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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"

32532 results found.

  1. IPN triangulation of GRB 250309B
  2. IceCube-241224A: MASTER detection of PKS 1217+02 blazar flare with Zhirkov effect
  3. GRB 250309B/AT2025dws : COLIBRÍ Detection of the Optical Counterpart
  4. GRB 250309B: Swift-XRT refined Analysis
  5. GRB 250309B / IceCube-250309A: GECAM-B observations
  6. GRB 250309B / AT2025dws: OSIRIS+/GTC spectroscopy z=1.898
  7. Liverpool Telecope observations of AT 2025dws / GRB 250309B
  8. GRB 250309B / AT2025dws: SAO RAS optical observations
  9. GRB 250309B / AT2025dws: Swift-UVOT detection
  10. AT 2025dws, likely optical counterpart of GRB 250309B: LCO confirmation of fast fading
  11. GRB 250309B: Fermi GBM Observation
  12. Fermi GRB 250309B: Global MASTER-Net observations report
  13. Fermi GRB 250309A: Global MASTER-Net observations report
  14. GRB250309B: One candidate counterpart from the Zwicky Transient Facility
  15. IceCube-250309A: No candidates from the Zwicky Transient Facility
  16. Fermi-LAT gamma-ray observations of IceCube-250309A
  17. GRB 250308A: SVOM/GRM detection of QPO in the tail emission
  18. Correction to GCN 39633 - Swift is observing GRB 250309B/IceCube-250309A!
  19. GRB 230509B: Tiled Swift observations
  20. IceCube-250309A - IceCube observation of a high-energy neutrino candidate track-like event
  21. EP250308a: Global MASTER-Net observations report
  22. EP250308a: GSP optical upper limit
  23. GRB 250306A: EIRSAT-1 GMOD detection
  24. Fermi GRB 250307A: Global MASTER-Net observations report
  25. Konus-Wind detection of GRB 250306A
  26. GRB 250306A: Swift-BAT refined analysis
  27. GRB 250306A: NuSTAR detection of the prompt emission
  28. EP250304a: MeerKAT detection of a possible radio counterpart
  29. IceCube-241016A: MASTER flaring blazar 5BZU J073038.29-320820.2 with Zhirkov effect
  30. GRB 250305A: AstroSat CZTI detection
  31. EP250302a:Xinglong optical observations
  32. GRB 250306A: AstroSat CZTI detection
  33. Swift GRB 250306A: Global MASTER-Net observations report
  34. LIGO/Virgo/KAGRA S250207bg: Updated Sky localization
  35. GRB250101A: Radio upper limits from VLA observations
  36. GRB 250305A: SVOM/GRM observation of a burst
  37. EP250304A: Upper limits from Fermi-GBM Observations
  38. Fermi GRB 250305A: Global MASTER-Net observations report
  39. Fermi-LAT Gamma-ray Observations of IceCube-250302A
  40. EP250302a: Optical Observations at CrAO and SAO RAS
  41. GRB 250219A: SVOM/C-GFT optical upper limit at early phase
  42. EP 250304A: Optical counterpart detection by LCO
  43. EP250302A: 1.3m DFOT optical afterglow detection
  44. IceCube-250302A: Upper limits from a search for additional neutrino events in IceCube
  45. EP250304a: refined analysis of the EP-WXT and EP-FXT observations
  46. Konus-Wind detection of GRB 250222A
  47. EP250304a: REM NIR upper limits
  48. IPN triangulation of GRB 250222A
  49. EP250304a: Swift/UVOT detection of an optical counterpart with a rising light curve
  50. EP250302a: Mondy Continued Optical Observations
  51. EP250304a: VLT/X-shooter redshift z = 0.200
  52. EP250304a: Swift-XRT detection of a fading X-ray source
  53. EP250304a: TRT optical counterpart detection
  54. LIGO/Virgo/KAGRA S250304cb: Identification of a GW compact binary merger candidate
  55. EP250304a: Global MASTER-Net observations report
  56. EP250302a: SVOM/VT optical observation
  57. LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: Swift/UVOT Upper Limits
  58. EP250302a: SAO RAS optical observations
  59. EP250302a : GIT optical follow-up
  60. EP250302a: VLT/X-shooter redshift confirmation
  61. EP250225a: the candidate optical counterpart is an AGN
  62. EP250302a: Kinder optical follow-up observations
  63. EP250302a: Swift/UVOT detection
  64. EP250302a: NUTTelA-TAO Early Measurments
  65. EP250302a: optical observation from the INAF Asiago Observatory
  66. EP250302a: REM NIR upper limits
  67. IceCube-241113A: MASTER flaring blazar 5BZB J1311+0853 with Zhirkov effect
  68. EP250302a: Mondy Observations and Optical Light Curve
  69. EP250302a: VLT/MUSE optical redshift z = 1.131
  70. INTEGRAL: end of scientific operations
  71. EP250302A: VLT near-infrared observations
  72. EP250302A: VLT/X-shooter tentative redshift
  73. EP250302a: OHP/T193 optical and spectroscopic observations
  74. EP250302a: Global MASTER-Net observations report
  75. EP250302a: Xinglong F60B optical observation
  76. EP250302a: Swift-XRT observations of a fading X-ray source
  77. EP250302a: Einstein Probe detection of an X-ray transient
  78. EP250302a: SVOM/C-GFT optical observations
  79. GRB 250226A: GRANDMA Optical Observations
  80. EP250302a: Montarrenti Observatory optical detection
  81. Fermi GRB 250302A: Global MASTER-Net observations report
  82. EP250302a: FTW optical and NIR detection
  83. LIGO/Virgo/KAGRA S250206dm: early X-ray upper limits from Einstein Probe WXT and preliminary results of FXT observations
  84. GRB 250225B: VLT near-infrared afterglow confirmation
  85. EP250228a: Optical observations with Kinder and Swift/UVOT
  86. Konus-Wind detection of GRB 250226A
  87. GRB 250225B: EIRSAT-1 GMOD Detection
  88. GRB 250226A: KAO Optical Upper Limit
  89. GRB 250226A: AbAO AS-32 Optical Upper Limit
  90. EP250227a: Global MASTER-Net observations report
  91. EP250223A: Upper limits from Fermi-GBM Observations
  92. EP250227a: TRT optical upper limit
  93. GRB 250225B: VLT/HAWKI near-infrared observations
  94. EP250227a: Optical upper limits with Kinder observations
  95. EP250227a: NOT optical observations
  96. EP250228a: updates on the EP observations
  97. GRB 250226A: Fermi GBM Observation
  98. EP250225a: EP-FXT follow-up observation
  99. EP250223a: J band upper limit by SYSU 80cm telescope
  100. EP250228a: Swift/XRT localisation

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