GRB 150101B
GCN Circular 22889
Subject
GRB150101B: INTEGRAL prompt gamma-ray signal from a possible GRB170817A-analogue
Date
2018-07-04T10:24:47Z (7 years ago)
From
Carlo Ferrigno at IAAT/ISDC <carlo.Ferrigno@unige.ch>
J. Rodi, A. Bazzano, P. Ubertini (IAPS-Roma)
E. Bozzo, C. Ferrigno, V. Savchenko (ISDC, University of Geneva, CH)
E. Kuulkers (ESTEC/ESA, The Netherlands)
D. Gotz (DRF/Irfu/DAp Saclay/CEA)
L. Hanlon, A. Martin-Carrillo (UCD, Ireland)
J. M. Mas-Hesse (CSIC-INTA, Spain)
S. Mereghetti (INAF IASF-Milano, Italy)
L. Natalucci (IAPS-Roma)
A. Lutovinov, R. Sunyaev (IKI, Russia)
report on behalf of the INTEGRAL Gravitational Wave Team
We have analyzed INTEGRAL archival data of the SPI-ACS and IBIS/PICsIT
in coincidence with GRB150101B (GCN 17267, GCN 17276). Troja et al.
(2018, arXiv:1806.10624) suggest that GRB150101B is a kilonova event
comparable to GW170817/GRB170817A, but at cosmological distance and
without the observations of a gravitational-wave trigger. The INTEGRAL
orientation was 24.9 degrees from the GRB location and implies a
somewhat suppressed response for SPI-ACS, but an improved response for
IBIS, especially IBIS/PICsIT (Savchenko et al. 2017, A&A 603, A46).
We confirm the independent detection by SPI-ACS and IBIS/PICsIT of a
short duration (~0.012 sec) event, consistent with that reported in
Troja et al. The signal in SPI-ACS (75 keV-10 MeV) and in IBIS/PICsIT
(200 keV-1.2 MeV) has a S/N of 5.1, and 4.2, respectively.
From the SPI-ACS observation, we estimate a 75 keV-2 MeV fluence of
GRB150101B in the time interval T_0-0.05s - T_0+0.1s of (1.3 ��
0.3)e-7 erg/cm2, assuming a simple power-law spectrum with a slope of
1.2 (as measured by Swift/BAT and Fermi/GBM).
Analysis is on-going to constrain any possible soft gamma-ray
afterglow with contemporaneous INTEGRAL observations.
A plot of the light curve can be found at
https://zenodo.org/record/1304812#.WzyLLa14VGw
GCN Circular 17431
Subject
GRB 150101B/ Swift J123205.1-105602: Second epoch Chandra observations
Date
2015-02-10T18:37:00Z (11 years ago)
From
Andrew Levan at U.of Leicester <A.J.Levan@warwick.ac.uk>
A.J. Levan (U. Warwick), J. Hjorth (DARK/NBI), N.R. Tanvir (U. Leicester), A.J. van der Horst (GWU) report on behalf of a larger collaboration:
"We obtained a second epoch of observations of the very short GRB 150101B/ Swift J123205.1-105602 (Cummings et al. GCN 17267) with Chandra. Observations began on 10 Feb 2015, 39 days after the burst, and 32 days after the first epoch of observations (Troja et al. GCN 17289). As in the first epoch of observations a total of ~15 ks of observations were obtained with the target placed on the ACIS-S3 chip.
In these observations we clearly identify the two sources identified in previous observations. In a 1.5" aperture to avoid contamination of the sources with light from each other, we finds count rates for source SRCX1 and SRCX2 as identified by Troja et al. (GCN 17289) to be SRCX1=(35.8 +/- 1.6)e-3 and SRCX2=(1.5 +/- 0.3)e-3 respectively. This compares to SRCX1= (38.3 +/- 1.6)e-3 cps and SRCX2=(9.4 +/- 0.9)e-3 cps in the first epoch. This implies that the AGN has remained constant, and that the second source, coincident with the optical afterglow (Fong et al. GCN 17333, Levan et al. 17321) has faded by a factor of ~6.
