GRB 190515B

M. J. Moss (George Washington University), C. Gronwall (PSU),
J.D. Gropp (PSU), J. A. Kennea (PSU), N. J. Klingler (PSU),
A. Y. Lien (GSFC/UMBC), F. E. Marshall (NASA/GSFC),
K. L. Page (U Leicester), M. H. Siegel (PSU) and A. Tohuvavohu (PSU)
report on behalf of the Neil Gehrels Swift Observatory Team:

At 16:04:21 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 190515B (trigger=903845).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 98.840, +52.295 which is 
   RA(J2000) = 06h 35m 22s
   Dec(J2000) = +52d 17' 41"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a complex
structure with a duration of about 20 sec.  The peak count rate
was ~800 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 16:05:43.7 UT, 82.4 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
uncatalogued X-ray source located at RA, Dec 98.84892, 52.31725 which
is equivalent to:
   RA(J2000)  = 06h 35m 23.74s
   Dec(J2000) = +52d 19' 02.1"
with an uncertainty of 3.7 arcseconds (radius, 90% containment). This
location is 82 arcseconds from the BAT onboard position, within the BAT
error circle. This position may be improved as more data are received;
the latest position is available at http://www.swift.ac.uk/sper.  We
cannot determine whether the source is fading at the present time. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density consistent with the Galactic value of 1.27
x 10^21 cm^-2 (Willingale et al. 2013). 

The initial flux in the 2.5 s image was 7.78e-10 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 92 seconds after the BAT trigger. No credible afterglow candidate has
been found in the initial data products. The 2.7'x2.7' sub-image covers 84% of
the XRT error circle. The typical 3-sigma upper limit has been about 19.6 mag. 
The 8'x8' region for the list of sources generated on-board covers 100% of the
XRT error circle. The list of sources is typically complete to about 18 mag. No
correction has been made for the expected extinction corresponding to E(B-V) of
0.09. 

Burst Advocate for this burst is M. J. Moss (mikejmoss3 AT gmail.com). 
Please contact the BA by email if you require additional information
regarding Swift followup of this burst. In extremely urgent cases, after
trying the Burst Advocate, you can contact the Swift PI by phone (see
Swift TOO web site for information: http://www.swift.psu.edu/)

[GCNOPS NOTE(15may19): Per author's request, the GRB name "190515A" was changed
to "190515B" in the Subject lines in the first paragraph.]

P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team:

Using  promptly downlinked XRT event data for GRB 190515B, we find an
enhanced XRT position of the afterglow: RA, Dec: 98.8489, 52.3168 which
is equivalent to:
   RA (J2000)  = 06 35 23.73
   Dec (J2000) = +52 19 00.4
with an uncertainty of 2.2 arcseconds (radius, 90% confidence).
Analysis of the promptly available data is online at
http://www.swift.ac.uk/sper/903845.

Position enhancement is is described by Goad et al. (2007, A&A, 476,
1401) and Evans et al. (2009, MNRAS, 397, 1177).

This circular is an official product of the Swift-XRT team.

[GCN OPS NOTE(15may19): Per author's request, the GRB name was changed from 
"190515A" to "190515B" in the Subject line and the first sentence.]

S. Belkin (IKI), A. Novichonok (KIAM), A. Pozanenko (IKI), E. Mazaeva 
(IKI), A. Volnova (IKI), I. Molotov (KIAM) report on behalf of larger 
IKI GRB FuN   collaboration:

We observed the field of the Swift GRB 190515B (Moss et al., GCN  24553
Loading...
 
 ) 
  with RC-36 0.36-m telescope of Kitab Observatory starting on May  15 
(UT) 16:13:02 in  Clear filter.    We do not find any optical source 
neither in the first image, nor in a stacked image  within prompt 
enhanced Swift-XRT position (Evans  et al., GCN  24554
Loading...
 
 ).
Preliminary photometry of the field is following.

