2014-06-20 05:25:25 UT (10 min after trigger),
we began our search for optical counterparts using the Palomar 48-inch
Oschin telescope (P48). Based on the the ground and final Fermi GBM
localizations, we observed 20 fields covering 147 deg^2, with an
estimated 59% chance of containing the true location of the event.
Sifting through candidate transient sources using image subtraction
and standard intermediate Palomar Transient Factory vetting procedures,
we detected several optical transients. The fastest fading transient was:
iPTF14cva, at the coordinates:
RA(J2000) = 18h 47m 29.01s (281.870873 deg)
Dec(J2000) = +49d 43' 51.7" (+49.731037 deg)
iPTF14cva faded from R=17.6 mag to R=18.8 mag between 05:30 UT to 06:42 UT.
We observed iPTF14cva with the Gemini Multi-Object Spectrograph
mounted on the 8m Gemini North telescope beginning at 14:00 UT on
2014 June 20 (~ 8.8 hr after the GBM trigger). Two 900 s spectra were
obtained, covering the wavelength range from 4000-9300 A.
Super-imposed on a relatively flat continuum, we detect a number of
strong absorption features, including Mg I, Mg II, Fe II, Al II, Si
II, and Si II*, at a common redshift of z = 2.04. The detection of
the fine structure Si II* feature, together with the lack of Ly-alpha
absorption in the spectrum, imply that this is the redshift of the
Fermi GBM GRB. In addition, we detect strong absorption features (Mg
II, Fe II) from an intervening system at a redshift of z = 0.88.
The diagram
http://www.its.caltech.edu/~lsinger/iptf/Fermi424934131.pdf shows the
locations of the afterglow and the 20 P48 fields in relation to the
Fermi GBM 1- and 2-sigma statistical+systematic contours.
We thank the Fermi-GBM team for promptly sharing their detailed
localizations
with us.
- GCN Circular #16426
G. Fitzpatrick (UCD), V. Connaughton (UAH)
report on behalf of the Fermi GBM Team:
At 05:15:28.02 UT on 20 June 2014, the Fermi Gamma-Ray Burst Monitor
triggered
and located GRB 140620A, which was observed by the intermediate Palomar
Transient Factory beginning 10 minutes after trigger time, and was reported
in GCN 16425 (Kasliwal, Cenko, and Singer) as iPTF14cva.
The on-ground calculated location, using the GBM trigger
data, is RA = 278, DEC = +43 (J2000 degrees,
equivalent to 18h 34m, +43d 0.0'), with an uncertainty
of 2 degrees (radius, 1-sigma containment,
statistical only; there is additionally a systematic
error which is currently estimated to be 2 to 3 degrees).
The angle from the Fermi LAT boresight is 110 degrees.
The GBM light curve consists of a single peak
with a duration (T90) of about 46 s (50-300 keV).
The time-averaged spectrum from T0-4 s to T0+35 s is
adequately fit by a power law function with an exponential
high-energy cutoff. The power law index is -1.1 +/- 0.1 and
the cutoff energy, parameterized as Epeak, is 77 +/- 5 keV.
The event fluence (10-1000 keV) in this time interval is
(5.3 +/- 0.2)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+1 s in the 10-1000 keV band is 6.3 +/- 0.4 ph/s/cm^2.
The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog.
- GCN Circular #16428
M. De Pasquale (IASF-Palermo) reports on behalf of the Swift-XRT team:
We have analysed 3.0 ks of XRT data for the Fermi/GBM-detected
burst GRB 140620A (Fitzpatrick et al., GCN circ 16426), from 37.6
ks to 43.9 ks after the Fermi/GBM trigger. The data are entirely
in Photon Counting (PC) mode.
An X-ray source is detected within the Fermi/GBM error circle
at the position of the iPTF transient (Kasliwal et al., GCN circ.
16425). Using 2966 s of PC mode data and 2 UVOT images, we find an
enhanced XRT position (using the XRT-UVOT alignment and matching
UVOT field sources to the USNO-B1 catalogue): RA, Dec = 281.87089,
+49.73093 which is equivalent to:
RA (J2000): 18h 47m 29.01s
Dec(J2000): +49d 43' 51.4"
with an uncertainty of 2.2 arcsec (radius, 90% confidence). This
is 0.4 arcsec from the iPTF position.
The late-time light curve (from T0+37.6 ks) is consistent with a
constant source of mean count rate 1.2e-01 ct/sec. A power-law fit
formally gives an index of -0.1 (+2.4, -1.3). Further observations
might be needed to confirm that this source is the X-ray afterglow
of 140620A.