The X-ray variability observed from source SRCX2 confirms it as the afterglow of GRB 150101B/Swift J123205.1-105602. The corresponding decay index is approximately t^-1.1, this is relatively slow for a short GRB afterglow so late after burst, and at z=0.134 (Levan et al. GCN 17281) places it in a region of parameter space much more luminous than most short bursts of comparable prompt fluence at similar times.
We thank Belinda Wilkes, Scott Wolk at the team at the Chandra X-ray Observatory for their help with these observations."
GCN Circular 17333
Subject
GRB 150101B: Confirmation of a fading optical counterpart
Date
2015-01-21T02:13:12Z (11 years ago)
From
Wen-fai Fong at U of Arizona <wfong@email.arizona.edu>
W. Fong (U. Arizona), E. Berger (Harvard), D. Fox (PSU) and B.J. Shappee
(Carnegie) report:
"We re-observed the field of the short/soft GRB 150101B (Cummings, GCN
17267) with the Gemini Multi-Object Spectrograph (GMOS) mounted on the
Gemini-South 8-m telescope starting on 2015 Jan 12.326 UT, 10.7 days after
the BAT trigger and 9.0 days after our initial Magellan observations (Fong
et al., GCN 17271). We obtained a total of 1710-sec of r-band imaging in
0.58" seeing. To assess fading of the candidate optical afterglow (Fong et
al., GCN 17271), we performed digital image subtraction using the ISIS
package between the Gemini and Magellan observations. We find a residual
point source with a refined position of
RA(J2000) = 12:32:05.08
Dec(J2000) = -10:56:03.16
with an uncertainty of 0.5" in each coordinate.
This indicates that the optical source has faded between 1.7 and 10.7 days
post-burst. Thus far, this is the only evidence for a fading source within
the BAT position. Fading is also supported by the lack of optical
counterpart in other filters from late-time VLT observations (Levan et al.,
GCN 17321). We note that digital image subtraction between our two Magellan
epochs at 1.7 days and 2.7 days post-burst revealed no residuals (Fong et
al., GCN 17285), suggesting that the source had an initial period of
shallow decay.
The optical source is ~3.1" offset from the center of the galaxy 2MASX
J12320498-1056010. Given the separation and optical brightness (Cummings et
al., GCN 17268), the galaxy has a low probability of chance coincidence of
~2e-3. At the redshift of the galaxy, z=0.134 (Levan et al., GCN 17281),
the projected physical offset is ~7.4 kpc. In addition, the location of the
optical source is consistent with the position of the faint Chandra source
(SRCX #2 in Troja et al., GCN 17289).
We conclude that the fading of the optical source, spatial coincidence with
an X-ray counterpart, and proximity to a galaxy with low probability of
chance coincidence confirms the source as the optical afterglow, and 2MASX
J12320498-1056010 as the host galaxy of GRB 150101B. At z=0.134, this is
the among the lowest confirmed redshifts for a short GRB to date."
GCN Circular 17326
Subject
GRB 150101B/Swift J123205.1-105602: TNG NIR follow-up
Date
2015-01-20T21:11:23Z (11 years ago)
From
Paolo D'Avanzo at INAF-OAB <paolo.davanzo@brera.inaf.it>
P. D'Avanzo (INAF-OAB), V. D'Elia (INAF/OAR & ASI/ASDC), V. Lorenzi, G. Mainella, W. Boschin, A. Garcia de Gurtubai Escudero (INAF-TNG) report on behalf of a larger collaboration:
We observed the field of GRB 150101B/Swift J123205.1-105602 (Cummings GCN 17267; Stanbro GCN 17276) using the NICS near-infrared camera on the 3.6m TNG Telescope (La Palma, Canary Islands).
We obtained two epochs of imaging observations in the J band on Jan 11 and Jan 16 at mean times of 9.62 and 14.56 days after the trigger, respectively.
In both epochs we covered about 50% of the the BAT error circle (Cummings GCN 17267) including the positions of the X-ray, optical and radio sources reported by Cummings et al. (GCN 17268), Fong et al. (GCN 17271), van der Horst et al. (GCN 17286), Fong (GCN 17288), Troja et al (GCN 17289), Campana (GCN 17318) and Levan et al. (GCN 17321).
Digital image subtraction between these two epochs carried out with the ISIS package (Alard 2000, A&AS, 144, 363) reveals no variable source within the field of view.