Date       UT start   t-T0       Filter Exp.   OT  Err.   UL(3sigma)
                       (mid, days)        (s)

2019-05-15 16:13:02   0.00655    CR     1*90   n/d  n/d       18.6
2019-05-15 16:13:02   0.02686    CR    40*90   n/d  n/d       20.3

The photometry is based on the nearby USNO-B1 (R2) star:
USNO-B1.0_id R2
1422-0205150 15.02

The closest object which is not presented in any catalogs marginally 
detected in our stacked image  has  coordinates   (J2000) 06:35:24.07 
+52:19:12.4 with uncertainty of 1 arcsec in both coordinates and 
brightness of 20.4m (S/N =2). The position of the object is 12 arcsec 
apart from the the center of  prompt enhanced Swift-XRT position (Evans 
et al., GCN  24554
Loading...
 
 ). At this time we cannot say about variability of the 
object.

[GCN OPS NOTE(15may19): The GRB anme "190515A" was changed to "190515B"
in the Subject line and in the first sentence.]

J.P. Osborne, A.P. Beardmore, P.A. Evans and M.R. Goad (U. Leicester) 
report on behalf of the Swift-XRT team.

Using 611 s of XRT Photon Counting mode data and 1 UVOT
images for GRB 190515B, we find an astrometrically corrected X-ray
position (using the XRT-UVOT alignment and matching UVOT field sources
to the USNO-B1 catalogue): RA, Dec = 98.84772, +52.31665 which is equivalent
to:

RA (J2000): 06h 35m 23.45s
Dec (J2000): +52d 18' 59.9"

with an uncertainty of 2.3 arcsec (radius, 90% confidence).

This position may be improved as more data are received. The latest
position can be viewed at http://www.swift.ac.uk/xrt_positions. Position
enhancement is described by Goad et al. (2007, A&A, 476, 1401) and Evans
et al. (2009, MNRAS, 397, 1177).

This circular was automatically generated, and is an official product of the
Swift-XRT team.

A. de Ugarte Postigo (HETH/IAA-CSIC, DARK/NBI), M. Blazek, L. Izzo, C.C. Thoene, D.A. Kann, K. Bensch (all HETH/IAA-CSIC), A. Sota (IAA-CSIC) report:

We observed the field of GRB 190515B (Moss et al. GCN 24553
Loading...
 
 ) with the 1.5m OSN telescope, at Sierra Nevada Observatory (Granada, Spain). The observation started at 21:13 UT (5.15 hr after the burst) when clouds over the observatory allowed, at an airmass of 2, and consisted of 3x300s exposures in I-band.

No new object is detected within the refined XRT error circle (Osborne et al. GCN 24557
Loading...
 
 ) down to a 3-sigma limit of I(AB) = 20.5 mag, as compared to stars of the PanSTARRS catalogue.

A.P. Beardmore (U. Leicester), V. D'Elia (ASDC), A. D'Ai (INAF-IASFPA),
A. Melandri (INAF-OAB), B. Sbarufatti (INAF-OAB/PSU), D.N. Burrows
(PSU), A. Tohuvavohu (PSU), P.A. Evans (U. Leicester), J.P. Osborne (U.
Leicester) and	report on behalf of the Swift-XRT team: report on
behalf of the Swift-XRT team:

We have analysed 6.3 ks of XRT data for GRB 190515B, from 88 s to 27.5
ks after the  BAT trigger. The data comprise 66 s in Windowed Timing
(WT) mode with the remainder in Photon Counting (PC) mode. The enhanced
XRT position for this burst was given by Osborne et al. (GCN Circ.
24557
Loading...
 
 ).

The light curve can be modelled with an initial power-law decay with an
index of alpha=3.85 (+0.26, -0.23), followed by a break at T+296 s to
an alpha of 0.38 (+0.11, -0.12).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 3.26 (+0.33, -0.30). The
best-fitting absorption column is  2.1 (+0.6, -0.5) x 10^21 cm^-2, in
excess of the Galactic value of 1.3 x 10^21 cm^-2 (Willingale et al.
2013). The PC mode spectrum has a photon index of 2.06 (+0.24, -0.15)
and a best-fitting absorption column consistent with the Galactic
value. 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:	     1.3 (+0.6, -0.0) x 10^21 cm^-2
Galactic foreground: 1.3 x 10^21 cm^-2
Excess significance: <1.6 sigma
Photon index:	     2.06 (+0.24, -0.15)

If the light curve continues to decay with a power-law decay index of
0.38, the count rate at T+24 hours will be 0.027 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 9.0 x
10^-13 (1.2 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/00903845.

