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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').
Advanced Search

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.

Advanced Search Examples (click to copy):

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

22091 results found.

  1. LIGO/Virgo/KAGRA S250727dc: DECam GW-MMADS upper limits of AT 2025smm
  2. LIGO/Virgo/KAGRA S250727dc: PRIME J-band upper limits of AT 2025smm
  3. GRB 250728A: Swift-XRT observations
  4. GRB 250728A: COLIBRÍ optical upper limit
  5. GRB 250728A: Swift/BAT-GUANO arcminute localization of a short burst
  6. GRB 250727A: EP-FXT counterpart detection
  7. GRB250727A: SVOM/VT optical upper limit
  8. GRB 250727A: Swift-XRT observations
  9. LIGO/Virgo/KAGRA S250727dc: Identification of a GW compact binary merger candidate
  10. LIGO/Virgo/KAGRA S250727cl: Identification of a GW compact binary merger candidate
  11. LIGO/Virgo/KAGRA S250725j: DECam GW-MMADS candidates
  12. GRB 250727A: SVOM detection of a burst
  13. Swift detection of the Soft Gamma Repeater PSR J1647-4552
  14. LIGO/Virgo/KAGRA S250726ak: Identification of a GW compact binary merger candidate
  15. GRB 250725A: Swift-XRT refined Analysis
  16. LIGO/Virgo/KAGRA S250725j: NED Galaxies in the 3-Initial Localization Volume
  17. GRB 250725A: SVOM/GRM observation
  18. GRB 250725A: Global MASTER-Net: First Optical Synchronous Observatios of Short GRB.
  19. GRB 250725A: Swift/UVOT Upper Limits
  20. GRB 250725A: SVOM/VT optical candidate
  21. LIGO/Virgo/KAGRA S250725l: Identification of a GW compact binary merger candidate
  22. LIGO/Virgo/KAGRA S250725j: Identification of a GW compact binary merger candidate
  23. GRB 250725A: Enhanced Swift-XRT position
  24. GRB 250725A: Swift detection of a burst
  25. EP250702a/GRB250702 B,E,D: MeerKAT radio observations at 3.06 GHz
  26. SVOM J195836+32283 is not a real source
  27. EP250702a/GRB250702 B,D,E: uGMRT Radio detection in 1.26 GHz
  28. SVOM J195836+32283/sb25072103: Liverpool Telescope detection of an extended source
  29. SVOM J195836+32283/sb25072103: Swift XRT/UVOT upper limits
  30. SVOM J195836+32283/sb25072103: NIR observations with WINTER
  31. GRB 250721A: Swift-XRT observations
  32. GRB 250717B: SVOM/GRM observation
  33. The SVOM alert sb25072103 is not due to a GRB, but to a new galactic transient SVOM J195836+32283.
  34. EP250702a/GRB250702B,D,E: SVOM/VT optical upper limit
  35. GRB 250717B: COLIBRÍ optical upper limit
  36. GRB 250717B: Swift-XRT observations
  37. Swift Trigger 1334535 / GRB 250718A: COLIBRÍ optical upper limits
  38. Swift Trigger 1334535: a possible GRB 250718A
  39. GRB 270713A: Kitab and AbAO Optical Observations
  40. GRB 250717B: Swift/BAT-GUANO arcminute localization of a burst
  41. GRB 250716A: Swift-XRT afterglow detection
  42. GRB 250716A: Lesedi Detection of Fading Optical Transient GOTO25eyp
  43. GRB 250714A: SVOM/GRM observation
  44. EP250702a / GRB 250702B,D,E: Hubble Space Telescope Observations
  45. GRB 250713A: Mephisto optical upper limits
  46. GRB 250713A: SVOM/VT optical upper limit
  47. GRB 250713A: NOT optical upper limits
  48. GRB 250713A: OHP/T193 upper limit
  49. GRB 250713A: SVOM/C-GFT upper limit
  50. GRB 250706B/C: 7DT Follow-up Observations
  51. GRB 250713A: Swift-XRT observations
  52. GRB 250713A: EP-FXT counterpart detection
  53. EP250711a: COLIBRÍ continuous optical observations
  54. GRB 250702F: Swift-BAT refined analysis
  55. GRB 250713A: JinShan optical upper limits
  56. GRB 250713A: SVOM detection of a long burst
  57. GRB 250711A: DDOTI Optical Upper Limit
  58. LIGO/Virgo/KAGRA S250712cd: Identification of a GW compact binary merger candidate
  59. EP250711a: COLIBRÍ refined photometry and optical confirmation of the candidate
  60. GRB 250711A: SVOM/GRM observation
  61. EP250711a: NOT optical counterpart candidate
  62. EP candidate (ID=08500000365): COLIBRÍ optical Upper limit
  63. Fermi GRB 250711A: Global MASTER-Net observations report
  64. EP250702a: gamma-ray upper limits from joint observations by the LST-1 and MAGIC telescopes
  65. GRB 250704A: GRANDMA observations
  66. LIGO/Virgo/KAGRA S250711q: Identification of a GW compact binary merger candidate
  67. GRB 250702B,D,E/EP250702A: JCMT sub-mm observations at 350 GHz
  68. IceCube-250708A: No Candidates from WINTER
  69. IceCube-250708A: No Candidate Transients from the Zwicky Transient Facility
  70. GRB 250702B,D,E/EP250702A: MeerKAT radio observations at 1.28GHz
  71. GRB 250702B,D,E / EP250702a: 10 GHz detection with the VLA
  72. IPN triangulation of GRB 250704B (short/hard, consistent with EP 250704a)
  73. EP250704a/GRB 250704B: 10 GHz VLA detection
  74. IceCube-250706A: No Candidates from WINTER
  75. IPN triangulation of GRB 250706C (consistent with the GRB 250706B)
  76. IceCube-250706A: No Candidates from the Zwicky Transient Facility
  77. LIGO/Virgo/KAGRA S250704ab: Updated Sky localization and EM Bright Classification
  78. EP250704a/GRB250704B : HCT optical and NIR upper limits
  79. GRB 250704B / EP250704a: Mondy and AbAO optical observations
  80. GRB 250702F: radio detection with the VLA
  81. GRB 250706B/C: Fermi-LAT detection
  82. GRB 250704A: SVOM/COLIBRÍ (FM-GFT) optical observations
  83. EP250702a/GRB250702 B,D,E: GRANDMA Upper Limit
  84. GRB 250706B: Swift/UVOT Detection
  85. EP250702a/ GRB 250702B: NuSTAR X-ray Observations
  86. GRB 250704A: Swift/BAT-GUANO localization skymap of a burst
  87. GRB 250702F: GRANDMA observations
  88. GRB 250706B: refined SVOM/MXT data analysis
  89. GRB 250706A: Swift/UVOT Upper Limits
  90. GRB 250706B: REM optical observations
  91. GRB 250706A: REM optical/NIR observations
  92. EP250706a/GRB 250706A: EP-WXT detection of a fast X-ray transient
  93. IceCube-250416A: DDOTI Optical Upper Limit
  94. IceCube-250706A: COLIBRÍ optical upper limits
  95. GRB 250706A: JinShan optical upper limits
  96. GRB 250706A: SAO RAS optical observations
  97. EP250704A: NOWT Detection
  98. GRB 250706A: SVOM/C-GFT upper limit in eary phase
  99. GRB 250706B: iTelescope optical observations
  100. EP250704a / GRB 250704B: end of optical plateau phase and rapid fading of the counterpart

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