The 3sigma limiting magnitude is J > 20.8 for epoch #1 and J > 21.5 for epoch #2 (Vega system, calibrated against the 2MASS catalogue).
GCN Circular 17321
Subject
GRB 150101B/Swift J123205.1-105602, deep VLT observations
Date
2015-01-20T15:31:06Z (11 years ago)
From
Andrew Levan at U.of Leicester <A.J.Levan@warwick.ac.uk>
A.J. Levan (U. Warwick), J. Hjorth (DARK/NBI), N.R. Tanvir, K. Wiersema (U. Leicester), A.J. van der Horst (George Washington University) report on behalf of a larger collaboration:
"We obtained further deep optical observations of the field of GRB 150101B/Swift J123205.1-105602 (Cummings; GCN17267, 17268) using the VLT and FORS2, on the 19 & 20 Jan 2015. At this epoch 1200s of observations were taken in both g, R and I, in dark time with seeing between 0.6-0.8".
Within these deep images we locate a faint counterpart to the radio source identified by van der Horst et al. (GCN 17286) and Fong et al. (GCN 17288). It appears to be a marginally extended source with R~25 (calibrated against USNO), and to be relatively blue given its non-detection in the IR. However, its persistent radio emission implies it is likely not related to the outburst.
We do not see any object at the location of the putative optical counterpart identified in Magellan imaging by Fong et al. (GCN 17271), whose location is consistent with the presence of an X-ray source with L_X ~ 1e43 ergs/s in Chandra observations (Troja et al. GCN 17289). Given our detection of the possible radio counterpart above, we conclude that these images are deeper than those reported previously by Fong et al. (GCN 17271, GCN 17288). Although the filters are slightly different, this may suggest optical fading of this source, which would strengthen its association with GRB 150101B.
We further note that this position clearly lies on the stellar field of the galaxy 2MASX J12320498-1056010. Such luminous, non-nuclear X-ray sources are extremely rare, and while a background AGN is possible, the small impact parameter makes this unlikely within the limited BAT error circle. The luminosity is much higher than for most short-GRB afterglows at this epoch, and there is apparently little evidence for X-ray variability (although this is complicated by the presence of the nearby AGN which is a factor ~4 brighter, Troja et al. GCN 17289). Hence, while we can not yet make firm claims about the relationship of the Magellan and Chandra source to GRB 150101B/ Swift J123205.1-105602, it remains a plausible candidate. "
GCN Circular 17318
Subject
GRB 150101B/Swift J123205.1-105602: XMM-Newton observation
Date
2015-01-20T11:20:51Z (11 years ago)
From
Sergio Campana at INAF-OAB <sergio.campana@brera.inaf.it>
S. Campana (INAF-Osservatorio astronomico di Brera) reports
XMM-Newton observed GRB 150101B/Swift J123205.1-10560
(Cummings 2015, GCN 17267) on Jan 07, 2015 10:13:31 UT
(5.79 d after the burst discovery). The last ~16 ks of the observation were
affected by a mildly-enhanced background and were filtered out.
The resulting EPIC/pn exposure times is 33.2 ks.
A source is well detected at a position consistent with the Swift's
(Cummings et al. 2015, GCN 17268), Chandra's (Troja et al. 2015, GCN
17289), and radio (Fong 2015, GCN 17288) ones.
No X-ray source is detected at the position of a second radio source (Fong
2015), whereas the two closeby sources detected by Chandra are too close
to be separated by XMM-Newton.
The source is relatively bright with a pn count rate of (2.8+/-0.1)x10^{-1}
cts/s.
We extracted 8620 source photons from the pn and fitted the X-ray spectrum
with a power law model including a non-negligible absorption component
at the galaxy redshift (z=0.134, Levan et al 2015, GCN 17281) in addition
to the Galactic one (3.5x10^{20} cm^{-2}).
The best fit power law (chi2=1.03 with 244 degrees of freedom) implies
a photon index of Gamma=2.29+/-0.06 (90% c.l. for one parameter of
interest) and an additional column density marginally not consistent
with zero NH_z=(1.3+/-0.9)x10^{20} cm^{-2} (90% c.l.).