This circular is an official product of the Swift-XRT team.

H. A. Krimm (NSF), S. D. Barthelmy (GSFC),
J. R. Cummings (CPI), A. Y. Lien (GSFC/UMBC),
C. B. Markwardt (GSFC), M. J. Moss (GWU),
D. M. Palmer (LANL), T. Sakamoto (AGU),
M. Stamatikos (OSU), T. N. Ukwatta (LANL)
(i.e. the Swift-BAT team):

Using the data set from T-239 to T+963 sec from the recent telemetry
downlink,
we report further analysis of BAT GRB 190515B (trigger #903845)
(Moss et al., GCN Circ. 24553
Loading...
 
 ).  The BAT ground-calculated position is
RA, Dec = 98.826, 52.322 deg which is
   RA(J2000)  =  06h 35m 18.3s
   Dec(J2000) = +52d 19' 17.6"
with an uncertainty of 1.5 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 67%.

The mask-weighted light curve shows a single-pulse structure that starts at
~T-30 s, peaks at ~T0, and ends at ~T+30 s. T90 (15-350 keV) is 46.4 +-
12.3 sec
(estimated error including systematics).

The time-averaged spectrum from T-30.84 to T+31.02 sec is best fit by a
simple
power-law model.  The power law index of the time-averaged spectrum is
1.74 +- 0.15.  The fluence in the 15-150 keV band is 1.6 +- 0.1 x 10^-6
erg/cm2.
The 1-sec peak photon flux measured from T-0.39 sec in the 15-150 keV band
is 1.1 +- 0.2 ph/cm2/sec.  All the quoted errors are at the 90% confidence
level.

The results of the batgrbproduct analysis are available at
http://gcn.gsfc.nasa.gov/notices_s/903845/BA/

Y.-D. Hu, X.-Y. Li, E. Fernandez-Garcia, A. Ayala, A. J. Castro-Tirado 
(IAA-CSIC), C. Perez del Pulgar, A. Castellon, I. Carrasco (Univ. de 
Malaga), S. Guziy (Univ. of Nikolaev), D. Xiong, Y. Fan, X. Zhao, J. 
Bai, C. Wang, Y. Xin, J. Mao (Yunnan Nacional Astronomical Observatory), 
A. Fernandez and I. Hermelo (CAHA),  on behalf of a larger 
collaboration, report:

Following the detection of GRB 190515B by Swift (Moss et al. GCNC 
24553), the 0.6m BOOTES-4/MET robotic telescope at Lijiang Astronomical 
Observatory (China) automatically responded gathering 9 frames (g��� 
filter, 30s exposures) starting at 16:10:44UT (0.11 hr after trigger). 
In addition, 23 frames at the 2.2m Calar Alto telescope equipped with 
CAFOS (I-band, 120s exposures) were taken starting at 20:45:41 UT (4.69 
h post burst). On the co-added images, no optical afterglow is found 
down to 18.9 mag (g-band) or 22.1 (I-band) respectively at the enhaced 
XRT position (Evans et al. GCNC 24554), in agreement with Belkin et al. 
(GCNC 24556) and de Ugarte Postigo et al. (GCNC 24558). Particularly the 
Calar Alto co-add I-band frame does not detect the marginal object 
reported in GCNC 24556.

We thank the CAHA staff for excellent support.

M. H. Siegel (PSU) and M. J. Moss (George Washington University)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 190515B
93 s after the BAT trigger (Moss et al., GCN Circ. 24553
Loading...
 
 ).
No optical afterglow consistent with the XRT position
(Osborne et al. GCN Circ. 24557
Loading...
 
 )
is detected in the initial UVOT exposures.
Preliminary 3-sigma upper limits using the UVOT photometric system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first
finding chart (FC) exposure and subsequent exposures are:

Filter         T_start(s)   T_stop(s)      Exp(s)         Mag

white_FC            93          242          147         >19.9
u_FC               305          555          246         >19.4
white               93          605          167         >20.0
v                  636         4442          216         >18.9
b                  561          754           39         >18.7
u                  305          730          265         >19.5
w1                 685         4722           88         >18.9
m2                 661         4647          216         >19.6
w2                 612         4237          216         >19.0

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.09 in the direction of the burst
(Schlegel et al. 1998).