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GCN Circulars

GCN Circulars are rapid astronomical bulletins submitted by and distributed to community members worldwide. They are used to share discoveries, observations, quantitative near-term predictions, requests for follow-up observations, or future observing plans related to high-energy, multi-messenger, and variable or transient astrophysical events. See the documentation for help with subscribing to or submitting Circulars.

Search for Circulars by submitter, subject, or body text (e.g. 'Fermi GRB').
To navigate to a specific circular, enter the associated Circular ID (e.g. 'gcn123', 'Circular 123', or '123').
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To narrow the search results, use advanced search syntax. This allows for specifying which circular field to search (submitter, subject, and/or body). For additional information, refer to the advanced search documentation.

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subject:"Swift"
body:"GRB"
submitter:"Judith Racusin"

20366 results found.

  1. EP250827b: SVOM/VT observation of AT 2025wkm
  2. LIGO/VIRGO/KAGRA S250818k: No evidence for radio variability of AT2025ulz in MeerKAT 3 GHz data
  3. GRB 250831A (SVOM trigger sb25083102): KAIT confirmation of stellar flare
  4. Fermi-LAT Gamma-ray Observations of IceCube-250831A
  5. GRB 250901A: Swift/UVOT Upper Limit
  6. IceCube-250831A: Upper limits from a search for additional neutrino events in IceCube
  7. GRB 250830B: Swift-XRT afterglow detection
  8. GRB 250831A (SVOM trigger sb25083102): confirmation of a stellar flare by SVOM/VT
  9. GRB 250902A: SVOM/GRM observation
  10. EP250828a: Early near-infrared follow-up with MIRAGE on the MDM 1.3m telescope
  11. EP250901a: refined analysis of the EP-WXT and EP-FXT observations
  12. IceCube-Cascade 250828A: Upper limits from a search for additional neutrino events in IceCube
  13. GRB 250901A: SVOM/VT optical afterglow with VHF data
  14. GRB 250901A: Swift-XRT afterglow detection
  15. LIGO/Virgo/KAGRA S250830bp: DECam GW-MMADS candidates
  16. GRB 250901A: LCO optical upper limit
  17. LIGO/Virgo/KAGRA S250901cb: Identification of a GW compact binary merger candidate
  18. EP250831a: NOT optical observations and tentative afterglow candidate
  19. EP250827b: Contemporaneous detection of EP X-ray flare EP250827b and ZTF transient ZTF25abmpngy/AT2025wkm
  20. GRB 250901A: SVOM detection of a burst
  21. EP250901a: Mephisto optical upper limits
  22. GRB 250830C: AstroSat CZTI detection of a long burst
  23. EP250901a: Einstein Probe detection of an X-ray transient
  24. EP250831a: EP-WXT detection of a fast X-ray transient
  25. GRB 250831A: Swift-XRT counterpart detection
  26. GRB 250831A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  27. GRB 250831A: SVOM/VT upper limit with VHF data
  28. GRB 250831A: SVOM detection of a soft burst
  29. EP250830a/GRB 250830B: Einstein Probe detection of an X-ray transient and Swift/XRT follow-up
  30. LIGO/Virgo/KAGRA S250830bp GLADEnet Completeness: Potential Host Galaxies in the 90% Credible Volume
  31. LIGO/Virgo/KAGRA S250830bp: NED Galaxies in the 4-Update Localization Volume
  32. LIGO/Virgo/KAGRA S250830bp: Updated Sky localization, EM Bright Classification, and Source Classification
  33. LIGO/Virgo/KAGRA S250830bp: Identification of a GW compact binary merger candidate
  34. EP-WXT trigger 01709200994: Liverpool Telescope upper limits
  35. LIGO/Virgo/KAGRA S250830m: Identification of a GW compact binary merger candidate
  36. LIGO/Virgo/KAGRA S250725j: Observations with the NSF-DOE Vera C. Rubin Observatory
  37. LIGO/Virgo/KAGRA S250818k: MeerKAT detection of an increase in radio flux from AT2025ulz
  38. GRB 250808B: SVOM detection of a burst through offline search