Any unresolved iron emission line (6.4-6.9 keV interval) should have an
equivalent width <230 eV.
The 0.5-8 keV unabsorbed flux is (4.3+/-0.1)x10^{-13} erg/cm^2/s, fully
consistent with the with the Chandra observation (Troja et al 2015).
This testifies that we are observing emission from a low luminosity Active
Galactic Nucleus (2x10^{43} erg/s) and not from the GRB afterglow.
GCN Circular 17309
Subject
GRB 150101B/Swift J123205.1-105602: continued WSRT radio and VLT optical observations
Date
2015-01-19T17:06:48Z (11 years ago)
From
Alexander van der Horst at George Washington U <ajvanderhorst@gwu.edu>
A.J. van der Horst (George Washington Univ.), A.J. Levan (Univ. of
Warwick), K. Wiersema, N.R. Tanvir (Univ. of Leicester), J. Hjorth
(DARK/NBI) report on behalf of a large collaboration:
"We reobserved the field of GRB 150101B/Swift J123205.1-105602 at 4.9 GHz
with the Westerbork Synthesis Radio Telescope (WSRT) at January 9 00.25
to 09.00 UT, and January 17 23.75 to January 18 08.50 UT, i.e. 7.37 -
7.73 and 16.35 - 16.71 days after the burst (GCN 17267), respectively.
The two radio sources within the BAT error circle (GCN 17267) that were
detected in the first WSRT observation (GCN 17286) do not display
significant variability. The flux density of the brightest source is
7.21 +/- 0.07, 7.56 +/- 0.07, and 7.40 +/- 0.07, in the three epochs,
which is consistent with a steady source when a 5% calibration uncertainty
is taken into account. The second source has a flux density of 0.99 +/-
0.18, 0.77 +/- 0.19, and 0.78 +/- 0.18 mJy, in the three epochs, again
consistent with a steady source.
In addition, we obtained IR observations with VLT/HAWK-I on January 16,
deeper than the ones reported in GCN 17281. There is still no evidence
for any source at the location of the second, fainter radio source to a
preliminary limiting magnitude of H(AB)>23.5.
We would like to thank the WSRT staff for scheduling and obtaining
these observations."
GCN Circular 17289
Subject
GRB 150101B/Swift J123205.1-105602: Chandra observations
Date
2015-01-10T14:33:55Z (11 years ago)
From
Eleonora Troja at GSFC <eleonora.troja@nasa.gov>
E. Troja (NASA/GSFC/UMCP), T. Sakamoto (AGU), A. Lien (NASA/GSFC/UMBC),
S. B. Cenko (NASA/GSFC), and N. Gehrels (NASA/GSFC) report:
We observed the field of the transient Swift J123205.1-105602 (Cummings;
GCN 17267) with the Chandra X-ray Observatory beginning on
2015 Jan 09.48 UT (7.83 days post-burst) for a total exposure of 14.9 ks.
At the transient position we detect two X-ray sources within the Swift/XRT
point spread function:
SRCX #1
The first source is located at:
RA(J2000) = 12:32:04.985
Dec(J2000) = -10:56:00.21
with a 90% uncertainty of 0.6 arcsec. This position is consistent with the
XRT position (http://www.swift.ac.uk/xrt_positions/00020464/), the bright
radio source reported by van der Horst et al. (GCN 17286), and the nucleus
of 2MASX J12320498-1056010.
The source is well described by an absorbed power-law with photon index
Gamma=2.3 �� 0.2, and absorption column consistent with the Galactic value
of 3E20 cm^-2 (Kalberla et al. 2005). The observed flux in the 0.5-8.0 keV
energy band is (4.0 �� 0.4)E-13 erg cm^-2 s^-1.
SRCX #2
The second, fainter source is located at:
RA(J2000) = 12:32:05.104
Dec(J2000) = -10:56:02.78
with a 90% uncertainty of 0.6 arcsec. This position is consistent with the
optical source reported by Fong et al. (GCN 17271).
The source is well described by an absorbed power-law with photon index
Gamma=1.8 �� 0.3, and absorption column consistent with the Galactic value
of 3E20 cm^-2 (Kalberla et al. 2005). The observed flux in the 0.5-8.0 keV
energy band is (1.2 �� 0.2)E-13 erg cm^-2 s^-1.