A spectrum formed from the PC mode data can be fitted with an
absorbed power-law with a photon spectral index of 2.04 (+0.26,
-0.24). The best-fitting absorption column is 1.4 (+0.7, -0.6) x
10^21 cm^-2, in excess of the Galactic value of 5.2 x 10^20 cm^-2
(Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10
keV flux conversion factor deduced from this spectrum is 3.3 x 10^-11
(4.3 x 10^-11) erg cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
Total column: 1.4 (+0.7, -0.6) x 10^21 cm^-2
Galactic foreground: 5.2 x 10^20 cm^-2
Excess significance: 2.3 sigma
Photon index: 2.04 (+0.26, -0.24)
If the light curve continues to evolve with a power-law index
of -0.1, the count rate at T+24 hours will be 0.13 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 4.3 x
10^-12 (5.6 x 10^-12) erg cm^-2 s^-1.
The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00020387.
This circular is an official product of the Swift-XRT team.
- GCN Circular #16432
M. H. Siegel (PSU) and M. De Pasquale (IASF-Palermo) report on behalf of the
Swift/UVOT team:
The Swift/UVOT observed the field of the Fermi/GBM-detected burst GRB 140620A
beginning 37.6 ks after the trigger (Fitzpatrick et al., GCN circ 16426). We confirm
the fading optical transient reported by iPTF (Kasliwal et al., GCN circ 16425) at
a position of:
RA (J2000) = 18:47:29.00 = 281.87082 (deg.)
Dec (J2000) = 49:43:51.0 = 49.73085 (deg.)
with an uncertainty of 0.3 arcsec (radius, 90% confidence). This
is 0.7 arcsec from the iPTF position.
Preliminary detections using the UVOT photometric system (Breeveld et
al. 2011, AIP Conf. Proc. 1358, 373) are given in the following table:
Filter T_start(ks) T_stop(ks) Exp(s) Mag
u 37.6 43.9 1718 19.78+-0.10
u 124.0 125.3 1251 20.38+-0.18
The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.06 in the direction of the burst
(Schlegel et al. 1998).
- GCN Circular #16440
J. Kelemen (kelemen at konkoly.hu) on behalf of the GRB OT observing program
at the Konkoly Observatory.
Starting on the evening of 21/06/2014 UT we observed the field of GRB 140620A
(Fermi GBM reported trigger 424934131 at 2014-06-20 05:15:28.02 UT)
150898 sec. after the burst, using a 60/90/180 cm Schmidt telescope
located at the Mountain Station of the Konkoly Observatory . On the
coadded R images (total exp.time 900 sec) we easily detected the OT at the
position reported by M. M. Kasliwal et al. (GCN 16425)
Based on the nearby UCAC-4 stars we provide 21.9 +/- 0.15 magnitude in the R
band for the OT.
time from GRB. exp filter Mag.
------------------------------------------------
150898 s. 900 s R 21.9 +/-0.15
------------------------------------------------
- GCN Circular #16453
A. Volnova (IKI), W. Mundrzyjewski (Fesenkov Astrophysical Institute), A.
Kusakin (Fesenkov Astrophysical Institute), A. Pozanenko (IKI) report on
behalf of larger GRB follow-up collaboration:
We observed the optical candiadate iPTF14cva (Kasliwal et al., GCN 16425) of
Fermi GRB 140620A (Fermi trig. # 424934131) (Fitzpatrick et al., GCN
16426) with Zeiss-1000 (East) 1m telescope of Tien Shan Astronomical
Observatory on June, 20 starting (UT) 21:22:56. We took several images in
R-filter. We clearly detected optical transient (Siegel et al., GCN 16432;
Kelemen GCN 16440) in a stacked image.
Details of the photometry are following:
date UT start t-T0 Filter Exp. OT
(mid, days) (s)
2014-06-20 21:22:56 0.68914 R 20*120 20.37 +/- 0.09
The photometry is based on star USNO-B1.0 1397-0294956 (RA 18:47:28.76 Dec
+49:43:44.5) assuming R=16.35.
- GCN Circular #16455
M. De Pasquale (INAF-Palermo) reports on behalf of the Swift team:
Analyzing XRT data of the X-ray source at the position of the iPTF14cva transient
(De Pasquale, GCN Circ. 16428) from 37.6 to 367.3 ks after the trigger, we found
that this source is fading with a decay slope of 1.32 (+0.18, -0.15). We therefore
confirm that this source is the X-ray afterglow of the GRB associated with this
transient.
The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00020387.
This circular is an official product of the Swift-XRT team.
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