  39. EP250828a: refined analysis of the EP-WXT and EP-FXT observations
  40. EP250828a: Optical counterpart detection with Kinder observations
  41. EP250828a: Liverpool Telescope upper limits
  42. EP-WXT trigger 01709200800 : KAIT optical observations
  43. EP250828a: KAIT optical upper limit
  44. EP250827a: Swift/UVOT Detection
  45. EP250828a: NOT optical counterpart confirmation
  46. EP250828a: SVOM/VT optical candidate
  47. EP250828a: Seimei/TriCCS optical counterpart detection
  48. EP250828a: Optical upper limit with Kinder observations
  49. EP250828a: Einstein Probe detection of an X-ray transient
  50. EP250827a: Preliminary analysis of the EP-WXT and EP-FXT observations
  51. GRID detection of GRB 250824A
  52. LIGO/Virgo/KAGRA S250827fo: Identification of a GW compact binary merger candidate
  53. EP250827a: confirmation of optical rebrightening with LCO
  54. GRB 250826A: SVOM/GRM observation
  55. EP250827A: An optical rebrightening was detected by LCO.
  56. EP250827a: TRT optical observations
  57. EP250827a: Einstein Probe detection of an X-ray transient
  58. LIGO/Virgo/KAGRA S250827l: Identification of a GW compact binary merger candidate
  59. GRB 250806A: HiPERCAM/GTC limits on a possible supernova
  60. LIGO/Virgo/KAGRA S250818k: SAO RAS BTA z-band observations of AT2025ulz
  61. Fermi GRB 250824B: Global MASTER-Net observations report
  62. LIGO/Virgo/KAGRA S250818k: VLA upper limits on AT2025ulz
  63. LIGO/Virgo/KAGRA S250818k: Pan-STARRS imaging confirms re-brightening of SN2025ulz
  64. LIGO/Virgo/KAGRA S250818k: MASTER predicovery limits of the AT2025ulz/ZTF25abjmnps KN candidate
  65. LIGO/Virgo/KAGRA S250818k: ENGRAVE observations of SN 2025ulz as a type II supernova
  66. EP250821a: MeerKAT radio counterpart
  67. GRB 250823A: COLIBRÍ optical observations
  68. GRB 250823A: SVOM/VT optical observation
  69. GRB 250823A: Swift/UVOT Detection
  70. LIGO/Virgo/KAGRA S250818k: COLIBRÍ confirmation of rebrightening of AT2025ulz
  71. GRB 250823A: Enhanced Swift-XRT position
  72. GRB 250823A: LCOGT Optical Detection
  73. GRB 250823A: Swift detection of a burst
  74. LIGO/Virgo/KAGRA S250818k: HST nIR detection of AT 2025ulz
  75. LIGO/Virgo/KAGRA S250818k: GTC/OSIRIS Optical Detection of AT2025ulz
  76. LIGO/Virgo/KAGRA S250818k: 3 GHz MeerKAT observations of AT2025ulz
  77. GRB 250806A: Gemini observations of host galaxy candidate
  78. GRB 250821A: Kilonova-Catcher optical upper limits
  79. GRB 250812A: SVOM/ECLAIRs refined analysis
  80. LIGO/Virgo/KAGRA S250818k: Pan-STARRS coverage of the skymap and candidate counterparts
  81. EP250821a: VLT X-shooter spectroscopic redshift z = 0.577
  82. GRB 250821A: VLT/FORS2 Optical Observation
  83. GRB 250821B: SVOM/GRM observation
  84. EP250821a: SVOM/VT optical observation
  85. GRB 250821A: NOT z-band upper limit
  86. GRB 250821A: KAIT optical upper limit
  87. GRB 250821A: Swift-XRT refined Analysis
  88. GRB 250821A: Enhanced Swift-XRT position
  89. GRB 250821A: Swift/UVOT Upper Limits
  90. LIGO/Virgo/KAGRA S250818k: GOTO counterpart search and upper limits
  91. EP250821a: Preliminary analysis of the EP-WXT and EP-FXT observations
  92. GRB 250821A: LCOGT Optical Upper Limits
  93. GRB 250814A: CMO SAI and SAO RAS izJ observations.
  94. LIGO/Virgo/KAGRA S250818k: 10 GHz VLA observations of AT2025ulz
  95. GRB 250821A: Swift detection of a burst
  96. LIGO/Virgo/KAGRA S250818k: WFST pre-discovery limits and follow-up observations of AT 2025ulz
  97. EP250821a: Einstein Probe detection of an X-ray transient
  98. GRB 250819A: SVOM/GRM observation of a possible “long” duration type I burst
  99. LIGO/Virgo/KAGRA S250818k: WINTER J-band observations of AT 2025ulz
  100. GRB 250818B: 10 GHz VLA detection

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