Both sources do not display significant temporal variability during our
observation.
We do not detect any X-ray counterpart at the position of the second radio
source reported by van der Horst et al. (GCN 17286) down to a limit of
3E-4 cts s^-1 (95% confidence level).
We thank Belinda Wilkes and the entire Chandra staff for approving and
rapidly executing this observation.
GCN Circular 17288
Subject
GRB 150101B / Swift J123205.1-105602: 9.8 GHz VLA observations
Date
2015-01-09T16:06:35Z (11 years ago)
From
Wen-fai Fong at U of Arizona <wfong@email.arizona.edu>
W. Fong (U. Arizona) reports on behalf of a larger collaboration:
"We observed the field of the short/soft GRB 150101B (Cummings; GCN
17267) with the Karl G. Jansky Very Large Array (VLA) beginning on
2015 Jan 07.378 UT (5.73 days post-burst) at a mean frequency of 9.8
GHz. These observations are contemporaneous with the WSRT observations
at 4.9 GHz (van der Horst et al.; GCN 17286) and cover the
BAT position (90% containment). In 1 hour of observations, we detect
two sources within the BAT position also identified by WSRT.
The first source coincides with the galaxy 2MASX J12320498-1056010,
the XRT position (Cummings et al.; GCN 17268) and the bright source at
4.9 GHz (van der Horst et al.; GCN 17286). The 9.8 GHz flux density is
3.15 +/- 0.02 milliJy which translates to nuLnu ~ 1.5e40 erg/s (at
z=0.134; Levan et al.; GCN 17281), consistent with the interpretation
that this source is an AGN (Fong et al.; GCN 17285).
The second, fainter source is located at:
RA(J2000) = 12:32:08.19
Dec(J2000) = -10:56:14.2
with an uncertainty of 1" in each coordinate, and coincides with the
WSRT position (van der Horst et al.; GCN 17286). This
source has a 9.8 GHz flux density of 0.45 +/- 0.01 milliJy. Assuming a
single power law between 4.9 and 9.8 GHz, we calculate a spectral
index of -1.13 +/- 0.25 for this source. We note that there is no
optical source at this position in our Magellan r-band observations
(Fong et al.; GCN 17285) or in deeper r-band imaging we
obtained with Gemini-South/GMOS (17x90-sec) at 5.67 days post-burst.
We do not detect any other radio sources within the BAT position to a
3-sigma limit of 27 microJy.
We thank the VLA staff for quickly executing these observations."
GCN Circular 17286
Subject
GRB 150101B/Swift J123205.1-105602: WSRT radio observation
Date
2015-01-07T20:25:51Z (11 years ago)
From
Alexander van der Horst at U of Amsterdam <A.J.vanderHorst@uva.nl>
A.J. van der Horst (Univ. of Amsterdam), K. Wiersema (Univ. of Leicester),
A.J. Levan (Univ. of Warwick), J. Hjorth (DARK/NBI), N.R. Tanvir (Univ.
of Leicester) report on behalf of a large collaboration:
"We observed the position of GRB 150101B/Swift J123205.1-105602 at 4.9 GHz
with the Westerbork Synthesis Radio Telescope at January 7 00.30 to 09.15
UT, i.e. 5.38 - 5.74 days after the burst (GCN 17267).
We detect two radio sources within the BAT error circle (GCN 17267), with
flux densities of 7.21 +/- 0.07 and 0.99 +/- 0.18 mJy. The brightest
source coincides with the XRT position (GCN 17268), the position of the
galaxy 2MASX J12320498-1056010 (GCN 17271), and the NRAO VLA Sky Survey
source at 1.4 GHz (GCN 17285). The spectral index from 1.4 to 4.9 GHz of
this source is -0.3, consistent with the radio emission emanating from
an AGN (GCN 17285).
The second source is located at
RA (J2000) = 12:32:08.2
Dec (J2000) = -10:56:14
with an uncertainty of 5", which is large because of its low declination.
There is no counterpart of this source in a stacked XRT image, no optical
counterpart in our VLT observation (GCN 17281), and also not at 1.4 GHz
in the NRAO VLA Sky Survey.
We would like to thank the WSRT staff for scheduling and obtaining
these observations."
GCN Circular 17285
Subject
GRB 150101B / Swift J123205.1-105602: X-ray counterpart is likely an AGN
Date
2015-01-06T18:57:28Z (11 years ago)
From
Wen-fai Fong at U of Arizona <wfong@email.arizona.edu>
W. Fong (U. Arizona), E. Berger (Harvard) and B. J. Shappee (Carnegie)
report:
"We re-observed the location of the short soft GRB 150101B (Cummings; GCN
17267) with Magellan/IMACS starting on 2015 Jan 04.30 UT (2.66 days
post-burst and 24.0 hr after our initial observations; Fong et al., GCN
17271). We obtained 10x120-sec of r-band observations in 0.82" seeing at an
airmass of 1.5. Digital image subtraction with our first set of
observations using the ISIS package reveals no variable sources within or
near the location of the XRT source (
http://www.swift.ac.uk/xrt_positions/00020464/). This indicates that the
unresolved optical source identified by Fong et al., (GCN 17271) is
unrelated to the GRB.
Using the redshift of z=0.134 (Levan et al. GCN 17281) for the galaxy 2MASX
J12320498-1056010 which coincides with the XRT position, we find that the
XRT source has an X-ray luminosity of LX ~ 3e43 erg/s, and remains steady
from 1.7 to 4.0 days post-burst (http://www.swift.ac.uk/xrt_curves/00020464/).
The galaxy also coincides with a bright radio source in the NRAO VLA Sky
Survey (Condon et al., 1998, AJ, 115, 1693), with a luminosity at 1.4 GHz
of nuLnu ~ 6e39 erg/s. If due to star formation, this requires SFR ~ 150
solar masses per year, which contradicts the lack of emission lines from
the galaxy (Levan et al. GCN 17281). On the other hand, the radio and X-ray
luminosities match the properties of low-luminosity AGN with Lbol/LEdd <
10^-3 (e.g., Ho 2008, ARA&A, 46, 475). This interpretation is also
supported by the large NIR luminosity and very red UV-NIR color (from GALEX
and 2MASS). We therefore conclude that 2MASX J12320498-1056010 is a
low-luminosity AGN, and that the XRT source is unrelated to GRB 150101B."
GCN Circular 17281
Subject
GRB 150101B/Swift J123205.1-105602: VLT observations and redshift
Date
2015-01-04T21:00:02Z (11 years ago)
From
Andrew Levan at U.of Leicester <A.J.Levan@warwick.ac.uk>
A.J. Levan (U. Warwick), J. Hjorth (DARK/NBI), K. Wiersema, N.R. Tanvir (U. Leicester) report on behalf of a larger collaboration:
"We obtained imaging and spectroscopy of GRB 150101B/Swift J123205.1-105602 (Cummings et al. ATel 6871) with the ESO VLT on 4 Jan 2015, beginning at approximately 06:40 UT. At this epoch 1280s of I-band and1080s of z-band observations were obtained with FORS2 in ~1" seeing. The known galaxy, 2MASX J12320498-1056010, is clearly detected in these images, and its light extends under the position of the candidate optical counterpart reported by Fong et al. (GCN 17271). We do not detect any point source at this location, although the combination of differing seeing, band and the underlying host galaxy mean that we cannot make any strong statements about the variability of the source. We additionally note that the 90% confidence of the refined XRT position (http://www.swift.ac.uk/xrt_live_cat/00020464/) currently includes the nucleus of 2MASX J12320498-1056010, but not the source identified by Fong et al.
In addition we obtained spectroscopic observations of 2MASX J12320498-1056010, covering the wavelength range 5300-8500A. The continuum is well detected across this wavelength range, with several prominent absorption features, most notably Mg b, and Na D at a preliminary redshift of z=0.134. We do not see any emission lines, although H-beta, [OIII] (4959,5007) and H-alpha all fall within our wavelength range at this redshift. We are not sensitive to the line identified by Castro-Tirado et al. (GCN 17278) as [OII] at z=0.093 since it lies blueward of our spectrum, but note that z=0.093 is not consistent with the observed absorption features. The absence of emission lines implies that the galaxy is a passive system. With an absolute magnitude of M_K ~ -25.5 (Vega), it lies the bright end of the luminosity function.
The properties of the galaxy are broadly similar to those of some short-GRBs (most notably GRB 050509B, Gehrels et al. 2005 Nature 437 851; Fong et al. 2013 ApJ 769 56). At z=0.134 the isotropic energy release, E_iso, would be approximately 1e48 erg, again in the energy range seen for other short-GRBs. However, the soft gamma-ray spectrum of the prompt emission is unusual, as is the long lived X-ray emission of the potential counterpart. The X-rays persist for several days post burst, at a luminosity of approximately 2e43 ergs/s. This is typical of an AGN, but such bright sources are unusual in the small BAT error box. The log(N)-log(S) of Manners et al. (2003 MNRAS 343 293), predicts <10 sources of this flux or brighter per square degree (<~0.05 in a region the size of the BAT error box). Furthermore, the optical spectrum does not show obvious signs of AGN activity. Hence it is likely, but not yet conclusive, that the X-ray source, and galaxy are associated with GRB 150101B/Swift J123205.1-105602.
If associated with a short-GRB we might expect the development of kilonova emission over the next few days which may peak at a H-band magnitude of around H(AB)=22-23, if similar to that seen in GRB 130603B (Tanvir et al. 2013 Nature 500 547, Berger et al. 2013 ApJ 774 23). Alternatively, the soft gamma-ray emission, prolonged X-rays, and location close to the nucleus of its host galaxy could be indicative of an unusual AGN outburst or tidal disruption flare.
We thank Dimitri Mawet and the staff of Paranal for their excellent assistance with these observations."
GCN Circular 17278
Subject
GRB 150101B: potential host galaxy redshift by GTC
Date
2015-01-04T12:07:07Z (11 years ago)
From
Alberto Castro-Tirado at Inst.de Astro. de Andalucia <ajct@iaa.es>
A. J. Castro-Tirado (IAA-CSIC, ISA-UMA), R. Sanchez-Ramirez, J.
Gorosabel (IAA-CSIC, UPV/EHU) and R. Scarpa (GTC), on behalf of a
larger collaboration, report:
Following the detection of the short-duration GRB 150101B by Swift/BAT
(Cummings et al. 2015, GCNC 17267) and Fermi (Stanbro et al. GCNC 17276),
we have obtained an optical spectrum with the 10.4 m GTC (+OSIRIS)
starting on Jan 4, 5:41 UT (i.e. 38.1 hr postburst), covering the
3700-10000 A wavelength range, under poor weather conditions (passing
clouds) and bad (>2.5���) seeing. The slit included the position of the
proposed optical afterglow (Fong et al. GCNC 17271) as well as the
putative host galaxy also detected by Swift/UVOT (Cummings et al. GCNC
17258). We detect a faint emission line consistent with [OII] at z =
0.093, which we propose to be that of the potential host galaxy. If the
association is confirmed, this would make of GRB 150101B the nearest
short-duration GRB found to date. Observations at all wavelengths are
encouraged.
GCN Circular 17276
Subject
GRB 150101B: Fermi GBM detection
Date
2015-01-04T05:56:32Z (11 years ago)
From
Matthew Stanbro at UAH/Fermi <mcs0001@uah.edu>
Matthew Stanbro (UAH) reports on behalf of the Fermi GBM Team:
"At 15:23:34.47 UT on 01 January 2015, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 150101B (trigger 441818617 / 150101641).
which was also detected by the BAT during a slew (Cummings et al.
2015, GCN 17267).
The GBM on-ground location is consistent with the Swift/BAT position.
The angle from the Fermi LAT boresight is 44 degrees.
The GBM light curve consists of one peak
with a duration (T90) of about 0.08 s (50-300 keV).
The time-averaged spectrum from T0-0.016 s to T0+0.064 s is
best fit by a simple power law function with index -1.70 +/- 0.09.
The event fluence (10-1000 keV) in this time interval is
(1.09 +/- 0.14)E-07 erg/cm^2. The 64-ms peak photon flux measured
starting from T0+0.00 s in the 8-1000 keV band
is 10.48 +/- 1.35 ph/s/cm^2.
The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog."